A survey of global water temperature datasets and their applicability to passive remote sensing of soil moisture near inland/coastal water bodies

Abstract:

Satellite-based surface soil moisture products have created extensive opportunity to study the terrestrial-atmosphere interactions and hydrological circulation at a global scale. Compared to the optical and active microwave sensors, passive microwave sensors are more sensitive to surface soil moisture in the presence of the same confounding factors (e.g. clouds, vegetation, surface roughness, etc.) that would degrade soil moisture estimation accuracy with optical and active microwave sensors. These advantages of passive microwave remote sensing of soil moisture have been the principal driving force behind the application of various spaceborne radiometers (e.g. SMMR, AMSR-E, AMSR2, Aquarius, SMOS and SMAP) in soil moisture retrieval over the last few decades.

Coastal water and inland open water bodies (e.g. lakes, rivers, wetlands, etc.) in close proximity to land often pose an error source to passive remote sensing of soil moisture. Without proper correction procedures in place, the contribution of microwave emission from water can easily be mistaken as microwave emission from the adjacent land, resulting in a systematic wet bias in soil moisture estimates. To mitigate this contamination, it is necessary to disentangle the mixture of land-water brightness temperature and remove the water portion using ancillary surface water temperature of inland/coastal water bodies.

In this investigation, we will present a survey of several newly released assimilative coastal/inland surface water temperature datasets that incorporate long-term satellite-based observations and in situ measurements. These datasets vary in their spatial/temporal resolution but all provide long-term coverage. Given the use of a variety of input data sources and diverse procedures in the respective assimilation processes, the differences among these products are likely to exist and rarely investigated. A survey of six global sea surface temperature products and three lake surface water temperature products will be provided, with a significant emphasis on individual datasets’ relevance in correction for microwave emission from water in the context of soil moisture retrieval. An evaluation on criteria such as long-term availability, global coverage, spatial resolution, temporal resolution, data friendliness, product documentation, and institution-based production support have led us to conclude that the ECMWF ERA5 reanalysis surface water temperature products represent the most optimal path forward for the development and production of a long-term soil moisture product.