A sparsity based approach to velocity SAR imaging

Abstract

Abstract-We recently successfully developed an airborne MSAR (Multichannel Synthetic Aperture Radar) test bed system that consists of 32 along-track phase centers through the use of two transmit horns and 16 receive antennas [1-4]. We have subsequently deployed this system, both in September 2014 and more recently in October 2015, to perform extensive and systematic data collections on a variety of land-based and maritime targets under different environmental conditions. The resulting data poses important signal processing challenges pertaining to optimum ways of combining the signals obtained from various channels so that the underlying information of interest can be effectively extracted in the presence of noise and clutter. In this paper we focus on the imaging problem and propose a novel method of simultaneously exploiting the multichannel structure of the data acquisition and the underlying sparse structure of the scene being imaged. After giving a brief overview of our airborne NRL MSAR system and the basics of velocity processing, we proceed to describe our novel algorithm and demonstrate our initial experimental results. The novelty of this paper is two-fold: to the best of our knowledge, this is first time that velocity processing has been used in conjunction with sparsity based processing; and that the resulting approach is applied to real data captured by our airborne NRL MSAR system.Keywords-Imaging; Synthetic Aperture Radar (SAR); Multichannel SAR (MSAR); Sparsity; Velocity Processing; Wavelets I.NRL MSAR SYSTEM The NRL MSAR is an airborne system based on the NRL Focused Phased Array Imaging Radar (FOPAIR), a groundbased MSAR test bed [3,5]. The MSAR system operates at Xband with a center frequency of 9.875 GHz and uses linear FM chirped waveforms with a bandwidth of 220 MHz to achieve a range resolution of approximately 0.7 m. The peak radiated power is approximately 1.4 kW, while the aggregate pulse repetition frequency (PRF) of 25 kHz and pulse length of 6 µs produce an average power of 210 W. The system flies on a Saab 340 aircraft using a belly-mounted radome with a nominal incidence angle of 70 o . Typical altitude and airspeeds are 914 m (3000 ft.) and 70 m/s, respectively. Fig. 1 shows a schematic of our airborne system for data collection of land and maritime targets; and Fig. 2 shows a close-up of the radome and our MSAR system. The airborne MSAR system consists of two modularly constructed 16 channel sections from FOPAIR. Though we had a maximum of 16 receive elements in our MSAR system, due to our on-board data storage constraints we received on every other element which was found to be the maximum that we could process while still providing sufficient velocity resolution. To improve the system still further we used two independent transmitters, one at either end of the array to effectively double the number of phase centers (and halve the minimum detectable velocity). This system provides up to 32 velocity bins from 1 to 20 m/s with a resolution of 0.7 m/s.All elements are vertically po...