Theoretical Analysis of the Spatial Baseline for Moon-Based SAR Cross-Track Interferometry

Abstract

The vast Moon surface, lower thermal environment, predictable orbit, and long distance of Earth-Moon centroid have provided long-term, large-scale, unique, stable, and many other advantages for Moon-based Earth observation, including the synthetic aperture radar interferometry. Compared with the space-borne method, the Moon-based cross-track interferometry (MB-CTI) that works in one transmitter dual-receiver mode undoubtedly not only has larger coverage at single gaze but also has stable baseline. Relatively speaking, the changeable baseline of representative Moon-based repeat-track interferometry has deteriorated its coherent pairs without full use of revisit even in month span. However, the constant baseline of MB-CTI concretizes the relatively regular, stable, and latitude difference sensitive effective vertical baseline (EVB) throughout long Earth-Moon periodic motion. The closely distributed MB-CTI make it more similar to monostatic ways, and two poles where permanent shadow area exists can provide EVB close to diameter, thus increasing coherence possibility and related height measurement accuracy. Common part between two received spectrums contains necessary interference information. The flat region of interested (e.g., Amazon Plain) at low latitude is not preferred for MB-CTI, yet exactly the opposite while in mid-and high-latitude area (e.g., Arctic land, Tibet Plateau, and Antarctic land). A larger incident angle range or ratio of band to frequency uplift valid coherence pairs where lay-over or shadow happen because of complicate topography; meanwhile, regions tilted away Moon with slope larger than incident is more likely to be in decoherence. The defined spatial geometry has provided guidance for the application of MB-CTI in the future.