Accuracy Requirements for a Soil Moisture Mission

Jeffrey P. Walker and Paul R. Houser

Poster Presentation

Defensible requirements of a remote sensing mission for the measurement of surface soil moisture are of vital importance to scientists planning such a mission. In particular, mission planners need: (i) justification for polarization, wavelength and look angle requirements of the sensor; and (ii) accuracy, temporal resolution and spatial resolution requirements of the measurement. The requirements of (i) have been fairly well defined, with horizontally polarized L-band radiometer measurements at a look angle of less than 50º yielding the greatest sensitivity to soil moisture. However, the requirements of (ii) have been less well defined. This paper seeks to address the first of those three issues; accuracy requirements.

The accuracy requirements are addressed through a synthetic data assimilation study. First, a land surface model was used to generate a “truth” data set that provided both the surface soil moisture “observation” and evaluation data. The land surface forcing data and initial conditions were then degraded to simulate the uncertainties in these data and a second simulation performed. Finally, simulations were made where the observations were assimilated into the simulation with degraded atmospheric forcing data and initial conditions with various levels of error imposed on the observations (0, 1, 2, 3, 4, 5 and 10%v/v). It was found that observation error in surface soil moisture must be less than the error required in model forecasts of soil moisture, else a slight degradation of the model forecasts may result. Typically, observations of surface soil moisture must have an accuracy better than 5% v/v.