Accounting for soil surface roughness in the inversion of ultrawideband off-ground GPR signal for soil moisture retrieval

摘要

We combined a full-waveform ground-penetrating radar (GPR) model with a roughness model to retrieve surface soil moisture through signal inversion. The proposed approach was validated under laboratory conditions with measurements per-formed above a sand layer subjected to seven different water con-tents and four different surface roughness conditions. The radar measurements were performed in the frequency domain in the range of 1-3 GHz and the roughness amplitude standard devia-tion was varied from 0 to 1 cm. Two inversion strategies were investigated: (1) Full-waveform inversion using the correct model configuration, and (2) inversion focused on the surface reflection only. The roughness model provided a good descrip-tion of the frequency-dependent roughness effect. For the full-waveform analysis, accounting for roughness permitted us to simultaneously retrieve water content and roughness amplitude. However, in this approach, information on soil layering was assumed to be known. For the surface reflection analysis, which is applicable under field conditions, accounting for rough-ness only enabled water content to be reconstructed, but with a root mean square error (RMS) in terms of water content of 0.034 m~3 m~(-3) compared to an RMS of 0.068 m~3 m~(-3)for an analysis where roughness is neglected. However, this inversion strategy required a priori information on soil surface roughness, estimated, e.g., from laser profiler measurements.