Sensitivity of spaceborne radar to near-surface soil moisture in grasslands across southern Ireland

Article English OPEN
Barrett, Brian ; Dwyer, Edward ; Whelan, Padraig (2013)

The amount of water stored in the soil is a key parameter for the energy and mass fluxes at the land surface and is of fundamental importance to many agricultural, meteorological, biological and biogeochemical processes. This study investigates the potential of retrieving surface soil moisture in grassland areas from a time series of 68 ENVISAT advanced synthetic aperture radar (ASAR) wide swath mode (WSM) scenes, acquired between 2007 and 2009, using an empirical regression approach. WSM data enable larger areas to be observed with a higher temporal sampling capability, compared to image mode (IM) data, and provide an appropriate spatial resolution for regional applications. As expected, the radar backscatter signal was found to increase with increasing soil moisture. Inter-seasonal analysis showed that the VV (Vertical transmit–Vertical receive) polarisation radar signal is more sensitive to surface soil moisture during the spring and autumn months, where average signal increases of about 4 dB corresponding to relative soil moisture increases of ~40% were obtained. Results also display significant (p<0.05) correlations between the HH (Horizontal transmit–Horizontal receive) polarisation signal and surface soil moisture, with r 2 values ranging from 0.67 to 0.86 for some of the test sites. Overall, the results suggest that the use of an empirical linear regression approach is a good approximation of the relationship between ASAR WSM backscatter coefficients and surface soil moisture over grassland areas.
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