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DP Operator Course Artemis

Training Manual

Jan. 2010 © Kongsberg Maritime AS Page 6.4.1

Rev. 07 Training

Artemis Principle

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Artemis DP Operator Course

Training Manual

Page 6.4.2 © Kongsberg Maritime AS Jan. 2010

Training Rev. 07

The purpose of the Artemis positioning system is to accurately determine and locate the

position of a mobile unit, for example a vessel, with respect to a known fixed point. The

system consists of two stations, the Mobile station on the moving unit and the Fix station on

the known fixed point.

To obtain the azimuth (bearing relative to north) of the Mobile station, the Fix antenna isaimed at a reference object with known azimuth prior to locking the system. The distance of

the Mobile station to the Fix station is obtained by measuring the time elapse of coded

interruptions in the microwave signal transmitted by both stations.

The antennas of the Fix and Mobile stations automatically track each other by maintaining a

continuous microwave link. A precision shaft encoder, coupled to the Fix station’s antenna

drive shaft, measures the angle of the antenna with respect to a known reference direction,

providing the bearing of the Mobile station.

To avoid mutual interference in areas where two Artemis systems are operational, four

Fix/Mobile station frequency pairs are available. Frequency pair selection is done from the

operating panel. Automatic frequency control at the Mobile station keeps the frequencies ofthe two stations exactly 30 MHz apart.

The system is portable and easy to install and thus being ideal as a sensor for dynamic

positioning (DP). Performance is unaffected by rain, fog or haze. The minimum range is 10 m,

and maximum range when used with DP is 10 km.

System Specifications

Frequency

Frequency band : 9.2 - 9.3 GHz

Four fixed, user-selectable frequency pairs : MOBILE FIX9200 MHz 9230 MHz (pair 0)

9300 MHz 9270 MHz (pair 1)

9230 MHz 9200 MHz (pair 2)

9270 MHz 9300 MHz (pair 3)

Automatic frequency control at Mobile station.

Distance measurement

Range : 10 - 30.000 M

Display resolution : 0.01 or 0.1 m

Data update rate : 0.25 secAccuracy (short-term) : < 0.1 m standard deviation

Overall absolute accuracy accounting

for temperature effects, atmospheric

conditions and counter clock stability : 1 m standard deviation

Azimuth measurement

Range : 0 - 360 degrees

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Rev. 07 Training

Display resolution : 0.001 or 0.01 degree

Data update rate : 0.25 sec

Inherent accuracy : ±0.003 degree

Overall accuracy : 0.02 degree standard deviation

Antenna

Horizontal beam width : Approx. ±2 degrees @ -3 dB

Vertical beam width : Approx. ±11 degrees @ -3 dB

Approx. 40 degrees @ -10 dB

Horizontal side lobes : < -32 dB

Gain : Approx. 28 dB

Radiated microwave energy : Approx. 100 mW

Polarisation : Vertical

Standard Artemis System - Accuracy

- Range : 10 - 30 000 m ΔR = 1.5 m

- Bearing : 360° Δθ = 0.033°

- Lateral accuracy 58 cm/1000 m

Range ± 1.5 m irrespective of distance

Bearing ± 0.033° , that is 58cm/1 km, at 10 km this gives an inaccuracy of 5.8 m.

R

Δ θ

R

Δ R

Δ θ

Δ R

R m a x .

θ

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Training Rev. 07

Accurate Positioning Alignment

To get an accurate positioning alignment, the exact location of the Fix station must be known,

and a reference object (of which the bearing is known) is required.

The antenna of the Fix station is aligned with the reference object and the bearing is entered

into the system.

Relative Positioning Alignment

When using Artemis as a position reference system for DP, relative positioning is generally

used. Knowledge of the exact position of the Fix station is not required.

The Mobile and Fix stations are set in operation and the antennas locked. The bearing is taken

from the vessel and reported to the Fix station. At the Fix station 180° is added to the bearing,

and the resultant bearing is entered into the system.

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Rev. 07 Training

Antenna Tracking

The Artemis antenna type A010 consists of two-slotted wave-guides of equal length, which

are joined in the centre. This is a special four port microwave device that combines the two

antenna halves to two input/output wave-guide ports, the SUM and the DIF ports. The SUM

port is used for transmitting as well as for receiving. The DIF port is used for receiving only.

The figure shows the antenna SUM and DIF pattern. The left lobe of the DIF pattern has a

phase difference of -90° and the right lobe a phase difference of +90° with respect to the phase

of the SUM pattern.

ϕ

ϕ

ϕ

Antenna SUM and DIF pattern

Acting as a receiving antenna, the antenna outputs maximum SUM signal and zero DIF signal

if the incoming wave front is in parallel with the antenna. Deviations in the parallelism of the

incoming wave front result in a slowly decreasing SUM signal and a rapidly increasing DIF

signal.

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Training Rev. 07

By feeding the received SUM and DIF signals to a servo detector, an error voltage is

generated.

−

The error voltage is amplified and fed to a servomotor, which drives the antenna shaft, until

the error voltage is zero, which means that the incoming wave front is in parallel with the

antenna. When the servo detector’s error voltage drives the antenna, the station is said to be

locked onto or in lock with the counter station.

Distance Measurement (Range)

The distance measurement is based on measuring the time elapse between a coded interruption

in the microwave signal transmitted by the Mobile station and the reception of a single coded

interruption in the microwave signal transmitted by the Fix station as a response to that.

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Dip Zones

Reflection of microwave against the water surface

Although microwaves propagate

as direct waves (from antenna to

antenna), a part of the radiated

microwave energy is reflected

against the water surface and

reaches the receiving antenna

indirectly. Since the reflected

signal has to travel longer and

undergoes a 180° phase change

at the reflection point, there may

be a difference in phase between

the direct and the indirect signal

at the receiving antenna. This

may cause the direct signal to be

amplified (direct and indirect

signal in phase) or attenuated

(direct and indirect signal 180°out of phase).

The positions at which this phenomenon is experienced are generally referred to as dip zones,

range-holes, or interference zones, and are only dependent on the antenna heights and the

wavelength of the transmitted signal. The strength of the interference depends on the distance

between the transmitting and receiving antenna, and the nature of the water surface. A smooth

surface reflects the signal better than a choppy one.

PRODUCT

H1 x H2

H1 =

Mobile

antenna

height

H2 =

Fixed

antenna

height

800

700

600

500

400

300

DISTANCE (metres)

6000 10000 14000 18000 22000 26000 30000

6000 10000 14000 18000 22000 26000 30000

DIP

ZONES

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H

=

2 0 m

1 H

=

3 0 m

2

H

X H

= 6 0 0

1

2

H

=

2 m

1 H

=

3 0 m

2

H

X H

= 6 0

1

2

1

2

3

4

5

6

7

8

9

3 0

4 0

5 0

6 0

7 0

3 0

4 0

5 0

6 0

7 0

3 0

4 0

6 0

7 0 3

0 4 0

6 0

7 0 2

0 2 0

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Rev. 07 Training

Artemis Mk III System

Artemis Mk IV Mobile stations can also be used together with an Artemis Mk III Fix station.

Fix Control Data Unit Mobile Control Data Unit

When using a Mk III Fix station, the frequency on which to work is selected at the Mobile

station. The frequency must lie between 9200 - 9300 MHz, and it must be defined whether the

Fix station frequency is to be 30 MHz higher or lower than the Mobile station frequency. In

addition, the transmitting power and the preamplifier have to be set manually according to the

operating range.

Artemis Mk IV System

Artemis Basic Unit (ABU)

with antenna

Basic Operating Panel (BOP)

Extended Operating Panel (EOP)

Artemis Mk IV is a microwave position

reference system of the range-bearing

type. The system comprises two identical

stations (Artemis Basic unit); one station

configured as Fix station and the other as

Mobile station. Each station consists of

an ABU, on top of which a radar-like

tracking antenna is mounted, and a BOP

if it is used as a Fix station, or an EOP if

it is used as a Mobile station.

The Fix station is set up on a known,

fixed location and the Mobile station is

installed onboard the vessel.

The antenna is specially designed and of

the slotted wave guide type. It is fitted in

a completely sealed, lightweight

aluminium structure and has a fiberglas

radome. It is suitable for exposed

conditions. For operation in polar areas,antennas with an integrated radome-

heating element are available.

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Antenna Indicator Display

The antenna indicator display shows:

a) The ANTENNA DIRECTION marker, which indicates the direction of the antenna

with respect to the chosen reference direction. When the EOP is connected to the

Mobile station, the marker indicates the relative antenna bearing. When connected to

the Fix station, the marker indicates the azimuth.

b) The MAIN BEAM marker, if signal containing the correct address code is received

and the antenna is locked to the counter station.

c) The AUTOSEARCH SCAN SECTOR marker, if the autosearch operating mode is

selected and an autosearch scan sector is set. The unshaded area indicates the actual

scan sector.

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Rev. 07 Training

Operation

The Mobile and Fix stations are operated via the keyboard and display of the operating panels.

Once a link has been established between the two stations, the complete system can be

controlled from one station, generally the Mobile station.

Operator interaction between the keyboard and the display of the operating panel is via a

menu structure. This is basically the same for both the Mobile and Fix station.

OPERATE

MODIFY

MONITOR

WAKE-UP

FIX

CONFIG

1

2

3

4

5

6

MOB

Main menu Mobile station

OPERATE

MODIFY

MONITOR

WAKE-UP

MOBILE

CONFIG

1

2

3

4

5

6

FIX

Main Menu Fix station

From the main menu a selection can be made from the six categories by keying in the number

adjacent to the category.

- OPERATE

is selected to display the position parameters distance and azimuth.

- MODIFY

is selected to read and/or change station parameters, location parameters, autosearch

scan angles, clock, operating mode, communication parameters and voice channel

volume.

- MONITORis selected to monitor supply voltages, mixer crystal currents, Automatic Gain Control,

tuning and servo signal readings, temperature of wave guide and distance measuring

circuit.

- WAKE-UP

is selected to define the time and date the station is to switch itself on, this function is

normally not used.

- FIX (if Mobile station)

is selected at the Mobile station to remotely access the Fix menu structure to read

and/or modify Fix station parameters.

- MOBILE (if Fix station)

is selected at the Fix station to remotely access the Mobile menu structure to readand/or modify Mobile station parameters.

- CONFIG

is selected to configure an ABU before it is put into operation for the first time.

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Training Rev. 07

Artemis Mk IV Beacon

For short range positioning the Artemis Mk IV Beacon is a good alternative to the Artemis

Mk III or Mk IV Fix station. Typical applications are Floating Storage Tankers and Loading

Buoys.

The beacon provides only the distance to the Artemis Mobile station. The bearing is obtained

by combining the Mobile antenna bearing with the heading of the vessel as measured by the

vessel’s gyro compass.

There are three different antennas available:

Omni-directional antenna for range 10 - 2500 m

Semi-omni-directional antenna for range 10 - 5000 m

Horn antenna for range 15 - 1000 m

The horn antenna is specially intended for applications where the beacon is mounted in a

substantially higher position than the Mobile station and the system is operated at very short

ranges.

ARTEMIS BEACONBASE

POSITION

ARTEMIS

BEACON

ARTEMIS MICROWAVELINK

THE BEACON IS SIMPLY A TRANSPONDER. NO

BEARING DATA TRANSMITTED

ARTEMIS

MOBILE

ANTENNA

SHUTTLE TANKER

DURING APPROACH

OFFSHORE LOADING

TERMINAL WITH

BEARING MEASURED

AT MOBILE ANTENNA

TELEMETRY LINK ALLOWS TURNTABLE AZIMUTH TO BE

TRANSMITTED TO THE VESSEL SUCH THAT BEACON OFFSET

CAN BE COMPENSATED FOR, CORRECTING THE RANGE TO

THE BASE LOCATION

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Rev. 07 Training

Operation of two Systems

Given the available Artemis frequency band of 9200-9300 MHz, two Artemis systems can be

operated simultaneously in the same area by choosing frequency pair 0 or 2 for one system

and frequency pair 1 or 3 respectively for the other system. Whether more than two systems

can be operated simultaneously depends on the relative position of the vessels’ work areas.

Two Vessels using Artemis in different Sectors

Normally no interference will occur if a

spatial beam separation of at least 10° is

maintained. If, for instance, the vessels

are working at different faces of a

platform, i.e. have their Fix station

installed on different sides of the

platform, there is no interference to beexpected as long as the two beams do not

come within 10° of each other.

Vessels working in the same Direction

In the above figure the direction of the

microwave beams of Fix 1 - Mobile 1and Fix 2 - Mobile 2 differs less than

10°, so mutual interference can be

expected. This is especially the case at

larger working distances where the

beams converge. The solution is to

choose different frequency pairs.

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