MirrorSAR: A fractionated space radar for bistatic, multistatic and high-resolution wide-swath SAR imaging

Abstract

This paper introduces the concept of a fractionated MirrorSAR which is based on a set of mutually separated transmitter and receiver satellites. As opposed to previously published bi-and multistatic SAR systems, the receiver satellites are considerably simplified, as their main functionality is reduced to a kind of microwave mirror (or space transponder) which routes the radar echoes towards the transmitter. The forwarded radar signals are then coherently demodulated within the transmitter by using the same oscillator that had been used for radar pulse generation. This avoids the necessity of a bidirectional phase synchronization link as currently employed in TanDEM-X. Since the needs for fully equipped radar receivers, on-board memory and downlink are also overcome, the weight and costs of the receiver satellites can be significantly reduced. This allows for a scaling of their number without cost explosion, thereby paving the way for novel applications like multibaseline SAR interferometry and single-pass tomography. Several additional opportunities make the MirrorSAR concept even more attractive. First, the separation of the transmitter and receiver front-ends reduces not only RF losses by avoiding switches and circulators, but it may also lower the peak power in the transmitter satellite by employing a frequency-modulated continuous wave (FMCW) illumination. This simplifies the design of the high-power amplifier and increases its efficiency. Second, the opportunity for continuous radar data collection enables new modes for the imaging of ultra-wide swaths with very high resolution, thereby overcoming an inherent limitation of conventional monostatic SAR systems. Third, the joint availability of all receiver signals in a centralized node offers new opportunities for efficient data compression, as the multistatic radar signals from close satellite formations are characterized by a high degree of mutual redundancy. Fourth, the use of a sufficiently separated transmitter satellite can avoid the risk for mutual illumination, which challenges the design and operation of fully-active multistatic SAR systems. Further advantages arise from the scalability and reconfigurability, which support new redundancy concepts and pave at the same time the way to new modes like MIMO-SAR tomography.

Tomographic Performance of Multi-Static Radar Formations: Theory and Simulations

“…The resolution coefficient ( ) depends on the multi-static mode [46] and, for MIMO, whether two-sided 3.9 dB resolution or one-sided peak-to-null (Rayleigh) resolution is considered:…”

“…Algorithms such as back-projection, Fourier, Capon [42], or the more recent backscatter-height histograms approach [43] belong to this group. While these algorithms are constantly improved and applied to new experimental and simulated data, research in TomoSAR is currently active on two main fronts: (1) how to extract biophysical parameters from SAR tomograms [43][44][45], and (2) how to optimize the multistatic SAR systems in order to maximize the quality of tomograms with constrained resources [36,[46][47][48].…”

A Comprehensive Method of Ambiguity Suppression for Constellation of Geostationary and Low Earth Orbit SAR

“…ONGALSAR is a novel short revisiting multi-static SAR system, which contains one geostationary illuminator and dozens of low Earth orbit (LEO) transponders [1]. With MirrorSAR technology [2]- [4], ConGaLSAR gives an economical way to construct a constellation with 3 m resolution and 72 min averaging revisiting interval while ensuring time and frequency synchronizations.…”

Bistatic-Like Differential SAR Tomography

“…• Sentinel-1 "tandem" (i.e., one-day separation) or bistatic mission concept involving the prospective Sentinel-1C and another satellite from the series [6]. • High Resolution Wide Swath (HRWS), the successor of TerraSAR-X comprising one or two SAR satellites operating in X-band [7], [8], and possibly several additional passive companion transponder satellites without bidirectional phase synchronization link (MirrorSAR) [9]- [11]. Above all, Tandem-L is the most intriguing mission to us, not only because it is the one and only concept that has already undergone very comprehensive and intensive studies (see for example [12]- [16] and the references therein), but it is also extremely promising for a huge variety of geophysical applications.…”