The combination of SCan-On-REceive with continuous variation of the pulse repetition interval during transmission (staggered operation) is a viable option for the acquisition of high-resolution synthetic aperture radar (SAR) data over wide areas. Since the acquired data are not uniformly sampled and contain gaps within the synthetic aperture mainly due to the interruption of reception during transmission (i.e., due to blockage), proper reconstruction strategies must be considered in order to minimize artifacts. Conventionally, large oversampling rates are required to ensure low ambiguity levels, but this is not always feasible due to data-rate constrains. This article presents a detailed analysis of the blockage recovery in the low-oversampling case. Moreover, we propose a data adaptive strategy to optimally perform this step, ensuring the best performance for point-like targets and avoiding degradation for distributed scatters. This paper also presents simulation results that show the impact of staggered data for interferometric applications.

Following an original proposal by the authors to the TerraSAR-X (TSX) scientific coordination board, a spaceborne-airborne bistatic experiment was successfully performed early November 2007. TSX was used as transmitter and DLR's new airborne radar system, F-SAR, as receiver; due to the capability of the latter to acquire data quasi-continuously, no echo window synchronisation is needed. Monostatic data were also recorded during the acquisition. This paper includes description and results of the spaceborne-airborne bistatic experiment, with special focus on data processing and image comparison. Given the acquisition scenario, with two-channel sampling and transmitter and receiver clocks operating independently, data processing must necessarily follow a three-step strategy: 1) channel balancing, 2) data synchronisation and 3) bistatic SAR processing. Since neither absolute range nor Doppler references are available in the bistatic data set, synchronisation is done with the help of calibration targets on ground and based on the analysis of the acquired data compared to expected data. Due to the variant nature of the bistatic acquisition and the required precision for the processing, data are processed using a bistatic backprojection approach.