James L. Farrell

Bio: James L. Farrell is an academic researcher from Westinghouse Electric. The author has contributed to research in topics: Radar imaging & Inverse synthetic aperture radar. The author has an hindex of 8, co-authored 27 publications receiving 257 citations.

Kalman estimator tracking system

Abstract: A radar tracking system having a Kalman estimator is disclosed. The estimator is provided with angle and range track error measurements in a coordinate system that is aligned with and normal to the antenna line of sight, commonly referred to as the LOS coordinate system. This estimator implementation uses less computing resources in converting the measurements provided relative to the antenna LOS coordinate system, to predict target position referenced to a stable coordinate system such as geographic, wander azimuth, or inertial.

Synthetic Aperture Imaging with Maneuvers

Abstract: A digital processing approach has been devised for performing motion compensation in a high-resolution airborne synthetic aperture radar in the presence of simultaneous longitudinal (speed change), lateral (turn), and vertical (climb or dive) maneuvers. Both side-look and squint are accommodated in a unified scheme, which is validated by various simulation runs reported herein. Present attention is focused on theoretical verification, irrespective of mechanization or specific parameter values.

Effects of Navigation Errors in Maneuvering SAR

Abstract: A maneuvering synthetic aperture radar in squint mode, during a loosely piloted maneuver, is simulated with presence of various navigation system errors. The error sources investigated place emphasis on short-term effects, involving platform servo transients, noise and quantization in accelerometers, interaction of angle pickoff uncertainty with the displacement from platform to radar antenna, and uncertainty in this displacement itself. Simulation results are accompained by interpretive discussion, and followed by suggested areas for further study.

Natural frequencies of a flexible gravity- gradient satellite.

Abstract: Oscillation behavior of gravity gradient librations and flexural modes of cruciform satellite with single degree of freedom

Performance of strapdown inertial attitude reference systems.

Abstract: This paper illustrates a method, verified by simulation, of analyzing the major error sources in a strapdown inertial attitude reference system consisting of three pulse-torqued gyros and a digital differential analyzer (DBA). Long-term propagation of commutation error is solved herein through a formulation of effective timing errors that vary \vith the rms angular rates in three orthogonal directions. The analysis also provides the long-term effects of various gyro errors. Complexity of realistic motion in no way inhibits a straightforwar d and accurate error analysis; only a general characterization of the dynamic environment is necessary. Results are insensitive to the parametrization, provided that the truncation error is satisfactorily bounded. If in addition low roundoff errors are maintained, there is no need to orthogonalize the computed attitude parameters.

Developments in Radar Imaging

Abstract: Using range and Doppler information to produce radar images is a technique used in such diverse fields as air-to-ground imaging of objects, terrain, and oceans and ground-to-air imaging of aircraft, space objects, and planets. A review of the range-Doppler technique is presented along with a description of radar imaging forms including details of data acquisition and processing techniques.

SAR calibration: an overview

Abstract: Progress in synthetic-aperture radar, (SAR) calibration is reviewed. The difficulties of calibrating both airborne and spaceborne SAR image data are addressed. The quantities measured by a SAR, i.e. radar backscatter, are defined and mathematical formulations for the three basic types of SAR image are developed. The difficulties in establishing science requirements for calibration are discussed. The measurement of SAR image quality is briefly addressed. The problem of radiometric calibration is introduced via the SAR form of the radar equation, with both internal and external calibration approaches considered. The development of algorithms for polarimetric radar calibration is reviewed and the problems involved in phase calibration of interferometric SAR are discussed. Future challenges in the field of SAR calibration are considered. >

Tutorial review of synthetic-aperture radar (SAR) with applications to imaging of the ocean surface

Abstract: A synthetic aperture radar (SAR) can produce high-resolution two-dimensional images of mapped areas. The SAR comprises a pulsed transmitter, an antenna, and a phase-coherent receiver. The SAR is borne by a constant velocity vehicle such as an aircraft or satellite, with the antenna beam axis oriented obliquely to the velocity vector. The image plane is defined by the velocity vector and antenna beam axis. The image orthogonal coordinates are range and cross range (azimuth). The amplitude and phase of the received signals are collected for the duration of an integration time after which the signal is processed. High range resolution is achieved by the use of wide bandwidth transmitted pulses. High azimuth resolution is achieved by focusing, with a signal processing technique, an extremely long antenna that is synthesized from the coherent phase history. The pulse repetition frequency of the SAR is constrained within bounds established by the geometry and signal ambiguity limits. SAR operation requires relative motion between radar and target. Nominal velocity values are assumed for signal processing and measurable deviations are used for error compensation. Residual uncertainties and high-order derivatives of the velocity which are difficult to compensate may cause image smearing, defocusing, and increased image sidelobes. The SAR transforms the ocean surface into numerous small cells, each with dimensions of range and azimuth resolution. An image of a cell can be produced provided the radar cross section of the cell is sufficiently large and the cell phase history is deterministic. Ocean waves evidently move sufficiently uniformly to produce SAR images which correlate well with optical photographs and visual observations. The relationship between SAR images and oceanic physical features is not completely understood, and more analyses and investigations are desired.

Doppler Parameter Estimation for Spaceborne Synthetic-Aperture Radars

Abstract: Problems in the determination of Doppler parameters for spaceborne synthetic-aperture radar (SAR) data processing are examined. The degradations in image quality due to errors in these parameters are summarized. We show that these parameters can be estimated using accurate spacecraft ancillary data. In cases where such data are not available, we propose two techniques to estimate these parameters using the coherent radar return. These techniques were tested with the Seasat SAR data and the test results demonstrate that the accuracies achieved exceed the system performance requirements. Possible applications of these techniques in other areas of SAR data utilization are briefly discussed.

Trajectory deviations in airborne SAR: analysis and compensation

Abstract: This paper concerns the analysis and compensation of trajectory deviations in airborne synthetic aperture radar (SAR) systems. Analysis of the received data spectrum is carried out with respect to the system geometry in the presence of linear, sinusoidal, and general aircraft displacements. This shows that trajectory deviations generally produce spectral replicas along the azimuth frequency that strongly impair the quality of the focused image. Based on the derived model, we explain the rationale of the motion compensation (MOCO) strategy that must be applied at the SAR processing stage in order to limit the resolution loss. To this end aberration terms are separated into range space invariant and variant components. The former can be accounted for either in a preprocessing step or efficiently at range compression stage. The latter needs a prior accommodation of range migration effect. We design the procedure for efficient inclusion of the MOCO within a high precision scaled FT based SAR processing algorithm. Finally, we present results on simulated data aimed at validating the whole analysis and the proposed procedure.