Improving Satellite Remote Sensing Estimates of the Global Terrestrial
Hydrologic Cycle via Neural Network Modeling
Abstract
Satellite remote sensing is commonly used to observe the hydrologic
cycle at spatial scales ranging from river basins to the globe. Yet it
remains difficult to obtain a balanced water budget using remote sensing
data, which highlights the errors and uncertainties in earth observation
(EO) data. Various methods have been proposed to correct EO datasets to
make them more coherent, so that they result in a more balanced water
budget. This study aimed to improve estimates of water budget components
(precipitation, evapotranspiration, runoff, and total water storage
change) at the global scale using the methods of optimal interpolation
(OI) and neural network (NN) modeling. We trained a set of NNs on a set
of 1,358 river basins and validated them on an independent set of 340
basins and in-situ observations of evapotranspiration and river
discharge. We extended the models to make pixel-scale predictions in
0.5° grid cells for near-global coverage. Calibrated datasets result in
lower water budget residuals in validation basins: the mean and standard
deviation of the imbalance is 11 ± 44 mm/mo when calculated with
uncorrected EO data and 0.03 ± 24 mm/mo after calibration by the NN
models. This study suggests to data producers where corrections should
be made to the EO datasets, and demonstrates the benefits of
physically-driven NN models for studying the hydrologic cycle at the
global scale.