Soil moisture mapping using Sentinel-1-Data and SNAP?

Microwave Toolbox
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Hi,

To derive soil moisture using SAR there are quite a few different techniques. The three most popular ones used extensively in remove sensing are the following:

  • Soil moisture using Neural Network (NN)
    Reference: Sahebi, M.R.; Bonn, F.; Bénié, G.B. Neural networks for the inversion of soil surface parameters from synthetic
    aperture radar satellite data

  • Soil moisture using Water Cloud Model (WCM)
    reference: Estimation of surface soil moisture and roughness from multi-angular
    ASAR imagery in the Watershed Allied Telemetry Experimental Research

  • Soil moisture using change detection
    reference: Thoma, D.P.; Moran, M.S.; Bryant, R.; Rahman, M.; Holifield-Collins, C.D.; Skirvin, S.; Sano, E.E.; Slocum, K.
    Comparison of four models to determine surface soil moisture from C-band radar imagery in a sparsely vegetated semiarid landscape

If you do not know what methodology to use, i would recommend to use the change detection one. Not only there is a lot of literature for this technique and used by many scientists, it is the most straightforward as well.

Using this technique, it requires two images. One image captured under dry weather conditions and the other one captured under wet weather conditions. We assume that the vegetation and surface roughness have not changed between the images acquisitions. So, it is advised to remove areas of high and dense vegetation (use NDVI to mask-out vegations)

The collection of your field measurements can be used in two different ways:

  1. Validate the soil moisture results derived by Sentinel-1 (using any of the above technique mentioned). This can be done by fitting a linear model between the soil moisture of Sentinel-1 and your field measurements. Hopefully, there is going to be a strong correlation between the two measurements

  2. Your fields measurements can be used to derive volumetric soil moisture from Sentinel-1 (assuming that you have collected volumetric data on the filed). You need a linear relationship between Sentinel-1 soil moisture values and the volumetric data collected on the field. Have a look on this paper, especially in figure 5 where authors derive volumetric soil moisture based on regression analysis.

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