Timing and Design Issues in Formation Flying Distributed SAR

The paper investigates timing aspects of the design and the operations of a formation flying distributed Synthetic Aperture Radar (SAR). The analyzed system considers a satellite cluster including one transmitter and N receivers flying in formation with a dominant along-track baseline. This realizes a sensor receiving N samples at azimuth-displaced positions for each transmitted pulse, enabling several applications. In fact, besides the possibility to implement single-pass multi-baseline interferometric SAR techniques, the bistatic raw data collected by each receiver can be combined to generate a single higher performance image, e.g. High-Resolution Wide-Swath (HRWS) imaging. The paper investigates the latter topic, proposing dedicated solutions to preserve the imaging performance against the effects of relative orbit dynamics and residual orbit control errors. In details, the factor N can be interpreted as the redundancy, or the maximum number of degrees of freedom of the distributed system when compared to a single-channel monostatic SAR. Such a redundancy can be exploited in different ways pending on the application of suitable signal reconstruction and it represents an important parameter affecting the system timing. In this contest, the manuscript proposes an approach to system timing, satisfying not only ambiguity-related issues but also requirements concerning signal parameters, like SNR andor Peak-to-Side-Lobe Ratio (PSLR). Finally, the timing considerations are recast in the framework of the overall design of a formation flying SAR.