As the spaceborne mission dedicated to bistatic SAR interferometry (InSAR), the TerraSAR-X/TanDEM-X satellite constellation can acquire highly coherent data pairs with flexible baseline configurations and minimal atmospheric disturbances, which are well suited for high-accuracy DEM generation. However, hindered by the intrinsic contradiction between sensitivity of height measurement and reliability of phase unwrapping in terms of normal baseline length, as well as geometric distortions of layover and shadow, it is still difficult to generate high-quality DEM in mountainous areas using single-baseline InSAR data. Aiming at these two problems, we developed a cascaded multi-baseline InSAR processing framework for DEM generation from multiple bistatic InSAR observations with variable normal baselines and different imaging geometries. By starting from phase unwrapping and phase-to-height conversion for the interferogram with shortest normal baseline, this approach adopted a strategy of DEM updating assisted by a reference elevation dataset. The updated DEM is then used as the reference for processing interferograms with longer baselines successively. In this iterative way, the quality of the resultant InSAR DEM can be improved gradually. In addition, fusion between multiple geocoded InSAR DEMs derived from different orbits is carried out to further refine the results by filling data voids and reducing random height noise. To demonstrate the effectiveness of the proposed method, we apply it to four pairs of stripmap-mode TerraSAR-X/TanDEM-X bistatic data covering the Mount Song area in central China. The vertical accuracies of the generated DEMs are evaluated using an aerial photogrammetric DEM, ICESat/GLAS measurements, and the standard TanDEM-X global DEM product. The experimental results show that the absolute height error of the generated multi-baseline InSAR DEM at 5 m posting is less than 10 m in typical mountainous areas and can meet the American HRTI-3 standard, which means the generated DEM has similar height accuracy and higher spatial resolution in comparison with the 12 m TanDEM-X global DEM products.

作为致力于双基地SAR干涉测量（InSAR）的太空任务，TerraSAR-X / TanDEM-X卫星星座图可以获取具有相干基线配置和最小的大气干扰的高度相干的数据对，非常适合于高精度DEM生成。但是，受制于高度测量的灵敏度与相位展开的可靠性（在正常基线长度方面）之间的内在矛盾，以及中途停留和阴影的几何变形，仍然难以在山区使用单点采样生成高质量的DEM。基线InSAR数据。针对这两个问题，我们开发了一个级联的多基线InSAR处理框架，用于从具有可变法线基线和不同成像几何形状的多个双基地InSAR观测中生成DEM。从具有最短正常基线的干涉图的相位展开和相位高度转换开始，该方法采用了DEM更新策略，并具有参考高程数据集。然后，将更新的DEM用作连续处理基线较长的干涉图的参考。以这种迭代方式，可以逐渐提高所得InSAR DEM的质量。此外，对来自不同轨道的多个经过地理编码的InSAR DEM进行了融合，以通过填充数据空白并减少随机高度噪声来进一步完善结果。为了证明该方法的有效性，我们将其应用于覆盖华中山地区的四对带状图模式TerraSAR-X / TanDEM-X双基地数据。使用航空摄影测量DEM，ICESat / GLAS测量和标准TanDEM-X全球DEM产品评估生成的DEM的垂直精度。实验结果表明，在典型的山区，生成的多基线InSAR DEM在5 m处的绝对高度误差小于10 m，可以满足美国HRTI-3标准，这意味着生成的DEM具有相似的高度精度和与12 m TanDEM-X全球DEM产品相比，具有更高的空间分辨率。