Separation of Ground and Volume Scattering in Multibaseline Polarimetric SAR Data and Its Application in DTM and CHM Inversion

Polarimetric synthetic aperture radar (SAR) tomography (Pol-TomoSAR) can be used for global forest digital terrain model (DTM) and canopy height model (CHM) mapping with high spatial and temporal resolution at low economic cost. However, the performance of DTM and CHM inversion in current Pol-TomoSAR methods is often compromised when the ground-to-volume ratio (GVR) is low, which usually happens in complicated terrain where large negative slope angles are commonly present, or in dense tropical forest where the ground visibility is low due to strong attenuation by the dense vegetation layer. In this work, a novel method for the separation of ground and volume scattering, aiming at robust and accurate DTM and CHM inversion in dense tropical forest and complicated terrain, is proposed. By fully exploiting multibaseline polarimetric SAR data, the proposed method can perform a more effective separation of ground and volume scattering. Subsequently, by applying the SAR tomography technology on the separated ground and volume scattering, the proposed method can retrieve accurate DTM and CHM information even at low GVR areas. Numerical experiments conducted on both simulated data and P-band airborne F-SAR data show that, compared to the most commonly used two-component algebraic synthesis method, the proposed one has a much better performance in terms of separation of ground and volume scattering. Furthermore, the inversed DTM and CHM present better agreement with light detection and ranging (LiDAR) measurements, especially in large negative slope angle terrain where the GVR is rather low.