Uttam Majumder

A challenge problem for 2D/3D imaging of targets from a volumetric data set in an urban environment

This paper describes a challenge problem whose scope is the 2D/3D imaging of stationary targets from a volumetric data set of X-band Synthetic Aperture Radar (SAR) data collected in an urban environment. The data for this problem was collected at a scene consisting of numerous civilian vehicles and calibration targets. The radar operated in circular SAR mode and completed 8 circular flight paths around the scene with varying altitudes. Data consists of phase history data, auxiliary data, processing algorithms, processed images, as well as ground truth data. Interest is focused on mitigating the large side lobes in the point spread function. Due to the sparse nature of the elevation aperture, traditional imaging techniques introduce excessive artifacts in the processed images. Further interests include the formation of highresolution 3D SAR images with single pass data and feature extraction for 3D SAR automatic target recognition applications. The purpose of releasing the Gotcha Volumetric SAR Data Set is to provide the community with X-band SAR data that supports the development of new algorithms for high-resolution 2D/3D imaging.

A challenge problem for SAR-based GMTI in urban environments

This document describes a challenge problem whose scope is the detection, geolocation, tracking and ID of moving vehicles from a set of X-band SAR data collected in an urban environment. The purpose of releasing this Gotcha GMTI Data Set is to provide the community with X-band SAR data that supports the development of new algorithms for SAR-based GMTI. To focus research onto specific areas of interest to AFRL, a number of challenge problems are defined. The data set provided is phase history from an AFRL airborne X-band SAR sensor. Some key features of this data set are two-pass, three phase center, one-foot range resolution, and one polarization (HH). In the scene observed, multiple vehicles are driving on roads near buildings. Ground truth is provided for one of the vehicles.

A Challenge Problem for SAR Change Detection and Data Compression.

This document describes a challenge problem whose scope is two-fold. The first aspect is to develop SAR CCD algorithms that are applicable for X-band SAR imagery collected in an urban environment. The second aspect relates to effective data compression of these complex SAR images, where quality SAR CCD is the metric of performance. A set of X-band SAR imagery is being provided to support this development. To focus research onto specific areas of interest to AFRL, a number of challenge problems are defined. The data provided is complex SAR imagery from an AFRL airborne X-band SAR sensor. Some key features of this data set are: 10 repeat passes, single phase center, and single polarization (HH). In the scene observed, there are multiple buildings, vehicles, and trees. Note that the imagery has been coherently aligned to a single reference.

Implementation and analysis of a fast backprojection algorithm

The convolution backprojection algorithm is an accurate synthetic aperture radar imaging technique, but it has seen limited use in the radar community due to its high computational costs. Therefore, significant research has been conducted for a fast backprojection algorithm, which surrenders some image quality for increased computational efficiency. This paper describes an implementation of both a standard convolution backprojection algorithm and a fast backprojection algorithm optimized for use on a Linux cluster and a field-programmable gate array (FPGA) based processing system. The performance of the different implementations is compared using synthetic ideal point targets and the SPIE XPatch Backhoe dataset.

Radar Signals Dismount Tracking for Urban Operations

It is critical in urban environments to not only track cars and tanks; but also individuals. Tracking dismounts, whereby an individual exits a car, can be done using conventional Electro-Optical (full color) or Infrared (thermal) cameras. However, EO/IR systems are subject to weather and line-of-sight conditions (i.e. person blocked by cloud) as well are degraded for long ranges. In this study, we pursue the use of radar images for dismount tracking. Radar dismount tracking will not entail the same robust features for person identification as EO systems; however, by being able to maintain track in all-weather conditions would afford friendly forces a location of all moving individuals. We show, using a feature-based tracker, that dismount detection, tracking, and potential intent, is possible. Radio Frequency (RF) tracking of dismounts is a relatively new concept because the data has not been available. By forming a data set based on the POSERTM program, and post-processing the data, we are interested in exploring the possibility of RF dismount tracking. In this paper, we (1) explore the generation of RF dismount data, (2) apply feature-based tracking algorithm to locate the moving target, and (3) assess the performance.

Spatially-varying calibration of along-track monopulse synthetic aperture radar imagery for ground moving target indication and tracking

In this research, we have developed an algorithm to reduce the residual artifacts of the background clutter (that is, stationary targets) that appear in the MTI imagery that are generated by Global Signal Subspace Difference (GSSD) of the monostatic and bistatic images of an along-track monopulse synthetic aperture radar (SAR) data. We have also established the theoretical foundation for estimating the motion track and parameters of the detected moving targets. We will show the results of these algorithms on measured SAR data.

Synthetic Aperture Radar moving target indication processing of along-track monopulse nonlinear gotcha data

This paper is concerned with imaging and moving target detection using a Synthetic Aperture Radar (SAR) platform that is known as Gotcha. The SAR platform can interrogate a scene using an imperfect circular trajectory; we refer to this as nonlinear SAR data collection. This collection can make monostatic and quasi-monostatic measurements in the along-track domain. We present subaperture-based wavefront reconstruction algorithms for motion compensation and imaging from this nonlinear SAR database. We also discuss adaptive filtering algorithms to construct MTI imagery from the two receiver channels of the system. Results will be provided.

Radar signals dismount data production

It has recently become apparent that dismount tracking from non-EO based sources will have a large positive impact on urban operations. EO / camera imaging is subject to line of site and weather conditions which makes it a non-robust source for dismount tracking. Other sensors exist (e.g. radar) to track dismount targets; however, little radar dismount data exists. This paper examines the capability to generate synthetic and measured dismount data sets for radar frequency (RF) processing. For synthetic data, we used the PoserTM program to generate 500 facet models of human dismount walking. Then we used these facet models with Xpatch to generate synthetic wideband radar data. For measured dismount data, we used a multimode (X-Band and Ku-Band) radar system to collect RF data of volunteer human (dismount) targets.

An analytical expression for the three-dimensional response of a point scatterer for circular synthetic aperture radar

Three-dimensional (3-D) spotlight-mode synthetic aperture radar (SAR) images of point scatterers provide insight into the achievable effectiveness of exploitation algorithms given a variety of operating parameters such as elevation angle, azimuth or synthetic aperture extent, and frequency bandwidth. Circular SAR, using 360 degrees of azimuth, offers the benefit of persistent surveillance and the potential for 3-D image reconstruction improvement compared with limited aperture SAR due in part to the increase in favorable viewing angles of unknown objects. The response of a point scatter at the origin, or center of the imaging scene, is known and has been quantified for circular SAR in prior literature by a closed-form solution. The behavior of a point scatterer radially displaced from the origin has been previously characterized for circular SAR through implementation of backprojection image reconstructions. Here, we derive a closed-form expression for the response of an arbitrarily located point scatterer given a circular flight path. In addition, the behavior of the response of an off-center point target is compared to that of a point scatterer at the origin. Symmetries within the 3-D point spread functions (PSFs), or impulse response functions (IPRs), are also noted to provide knowledge of the minimum subset of SAR images required to fully characterize the response of a particular point scatterer. Understanding of simple scattering behavior can provide insight into the response of more complex targets, given that complicated targets may sometimes be modeled as an arrangement of geometrically simple scattering objects.

Design and analysis of radar waveforms achieving transmit and receive orthogonality

This paper presents the design and analysis of orthogonal, Doppler-tolerant waveforms for waveform agile radar (e.g. multiple-input multiple-output (MIMO) radar) applications. Previous work has given little consideration to the design of radar waveforms that remain orthogonal when they are received. Our research is focused on: 1) developing sets of waveforms that are orthogonal on both transmit and receive, and 2) ensuring that these waveforms are Doppler tolerant when properly processed. Our proposed solution achieves the above-mentioned goals by incorporating direct sequence spread spectrum (DSSS) coding techniques on linear frequency modulated (LFM) signals. We call this spread spectrum coded LFM (SSCL) signaling. Our transmitted LFM waveforms are rendered orthogonal with a unique spread spectrum (SS) code. At the receiver, the echo signal will be decoded using its spreading code. In this manner, transmitted orthogonal waveforms can be match filtered only with the intended received signals. From analytical expressions of the waveforms we have designed and from simulation results, we found that: 1) cross-ambiguity function (CAF) of two LFM SS coded (orthogonal) waveforms is small for all delays and Dopplers (i.e. transmit and receive signals satisfy near orthogonality constraint); 2) the length of the SS code determines the amount of interference suppression (i.e., complete orthogonal or near orthogonal of the received signal); 3) we can process the same received signal in two different ways; one method can provide LFM signal resolution and the other method can provide ultrahigh resolution; 4) biorthogonal codes can be used to reduce bandwidth when code length is large. Our proposed waveforms inherit multiple attributes (e.g. chirp diversity, code diversity, frequency diversity) of diverse waveforms.