Estimation of Surface Parameters of Tidal Flats Using Sentinel-1A SAR Data in the Northern Coast of Vietnam

Abstract

Tidal flat is a special environment which is submerged during flood tide and exposing the air during ebb tide. Tidal flats in the north coast in Vietnam surfer diurnal tide with tide range varying from 0.3 m to 3.5 m. Along 350 km coastline of the study area, the diversity of constituent conditions forms various tidal flats with different characteristics. Soil moisture and surface roughness are the key parameters for the studies concerning tidal flat environment. These surface parameters of tidal flats can be investigated using inversion models with SAR data. This study applies the inversion method of the Oh model 2004 to estimate vertical surface roughness and soil moisture. Two Sentinel-1A SAR data are acquired and preprocessed to yield backscattering coefficients of VV and VH polarizations of C band. In condition of missing co-polarization data (HH) for fully applying the Oh inversion model, a calibration function is generated to calibrate estimated roughness and soil moisture. This is the first time that the surface roughness and soil moisture of tidal flats are successfully estimated from SAR data in the study area. Even now, the applications of the Oh model for estimating surface parameters of tidal flat using Sentinel-1A SAR images have not found yet in literatures. Vertical roughness after calibrating is estimated with an accuracy of 0.09 cm. The accuracy of estimated soil moisture of tidal flats is not assessed due to lacking the referent data. However, the estimated soil moisture is good correlation with the real environmental conditions in the study area.