|SHELLITO, PETER - University Of Colorado|
|SMALL, ERIC - University Of Colorado|
|COLLIANDER, ANDREAS - Jet Propulsion Laboratory|
|BINDLISH, R. - Science Systems, Inc|
|BERG, A. - University Of Guelph|
|Bosch, David - Dave|
|CALDWELL, T. - University Of Texas|
|Goodrich, David - Dave|
|LOPEZ-BAEZA, E. - University Of Valencia|
|MCNAIRN, H. - Agriculture And Agri-Food Canada|
|Starks, Patrick - Pat|
Submitted to: Geophysical Research Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2016
Publication Date: 6/16/2016
Citation: Shellito, P., Small, E., Colliander, A., Bindlish, R., Cosh, M.H., Berg, A., Bosch, D.D., Caldwell, T., Goodrich, D.C., Lopez-Baeza, E., McNairn, H., Prueger, J.H., Starks, P.J. 2016. SMAP soil moisture drying more rapid than observed in situ following rainfall events. Geophysical Research Letters. 43(15):8068-8075.
Interpretive Summary: Soil drying rates can vary depending on soil texture and land surface cover, but this study focuses on the measurement method. Soil moisture from satellite data and from in situ sensors are compared to determine how drying rates behave after significant rainfall events. It was determined that the satellite rates were twice as much as the in situ rates. It is hypothesized that this is a result of the difference in sensing depths between the two sensing systems. This is important to understand for modelers who are beginning to incorporate remote sensing estimates into land surface models which have up until this point used only in situ data sources.
Technical Abstract: We examine soil drying rates by comparing observations from the NASA Soil Moisture Active Passive (SMAP) mission to surface soil moisture from in situ probes during drydown periods at SMAP validation sites. SMAP and in situ probes record different soil drying dynamics after rainfall. We modeled this process by fitting an exponential curve to 63 drydown events: the median SMAP drying timescale is 44% shorter and the magnitude of drying is 35% greater than in situ measurements. We also calculated drying rates between consecutive observations from 193 events. For 6 days after rainfall, soil moisture from SMAP dries at twice the rate of in situ measurements. Restricting in situ observations to times of SMAP observations does not change the drying timescale, magnitude, or rate. Therefore, observed differences are likely due to SMAP's sensing depth being shallowest (<5 cm) following a rainfall event and increasing as the soil dries.