CHAPTER 1

INTRODUCTION

Kakinada Seaports Limited

It is a dynamic gateway port on East Coast of India which is ideally located between

Visakhapatnam and Chennai Ports. Hope Island, a natural formation offers protection

as natural breakwater for Kakinada Port and 1.2 Km breakwater of tetra pods provides

tranquil bay conditions round the year for vessels to operate in sheltered waters of

Kakinada Deep Water Port.

The vantagious position of Port gives a unique opportunity to handle a mix of bulk,

liquid, break bulk, containers, project cargoes & service offshore Oil & Gas exploration

activities of Krishna – Godavari Basin. KSPL team is truly committed to Customer

needs, safe working practices, supply chain management and environment protection.

As a Corporate philosophy, Kakinada Seaports Ltd has always embraced Modern

practices

Kakinada Deep Water Port was constructed with a quay length of 610 Meters by

Government of Andhra Pradesh (Gov., AP) and it was commissioned in November

1997. In line with national port privatization policy, Government of Andhra Pradesh

has given concession to operate Kakinada Deep Water Port under OMST scheme on

16.12.1998.

Services: Kakinada Seaport is known for its strategic development of service modules

to meet unique requirements of specialized port users as of Offshore sector & Crude

Lightening.

Port Particulars: Kakinada Deep Water Port was commissioned in November 1997

with a quay length of 610 Meters which was privatized in 1999 and as of 2009 port

developed to have 910 meters of single quay length for multiproduct handling and stand

alone facility for OSVs.

Cargo: As a Corporate philosophy, Kakinada Seaports Ltd has always embraced

Modern practices, Systems and Technology to Excel in Port Management and uniquely

positioned as a multi product dynamic port handling liquid, bulk, break bulk cargoes.

Tariff the services at KDWP are pegged against tariff structure for various services

offered to port users using the facility round the year.

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CHAPTER 2

RADIO DETECTION AND RANGING

2.1 Introduction to Radar

Radar is an object detection system that uses electromagnetic waves to identify

the range, altitude, direction, or speed of both moving and fixed objects such as aircraft,

ships, motor vehicles, weather formations, and terrain. The term RADAR was coined in

1940 by the U.S. Navy as an acronym for Radio Detection And Ranging. The term has

since entered the English language as a standard word, radar, losing the capitalization.

Radar was originally called RDF (Range and Direction Finding) in the United

Kingdom, using the same acronym as Radio Direction Finding to preserve the secrecy

of its ranging capability.

A radar system has a transmitter that emits radio waves. When they come into

contact with an object they are scattered in all directions. The signal is thus partly

reflected back and it has a slight change of wavelength (and thus frequency) if the

target is moving. The receiver is usually, but not always, in the same location as the

transmitter. Although the signal returned is usually very weak, the signal can be

amplified through use of electronic techniques in the receiver and in the antenna

configuration. This enables radar to detect objects at ranges where other emissions,

such as sound or visible light, would be too weak to detect. Radar uses include

meteorological detection of precipitation, measuring ocean surface waves, air traffic

control, police detection of speeding traffic, military applications, or to simply

determine the speed of a baseball.

2.2 History

Several inventors, scientists, and engineers contributed to the development of

radar. The first to use radio waves to detect "the presence of distant metallic objects"

was Christian Hulsmeyer, who in 1904 demonstrated the feasibility of detecting the

presence of a ship in dense fog, but not its distance. He received Reich patent Nr.

165546 for his pre-radar device in April 1904, and later patent 169154 for a related

amendment for ranging. He also received a patent in Britain for his telemobiloscope on

September 23, 1904.

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In August 1917 Nikola Tesla first established principles regarding frequency

and power level for the first primitive radar units. He stated, by their [standing

electromagnetic waves] use we may produce at will, from a sending station, an

electrical effect in any particular region of the globe with which we may determine the

relative position or course of a moving object, such as a vessel at sea, the distance

traversed by the same, or its speed."

Before the Second World War developments by the British, the Germans, the

French, the Soviets and the Americans led to the modern version of radar. In 1934 the

French Emile Girardeau stated he was building a radar system "conceived according to

the principles stated by Tesla" and obtained a patent (French Patent in 1934) for a

working dual radar system, a part of which was installed on the Norman die liner in

1935. The same year, American Dr. Robert M. Page tested the first monopulse radar

and the Soviet military engineer P.K.Oschepkov, in collaboration with Leningrad

Electro physical Institute, produced an experimental apparatus RAPID capable of

detecting an aircraft within 3 km of a receiver. Hungarian Zoltan Bay produced a

working model by 1936 at the Tungsram laboratory in the same veins.

However, it was the British who were the first to fully exploit it as a defense

against aircraft attack. This was spurred on by fears that the Germans were developing

death rays. Following a study of the possibility of propagating electromagnetic energy

and the likely effect, the British scientists asked by the Air Ministry to investigate,

concluded that a death ray was impractical but detection of aircraft appeared feasible.

Http Robert demonstrated to his superiors the capabilities of a working prototype and

patented the device in 1935.It served as the basis for the Chain Home network of radars

to defend Great Britain.

The war precipitated research to find better resolution, more portability and

more features for radar. The post-war years have seen the use of radar in fields as

diverse as air traffic control, weather monitoring, astrometry and road speed control.

2.3 Applications of Radar

The information provided by radar includes the bearing and range (and therefore

position) of the object from the radar scanner. It is thus used in many different fields

where the need for such positioning is crucial. The first use of radar was for military

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purposes; to locate air, ground and sea targets. This has evolved in the civilian field into

applications for aircraft, ships and roads.

In aviation, aircraft are equipped with radar devices that warn of obstacles in or

approaching their path and give accurate altitude readings. They can land in fog at

airports equipped with radar-assisted ground-controlled approach (GCA) systems, in

which the plane's flight is observed on radar screens while operators radio landing

directions to the pilot.

Marine radars are used to measure the bearing and distance of ships to prevent

collision with other ships, to navigate and to fix their position at sea when within range

of shore or other fixed references such as islands, buoys, and lightships. In port or in

harbor, Vessel traffic service radar systems are used to monitor and regulate ship

movements in busy waters. Police forces use radar guns to monitor vehicle speeds on

the roads.

Radar has invaded many other fields. Meteorologists use radar to monitor

precipitation. It has become the primary tool for short-term weather forecasting and to

watch for severe weather such as thunderstorms, tornadoes, winter storms precipitation

types, etc... Geologists use specialized ground-penetrating radars to map the

composition of the Earth crust. The list is getting longer all the time.

2.4 Principles

The radar dish, or antenna, transmits pulses of radio waves or microwaves

which bounce off any object in their path. The object returns a tiny part of the wave's

energy to a dish or antenna which is usually located at the same site as the transmitter.

The time it takes for the reflected waves to return to the dish enables a computer to

calculate how far away the object is, its radial velocity and other characteristics.

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a. Reflection

Fig. 1 Reflection of Radar

Brightness can indicate reflectivity as in this 1960 weather radar image (of Hurricane

Abby). The radar's frequency, pulse form, polarization, signal processing, and antenna

determine what it can observe in fig. 1

Electromagnetic waves reflect from any large change in the dielectric constant

or diamagnetic constants. This means that a solid object in air or a vacuum, or other

significant change in atomic density between the object and what is surrounding it, will

usually scatter radar (radio) waves. This is particularly true for electrically conductive

materials, such as metal and carbon fiber, making radar particularly well suited to the

detection of aircraft and ships. Radar absorbing material, containing resistive and

sometimes magnetic substances, is used on military vehicles to reduce radar reflection.

This is the radio equivalent of painting something a dark color so that it cannot be seen

through normal means.

Radar waves scatter in a variety of ways depending on the size of the radio

wave and the shape of the target. If the wavelength is much shorter than the target's

size, the wave will bounce off in a way similar to the way light is reflected by a mirror.

If the wavelength is much longer than the size of the target, the wave is polarized

(positive and negative charges are separated), like a dipole antenna. This is described

by Rayleigh scattering, an effect that creates the Earth's blue sky and red sunsets. When

the two length scales are comparable, there may be resonances. Early radars used very

long wavelengths that were larger than the targets and received a vague signal, whereas

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some modern systems use shorter wavelengths that can image objects as small as a loaf

of bread.

Short radio waves reflect from curves and corners, in a way similar to glint from

a rounded piece of glass. The most reflective targets for short wavelengths have 90°

angles between the reflective surfaces. A structure consisting of three flat surfaces

meeting at a single corner, like the corner on a box, will always reflect waves entering

its opening directly back at the source. These so-called corner reflectors are commonly

used as radar reflectors to make otherwise difficult-to-detect objects easier to detect,

and are often found on boats in order to improve their detection in a rescue situation

and to reduce collisions.

For similar reasons, objects attempting to avoid detection will angle their

surfaces in a way to eliminate inside corners and avoid surfaces and edges

perpendicular to likely detection directions, which leads to "odd" looking stealth

aircraft. These precautions do not completely eliminate reflection because of

diffraction, especially at longer wavelengths. Half wavelength long wires or strips of

conducting material, such as chaff, are very reflective but do not direct the scattered

energy back toward the source. The extent to which an object reflects or scatters radio

waves is called its radar cross section.

b. Radar equation

The power Pr returning to the receiving antenna is given by the radar equation:

Pr=¿

Pt Gt A r σ F 4

( 4π 2) R t2 Rr

2¿

Where

Pt = transmitter power

Gt = gain of the transmitting antenna

Ar = effective aperture (area) of the receiving antenna

σ = radar cross section, or scattering coefficient, of the target

F = pattern propagation factor

Rt = distance from the transmitter to the target

Rr = distance from the target to the receiver.

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In the common case where the transmitter and the receiver are at the same location,

Rt = Rr and the term Rt² Rr² can be replaced by R4, where R is the range. This yield:

Pr=¿

Pt Gt A r σ F 4

( 4 π 2) R 4¿

This shows that the received power declines as the fourth power of the range, which

means that the reflected power from distant targets is very, very small.

The equation above with F = 1 is a simplification for vacuum without interference. The

propagation factor accounts for the effects of multipath and shadowing and depends on

the details of the environment. In a real-world situation, path loss effects should also be

considered.

c. Doppler Effect

Ground-based radar systems used for detecting speeds rely on the Doppler

Effect. The apparent frequency (f) of the wave changes with the relative position of the

target. The Doppler equation is stated as follows for vobs (the radial speed of the

observer) and vs. (the radial speed of the target) and f0 frequency of wave:

f =v+vobs

v−vs

f 0

However, the change in phase of the return signal is often used instead of the change in

frequency. It is to be noted that only the radial component of the speed is available.

Hence when a target moving at right angle to the radar beam, it has no velocity while

one parallel to it has maximum recorded speed even if both might have the same real

absolute motion.

d. Polarization

In the transmitted radar signal, the electric field is perpendicular to the direction

of propagation, and this direction of the electric field is the polarization of the wave.

Radars use horizontal, vertical, linear and circular polarization to detect different types

of reflections. For example, circular polarization is used to minimize the interference

caused by rain. Linear polarization returns usually indicate metal surfaces. Random

polarization returns usually indicate a fractal surface, such as rocks or soil, and are used

by navigation radars.

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2.4. Limiting factors

a. Beam height with distance

H=√r2+( ke ae )2

H=(√r2+(ke ae)2+2 r ke ae sin θc )−k e ae+ha

r : distance k e: 4/3 (standard refraction coefficient)

ae: Earth Radius θc : Elevation angle

ha: Height of radar above ground

Fig. 2 Beam Height with Distance

The radar beam would follow a linear path in vacuum but it really follows a

somewhat curved path in the atmosphere due to the variation of the refractive index of

air. Even when the beam is emitted parallel to the ground, it will raise above it as the

Earth curvature sink below the horizon. Furthermore, the signal is attenuated by the

medium it crosses and the beam disperses as it’s not a perfect pencil shape as shown in

Fig. 2.

The maximum range of conventional radar at a certain height above ground is thus

limited by the maximum non-ambiguous range determined by the Pulse repetition

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frequency (PRF), the two way intensity of the returned signal according to the radar

equation and the Earth curvature.

b. Noise

Signal noise is an internal source of random variations in the signal, which is

generated by all electronic components. Noise typically appears as random variations

superimposed on the desired echo signal received in the radar receiver. The lower the

power of the desired signal, the more difficult it is to discern it from the noise (similar

to trying to hear a whisper while standing near a busy road). Noise figure is a measure

of the noise produced by a receiver compared to an ideal receiver, and this needs to be

minimized.

Noise is also generated by external sources, most importantly the natural

thermal radiation of the background scene surrounding the target of interest. In modern

radar systems, due to the high performance of their receivers, the internal noises is

typically about equal to or lower than the external scene noise. An exception is if the

radar is aimed upwards at clear sky, where the scene is so "cold" that it generates very

little thermal noise.

There will be also flicker noise due to electrons transit, but depending on 1/f,

will be much lower than thermal noise when the frequency is high. Hence, in pulse

radar, the system will be always heterodyne. See intermediate frequency.

c. Interference

Radar systems must overcome unwanted signals in order to focus only on the

actual targets of interest. These unwanted signals may originate from internal and

external sources, both passive and active. The ability of the radar system to overcome

these unwanted signals defines its signal-to-noise ratio (SNR). SNR is defined as the

ratio of a signal power to the noise power within the desired signal.

In less technical terms, SNR compares the level of a desired signal (such as targets) to

the level of background noise. The higher a system's SNR, the better it is in isolating

actual targets from the surrounding noise signals.

d. Clutter

Clutter refers to radio frequency (RF) echoes returned from targets which are

uninteresting to the radar operators. Such targets include natural objects such as ground,

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sea, precipitation (such as rain, snow or hail), sand storms, animals (especially birds),

atmospheric turbulence, and other atmospheric effects, such as ionosphere reflections,

meteor trails, and three body scatter spike. Clutter may also be returned from man-made

objects such as buildings and, intentionally, by radar countermeasures such as chaff.

Some clutter may also be caused by a long radar waveguide between the radar

transceiver and the antenna. In a typical plan position indicator (PPI) radar with a

rotating antenna, this will usually be seen as a "sun" or "sunburst" in the centre of the

display as the receiver responds to echoes from dust particles and misguided RF in the

waveguide. Adjusting the timing between when the transmitter sends a pulse and when

the receiver stage is enabled will generally reduce the sunburst without affecting the

accuracy of the range; since most sunburst is caused by a diffused transmit pulse

reflected before it leaves the antenna.

While some clutter sources may be undesirable for some radar applications

(such as storm clouds for air-defense radars), they may be desirable for others

(meteorological radars in this example). Clutter is considered a passive interference

source, since it only appears in response to radar signals sent by the radar.

There are several methods of detecting and neutralizing clutter. Many of these

methods rely on the fact that clutter tends to appear static between radar scans.

Therefore, when comparing subsequent scans echoes, desirable targets will appear to

move and all stationary echoes can be eliminated. Sea clutter can be reduced by using

horizontal polarization, while rain is reduced with circular polarization (note that

meteorological radars wish for the opposite effect, therefore using linear polarization

the better to detect precipitation). Other methods attempt to increase the signal-to-

clutter ratio.

Constant False Alarm Rate (CFAR, a form of Automatic Gain Control, or AGC)

is a method relying on the fact that clutter returns far outnumber echoes from targets of

interest. The receiver's gain is automatically adjusted to maintain a constant level of

overall visible clutter. While this does not help detect targets masked by stronger

surrounding clutter, it does help to distinguish strong target sources. In the past, radar

AGC was electronically controlled and affected the gain of the entire radar receiver. As

radars evolved, AGC became computer-software controlled, and affected the gain with

greater granularity, in specific detection cells.

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Fig. 3 Radar Multipath Echoes From a Target

Radar multipath echoes from a target cause ghosts to appear as shown in fig .3.

Clutter may also originate from multipath echoes from valid targets due to ground reflection,

atmospheric ducting or ionosphere reflection/refraction. This clutter type is especially

bothersome, since it appears to move and behave like other normal (point) targets of interest,

thereby creating a ghost. In a typical scenario, an aircraft echo is multipath-reflected from the

ground below, appearing to the receiver as an identical target below the correct one. The radar

may try to unify the targets, reporting the target at an incorrect height, or - worse - eliminating

it on the basis of jitter or a physical impossibility. These problems can be overcome by

incorporating a ground map of the radar's surroundings and eliminating all echoes which appear

to originate below ground or above a certain height. In newer Air Traffic Control (ATC) radar

equipment, algorithms are used to identify the false targets by comparing the current pulse

returns, to those adjacent, as well as calculating return improbabilities due to calculated height,

distance, and radar timing.

e. Jamming

Radar jamming refers to radio frequency signals originating from sources

outside the radar, transmitting in the radar's frequency and thereby masking targets of

interest. Jamming may be intentional, as with an electronic warfare (EW) tactic, or

unintentional, as with friendly forces operating equipment that transmits using the same

frequency range. Jamming is considered an active interference source, since it is

initiated by elements outside the radar and in general unrelated to the radar signals.

Jamming is problematic to radar since the jamming signal only needs to travel

one-way (from the jammer to the radar receiver) whereas the radar echoes travel two-

ways (radar-target-radar) and are therefore significantly reduced in power by the time

they return to the radar receiver. Jammers therefore can be much less powerful than

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their jammed radars and still effectively mask targets along the line of sight from the

jammer to the radar (Main lobe Jamming). Jammers have an added effect of affecting

radars along other lines of sight, due to the radar receiver's side lobes.

Main lobe jamming can generally only be reduced by narrowing the main lobe

solid angle, and can never fully be eliminated when directly facing a jammer which

uses the same frequency and polarization as the radar. Side lobe jamming can be

overcome by reducing receiving side lobes in the radar antenna design and by using an

Omni directional antenna to detect and disregard non-main lobe signals. Other anti-

jamming techniques are frequency hopping and polarization. See Electronic counter-

counter-measures for details. Interference has recently become a problem for C-band

(5.66 GHz) meteorological radars with the proliferation of 5.4 GHz band Wi-Fi

equipment.

2.5 Radar signal processing

Distance measurement:

a. Transit time: One way to measure the distance to an object is to transmit a short

pulse of radio signal (electromagnetic radiation), and measure the time it takes for the

reflection to return. As shown fig. 4

Fig. 4 Transit time

b. Pulse radar: The round-trip time for the radar pulse to get to the target and return is

measured. The distance is proportional to this time as shown at fig.5

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Fig. 5 Pulse radar

c. Sonar radar

One way to measure the distance to an object is to transmit a short pulse of

radio signal (electromagnetic radiation), and measure the time it takes for the reflection

to return. The distance is one-half the product of the round trip time (because the signal

has to travel to the target and then back to the receiver) and the speed of the signal.

Since radio waves travel at the speed of light (186,000 miles per second or 300,000,000

meters per second), accurate distance measurement requires high-performance

electronics.

In most cases, the receiver does not detect the return while the signal is being

transmitted. Through the use of a device called a duplexer, the radar switches between

transmitting and receiving at a predetermined rate. The minimum range is calculated by

measuring the length of the pulse multiplied by the speed of light, divided by two. In

order to detect closer targets one must use a shorter pulse length.

A similar effect imposes a maximum range as well. If the return from the target

comes in when the next pulse is being sent out, once again the receiver cannot tell the

difference. In order to maximize range, longer times between pulses should be used,

referred to as a pulse repetition time (PRT), or it’s reciprocal, pulse repetition frequency

(PRF).

These two effects tend to be at odds with each other, and it is not easy to

combine both good short range and good long range in single radar. This is because the

short pulses needed for a good minimum range broadcast have less total energy,

making the returns much smaller and the target harder to detect. This could be offset by

using more pulses, but this would shorten the maximum range again. So each radar

uses a particular type of signal. Long-range radars tend to use long pulses with long

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delays between them, and short range radars use smaller pulses with less time between

them. This pattern of pulses and pauses is known as the pulse repetition frequency (or

PRF), and is one of the main ways to characterize a radar. As electronics have

improved many types of radar now can change their PRF thereby changing their range.

The newest radars fire 2 pulses during one cell, one for short range 10 km / 6 miles and

a separate signal for longer ranges 100 km /60 miles.

The distance resolution and the characteristics of the received signal as

compared to noise depend heavily on the shape of the pulse. The pulse is often

modulated to achieve better performance using a technique known as pulse

compression. Distance may also be measured as a function of time. The radar mile is

the amount of time it takes for a radar pulse to travel one nautical mile, reflect off a

target, and return to the radar antenna. Since a nautical mile is defined as exactly 1,852

meters, then dividing this distance by the speed of light (exactly 299,792,458 meters

per second), and then multiplying the result by 2 (round trip = twice the distance),

yields a result of approximately 12.36 microseconds in duration.

d. Frequency modulation

Another form of distance measuring radar is based on frequency modulation.

Frequency comparison between two signals is considerably more accurate, even with

older electronics, than timing the signal. By changing the frequency of the returned

signal and comparing that with the original, the difference can be easily measured.

This technique can be used in continuous wave radar, and is often found in

aircraft radar altimeters. In these systems a "carrier" radar signal is frequency

modulated in a predictable way, typically varying up and down with a sine wave or saw

tooth pattern at audio frequencies. The signal is then sent out from one antenna and

received on another, typically located on the bottom of the aircraft, and the signal can

be continuously compared using a simple beat frequency modulator that produces an

audio frequency tone from the returned signal and a portion of the transmitted signal.

Since the signal frequency is changing, by the time the signal returns to the

aircraft the broadcast has shifted to some other frequency. The amount of that shift is

greater over longer times, so greater frequency differences mean a longer distance, the

exact amount being the "ramp speed" selected by the electronics. The amount of shift is

therefore directly related to the distance traveled, and can be displayed on an

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instrument. This signal processing is similar to that used in speed detecting Doppler

radar. Example systems using this approach are AZUSA, MISTRAM, and UDOP.

A further advantage is that the radar can operate effectively at relatively low

frequencies, comparable to that used by UHF television. This was important in the early

development of this type when high frequency signal generation was difficult or

expensive.

New terrestrial radar uses low-power FM signals that cover a larger frequency

range. The multiple reflections are analyzed mathematically for pattern changes with

multiple passes creating a computerized synthetic image. Doppler effects are not

utilized which allows slow moving objects to be detected as well as largely eliminating

"noise" from the surfaces of bodies of water. Used primarily for detection of intruders

approaching in small boats or intruders crawling on the ground toward an objective.

e. Speed measurement

Speed is the change in distance to an object with respect to time. Thus the

existing system for measuring distance, combined with a memory capacity to see where

the target last was, is enough to measure speed. At one time the memory consisted of a

user making grease-pencil marks on the radar screen, and then calculating the speed

using a slide rule. Modern radar systems perform the equivalent operation faster and

more accurately using computers.

However, if the transmitter's output is coherent (phase synchronized), there is

another effect that can be used to make almost instant speed measurements (no memory

is required), known as the Doppler Effect. Most modern radar systems use this principle

in the pulse-Doppler radar system. Return signals from targets are shifted away from

this base frequency via the Doppler Effect enabling the calculation of the speed of the

object relative to the radar. The Doppler Effect is only able to determine the relative

speed of the target along the line of sight from the radar to the target. Any component

of target velocity perpendicular to the line of sight cannot be determined by using the

Doppler Effect alone, but it can be determined by tracking the target's azimuth over

time. Additional information of the nature of the Doppler returns may be found in the

radar signal characteristics article.

It is also possible to make a radar without any pulsing, known as a continuous-

wave radar (CW radar), by sending out a very pure signal of a known frequency. CW

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radar is ideal for determining the radial component of a target's velocity, but it cannot

determine the target's range. CW radar is typically used by traffic enforcement to

measure vehicle speed quickly and accurately where range is not important.

Other mathematical developments in radar signal processing include time-

frequency analysis (Weyl Heisenberg or wavelet), as well as the chirplet transform

which makes use of the fact that radar returns from moving targets typically "chirp"

(change their frequency as a function of time, as does the sound of a bird or bat).

f. Reduction of interference effects

Signal processing is employed in radar systems to reduce the radar interference

effects. Signal processing techniques include moving target indication (MTI), pulse

Doppler, moving target detection (MTD) processors, correlation with secondary

surveillance radar (SSR) targets, space-time adaptive processing (STAP), and track-

before-detect (TBD). Constant false alarm rate (CFAR) and digital terrain model

(DTM) processing are also used in clutter environments.

g. Plot and Track Extraction

Radar video returns on aircraft can be subjected to a plot extraction process

whereby spurious and interfering signals are discarded. A sequence of target returns can

be monitored through a device known as a plot extractor. The non relevant real time

returns can be removed from the displayed information and a single plot displayed. In

some radar systems, or alternatively in the command and control system to which the

radar is connected, a radar tracker is used to associate the sequence of plots belonging

to individual targets and estimate the targets' headings and speeds.

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2.6 Radar engineering

Fig. 6 Radar Components

a. Radar components

Fig. 6 shows the components of radar.

Radar components are

A transmitter that generates the radio signal with an oscillator such as a klystron or a

magnetron and controls its duration by a modulator

1. A waveguide that links the transmitter and the antenna.

2. A duplexer that serves as a switch between the antenna and the transmitter or the

receiver for the signal when the antenna is used in both situations.

3. A receiver. Knowing the shape of the desired received signal (a pulse), an optimal

receiver can be designed using a matched filter.

4. An electronic section that controls all those devices and the antenna to perform the

radar scan ordered by a software.

5. A link to end users.

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a. Antenna design

Radio signals broadcast from a single antenna will spread out in all directions,

and likewise a single antenna will receive signals equally from all directions. This

leaves the radar with the problem of deciding where the target object is located.

Early systems tended to use Omni-directional broadcast antennas, with directional

receiver antennas which were pointed in various directions. For instance the first

system to be deployed, Chain Home, used two straight antennas at right angles for

reception, each on a different display. The maximum return would be detected with an

antenna at right angles to the target, and a minimum with the antenna pointed directly at

it (end on). The operator could determine the direction to a target by rotating the

antenna so one display showed a maximum while the other shows a minimum.

One serious limitation with this type of solution is that the broadcast is sent out

in all directions, so the amount of energy in the direction being.

Examined is a small part of that transmitted? To get a reasonable amount of power on

the "target", the transmitting aerial should also be directional.

1. Parabolic reflector

More modern systems use a steerable parabolic "dish" to create a tight broadcast

beam, typically using the same dish as the receiver. Such systems often combine two

radar frequencies in the same antenna in order to allow automatic steering, or radar

lock.

Parabolic reflectors can be either symmetric parabolas or spoiled parabolas. As shown

Fig. 7

Symmetric parabolic antennas produce a narrow "pencil" beam in both the X

and Y dimensions and consequently have a higher gain. The NEXRAD Pulse-Doppler

weather radar uses a symmetric antenna to perform detailed volumetric scans of the

atmosphere.

Fig. 7 Parabolic Reflector

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2. Surveillance radar antenna

Spoiled parabolic antennas produce a narrow beam in one dimension and a

relatively wide beam in the other. This feature is useful if target detection over a wide

range of angles is more important than target location in three dimensions. Most 2D

surveillance radars use a spoiled parabolic antenna with a narrow azimuthal beam width

and wide vertical beam width. This beam configuration allows the radar operator to

detect an aircraft at a specific azimuth but at an indeterminate height. Conversely, so-

called "nodder" height finding radars use a dish with a narrow vertical beam width and

wide azimuthal beam width to detect an aircraft at a specific height but with low

azimuthal precision.

Types of scan

1. Primary Scan: A scanning technique where the main antenna aerial is moved to

produce a scanning beam, examples include circular scan, sector scan etc

2. Secondary Scan: A scanning technique where the antenna feed is moved to produce

a scanning beam, examples include conical scan, unidirectional sector scan, lobe

switching etc.

3. Palmer Scan: A scanning technique that produces a scanning beam by moving the

main antenna and its feed. A Palmer Scan is a combination of a Primary Scan and a

Secondary Scan.

c. Slotted wave guide

Fig. 8 slotted wave guide

Slotted waveguide shown Fig. 8.Applied similarly to the parabolic reflector, the

slotted waveguide is moved mechanically to scan and is particularly suitable for non-

tracking surface scan systems, where the vertical pattern may remain constant. Owing

19

to its lower cost and less wind exposure, shipboard, airport surface, and harbor

surveillance radars now use this in preference to the parabolic antenna.

b. Phased array

Fig. 9 Phased Array

Phased array: Not all radar antennas must rotate to scan the sky. The phased array

observed in Fig. 9

Another method of steering is used in phased array radar. This uses an array of

similar aerials suitably spaced, the phase of the signal to each individual aerial being

controlled so that the signal is reinforced in the desired direction and cancels in other

directions. If the individual aerials are in one plane and the signal is fed to each aerial in

phase with all others then the signal will reinforce in a direction perpendicular to that

plane. By altering the relative phase of the signal fed to each aerial the direction of the

beam can be moved because the direction of constructive interference will move.

Because phased array radars require no physical movement the beam can scan at

thousands of degrees per second, fast enough to irradiate and track many individual

targets, and still run a wide-ranging search periodically. By simply turning some of the

antennas on or off, the beam can be spread for searching, narrowed for tracking, or

even split into two or more virtual radars. However, the beam cannot be effectively

steered at small angles to the plane of the array, so for full coverage multiple arrays are

required, typically disposed on the faces of a triangular pyramid (see picture).

Phased array radars have been in use since the earliest years of radar use in

World War II, but limitations of the electronics led to fairly poor accuracy. Phased

array radars were originally used for missile defense. They are the heart of the ship-

borne Aegis combat system, and the Patriot Missile System, and are increasingly used

in other areas because the lack of moving parts makes them more reliable, and

sometimes permits a much larger effective antenna, useful in fighter aircraft

applications that offer only confined space for mechanical scanning.

20

As the price of electronics has fallen, phased array radars have become more

and more common. Almost all modern military radar systems are based on phased

arrays, where the small additional cost is far offset by the improved reliability of a

system with no moving parts. Traditional moving-antenna designs are still widely used

in roles where cost is a significant factor such as air traffic surveillance, weather radars

and similar systems.

Phased array radars are also valued for use in aircraft, since they can track

multiple targets. The first aircraft to use phased array radar is the B-1B Lancer. The

first aircraft fighter to use phased array radar was the Mikoyan MiG-31. The MiG-

31M's SBI-16 Zaslon phased array radar is considered to be the world's most powerful

fighter radar. Phased-array interferometry or, aperture synthesis techniques, using an

array of separate dishes that are phased into a single effective aperture, are not typically

used for radar applications, although they are widely used in radio astronomy. Because

of the Thinned array curse, such arrays of multiple apertures, when used in transmitters,

result in narrow beams at the expense of reducing the total power transmitted to the

target. In principle, such techniques used could increase the spatial resolution, but the

lower power means that this is generally not effective. Aperture synthesis by post-

processing of motion data from a single moving source, on the other hand, is widely

used in space and airborne radar systems (see Synthetic aperture radar).

2.7 Frequency bands

The traditional band names originated as code-names during World War II and

are still in military and aviation use throughout the world in the 21st century are shown

in table 1. They have been adopted in the United States by the IEEE, and internationally

by the ITU. Most countries have additional regulations to control which parts of each

band are available for civilian or military use. Other users of the radio spectrum, such

as the broadcasting and electronic countermeasures (ECM) industries, have replaced the

traditional military designations with their own systems.

21

Band name Frequency

range

Wave

length

Notes

HF 3–30 MHz 10–100 m Coastal radar systems

P < 300 MHz 1 m+ 'P' for 'previous', applied retrospectively

to early radar systems

VHF 30–330 MH

z

0.9–6 m Very long range, ground penetrating;

'very high frequency'

UHF 300–1000 M

Hz

0.3–1 m Very long range (e.g. ballistic missile)

L 1–2 GHz 15–30 cm Long range air traffic control and

surveillance; 'L' for 'long' range

S 2–4 GHz 7.5–15 c

m

Terminal air traffic control, long-range

weather,

C 4–8 GHz 3.75–7.5 

cm

Satellite transponders; a compromise

(hence 'C') between X and S bands;

weather

X 8–12 GHz 2.5–3.75 cm

Missile guidance, marine radar

Ku12–18 GHz 1.67–2.5 c

mHigh-resolution

K 18–24 GHz 1.11–1.67 

cm

K-band is used for detecting clouds by Meteorologists.

Ka 24–40 GHz 0.75–1.11 

cm

Mapping, short range, airport

surveillance

Table 1 Frequency Bands

22

2.8 Radar modulators

Modulators act to provide the short pulses of power to the magnetron, a special

type of vacuum tube that converts DC (usually pulsed) into microwaves. This

technology is known as Pulsed power. In this way, the transmitted pulse of RF radiation

is kept to a defined, and usually, very short duration. Modulators consist of a high

voltage pulse generator formed from an HV supply, a pulse forming network, and a

high voltage switch such as a thyratron. A klystron tube may also be used as a

modulator because it is an amplifier, so it can be modulated by its low power input

signal.

2.9 Radar configurations and types

Radars configurations include Monopulse radar, Bistatic radar, Doppler radar,

Continuous-wave radar, etc… Depending on the types of hardware and software used.

It is used in aviation (Primary and secondary radar), sea vessels, law enforcement,

weather surveillance, ground mapping, geophysical surveys, and biological research.

23

CHAPTER 3

VERY HIGH FREQUENCY

VHF (Very high frequency) is the radio frequency range from 30 MHz to 300

MHz Frequencies immediately below VHF are denoted High frequency (HF), and the

next higher frequencies are known as Ultra high frequency (UHF). The frequency

allocation is done by ITU. Common uses for VHF are FM radio broadcast, television

broadcast, land mobile stations (emergency, business, and military), long range data

communication with radio modems, Amateur Radio, marine communications, air

traffic control communications and air navigation systems (e.g. VOR, DME & ILS).

3.1 Propagation characteristics

VHF propagation characteristics are ideal for short-distance terrestrial

communication, with a range generally somewhat farther than line-of-sight from the

transmitter (see formula below). Unlike high frequencies (HF), the ionosphere does not

usually reflect VHF radio and thus transmissions are restricted to the local area (and

don't interfere with transmissions thousands of kilometers away). VHF is also less

affected by atmospheric noise and interference from electrical equipment than lower

frequencies. Whilst it is more easily blocked by land features than HF and lower

frequencies, it is less affected by buildings and other less substantial objects than UHF

frequencies.

Two unusual propagation conditions can allow much farther range than normal.

The first, tropospheric ducting can occur in front of and parallel to an advancing cold

weather front, especially if there is a marked difference in humidities between the cold

and warm air masses. A duct can form approximately 250 km (155 mi) in advance of

the cold front, much like a ventilation duct in a building, and VHF radio frequencies

can travel along inside the duct, bending or refracting, for hundreds of kilometers. For

example, a 50 watt Amateur FM transmitter at 146 MHz can talk from Chicago, to

Joplin, Missouri, directly, and to Austin, Texas, through a repeater. In a July 2006

incident, a NOAA Weather Radio transmitter in north central Wisconsin was blocking

out local transmitters in west central Michigan, quite far out of its normal range. In

midsummer 2006, central Iowa stations were heard in Columbus, NE and blocked out

Omaha radio and TV stations for several days. Similar propagation effects can affect

land-mobile stations in this band, rarely causing interference well beyond the usual

24

coverage area. The second type, much more rare, is called Sporadic E, referring to the

E-layer of the ionosphere. Phenomena still not completely understood (as of 2010) may

allow the formation of ionized "patches" in the ionosphere, dense enough to reflect

back VHF frequencies the same way HF frequencies are usually reflected (sky wave).

For example, KMID (TV Channel 2; 54–60 MHz) from Midland, Texas was seen

around Chicago, pushing out Chicago's WBBM-TV. [Citation needed] These patches may last

for seconds, or extend into hours. FM stations from Miami, Florida; New Orleans,

Louisiana; Houston, Texas and even Mexico were heard for hours in central Illinois

during one such event.

Line-of-sight calculation

For analog TV, VHF transmission range is a function of transmitter power,

receiver sensitivity, and distance to the horizon, since VHF signals propagate under

normal conditions as a near line-of-sight phenomenon. The distance to the radio

horizon is slightly extended over the geometric line of sight to the horizon, as radio

waves are weakly bent back toward the Earth by the atmosphere.

An approximation to calculate the line-of-sight horizon distance (on Earth) is:

Distance in miles = √1.5 × A f

Where AF is the height of the antenna in feet

Distance in kilometers = √12.746 × Am

Where Am the height of the antenna in meters.

These approximations are only valid for antennas at heights that are small

compared to the radius of the Earth. They may not necessarily be accurate in

mountainous areas, since the landscape may not be transparent enough for radio waves.

In engineered communications systems, more complex calculations are required

to assess the probable coverage area of a proposed transmitter station. The accuracy of

these calculations for digital TV signals is being debated. By country

25

Fig. 10 Vhf Frequency Used In Tv, Fm

Fig. 10 A plan showing VHF use in television, FM radio, amateur radio, marine radio

and aviation.

3.2 Countries

a. Australia

The VHF TV band in Australia was originally allocated channels 1 to 10 - with

channels 2, 7 and 9 assigned for the initial services in Sydney and Melbourne, and later

the same channels were assigned in Brisbane, Adelaide and Perth. Other capital cities

and regional areas used a combination of these and other frequencies as available. For

some strange reason, the initial commercial services in Hobart and Darwin were

respectively allocated channels 6 and 8 rather than 7 or 9.

By the early 1960s it became apparent that the 10 VHF channels were

insufficient to support the growth of television services. This was rectified by the

addition of three additional frequencies - channels 0, 5A and 11. Older television sets

using rotary dial tuners required adjustment to receive the new channels.

Several TV stations were allocated to VHF channels 3, 4 and 5A, which were

within the FM radio bands although not yet used for that purpose. A couple of notable

examples were NBN Newcastle, WIN-4 Wollongong and ABC Illawarra on channel

5A. Most TVs of that era were not equipped to receive these broadcasts, and so were

modified at the owners' expense to be able to tune into these bands; otherwise the

owner had to buy a new TV. Beginning in the 1990s, the Australian Broadcasting

Authority began a process to move these stations to UHF bands to free up valuable

26

VHF spectrum for its original purpose of FM radio. In addition, by 1985 the federal

government decided new TV stations are to be broadcast on the UHF band.

Two new VHF frequencies, 9A and 12, have since been made available and are

being used primarily for digital services (e.g. ABC in capital cities) but also for some

new analogue services in regional areas. Because channel 9A is not used for television

services in or near Sydney, Melbourne, Brisbane, Adelaide or Perth, digital radio in

those cities are broadcast on DAB frequencies blocks 9A, 9B and 9C.

b. New Zealand

44–51, 54–68 MHz: Band I Television (channels 1–3)

87.5–108 MHz: Band II Radio

174–230 MHz: Band III Television (channels 4–11)

In New Zealand, the four main Free-to-Air TV stations still use the VHF

Television bands (Band I and Band III) to transmit their programmes to New Zealand

households. Other stations, including a variety of pay and regional free-to-air stations,

are forced to broadcast their programmes in the UHF band, since the VHF band is very

overloaded with four stations sharing a very small frequency band, which can be so

overcrowded that one or more channels, more often than not one of the Media Works-

owned channels (TV3 and C4), is unavailable in some smaller towns.

c. United Kingdom

British television originally used VHF band I and band III. Television on VHF

was in black and white with 405-line format (although there were experiments with all

three colour systems—NTSC, PAL, and SECAM—adapted for the 405-line system in

the late 1950s and early 60s).

British colour television was broadcast on UHF (channels 21–69), beginning in

the late 1960s. From then on, TV was broadcast on both VHF and UHF (VHF being a

monochromatic down conversion from the 625-line colour signal), with the exception

of BBC2 (which had always broadcast solely on UHF). The last British VHF TV

transmitters closed down on January 3, 1985. VHF band III is now used in the UK for

digital audio broadcasting. Unusually, the UK has an amateur radio allocation at 4

meters, 70-70.5 MHz

27

d. United States and Canada

Frequency assignments between US and Canadian users are closely coordinated

since much of the Canadian population is within VHF radio range of the US border.

Certain discrete frequencies are reserved for radio astronomy. The general services in

the VHF band are:

30–88 MHz: Military VHF-FM, including SINCGARS

30–46 MHz: Licensed 2-way land mobile communication.

43–50 MHz: Cordless telephones, 49 MHz FM walkie-talkies and radio controlled toys,

and mixed 2-way mobile communication.

The FM broadcast band originally operated here (42-50 MHz) before moving to 88-

108 MHz.

50–54 MHz: Amateur radio 6 meter band; 50 MHz is an amateur radio band used for a

variety of uses including DXing, FM repeaters and radio control, which usually takes

place on a "set-aside" band between 50.8 and 51 MHz.

55-72 and 77-88 MHz TV channels 2 through 6 (VHF-Lo), known as "Band I"

internationally; a tiny number of DTV stations will appear here. See North American

broadcast television frequencies

72–76 MHz: Radio controlled models, industrial remote control, and other devices.

Model aircraft operate on 72 MHz while surface models operate on 75 MHz in the USA

and Canada, air navigation beacons 74.8-75.2 MHz.

88–108 MHz: FM radio broadcasting (88–92 non-commercial, 92–108 commercial in

the United States) (Known as "Band II" internationally)

108–118 MHz: Air navigation beacons VOR

118–137 MHz: Air band for air traffic control, AM, 121.5 MHz is emergency

frequency

137-138 Space research, space operations, meteorological satellite

138–144 MHz: Land mobile, auxiliary civil services, satellite, space research, and other

miscellaneous services

144–148 MHz: Amateur radio band 2 Meters

28

148-150 Land mobile, fixed, satellite

150–156 MHz: "VHF Business band," the unlicensed Multi-Use Radio Service

(MURS), and other 2-way land mobile, FM

156–158 MHz VHF Marine Radio; narrow band FM, 156.8 MHz (Channel 16) is the

maritime emergency and contact frequency.

160-161 MHz Railways

162.40–162.55: NOAA Weather Stations, narrowband FM

175-216 MHz television channels 7 - 13 (VHF-Hi), known as "Band III"

internationally. A minority of DTV channels may appear here.

174–216 MHz: professional wireless microphones (low power, certain exact

frequencies only)

216–222 MHz: land mobile, fixed, maritime mobile,

222–225 MHz: 1.25 meters (US) (Canada 219-220, 222-225 MHz) Amateur radio

225 MHz and above: Military aircraft radio (225–400 MHz) AM, including HAVE

QUICK, dGPS RTCM-104

The large technically and commercially valuable slice of the VHF spectrum taken up by

television broadcasting has attracted the attention of many companies and governments

recently, with the development of more efficient digital television broadcasting

standards. In some countries much of this spectrum will likely become available

(probably for sale) in the next decade or so (June 12, 2009, in the United States).

3.4.1 87.5-87.9 MHz:-

87.5-87.9 MHz is a radio frequency which, in most of the world, is used for FM

broadcasting. In North America, however, this bandwidth is allocated to VHF

television channel 6 (82-88 MHz). The audio for TV channel 6 is broadcast at

87.75 MHz (adjustable down to 87.74). Several stations, most notably those joining the

Pulse 87 franchise, operate on this frequency as radio stations, though they use

television licenses. As a result, FM radio receivers such as those found in automobiles

which are designed to tune into this frequency range can receive the audio for

programming on the local TV channel 6 while in North America.

29

87.9 MHz is normally off-limits for FM audio broadcasting except for displaced class

D stations which have no other frequencies in the normal 88.1-107.9 MHz sub band on

which to move. So far, only 2 stations have qualified to operate on 87.9 MHz: 10-watt

KSFH in Mountain View, California and 34-watt translator K200AA in Sun Valley,

Nevada.

Unlicensed operation:

In some countries, particularly the United States and Canada, limited low-power

license-free operation is available in the FM broadcast band for purposes such as micro-

broadcasting and sending output from CD or digital media players to radios without

auxiliary-in jacks, though this is illegal in some other countries. This practice was

legalized in the United Kingdom on 8 December 2006.

30

CHAPTER 4

AUTOMATIC IDENTIFICATION SYSTEM

4.1 Basic overview

AIS transponders automatically broadcast information, such as their position,

speed, and navigational status, at regular intervals via a VHF transmitter built into the

transponder. The information originates from the ship's navigational sensors, typically

its global navigation satellite system (GNSS) receiver and gyrocompass. Other

information, such as the vessel name and VHF call sign, is programmed when installing

the equipment and is also transmitted regularly. The signals are received by AIS

transponders fitted on other ships or on land based systems, such as VTS systems. The

received information can be displayed on a screen or chart plotter, showing the other

vessels' positions in much the same manner as a radar display.

Fig. 11 Automatic Identification System (AIS)

System Overview from US Coast Guard shown in Fig. 11

The AIS standard describes two major classes of AIS units

1. Class A – mandated for use on SOLAS Chapter V vessels (and others in some

countries).

2. Class B – a low power, lower cost derivative for leisure and non-SOLAS markets.

31

Other variants are under development specifically for base stations, aids to navigation

and search and rescue, though they will all be derived from one of the existing

standards and inter-operate with them.

4.2 Message Types

There are 26 different types of messages capable of being sent by an AIS transponder.

Detailed description: Class A units

Each AIS transponder consists of one VHF transmitter, two VHF TDMA

receivers, one VHF Digital Selective Calling (DSC) receiver, and links to shipboard

display and sensor systems via standard marine electronic communications (such as

NMEA 0183, also known as IEC 61162). Timing is vital to the proper synchronization

and slot mapping for a Class A unit. Therefore, every unit is required to have an

internal global navigation satellite system (e.g. GPS) receiver. This internal receiver

may also be used for position information. However, position is typically provided by

an external receiver such as GPS, LORAN or an inertial navigation system and the

internal receiver is only used as a backup for position information. Other information

broadcast by the AIS, if available, is electronically obtained from shipboard equipment

through standard marine data connections. Heading information and course and speed

over ground would normally be provided by all AIS-equipped ships. Other information,

such as rate of turn, angle of heel, pitch and roll, and destination and ETA could also be

provided.

The AIS transponder normally works in an autonomous and continuous mode,

regardless of whether it is operating in the open seas or coastal or inland areas.

Transmissions are found on two frequencies, VHF maritime channels 87B

(161.975 MHz) and 88B (162.025 MHz) and use 9600 bit/s Gaussian minimum shift

keying (GMSK) modulation over 25 or 12.5 kHz channels using the High-level Data

Link Control (HDLC) packet protocol. Although only one radio channel is necessary,

each station transmits and receives over two radio channels to avoid interference

problems, and to allow channels to be shifted without communications loss from other

ships. The system provides for automatic contention resolution between itself and other

stations, and communications integrity is maintained even in overload situations.

In order to ensure that the VHF transmissions of different transponders do not

occur at the same time the signals are time multiplexed using a technology called Self-

32

Organized Time Division Multiple Access (STDMA). The design of this technology is

patented, and whether this patent has been waived for use by SOLAS vessels is a matter

of debate between the manufacturers of AIS systems and the patent holder. In order to

make the most efficient use of the bandwidth available, vessels which are anchored or

are moving slowly transmit less frequently than those that are moving faster or are

maneuvering. The update rate of fast maneuvering vessels is similar to that of

conventional marine radar. The time reference is derived from the navigation system.

Each station determines its own transmission schedule (slot), based upon data

link traffic history and knowledge of future actions by other stations. A position report

from one AIS station fits into one of 2250 time slots established every 60 seconds on

each frequency. AIS stations continuously synchronize themselves to each other, to

avoid overlap of slot transmissions. Slot selection by an AIS station is randomized

within a defined interval, and tagged with a random timeout of between 0 and 8 frames.

When a station changes its slot assignment, it announces both the new location and the

timeout for that location. In these way new stations, including those stations which

suddenly come within radio range close to other vessels will always be received by

those vessels.

The required ship reporting capacity according to the IMO performance

standard amounts to a minimum of 2000 time slots per minute, though the system

provides 4500 time slots per minute. The SOTDMA broadcast mode allows the system

to be overloaded by 400 to 500% through sharing of slots, and still provide nearly

100% throughputs for ships closer than 8 to 10 NM to each other in a ship to ship

mode. In the event of system overload, only targets further away will be subject to

drop-out, in order to give preference to nearer targets that are a primary concern to ship

operators. In practice, the capacity of the system is nearly unlimited, allowing for a

great number of ships to be accommodated at the same time.

The system coverage range is similar to other VHF applications, essentially

depending on the height of the antenna, but slightly better due to digital VHF and not

analog VHF. Its propagation is better than that of radar, due to the longer wavelength,

so it’s possible to “see” around bends and behind islands if the land masses are not too

high. A typical value to be expected at sea is nominally 20 nautical miles (37 km). With

the help of repeater stations, the coverage for both ship and VTS stations can be

improved considerably.

33

The system is backwards compatible with digital selective calling systems,

allowing shore-based GMDSS systems to inexpensively establish AIS operating

channels and identify and track AIS-equipped vessels, and is intended to fully replace

existing DSC-based transponder systems.

Shore-based AIS network systems are now being built up around the world. One

of the biggest fully-operational, real time systems with full routing capability is in

China. This system was built between the years 2003–2007 and delivered by Saab

Transponder Tech. The entire coastline is covered with approximately 250 base stations

in hot-standby configurations including 70 computer servers in three main regions.

Hundreds of shore based users, including ca 25 VTS centers, are connected to the

network and are able to see the maritime picture, but also to communicate with the ship

using SRM's (Safety Related Messages). All data are in real time and will improve

safety and security of ships and port facilities. It is also designed according to SOA

architecture with socket based connection and using IEC AIS standardized protocol all

the way to the VTS users. The base stations have hot-standby units (IEC 62320-1) and

the network is the third generation network solution.

By beginning of 2007 a new worldwide standard for AIS Base Stations was

approved – the IEC 62320-1 standard. The old IALA recommendation and the new IEC

62320-1 standard are in some functions incompatible and therefore attached network

solutions have to be upgraded. This will not impact users, but system builders have to

upgrade software to accommodate this. A standard for AIS base stations has been long

awaited. Currently many ad-hoc networks exist with class A mobiles. Base stations can

control the AIS message traffic in a region, which will hopefully reduce the number of

packet collisions.

Broadcast information

AIS transceiver sends the following data every 2 to 10 seconds depending on vessels

speed while underway, and every 3 minutes while vessel is at anchor. These data

include

1. The vessel's Maritime Mobile Service Identity (MMSI) – a unique nine digit

identification number.

2. Navigation status – "at anchor", "under way using engine(s)", "not under

command", etc

34

3. Rate of turn – right or left, 0 to 720 degrees per minute

4. Speed over ground – 0.1-knot (0.19 km/h) resolution from 0 to 102 knots

(189 km/h)

5. Position accuracy:

6. Longitude – to 1/10000 minute

7. Latitude – to 1/10000 minute

8. Course over ground – relative to true north to 0.1 degree

9. True Heading – 0 to 359 degrees from eg: gyro compass

10. Time stamp – UTC time accurate to nearest second when these data were

generated

In addition, the following data are broadcast every 6 minutes:

1. IMO ship identification number – a seven digit number that remains unchanged

upon transfer of the ship's registration to another country

2. Radio call sign – international radio call sign, up to seven characters, assigned

to the vessel by its country of registry

3. Name – 20 characters to represent the name of the vessel

4. Type of ship/cargo

5. Dimensions of ship – to nearest meter

6. Location of positioning systems (eg. GPS) antenna onboard the vessel

7. Type of positioning system – such as GPS, DGPS or LORAN-C. LORAN-C Is

no longer used throughout most of the United States. The only Standing

LORAN towers are located in Alaska, on the small Island Attu. This is being

used in conjunction with the Russian LORAN chain. Caribou, Me and

Nantucket, Ma used in conjunction with the Canadian chain.

8. Draught of ship – 0.1 meter to 25.5 meters

9. Destination – max 20 characters

10. ETA (estimated time of arrival) at destination – UTC month/date hour: minute

35

Detailed description: Class B units

Class B transponders are designed for carriage by sub-SOLAS vessels. Each

consists of one VHF transmitter, two VHF CSTDMA receivers, one of which is

multiplexed with the VHF Digital Selective Calling (DSC) receiver, and a GPS active

antenna. Although the data output format supports heading information, in general units

are not interfaced to a compass, so these data are seldom transmitted. Output is the

standard AIS data stream at 38400bps, as RS232 and/or NMEA formats. To prevent

overloading of the available bandwidth, transmission power is restricted to 2W, giving

a range of about 5 – 10 miles.

Four messages are defined for class B units:

a. Message 14: Safety Related Message

This message is transmitted on request for the user – some transponders have a button

that enables it to be sent, or it can be sent through the software interface. It sends a pre-

defined safety message.

b. Message 18: Standard Class B CS Position Report

This message is sent every 3 minutes where Speed over Ground (SOG) is less than 2

knots, or every 30 seconds for greater speeds.

MMSI, Time, SOG, COG, Longitude, Latitude, True Heading

c. Message 19: Extended Class B Equipment Position Report

This message was designed for the SOTDMA protocol, and is too long to be

transmitted as CST digital radio DMA. However a coast station can poll the

transponder for this message to be sent. MMSI, Time, SOG, COG, Longitude, Latitude,

True Heading, Ship type, Dimensions.

d. Message 24: Class B CS Static Data Report

This message is sent every 6 minutes, the same time interval as for Class A

transponders. Because of its length, this message is divided into two parts, sent within a

minute of each other.

Note that this message was defined after the original AIS specifications, so some Class

A units may need a firmware upgrade to be able to decode this message.

MMSI, Boat Name, Ship Type, Call Sign, Dimensions, and Equipment vendor ID

36

4.3. Applications and limitations

a. Collision avoidance

AIS are used in navigation primarily for collision avoidance. Due to the

limitations of VHF radio communications, and because not all vessels are equipped

with AIS, the system is meant to be used primarily as a means of lookout and to

determine risk of collision rather than as an automated collision avoidance system, in

accordance with the International Regulations for Preventing Collisions at Sea

(COLREGS).

Fig. 12 AIS Display

A vessel's text-only AIS display, listing nearby vessels' range, bearings, and names are

shown in fig. 12

When a ship is navigating at sea, the movement and identity of other ships in

the vicinity is critical for navigators to make decisions to avoid collision with other

ships and dangers (shoal or rocks). Visual observation (unaided, binoculars, night

vision), audio exchanges (whistle, horns, VHF radio), and radar or Automatic Radar

Plotting Aid (ARPA) are historically used for this purpose. However, a lack of positive

identification of the targets on the displays, and time delays and other limitation of

radar for observing and calculating the action and response of ships around, especially

on busy waters, sometimes prevent possible action in time to avoid collision.

37

While requirements of AIS are only to display a very basic text information, the data

obtained can be integrated with a graphical electronic chart or a radar display,

providing consolidated navigational information on a single display.

Vessel traffic services

In busy waters and harbors, a local Vessel Traffic Service (VTS) may exist to

manage ship traffic. Here, AIS provides additional traffic awareness and provides the

service with information on the kind of other ships and their movement.

b. Aids to navigation

AIS were developed with the ability to broadcast positions and names of objects

other than vessels, like navigational aid and marker positions. These aids can be located

on shore, such as in a lighthouse, or on the water, on platforms or buoys. The US Coast

Guard suggests that AIS might replace RACON, or radar beacons, currently used for

electronic navigation aids.

The ability to broadcast navigational aid positions has also created the concepts

of Synthetic AIS and Virtual AIS. In the first case, an AIS transmission describes the

position of physical marker but the signal itself originates from a transmitter located

elsewhere. For example, an on-shore base station might broadcast the position of ten

floating channel markers, each of which is too small to contain a transmitter itself. In

the second case, it can mean AIS transmissions that indicate a marker which does not

exist physically, or a concern which is not visible (i.e. submerged rocks, or a wrecked

ship). Although such virtual aids would only be visible to AIS equipped ships, the low

cost of maintaining them could lead to their usage when physical markers are

unavailable.

Search and rescue

For coordinating resources on scene of marine search & rescue operation, it is

important to know the position and navigation status of ships in the vicinity of the ship

or person in distress. Here AIS can provide additional information and awareness of the

resources for on scene operation, even though AIS range is limited to VHF radio range.

The AIS standard also envisioned the possible use on SAR Aircraft, and included a

message (AIS Message 9) for aircraft to report position. To aid SAR vessels and

aircraft in locating people in distress a standard for an AIS-SART AIS Search and

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Rescue Transmitter is currently being developed by the International Electro technical

Commission (IEC), the standard is scheduled to be finished by the end of 2008 and

AIS-SARTs will be available on the market from 2009.

c. Accident Investigation

AIS information received by VTS is important for accident investigation to

provide the accurate time, identity, position by GPS, compass heading, course over

ground (COG), Speed (by log/SOG) and rate of turn (ROT) of the ships involved for

accident analysis, rather than limited information (position, COG, SOG) of radar echo

by radar.

The maneuvering information of the events of the accident is important to

understand the actual movement of the ship before accident, particularly for collision,

grounding accidents. A more complete picture of the events could be obtained by

Voyage Data Recorder (VDR) data if available and maintained onboard for details of

the movement of the ship, voice communication and radar pictures during the

accidents. However, VDR data are not maintained due to the limited 12 hours storage

by IMO requirement.

4.4. Other reference

Automatic Identification System (AIS): A Human Factors Approach

Binary messages

The Saint Lawrence Seaway uses AIS binary messages (message type 8) to

provide information about water levels, lock orders, and weather in its navigable

system. The Panama Canal uses AIS binary messages (message type 8) to provide

information about rain along the Canal and wind in the locks.

Computing & networking

Several computer programs have been created for use with AIS data. Some

programs (such as Ship Plotter and gnuais) use a computer to demodulate the raw audio

from a modified marine VHF radio telephone when tuned to the AIS broadcast

frequency (Channel 87 & 88) into AIS data. Some programs can re-transmit the AIS

information to a local or global network allowing the public or authorized users to

observe vessel traffic from the web. Some programs display AIS data received from a

dedicated AIS receiver onto a computer or chart plotter. Most of these programs are not

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AIS transmitters, thus they will not broadcast your vessel's position but may be used as

an inexpensive alternative for smaller vessels to help aid navigation and avoid collision

with larger vessels that are required to broadcast their position. Ship enthusiasts also

use receivers to track and find vessels to add to their photo collections.

AIS data on the Internet

AIS position data are available on the Internet through many privately operated

geographic information systems. In December 2004, the International Maritime

Organization's (IMO) Maritime Safety Committee condemned the Internet publication

of AIS data as follows.

In relation to the issue of freely available automatic identification system (AIS)-

generated ship data on the world-wide web, the publication on the world-wide web or

elsewhere of AIS data transmitted by ships could be detrimental to the safety and

security of ships and port facilities and was undermining the efforts of the Organization

and its Member States to enhance the safety of navigation and security in the

international maritime transport sector.

Others have countered that AIS provides the same information that can be

obtained with a pair of binoculars and that ships have the option of turning off AIS

when they are in areas with security concerns.

Range limitations and space-based tracking

Shipboard AIS transponders have a horizontal range that is highly variable but

typically only about 74 kilometers (46 mi). They reach much further vertically, up to

the 400 km orbit of the International Space Station (ISS).

In November 2009, the STS-129 space shuttle mission attached two antennas -

an AIS VHF antenna, and an Amateur Radio antenna to the Columbus module of the

ISS. Both antennas were built in cooperation between ESA and the ARISS team

(Amateur Radio on ISS). Starting from May 2010 the European Space Agency is

testing two different AIS receivers, one from Luxspace (GdL), one from FFI (Norway)

in the frame of technology demonstration for space-based ship monitoring. This is a

first step towards a satellite-based AIS-monitoring service.

In 2008, ORBCOMM launched new low-earth orbit (LEO) satellites, equipped

with the capability to collect AIS data. Additionally, ORBCOMM has incorporated the

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ability to receive, collect and forward AIS data in the design of the next 18

ORBCOMM Generation 2 (0G2) satellites under development. As additional satellites

are launched, ORBCOMM will increase its capability by providing greater redundancy

and more frequent updates of AIS data. In 2009, LUXSPACE, a Grand Duchy of

Luxembourg based company has launched PathFinder2, (ex-Rubin) and is now the only

European company to have an operational system in orbit providing data from all over

the world on a daily basis. The satellite is operated in cooperation with SES ASTRA

and REDU Space Services. In 2007, a previous test of space-based AIS tracking by the

U.S. TacSat-2 satellite suffered from signal corruption because the many AIS signals

interfered with each other.

4.5. Detailed description: AIS Receivers

A number of manufacturers offer AIS receivers, designed for monitoring AIS

traffic, either from a shore station or for use on board a vessel that does not carry a

Class A or Class B unit. These may have two receivers, for monitoring both frequencies

simultaneously, or they may switch between frequencies (thereby missing some

messages, but coming in at a lower price). In general they will output RS232 or NMEA

data for display on an electronic chart plotter or on a computer.

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CONCLUSION

The radar system has performed well in measuring the velocity and distance to

targets and detecting target motion, both radial and tangential to the radar antenna. It is

possible to positively detect a human crawling even in a tangential fashion at a distance

of 100 meters. It can work effectively even in darkness or the presence of smoke, fog,

dust, and precipitation.

Radiotelephony is used on medium, high and very high frequencies to

communicate by voice with ship sat sea. On very high frequencies (VHF) people can

communicate over short ranges usually in a line of sight. On medium and low

frequencies they can communicate over hundreds of miles as these radio waves are less

densely spaced and tend to hug the curvature of the earth.

Today utilizing digital transmissions a ship equipped with an Automatic

Identification System (AIS) transponder sends data every 6 seconds to other ships and

coastal stations with the vessel's name, Identification number, position taken from the

GPS along with the ship's course and speed. By making use of a gadget like the AIS,

charting the routes and locations of ships has become very simple. . This is used to

ensure the safe and efficient movement of goods while protecting our environment

from shipping accidents

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REFERENCES

1. Barrett, Dick, "All you ever wanted to know about British air defense radar".

The Radar Pages.

2. Buderi, "Telephone History: Radar History". Privateline.com.

3. Ekco Radar WW2 Shadow Factory The secret development of British radar.

1. Grotticelli, Michael (2009-06-22). "DTV Transition Not So Smooth in Some

Markets". Broadcast Engineering. http://broadcastengineering.com/news/dtv-

transition-not-smooth-markets-0622/. Retrieved 2009-06-24.

2. The 42 MHz Segment is still currently used by the California Highway Patrol,

New Jersey State Police, Tennessee Highway Patrol and other state law

enforcement agencies.

3. Industry Canada, Canadian Table of Frequency Allocations 9 kHz - 275 GHz,

2005 Edition (revised February 2007) pg. 29

4. The 160 and 161 areas are AAR 99 channel railroad radios issued to the railroad

(Sample, AAR 21 is 160.425 and that is issued to TVRM and other railroads

that want AAR 21)

1. Types of Automatic Identification Systems. U.S. Coast Guard Navigation

Center. http://www.navcen.uscg.gov/

2. Top User Photos, Vessel Tracker Community. Retrieved October 14, 2008.

3. Maritime security – AIS ship data. 9th session: 1–10 December 2004. IMO

Maritime Safety Committee. Archived from the original on 2007-02-20.

http://web.archive.org/web/20070220201408/http://www.imo.org/

4. http://www.orbcomm.com/ais/ais.htm

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