Objectives The Hongtu-1 (HT-1) synthetic aperture radar (SAR) satellite system, the world's first multi-satellite distributed interferometric radar system, utilizes a four-satellite wheel formation to enable single-pass, multi-baseline interferometry. This system provides distinct advantages over traditional interferometric SAR (InSAR) systems by enabling the simultaneous acquisition of high-coherence SAR image pairs with varying baseline lengths. Most existing related research is based on simplified simulation data, overlooking practical challenges in real data processing.
Methods A method for high-precision InSAR elevation inversion based on multi-baseline phase unwrapping is proposed, tailored to HT-1's unique data characteristics. The approach involves constructing an equivalent phase center model for auxiliary satellites, generating interferograms from single-pass SAR geometry, and performing multi-baseline unwrapping on the flattened interferograms to recover the absolute terrain phase. The final phase data is converted into elevation measurements for the target area.
Results Simulation experiments using real terrain data from Henan Province, China, validate the method's effectiveness for elevation inversion in complex and steep terrains. The root mean square error (RMSE) in non-overlapping regions is under 2 meters. A 5 m resolution digital elevation model (DEM) of the experimental area was obtained by inverting the actual single-track HT-1 SAR data. In the overlapping area, the elevation RMSE between HT-1 DEM and GF-7 DEM is under 14 m. Additionally, the elevation profile of HT-1 DEM closely aligns with the trend observed in ICESat-2 laser altimetry data.
Conclusions The HT-1 system's wheel constellation and multi-baseline interferometry capabilities exhibit substantial potential for high-accuracy topographic mapping.
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