Retrieving Heterogeneous Surface Soil Moisture at 100 m across the Globe
via Synergistic Fusion of Remote Sensing and Land Surface Parameters
Abstract
Soil water is essential for maintaining global food security and for
understanding hydrological, meteorological, and ecosystem processes
under climate change. Successful monitoring and forecasting of soil
water dynamics at high spatio-temporal resolutions globally are hampered
by the heterogeneity of soil hydraulic properties in space and complex
interactions between water and the environmental variables that control
it. Current soil water monitoring schemes via station networks are
sparsely distributed while remote sensing satellite soil moisture maps
have a very coarse spatial resolution. In this study, an empirical
surface soil moisture (SSM) model was established via data fusion of
remote sensing (Sentinel-1 and Soil Moisture Active and Passive Mission
- SMAP) and land surface parameters (e.g. soil texture, terrain) using a
quantile random forest (QRF) algorithm. The model had a spatial
resolution of 100 m and performed moderately well across the globe under
cropland, grassland, savanna, barren, and forest soils (R = 0.53, RMSE =
0.08 m m). SSM was retrieved and mapped at 100 m every 6-12 days in
selected irrigated cropland and rainfed grassland in the OZNET network,
Australia. It was concluded that the high-resolution SSM maps can be
used to monitor soil water content at the field scale for irrigation
management. The SSM model is an additive and adaptable model, which can
be further improved by including soil moisture network measurements at
the field scale. Further research is required to improve the temporal
resolution of the model and map soil water content within the root zone.