Qurat Ul-Ann

A Bistatic Point Target Reference Spectrum for General Bistatic SAR Processing

A bistatic point target reference spectrum (BPTRS) based on Loffelds bistatic formula (LBF) is derived in this letter. For LBF, the same contributions of the transmitter and receiver to the total azimuth modulation are assumed. This assumption results in the failure of LBF in the extreme configuration (i.e., spaceborne/airborne configuration). For general bistatic configurations, the azimuth modulations are unequal for the transmitter and receiver due to the different slant ranges and velocities. Therefore, the azimuth time-bandwidth products (TBPs) from the transmitter and receiver are different; in some cases (e.g., spaceborne/airborne case), one of them might be very small, which might even result in a serious error of the principle of stationary phase. This letter uses TBP to weight the azimuth phase modulation contributions of the transmitter and receiver to the common azimuth spectrum to approximately obtain the point of stationary phase of the total azimuth phase history. Simulations show that the proposed BPTRS can work well for spaceborne/airborne configurations.

Frequency-Domain Bistatic SAR Processing for Spaceborne/Airborne Configuration

This paper focuses on the bistatic synthetic aperture radar (BiSAR) signal processing in the spaceborne/airborne configuration. Due to the extreme differences in platform velocities and slant ranges, the airborne system operates in the inverse sliding spotlight mode, while the spaceborne system works in the sliding spotlight mode to achieve a tradeoff between the azimuth scene size and azimuth resolution. Such a mode is generally called double sliding spotlight mode. In this configuration, the echoed signal has two characteristics. Firstly, both transmitter and receiver have very short synthetic aperture times. Secondly, the airborne platform operates with wide squint difference, while the spaceborne platform works in the small squint case. According to these two features, we use different Taylor expansions to address the slant range histories of transmitter and receiver. Based on the presented model, a two-dimensional space-variant bistatic point target reference spectrum (BPTRS) is derived. Furthermore, we linearize the BPTRS to derive the transfer function of the baseband scene. From the transfer function, the signal features of the spaceborne/airborne configuration become very clear. Using the transfer function, the two-dimensional inverse scaled Fourier transform (ISFT) is used to focus the bistatic signal in the spaceborne/airborne configuration.

Optimizing the Individual Azimuth Contribution of Transmitter and Receiver Phase terms in Loffeld's Bistatic Formula (LBF) for Bistatic SAR Processing

The individual azimuth contribution of transmitter and receiver phase terms has been optimized by weighting them unequally based on a weighting factor mu, in Loffelds bistatic formula (LBF). Analytical results are verified with the simulations.

A point target reference spectrum based on Loffeld's bistatic formula (LBF) for hybrid configurations

This paper concentrates on the focusing for hybrid bistatic SAR configurations, consisting of a space borne/airborne carrier configuration with considerable differences in velocities and altitudes of transmitter and receiver. Therefore the direct implementation of a bistatic SAR focusing algorithm based on Loffelds bistatic formulae (LBF) cannot be readily applied. An extension of the bistatic point target reference spectrum, based on LBF is derived. Simulated focusing results verify the proposed approach.

Analysis and Processing of Spaceborne/Airborne Bistatic SAR Data

This paper concentrates on the bistatic SAR (BiSAR) signal processing for the spaceborne/airborne hybrid bistatic configuration. A bistatic SAR experiment based on this hybrid configuration is being planned in cooperation with FGAN/FHR and DLR. Due to the extreme differences of the platforms velocities and altitudes, the spaceborne system works in the sliding spotlight mode, while the airborne system operates in the inverse sliding spotlight mode. In this paper, our previous work (i.e. ISFT) is applied to focus the hybrid bistatic SAR data based on the extended Loffelds Bistatic Formula (ELBF).

A two-step method to process bistatic SAR data in the general configuration

This paper describes a two-step processing procedure which has a capacity of processing bistatic Synthetic Aperture Radar (BSAR) data in the general configuration based on the extended Loffeldpsilas Bistatic Formula (LBF). For LBF, in any configuration, equal contributions to the total azimuth Doppler spectrum are assumed, which results in the failure of LBF in the high bistatic grade configurations (e.g. spaceborne/airborne configuration and highly different squint configuration). In this paper, we consider the different contributions of transmitter and receiver to the total Doppler spectrum to extend LBF. To illustrate the character of bistatic SAR signal, the two-dimension linearization operation is used to project the quasi-monstatic (QM) and bistatic deformation (BD) terms into the 2-dimensional space (slant range and azimuth time) domain. After the linearization, it can be seen that the bistatic point target reference spectrum (BPTRS) is linearly dependent on the two-dimension space variables. The azimuth-dependent phenomenon is an intrinsic feature of bistatic SAR in the general configuration. To address the two-dimension space-dependent problem, we use the two processing procedures: one is range processing which will remove the dependency of BPTRS on the range space variable, another is azimuth processing which will eliminate the dependency of BPTRS on the azimuth time variable. For the range processing, we prefer the well-known range-Doppler algorithm to cancel the dependency (i.e. RCM). For the azimuth, an additional interpolation operation is required to remove the dependency.

Considerations on the validity constraints for the bistatic SAR processing

This paper gives some considerations on the validity constraints for spaceborne/airborne configurations, based on Loffelds bistatic formula (LBF) for unequal azimuth contribution of transmitter and receiver phase terms.