Impact of surface soil moisture retrieval period on land surface regime detection skill

Authors: Crow, Wade; FELDMAN, ANDREW - Goddard Space Flight Center; BINDLISH, RAJAT - Goddard Space Flight Center

Submitted to: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Satellite-based estimates of soil moisture are useful for a variety of agricultural applications including drought monitoring, numerical weather prediction and irrigation scheduling. To ensure that future satellite missions meet the needs of the agricultural community, it is important to establish transparent requirements for such missions (i.e., minimum requirements with regards to the accuracy, resolution and observation frequency of soil moisture estimates). This paper establishes mission observation frequency requirements for satellite-based estimates of soil moisture that enable their future use in agricultural drought monitoring. Specifically, it demonstrates that satellite missions must provide, at least, one observation every four days to robustly detect dynamic soil moisture changes associated with the onset of drought. This result will be used to establish meaningful requirements for future NASA soil moisture missions and ensure that they are consistent with agricultural applications.

Technical Abstract: Fixed soil moisture (') thresholds associated with nonlinear changes in soil water loss rates can be used to detect transitions between land surface water flux regimes. Since such regimes are characterized by distinct soil water loss processes (e.g., energy- versus water-limited evapotranspiration), their identification is useful for applications reliant on the accurate parameterization of land surface water and energy fluxes. The most direct method for regime detection is the time differencing of successive ' retrievals acquired from long-term, satellite-based, L-band microwave data records. However, the adequate sampling of regime transitions requires access to historical ' time series that extend across multiple satellite missions. As a result, traceable measurement requirements are needed to ensure that future satellite missions can reliably continue such sampling. Here, we perform a synthetic analysis to examine the impact of the satellite ' retrieval period t (i.e., the total days in a time interval divided by the total number of retrievals within the same interval) on water-flux regime detection skill using the time differencing of a ' time series. Globally, results suggest a sharp reduction in regime-detection skill when t exceeds a threshold value in the range of 2 to 4 days. Therefore, to contribute to land surface regime-detection applications, future satellite soil moisture satellite missions must sample ' retrievals at t = 4 days.