Terrain Scattered Interference Research Articles

Auxiliary beam terrain‐scattered interference suppression: reflection system and radar performance

Terrain-scattered interference (TSI), that is, jammer signals reflected on the earth's surface, is a significant problem to military airborne radar. In auxiliary beam TSI suppression, the TSI in the main radar beam is estimated by a single or several auxiliary beams and is subtracted from the main beam channel. The signal to subtract is the auxiliary beam signals fed through an estimate of the ‘reflection system’, which describes scattering on the surface. The authors first present results on the structure of this TSI suppression, on the estimation of the reflection system and on the quality of the estimate. Then the authors derive theoretical expressions for the signal-to-interference plus noise ratio (SINR) and the remaining TSI power for a single auxiliary beam. Since the SINR is directly connected to the radar performance, it can be seen what factors affect the performance and how. It was noted that when the estimated reflection system is missing one or more delays of the true system, the TSI filter cannot suppress the TSI signal completely. This phenomenon, which is called ‘TSI leakage’, has a very large impact on the performance. The SINR cannot be kept constant. Instead, an ‘SINR improvement’ can be defined.

Constrained Fast-Time STAP for Interference Suppression in Multichannel SAR

Forming a synthetic aperture radar (SAR) image while suppressing an airborne broadband jammer can potentially destroy large regions of the image. In addition to this, multipath reflections from the ground known as hot clutter or terrain scattered interference (TSI) will add a nonstationary interference component to the image. A number of constrained fast-time space time adaptive processing (STAP) techniques are presented which exploit adaptive beamforming to suppress the interference with minimal distortion to the final image.

TSI Finders for Estimation of the Location of an Interference Source Using an Ariborne Array

An algorithm based on space fast time adaptive processing to estimate the physical location of an interference source closely associated with a physical object and enhancing the detection performance against that object using a phased array radar is presented. Conventional direction finding techniques can estimate all the signals and their associated multipaths usually in a single spectrum. However, none of the techniques are currently able to identify direct path (source direction of interest) and its associated multipath individually. Without this knowledge, we are not in a position to achieve an estimation of the physical location of the interference source via ray tracing. The identification of the physical location of an interference source has become an important issue for some radar applications. The proposed technique identifies all the terrain bounced interference paths associated with the source of interest only (main lobe interferer). This is achieved via the introduction of a postprocessor known as the terrain scattered interference (TSI) finder.

A Space/Fast-Time Adaptive Monopulse Technique

Mainbeam jamming poses a particularly difficult challenge for conventional monopulse radars. In such cases spatially adaptive processing provides some interference suppression when the target and jammer are not exactly coaligned. However, as the target angle approaches that of the jammer, mitigation performance is increasingly hampered and distortions are introduced into the resulting beam pattern. Both of these factors limit the reliability of a spatially adaptive monopulse processor. The presence of coherent multipath in the form of terrain-scattered interference (TSI), although normally considered a nuisance, can be exploited to suppress mainbeam jamming with space/fast-time processing. A method is presented offering space/fast-time monopulse processing with distortionless spatial array patterns that can achieve improved angle estimation over spatially adaptive monopulse. Performance results for the monopulse processor are obtained for mountaintop data containing a jammer and TSI, which demonstrate a dramatic improvement in performance over conventional monopulse and spatially adaptive monopulse.

Mainlobe Jammer Nulling via TSI Finders: A Space Fast-Time Adaptive Processor

An algorithm based on a space fast-time adaptive processor is presented for nulling the mainlobe jammer when the jammer and the target of interest share the same bearing. The computational load involved in the conventional processor, which blindly looks for the terrain-scattered interference (TSI), is required to stack a large number of consecutive range cell returns to form the space fast-time data snapshot making it almost impossible to implement in real time. This issue is resolved via the introduction of a preprocessor (a TSI finder which detects the presence of the minute levels of multipath components of the mainlobe jammer and associated time delays) which directs the STAP processor to select only two desired range returns in order to form the space fast-time data snapshot. The end result is a computationally extremely fast processor. Also a new space fast-time adaptive processor based on the super-resolution approach (eigenvector-based) is presented.

Beam-augmented STAP for joint clutter and jammer multipath mitigation

Combined monostatic clutter (MSC) and terrain scattered interference (TSI) pose a difficult challenge for adaptive radar processing. Mitigation techniques exist for each interference alone but are insufficient for their combined effects. Current approaches separate the problem into two stages, where TSI is suppressed first and then MSC is suppressed. However, during the initial TSI suppression stage, the MSC becomes corrupted. An innovative technique is introduced for achieving a significant improvement in cancellation performance for both MSC and TSI, even when the jammer appears in the mainbeam. The majority of the interference rejection, both TSI and MSC, is accomplished with an MSC filter, with further TSI suppression accomplished using an additional tapped reference beam. Simultaneous optimisation of the MSC filter weights and reference beam weights yields the desired processor. Performance results using Mountaintop radar data demonstrate the superiority of the proposed processor over existing processors.

Algorithms for mitigating terrain-scattered interference

This paper summarises a study of terrain-scattered interference (TSI) mitigation techniques, focusing on joint TSI mitigation and monostatic clutter nulling for airborne radars. It begins with an overview of TSI phenomenology and two-dimensional space-time adaptive processing (STAP) techniques for cancelling TSI. Two approaches for mitigating combined TSI and clutter are then examined. In the first approach, a sequence of two-dimensional adaptive filters is used. The first of these filters cancels TSI, while the second filter cancels monostatic clutter. In the second approach, a single, three-dimensional pre-Doppler STAP algorithm is used to cancel clutter and TSI simultaneously. Performance results for a representative system are shown to illustrate the trade-offs inherent in designing a mitigation approach.