Emitter Geolocation Research Articles

Emitter Location with Azimuth and Elevation Measurements Using a Single Aerial Platform for Electronic Support Missions.

Passive ground emitter geolocation techniques are essential to electronic warfare systems, as they provide threat warnings in hostile environments, while ensuring the electronic silence of the mission platform. Geolocation of enemy emitters indicates the position of and type of adversary troops, and allows for the use of guided munition against enemy targets. Three-dimensional geolocation solutions based on least squares and particle filter estimation, using only azimuth and elevation measurements, were considered. Three batch-processing and one instantaneous solution algorithms, i.e., using a single pulse or a single observation point, were developed and investigated. The performance of the proposed solutions was demonstrated by simulations. Results showed that the batch-processing solutions achieved acceptable accuracies with a sufficient number of observation points. The performance degraded with fewer observation points. The instantaneous geolocation solution improved performance with increasing observation points, i.e., working in the sequential mode, and therefore could approach the accuracy of the batch-processing solutions.

Modelling and Analysis of Received Signal Strength - Based Emitter Geolocation from Single Geostationary Satellite with Multiple Antennas using STK Toolkit

ABSTRACT This paper considers geolocation of a transmitter being steered by antennas installed on geostationary satellite using received signal strength (RSS) metric. The difference in the signal strengths is measured by the antennas and subsequently plotted as lines of position (LOP) on the surface of the earth. Intersection of these two or more LOP indicates the location of the terrestrial RF transmitters. This problem is appropriately modelled using Satellite Tool Kit (STK) to geolocate a transmitter based on spatially separated RSS measurements. Accuracy and size of the geolocation area depends on the distance between transmitter and the receiver and the contour widths geometry. Results of geolocation accuracy is compared by increasing the RF transmitter latitude at different contour widths. It is observed that transmitter placed at lower latitudes and having smaller contour widths provided a higher accuracy validating the proposed formulation.

Estimating Location Accuracy of Stationary Emitter in Presence of Biasing in Receiver Position and Velocity by Exploiting Cross Ambiguity Function

This paper proposes CAF algorithm to estimate localisation accuracy of a stationary emitter which is being monitored by a pair of sensors mounted on high altitudes. It computes joint Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA) using Cross Ambiguity Function (CAF) and measures geolocation accuracy in presence of biasing in sensor position and velocity. Previous work in this area utilizes TDOA and FDOA measurements with known sensor kinematics which is fed to Maximum Likelihood or Least Squares algorithm for post processing. However it is computation demanding. In the present work, surface peaks of TDOA and FDOA values are directly mapped to geographic coordinates. This method is computationally efficient. As sensor and emitter geometry keeps changing over time due to moving sensors, multiple CAF snapshots are taken for emitter geolocation. Simulations are carried out using MATLAB. It is observed that at 30 dB SNR, location accuracy of stationary emitter is 100 m at known sensor kinematics and by introducing bias in the receiver position and velocity, it is 200 meters. These measurements are well within and in accordance with theoretical developments.

Frequency Estimation in Coherent, Periodic Pulse Trains

Radars use coherence to increase the signal-processing gain. In electronic support, that same coherence can be exploited to accurately estimate carrier frequency when measured modulo the pulse repetition frequency. Such estimates can be used for passive emitter geolocation, for example. In the pioneering work of Howard & Lavoie on this topic [1], [2], results are demonstrated only where the pulse repetition interval (PRI) is an integer and where pulses are sinusoidal. In this paper, we show how the results can be generalised to a broad class of pulse shapes, without needing to know the pulse shape in advance. We also show how the signals may be efficiently processed when the PRI is non-integer.

Approximate Maximum Likelihood Radio Emitter Geolocation With Time-Varying Doppler

Direct geolocation of radio emitters has traditionally been formulated using short measurement intervals over which delay and Doppler frequency shift are approximated as constant. In this paper, we consider maximum likelihood position estimation using long measurement intervals for which the Doppler is time varying. A series of assumptions and approximations are used to develop an efficient solution involving coherent combining of traditional, complex ambiguity function processing outputs. Simulation results are used to demonstrate potential gains.

Direct emitter geolocation under local scattering

Emitter geolocation under local scattering environment is explored. We derive an analytic model for the received signal where the local scattering environment is modeled as a stochastic process using the Gaussian Angle of Arrival (GAA) model. For the signal model we provide both optimal and sub-optimal, computationally-simpler, 1-step (direct) emitter geolocation algorithms. The proposed algorithms enable to estimate the emitter ׳s position directly, using the received signal samples. The proposed algorithms extract the emitter position information from both fading channel statistics and temporal correlations when the fading channel is quasi-static. It is shown that the devised 1-step algorithms outperform 2-step emitter geolocation algorithms, formerly proposed for the problem. Numerical examples are provided to illustrate the performance. The results are compared with the theoretical performance projected by the Cramér–Rao lower bound.

유전 알고리즘 기반 레이더 펄스 모호성 해결방법

TDOA(Time Difference of Arrival) 기반 수동형 전자감시장비는 이격 동작하는 다수의 수신기에서 수신되는 전자파 신호의 펄스도착시간인 TOA(Time of Arrival) 정보를 이용하여 신호원의 공간상 위치를 탐지한다. 수신기 간 이격 거리 대비 신호원에서 방사되는 신호의 PRI(Pulse Repetition Interval)가 크지 않을 경우 TDOA 기반 위치탐지를 위한 각 수신기에서의 동일 펄스쌍 선정에 모호성이 발생될 수 있다. 본 논문에서는 이격 동작하는 각 수신기에서 수신한 펄스들과 신호원간의 순시 방향탐지결과인 AOA(Angle of Arrival)를 이용하여 펄스 선택의 모호성을 신호원의 위치와 신호원으로부터 수신한 펄스들과의 TDOA 최적화 문제로 변경하고 이를 유전 알고리즘 기반으로 TDOA 기반 위치탐지 과정에서 발생될 수 있는 동일 펄스 선택 모호성을 최소화할 수 있는 새로운 기법을 제안하며, 다양한 모의실험을 통해 제안된 기법의 성능을 분석하였다.

Emitter geolocation using single moving receiver

Emitter geolocation using a single moving receiving-station is explored. We propose algorithms for transponder-aided geolocation of an emitting station where the transmitted waveform is either known or unknown a priori. The emitter position is estimated directly (in a single-step) from the received signal samples. Numerical examples are provided to illustrate the performance. The results are compared with single-step algorithms for multiple-receivers geolocation system and with the Cramér–Rao lower bound.

Single Receiver Emitter Geolocation Based on Signal Periodicity With Oscillator Instability

We propose a method for localizing a stationary emitter, not necessarily cooperative, using a single moving receiver based on time of arrival (TOA) measurements. The sensor intercepts the incoming signal at different locations along its trajectory, thus, effectively creating an array of spatially separated sensors. This manuscript presents the method and its performance in the presence of noise and oscillator instability. The proposed method provides a few advantages over the traditional multi-sensor TOA method. These include the economic aspect of using a single receiver instead of several ones, synchronization between stations is not required since only a single sensor is used, on line optimization of the emitter-sensor geometry in order to improve performance (path design, number of data collection points, etc.), and finally, there is no requirement to transmit data between sensors. The method is applicable to any signal as long as it includes a portion that appears periodically such as a synchronization sequence, or a signal whose transmission time intervals are known, even if they are not identical. We derive the Cramer-Rao lower bound, perform small error analysis for the algorithm, and corroborate the results with simulations. We show that reasonable localization results can be obtained under realistic conditions.

TDOA/FDOA 융합 기반 신호원의 위치추정 및 성능 분석

TDOA (time difference of arrival)와 FDOA (frequency difference of arrival) 정보를 동시에 이용하는 신호원 위치추정 기법은 단일 정보를 이용하는 경우에 비해 높은 정확도를 가지는 장점을 가지고 있다. 이러한 위치추정 기법의 추정성능은 수신단 쌍의 조합, 수신단의 기하학적 배치 특성 및 속도 등의 다양한 운용변수에 따라 크게 달라진다. 그러므로 전자전 시스템의 효율적인 운용을 위해서는 다양한 운용 조건에 따른 사전 성능 분석이 요구된다. 하지만 기존의 비 반복적인 위치추정 방법은 기준 수신단의 설정 및 수신단 배치 형태에 제약을 가진다. 따라서 본 논문에서는 임의의 다양한 수신단 조합과 배치 형태에서 적용이 가능한 Gauss-Newton 기법을 유도하고 이를 통해 위치추정을 수행한다. 또한 모의실험을 통해 TDOA/FDOA 융합 기반 위치추정 방법과 단일 TDOA 또는 FDOA를 독립적으로 사용했을 때의 성능을 비교 분석하고 CEP (circular error probability) 평면을 이용하여 융합 기반 위치추정 방법이 독립적 방법에 비해 상대적으로 높은 추정 성능을 가짐을 보인다. The emitter geolocation method using the time difference of arrival (TDOA) and the frequency difference of arrival (FDOA) has more accurate performance comparing to the single TDOA or FDOA based method. The estimation performance varies with the sensor paring strategies, the deployment and velocities of the sensors. Therefore, to establish effective strategy on the electronic warfare system, it is required to analyze the relation between the estimation accuracy and the operational condition of sensors. However, in the conventional non-iterative method, the restriction of the deployment of sensors and the reference sensor exists. Therefore, we derive the emitter geolocation method based on a Gauss-Newton method which is available to apply to any various sensor pairs and the deployment and velocities of the sensors. In addition, simulation results are included to compare the performance of geolocation method according to the used measurements: the combined TDOA/FDOA, TDOA, and FDOA. Also, we present that the combined TDOA/FDOA method outperforms over single TDOA or FDOA on the estimation accuracy with the CEP plane.

A multipath-driven approach to HF geolocation

A method is proposed for HF emitter geolocation and mode group-range estimation when the signal of interest is received via skywave propagation by a uniform linear array (ULA) of antennas at a single site. Ionospheric multipath and the geometrical relationships that constrain such propagation are exploited to derive a new class of estimator for a problem that inherently produces an ambiguous solution when the modes are considered individually. The introduced multipath-driven approach resolves the coning ambiguity and opens up the possibility to perform meaningful HF single site location (SSL) with a ULA. The method is also applicable to reduce estimation errors in traditional HF-SSL systems based on two-dimensional apertures. Field-data gathered in a controlled experiment with known truth is used to validate the method.

Geolocation‐aware security in a netcentric small unmanned‐aerial‐system for RF emitters

AbstractEnhancing security requires sensing devices surveilling over critical infrastructures for early warning of radio frequency (RF) emitter geolocations. Conventional geolocation of RF emitters has adopted active methodologies by illuminating targets, such as radar sensors. However, active geolocation draws unwanted attention of adversary, thus highly increases threats and vulnerabilities of the sensing devices. As security issues become a central concern in sensing applications, we propose a small unmanned‐aerial‐system for passive geolocation of RF emitters. Multiple electronic surveillance sensors are mounted on small unmanned‐aerial‐vehicles (UAVs) to provide geolocation awareness. Both sensors‐to‐UAV and UAVs‐to‐fusion‐center communications are investigated. Different with previous studies, our approach is based on an empirical path loss and log‐normal shadowing model, from a wireless communication and signal processing vision. The communication degradation from UAV to fusion center has been taken into consideration other than assuming lossless performance. The analyzed geolocation error and the error probability of distance shows that this approach provides robust performance at high frequencies, thus offers an effective solution for the security issue in RF emitter geolocation. Copyright © 2012 John Wiley & Sons, Ltd.

PULSE REPETITION INTERVAL ESTIMATION IN MOVING PASSIVE SENSORS BASED ON OBSERVATION CALIBRATION

High-accuracy pulse repetition interval (PRI) estimation is meaningful for passive sensors to identify radar emitters. This paper considers the problem of estimating the PRIs of motionless radars in moving passive sensor systems. A modifled method which based on observation calibration is proposed. This method can e-ciently compensate the estimation bias induced by model mismatch, through calibrating the pulse time of arrival (TOA) measurements with emitter geolocation information. Performance analysis and simulation results show that our method can improve the PRI estimation accuracy signiflcantly.

RF Emitter Geolocation using Amplitude Comparison with Auto-Calibrated Relative Antenna Gains

We consider an RF emitter localization problem that consists of a stationary RF emitter as a target and a moving RF receiver as an observer. An antenna system with unknown bias is deployed in the RF receiver to find the target direction of arrival (DOA) or bearing. This problem is conventionally solved by two separate stages, namely, to estimate target bearings through a relative amplitude direction finding (DF) algorithm, and to find the emitter location from the estimated bearings. The drawback of such a structure is that it is difficult to identify antenna bias through the DF algorithm alone, and the bearing error caused by antenna bias can significantly decrease the localization accuracy, especially when a target is located in longer range. To overcome this drawback, we merge the two stages together to formulate the localization problem as a discrete dynamic estimation problem. Thus, the target location and the antenna bias can be estimated simultaneously. Two algorithms are developed to cope with the merged system. The first algorithm, which is named as A-UKF, uses an unscented Kalman filter (UKF) to estimate the target location and the antenna bias in an augmented state. The second algorithm called MM-UKF further improves the A-UKF by introducing a multiple model (MM) approach to overcome the problem caused by an inaccurate initial state. The inaccurate initial state can seriously affect the performance of subsequent nonlinear estimation. The results show that both proposed algorithms are obviously superior to the conventional two-stage localization algorithm, and the MM-UKF algorithm outperforms the A-UKF.

Mobile Emitter Geolocation and Tracking Using TDOA and FDOA Measurements

This paper considers recursive tracking of one mobile emitter using a sequence of time difference of arrival (TDOA) and frequency difference of arrival (FDOA) measurement pairs obtained by one pair of sensors. We consider only a single emitter without data association issues (no missed detections or false measurements). Each TDOA measurement defines a region of possible emitter locations around a unique hyperbola. This likelihood function is approximated by a Gaussian mixture, which leads to a dynamic bank of Kalman filters tracking algorithm. The FDOA measurements update relative probabilities and estimates of individual Kalman filters. This approach results in a better track state probability density function approximation by a Gaussian mixture, and tracking results near the Cramer-Rao lower bound. Proposed algorithm is also applicable in other cases of nonlinear information fusion. The performance of proposed Gaussian mixture approach is evaluated using a simulation study, and compared with a bank of EKF filters and the Cramer-Rao lower bound.