International Journal of Recent Trends in Engineering & Research (IJRTER) Conference on Electronics, Information and Communication Systems (CELICS’17)

Special Issue; March - 2017 [ISSN: 2455-1457] DOI : 10.23883/IJRTER.CONF.20170331.036.4TK4E

@IJRTER-2017, All Rights Reserved 182

GEO-LOCATION OF RADAR

Abstract—Geo-location of Radars provides

great benefits to military surveillance and security

operations for threat avoidance and

implementation of Electronic Countermeasures.

Geo-location is done by satellite based on

Direction of Arrival (DOA) of Signal. The satellite

scans the area of interest and it records the value

of the angles generated by the radar pulses using a

2-D Direction Finding (DF) antenna. The numbers

of pulses that can be intercepted by the satellite at

different scenarios are calculated as Probability of

Intercepts (POI). To allow the maximum visibility

to the antenna, attitude rotation is applied to the

satellite so that the payload can intercept

maximum number of pulses. As the payload

intercepts the pulses, it records the direction of

arrival of the pulses in the form of unit vectors

(direction cosines). The direction Cosines are in

body centered coordinate system. The attitude

information of the satellite is obtained from the

body quaternion. Then the position of the emitter

on earth is calculated by the direction cosines and

the attitude information of the satellite (yaw, roll,

pitch).From direction cosines and the attitude

information, azimuth and elevation of the emitter is

obtained. It gives the position of emitter from

satellite body. The position of the emitter on earth

in body centered coordinate system is transformed

to ECEF coordinate system. Various errors like

direction cosine measurement error, attitude

measurement error, altitude measurement error,

position error of the satellite etcetera effects the

location of the emitter on the earth.

Index Terms— Directional Antenna, Electronic

Warfare, Radar Detection, Reconnaissance,

Satellites

I. INTRODUCTION

With a rapid development of aerospace

technology, space has gradually become the

strategic commanding point for defending

national security and providing benefits. As the

electronic reconnaissance satellite is able to

acquire the full-time, all-weather, large-area,

detailed, near real-time battlefield information

(such as force deployment, military equipment

and operation information), it has become a

powerful way to acquire information and plays an

important role in ensuring information

superiority.

Space electronic reconnaissance (SER) refers to

the process in which signals from various

electromagnetic transmitters are intercepted with

the help of man-made satellites, and then features

of signal are analysed, contents of signal are

extracted, and the position of transmitters are

located. The main tasks for space reconnaissance

includes: intercepting signals from various

transmitting sources such as radars,

communication devices, navigation beacons, and

identification friend or foe (IFF) transponders,

determining the tactical or technological

parameters and location, and identifying its type,

purpose, and the related air defence system and

weapon system; intercepting and analysing

signals of remote control and estimating its

weapon system performance, experimental

situations and development trend; intercepting

and monitoring radio communications, analysing

the signal features and determining the location of

the transmitters, interpreting and deciphering the

communication contents from which the potential

military actions and operation plans can be

perceived; long-term monitoring of the changes in

the electromagnetic transmitters and obtaining the

information such as electronic equipment

Kalamani.N1, Anand.N2, Gowtam.P3, Priyadharshini.M4

1Professor,2,3,4 Student Members

Department of Electronic and Communication Engineering

Coimbatore Institute of Engineering and Technology

International Journal of Recent Trends in Engineering & Research (IJRTER) Conference on Electronics, Information and Communication Systems (CELICS’17)

Special Issue; March - 2017 [ISSN: 2455-1457] DOI : 10.23883/IJRTER.CONF.20170331.036.4TK4E

@IJRTER-2017, All Rights Reserved 183

development status and rules of force deployment

and activities.

According to the intended purpose, the

application of the SER system can be classified

into radio frequency spectrum surveillance,

ELINT, communication intelligence (COMINT),

signal intelligence (SIGINT), battlefield

surveillance, and characteristic measurement

intelligence reconnaissance. The major

reconnaissance objects are transmitters from air,

space, land, and sea. The major reconnaissance

signal types include radio signals, short wave and

ultra-short communication signals, satellite

communication signals, microwave The band of

the reconnaissance objects ranges from short

wave, ultra-short wave, VHF (very high

frequency), UHF (ultra-high frequency, L band, S

band, C band, X band, Ku band, Ka band to EHF

(extremely high frequency) band, while the

frequency can range from 0.3MHz to 70 GHz.

Generally speaking, SER tasks are mainly

conducted by electronic reconnaissance satellites

on a low earth orbit (LEO) (which includes a sun

synchronous orbit, polar orbit, the orbit with the

inclination near the critical value, and an inclined

orbit) The altitude of the electronic

reconnaissance satellites on a low orbit is

relatively low, most often 300–1100 km with an

inclination greater than 50∘. Thus a relatively

accurate location for the transmitters can be

achieved. These satellites can also be applied to

monitor the emitters on the sea through the

reconnaissance and location of the radar or

communication signal on vessels. The

reconnaissance can be run with one satellite or a

multiple-satellite network.

Almost every military asset, from large fixed

installations to an individual aircraft, vehicle, or

small unit must transmit signals of one kind or

another in order to perform its mission. Analysis

of the signals transmitted from that location can

usually identify the type of asset (weapon,

military unit, aircraft, and ship). Location and

identification of the asset support the following

military activities such as Threat avoidance,

Warning of imminent attack, Selection and

Implementation of Electronic Countermeasures,

Targeting.

As position information is one of the most

important parts in the intelligence generated from

the electronic reconnaissance (ER) system,

location technology plays a crucial role in the

SER and determines the means of operation for

the entire reconnaissance satellite.This paper

discusses direction finding geo-location based on

Direction of Arrival by a single Low Earth Orbit

satellite based on its kinematics.

II. PROPOSED SYSTEM

To find the presence of an emitter (radar) in the

area of interest the satellite is first rotated giving

suitable quaternion input when it comes in contact

with the base station. The satellite is rotated in

such a way that to gain maximum visibility of the

region to be scanned. If the satellite intercepts any

signal the payload identifies the direction of

arrival of the signal and records it in the form of a

unit vector. The number of pulses that the satellite

can intercept depends upon the visibility time of

the satellite and type of radar present in the area

and the elevation of the radar.

A. Problem Statement

A Satellite is launched with necessary properties

to cover the Area of Interest. Find the location of

an Emitter (Radar) on the earth surface which is

situated within the AOI, provided that the

position of satellite at respective time instant,

Satellite body quaternion and Direction Cosines

of the Intercepting signal are known.

B Orbital Elements

Six integral constants are required to be

determined to describe the motion of the satellite

in the inertial coordinates system. We often call

these six integral constants orbit elements as

semi-major axis(a), Eccentricity(e), Inclination(i),

Right Ascension of the ascending node(RAAN),

Argument of Perigee(w), mean anomaly(M).

International Journal of Recent Trends in Engineering & Research (IJRTER) Conference on Electronics, Information and Communication Systems (CELICS’17)

Special Issue; March - 2017 [ISSN: 2455-1457] DOI : 10.23883/IJRTER.CONF.20170331.036.4TK4E

@IJRTER-2017, All Rights Reserved 184

C. Coordinate Rotation

If a vector in an original coordinate system is

expressed as r and in a new coordinate system

after rotation as r′, then by rotating the yz plane,

zx plane, and xy plane an angle of 𝜃 (counter

clockwise is positive) around the x axis, y axis,

and z axis, respectively, then

𝑟′ = 𝑅𝑥(𝜃)𝑟 .......... 3

𝑟′ = 𝑅𝑦(𝜃)𝑟 ...........4

𝑟′ = 𝑅𝑧(𝜃) .......... 5

Where:

𝑅𝑥(𝜃) = [1 0 00 𝑐𝑜𝑠𝜃 𝑠𝑖𝑛𝜃0 −𝑠𝑖𝑛𝜃 𝑐𝑜𝑠𝜃

]

𝑅𝑦(𝜃) = [𝑐𝑜𝑠𝜃 𝑠𝑖𝑛𝜃 0

0 1 0𝑠𝑖𝑛𝜃 0 𝑐𝑜𝑠𝜃

]

𝑅𝑍(𝜃) = [𝑐𝑜𝑠𝜃 𝑠𝑖𝑛𝜃 0

−𝑠𝑖𝑛𝜃 𝑐𝑜𝑠𝜃 00 0 1

]

The rotation matrix R(𝜃) has the following

characteristics:

𝑅−1(𝜃) = 𝑅𝑇(𝜃) = 𝑅(−𝜃) .....6

Any coordinate can be rotated in a certain order

by resolving into x, y, and z axes. In such a case,

the final rotation matrix is the rotation matrix

product. More attention should be made to the

non-commutative principle of matrix

multiplication.

D.Tranformation of coordinates

the ECI coordinate system 𝑐{𝑥𝑐, 𝑦𝑐 , 𝑧𝑐} rotates in

the positivedirection a right ascension 𝜃 around

the 𝑧𝑐axis, and transforms into the ECEF

coordinate system 𝑒{𝑥𝑒, 𝑦𝑒, 𝑧𝑒}. 𝜃 is the right

ascension of the prime meridian of the earth at a

certain time. Due to the rotation of the earth, 𝜃 is

changing, with a sidereal day as a period.

Suppose that the epoch geocentric equatorial

coordinates and ECEF coordinates of a vector are

𝑥𝑐 = (𝑥𝑐 , 𝑦𝑐 , 𝑧𝑐)𝑇and,𝑥𝑒 = (𝑥𝑒, 𝑦𝑒, 𝑧𝑒)𝑇

respectively; then 𝑥𝑒 = 𝑅𝑧(𝜃)𝑥𝑐

Geo-location of an Emitter on the Earth

The fundamental characteristic of SER

geo-location is to locate the satellite through the

intersection between the geo-location line and the

a priori information of the ground emitter on the

earth’s surface.

In our project we use Geo-location of an emitter

by single LEO satellite.

The geo-location method used by a single

satellite based on the line of sight (LOS)

Angle Measurement Techniques

In the first two approaches, it is necessary

to determine a line of bearing from known

locations to the emitter location. This is

accomplished by measuring the direction-of-

arrival (DOA) of signals. It is often called

direction finding (DF).

Interferometer DF Technique:

The interferometer DF technique refers to

the method of measuring the direction of

incoming waves using the phase difference of

antenna receipt signals in different wave fronts.

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Since this method is to obtain the DOA through

comparison of the phases between two antennas,

it is also called the phase comparison method.

Theoretically, as the phase interferometer can also

achieve mono-pulse DF, it is also called the phase

mono-pulse DF.

If an emitter is far away from the DF

system, the incoming wave can be approximately

seen as a plane wave. Suppose the plane wave is

transmitted from the direction at an angle of 𝜃

with the antenna bore sight and the transmitted

narrowband signals received by two antennas are

𝑠1(𝑡) = 𝑘1 cos(2𝜋𝑓𝑡 + 𝜙0 + 𝜑) , 𝑠2(𝑡)

= 𝑘2𝑐𝑜𝑠𝐼(2𝜋𝑓𝑡 + 𝜙0).

Theoretical diagram of a single baseline phase

interferometer.

The phase difference φ between the two antennas

caused by the wave path DOA of signals to the

two antennas is

𝜙 =2𝜋𝑙

𝜆𝑠𝑖𝑛𝜃

Phase Ambiguity Problem:

The phase interferometer DF is used to

estimate the emitter arrived angle 𝜃 by using the

measured value of the phase difference 𝜙. The

phase difference 𝜙 has a period of 2𝜋. If the

phase exceeds 2𝜋, phase ambiguity may occur,

thus preventing the true direction of the emitter to

be found. The following introduces the derivation

of the unambiguous visual angle 𝜃u of the phase

interferometer.

The interferometer is bore sight symmetric

and can carry out DF on both sides. The

maximum

Phase difference on one side of the bore sight is

𝜋, the maximum phase difference on the other

side is −𝜋, and the single value range of 𝜙 is [−𝜋,

𝜋].

Emitter Location – Accuracy:

When comparing the operational value of

direction-finding systems, one key parameter is

the effective accuracy. For angle-of-arrival

(AOA) systems, this accuracy is usually stated as

the RMS angular error. In full emitter location

systems (e.g., multiple angle-of-arrival DF

stations), the emitter location accuracy is often

stated as the Circular Error Probability (CEP).

When an emitter location is reported to someone

making decisions based on that information—for

example, a commander trying to determine where

an enemy asset is located—the CEP defines the

location uncertainty in the measurements being

reported from the emitter location system. This

circle drawn on a map display can be useful in the

decision-making process.

Root Mean Square (RMS) Error:

There is always some error in any

direction of arrival or emitter location

measurement, but we need to be able to evaluate

and talk about the “effective” error Accuracy of

Emitter Location Systems. If it is critical that

every single measurement have less than some

specific angular error, the peak error will be

specified. However, in practical direction-finding

systems, particularly those which instantaneously

cover 360°, there can be a few specific angles and

frequencies at which the measured errors are

significantly larger than average. Therefore, we

usually consider the effective accuracy of the

system to be better represented by the root, mean,

square (RMS) error. To determine the RMS error,

data is taken at many different angles through the

full system angular range (typically 360°) and at

regular increments over the system’s full

frequency range. Each measured angle of arrival

is compared to the actual angle of arrival to

determine the error angle. The actual angle is

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determined from the position of a turntable on

which the system is parked, from the navigation

system of the aircraft or ship on which the system

is mounted, or from some other independent

angular reference.

The formula is,

𝑒𝑟𝑟𝑜𝑟𝑅𝑀𝑆 = √∑ (𝑒𝑟𝑟𝑜𝑟)2𝑛

𝑖=1

𝑛

The RMS error is often considered to have

two parts, the mean and the standard deviation.

The mean error is simply the average of all error

measurements— which can be corrected in all

output data. The standard deviation is the RMS

error that is calculated if the mean error has been

subtracted from each data point (in effect, the

RMS error without the mean error component).

The relationship between the RMS error, the

mean error, and the standard deviation is:

𝑅𝑀𝑆 = √µ2 + 𝜎2

Where

µ = the mean of the data points;

σ= the standard deviation.

If you have the urge to try the formulas,

you will find that the numbers 1, 4, 6, 8, and 12

yield a mean of 6.2, a standard deviation of 3.7,

and an RMS of 7.22.

Problem Approach:

● Find the value of Azimuth and Elevation

from the Direction Cosines by taking cos

inverse.

Azimuth = Acos(x)

Elevation= Acos(y)

● Find the position of emitter in BCC

coordinate system ( xtb ) using the

following formula.

xtb = r * u

Where,

r = range in kms

u= cos (azimuth)

cos (elevation)

𝑠𝑞𝑟𝑡√(1 − 𝑐𝑜𝑠 (cos (𝑎𝑧)𝑎𝑧) 2 − 𝑐𝑜𝑠 (cos (𝑒𝑙)𝑒𝑙) 2

) ]

● Transform the emitter position from BCC

(xtb) system to ECEF system (Xte). For

calculation of Xte we require

Transformation Matrix/Rotation Matrix

which can be acquired by two forms.

1.From Rx(θ),Ry(θ),Rz(θ) .

Where

𝑅𝑥(𝜃) = [1 0 00 𝑐𝑜𝑠𝜃 𝑠𝑖𝑛𝜃0 −𝑠𝑖𝑛𝜃 𝑐𝑜𝑠𝜃

],

𝑅𝑦(𝜃) = [𝑐𝑜𝑠𝜃 0 −𝑠𝑖𝑛𝜃

0 1 0𝑠𝑖𝑛𝜃 0 𝑐𝑜𝑠𝜃

]

𝑅𝑧(𝜃) = [𝑐𝑜𝑠𝜃 𝑠𝑖𝑛𝜃 0

−𝑠𝑖𝑛𝜃 𝑐𝑜𝑠𝜃 00 0 1

]

The Rotation Matrix,

M=Rz(θ)*(Ry(θ)*(Rx(θ)*(Rrg*(Ry(Ls)*Rz

(Bs)))))

Where,

𝑅𝑟𝑔 = [1 0 00 1 0

−1 0 0]

Ls = Latitude of sub-satellite point

Bs= Longitude of sub-satellite

point

1. From Quaternion values.

If q0,q1,q2,q3 are the quaternion

values then the rotation matrix is

calculated

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@IJRTER-2017, All Rights Reserved 187

For calculation of Xte the

following formula is used,

Xte = S – (M-1 * Xtb)

The output obtained here will be of

form,

Xte =

z

y

x

The tools mentioned in the requirement

analysis are used to check the results of the

algorithm. The azimuth and elevation angles can

be calculated from quaternions by using the above

mentioned formula or they can be simply

produced from the Systems tool kit. The

algorithms can be implemented by giving the

inputs such as:

● Time Instance of Satellite

● Respective Satellite Position in ECEF

(X,Y,Z)

● Axial Velocity of Satellite body ( vx, vy,

vz )

● Quaternion Values ( q1,q2,q3,q4 )

● Range in kms

● Direction Cosines ( x, y, z) or just by

giving the azimuth and elevation inputs

directly to the elevation

●

SCENARIO:

● The contition for the simulation

scenario is as follows:the satellite orbital

altitude is 600km,the circular orbit has an

inclination of 45°, orbital elemants are

(6978km, 0, 45°, 0, 0, 0), the target

emitter is located at taipei and the method

is a single satellite LOS geolocation

Azimuth elevation data from satellite

REFERENCES

1. “EW 101: a first course in

electronic warfare” by David L.

Adamy.

2. “EW 102: a second course in

electronic warfare” David L. Adamy.

3. ”EW 103: Tactical Battlefield

Communications Electronic Warfare”

David L.Adamy.

4. “EW 104: EW Against a new

generation of threat” David L.Adamy.

5. “Electronic Warfare Target

Location Methods” Second Edition,

Richard A. Poisel

6.”Space Electronic Reconnaissance”,

Funcheng Guo, Yun Fan.