A Novel Perspective of Urban Tomosar Imaging: The Unique off-Nadir Angle Model

Synthetic Aperture Radar Tomography (TomoSAR) thre-dimensional imaging technology is built upon the foundation of two-dimensional SAR imaging, utilizing multiple observations in the elevation direction to construct the synthetic aperture for the elevation imaging capability. The classic TomoSAR imaging algorithm typically refers to the third dimension as elevation, and research over the years has been based on this model. The process of three-dimensional imaging involves reconstructing the spatial distribution of scattering characteristics along the elevation direction. According to this model, for the same range-azimuth cell, discrimination of overlapping scatterers can be achieved based on different levels of sparsity. However, studies have found significant limitations of this model for urban buildings. Firstly, there is scatterer diffusion along the elevation direction, particularly at the junctions of building surfaces, such as the intersections between the facade and ground. Secondly, the maximum unambiguous range of the reconstruction model based on elevation is limited by the model. To address this issue, considering the characteristics of urban buildings, this paper proposes a novel imaging model based on the unique angle property. Specifically, the scatterer parameters to be estimated are transformed from the elevation coordinates to the off-nadir angle. Moreover, based on the non-penetrating property of electromagnetic waves for buildings, it is assumed that there is only one scatterer for each off-nadir angle, which is consistent with physical reality. Experiments were conducted based on measured data from two sites, and the results confirmed that the proposed model can effectively suppress clutter caused by multiple scattering, significantly improving the three-dimensional imaging quality.