Efficient Time-Domain Image Formation with Precise Topography Accommodation for General Bistatic SAR Configurations

Abstract

Due to the lack of an appropriate symmetry in the acquisition geometry, general bistatic synthetic aperture radar (SAR) cannot benefit from the two main properties of low-to-moderate resolution monostatic SAR: azimuth-invariance and topography-insensitivity. The precise accommodation of azimuth-variance and topography is a real challenge for efficent image formation algorithms working in the Fourier domain, but can be quite naturally handled by time-domain approaches. We present an efficient and practical implementation of a generalised bistatic SAR image formation algorithm with an accurate accommodation of these two effects. The algorithm has a common structure with the monostatic fast-factorised backprojection (FFBP), and is therefore based on subaperture processing. The images computed over the different subapertures are displayed in an advantageous elliptical coordinate system capable of incorporating the topographic information of the imaged scene in an analogous manner as topography-dependent monostatic SAR algorithms do. Analytical expressions for the Nyquist requirements using this coordinate system are derived. The overall discussion includes practical implementation hints and a realistic computational burden estimation. The algorithm is tested with both simulated and actual bistatic SAR data. The actual data correspond to the spaceborne-airborne experiment between TerraSAR-X and F-SAR performed in 2007 and to the DLR-ONERA airborne experiment carried out in 2003. The presented approach proves its suitability for the precise SAR focussing of the data acquired in general bistatic configurations.

An Accelerated Backprojection Algorithm for Monostatic and Bistatic SAR Processing

“…However, from the perspective of computational complexity, BiBulk_FFBP is more computational efficient. Equation (24) can be approximated as nN 2 log n N. Comparing with the computational complexity of FBP in [25], N 2.5 , the computational cost of BiBulk_FFBP is lower.…”

Image Formation Using Fast Factorized Backprojection Based on Sub-Aperture and Sub-Image for General Bistatic Forward-Looking Sar With Arbitrary Motion

“…Since the platform's speed is much less than the speed of light, the go-stop-go assumption is commonly used in the pulsed SAR [3,13]. For the pulsed BFSAR case, transmitter and receiver are assumed stationary during the transmission and reception of the signal, and they move to the next position only after the echo signal is received.…”

“…However, the huge computational burden limits the application of the BPA. In order to solve the shortcoming of the BPA, some bistatic fast backprojection algorithms (Bi-FBPA) and bistatic fast factorized backprojection algorithms (Bi-FFBPA) have been proposed in [13][14][15][16][17], and they can be divided into two categories: one works with sub-aperture and polar gird processing [13][14][15][16], and the other works on a sub-aperture and sub-image basis [17]. In theory, the extensions of Bi-FBPA and Bi-FFBPA are totally valid for BFSAR without any modification.…”

Along-Track Motion Compensation for Strip-Map Sar Based on Resampling

“…Since the bulk MOCO has been researched a lot in [18][19][20][21][22][23][24][25][26], here it is only simply mentioned for deriving the following residual error discussion.…”

“…Assuming that the motion error is known as a priori information, then the next step is to compensate the errors; based on some previous researches on this topic [18][19][20][21][22][23][24][25][26], a widely used algorithm is bulk MOCO. The algorithm is implemented in two steps to compensate the range-independent and range-dependent motion errors respectively [27].…”