James L. Farrell

Synthetic Aperture Imaging with Maneuvers

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

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.

Strapdown inertial navigation system requirements imposed by synthetic aperture radar

The purpose of this paper is to demonstrate a means of specifying strapdown inertial navigation system (INS) requirements from synthetic aperture radar (SAR) requirements. The latter include allowable levels for quadratic and cubic phase shift, and side lobe levels [i.e., peak side lobe ratio (PSLR) and integrated side lobe ratio (ISLR)]. When these multiple considerations produce different INS requirements, of course, the tightest governs. Results obtained constitute a technique demonstration only, and do not represent any specific mechanization. In the process of this investigation several pitfalls in common procedures were identified; these are highlighted in the discussion. A brief background description is provided in the Appendix for those unfamiliar with the analysis of SAR degradations.

Retention Probability in a Track-While-Scan Radar

The probability of maintaining the track file, after acquisition in a track-while-scan (TWS) radar, has been formulated and computed under various conditions of initial range, velocity, and track drop time. All calculations are based on a predetermined update probability versus range characteristic. Results, obtainable with a digital computer in just seconds of computing time, readily demonstrate the relative superiority of retention characteristics achievable for TWS radar with an electronically steerable array antenna.

Airborne transfer alignment simulation results

The author addresses transfer alignment for synthetic aperture radar (SAR) under conditions of nonrigidity between the master INS (inertial navigation system) and the radar antenna. A generic transfer alignment simulation is described, with results given for sample cases with and without rotational vibration. The author presents a design concept representing a radical departure from preceding approaches to SAR transfer alignment: Kalman updates are allowed during a frame. This allows small high-frequency changes in the velocity history so that buildup of low-frequency errors will be counteracted.<<ETX>>

Pulse Generator with Logarithmic Spacing

In this paper a circuit is developed which provides a train of uniform pulses logarithmically spaced in time. As applied to computing the system offers new methods for calculating products, quotients, powers, and roots. A pulse-interval error of less than one per cent (rms) was obtained with an experimental circuit.