Ground moving target parameter estimation for two-channel SAR C.H. Gierull Abstract: The author introduces and analyses the performance of different techniques to estimate the parameters of ground moving targets in multi-channel synthetic aperture radar (SAR) data. Candidates are matched filter banks, the along-track interferometric phase and direction-of- arrival estimation methods, which can work in either the raw data or in the compressed SAR image domain. Of particular interest are systems with only two channels because many existing or near-future SAR systems, such as RADARSAT-2 and TerraSAR-X, are restricted to a maximum of two sub-apertures. Desired parameters are the two velocity components (along- and across-track), acceleration if present and the true azimuth location. Theoretical results are evaluated and illustrated with experimental airborne SAR data. 1 Introduction In many civilian and military applications of airborne and spaceborne synthetic aperture radar (SAR) imaging, it is highly desirable to simultaneously monitor traffic on Earth’s surface. The measurement of object motion using SAR requires two consecutive operations. First, the detec- tion in the SAR data and, secondly, target parameter estimation such as location, speed and course. Target detection and estimation can either be performed incoher- ently with a single SAR sensor, or coherently, with much higher fidelity, with two or more apertures. Although many authors have investigated the detection part in the past, the estimation problem has been rarely dealt with [1]. Great importance is attached to the practical applicability of the presented techniques, particularly with regard to the experimental ground moving target indication (GMTI)- mode of RADARSAT-2 [2]. The techniques presented in this paper are analysed with real data acquired during an experiment conducted at Canadian Forces Base (CFB) Petawawa on 14 July 1999. The SAR data were acquired by the Environment Canada’s CV 580 C-band SAR config- ured in its along-track interferometric (ATI) mode [3]. The radar, operating at C-band (5.30 GHz), was configured to use a transmitting antenna situated on the belly of the aircraft and a two-aperture (0.27 m effective phase center separation) microstrip receiving antenna situated on the starboard side of the aircraft above the transmit antenna. Horizontally polarised radiation was transmitted and received by the system running in the nadir mode, with most targets of interest situated at incidence angles of approximately 508. To minimise azimuth ambiguity effects, the radar system was run at twice the usual pulse repetition frequency (PRF), that is, at PRF ¼ 678 Hz. At a 508 incidence angle, and an altitude of approximately 7 km, targets of interest were offset from the ground projec- tion of the radar flight track by approximately 9 km. The system parameters such as incidence angle and PRF (related to the clutter bandwidth) are chosen to resemble RADARSAT-2’s geometry. As RADARSAT-2’s spatial resolution of about 3 m is better than the Convair’s (4 m), a similar signal-to-cutter ratio (SCR) is anticipated. The only major difference is the lower SNR because of the significantly increased ranges to the targets with the corresponding signal power loss. 2 Moving target detection The first step in any MTI mode is the actual test for the presence of movers in the measured data. In air-to-ground applications, such as SAR, this task is challenging because of the simultaneously overlayed clutter power, which can, in the mainbeam regions of the antenna pattern, be a multiple of the signal power. As the clutter must be suppressed prior to target testing over the entire clutter Doppler spectrum, one-channel based techniques are typically very limited in performance. Although, real multi-channel SAR – GMTI is known to enhance the detec- tion and estimation performance significantly [4], many present and future radar systems are restricted to only two parallel receiver channels because of limited resources. This is particularly true for space-based sensors, such as upcoming RADARSAT-2 and TerraSAR-X. Ground moving target detection (GMTD) can be either achieved in the raw data domain, that is without actually focusing/compressing the data in along-track (azimuth direction) or it can be done on the processed data, that is in the image domain [5, 6]. Either domain has its advantages and disadvantages. While raw data techniques usually suffer from low SNR they usually allow detection of targets in a much wider velocity range than image-based techniques. This is due to the smearing effects of the point spread func- tion for fast moving targets when they are filtered with the optimum filter for the stationary world during SAR proces- sing [3]. Processing two SAR images with ATI for slow moving vehicles, that are still focused but displaced, has # Canadian Crown copyright 2006 IEE Proceedings online no. 20045094 doi:10.1049/ip-rsn:20045094 Paper first received 1st October 2004 and in revised form 11th October 2005 The author is with the Defence Research and Development Canada – Ottawa (DRDC Ottawa), Radar Systems Section, 3701 Carling Avenue, Ottawa, ON, Canada K1A 0Z4 E-mail: christoph.gierull@drdc-rddc.gc.ca IEE Proc.-Radar Sonar Navig., Vol. 153, No. 3, June 2006 224