Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2010
Publication Date: April 1, 2010
Citation: Du, J., Jackson, T.J., Bindlish, R., Cosh, M.H., Li, L., Hornbuckle, B. 2010. Passive microwave observations of soil moisture and dew in soil moisture experiments 2005 [abstract]. American Geophysical Union. 90(52)H11G-05. Technical Abstract: Microwave remote sensing can provide reliable measurements of surface soil moisture. However, there are a few land surface features that have a perturbing influence on the soil moisture retrievals. A lack of appropriate observations and physical characterization of target parameters contribute to retrieval problems. Also, some of these effects are relatively small and can be difficult to separate from other factors. Soil Moisture Experiments in 2005 (SMEX05) were designed to examine several aspects of soil moisture retrieval related to the WindSat satellite sensor. Early morning flights were conducted with an airborne microwave radiometer for several weeks from late June to early July 2005 in Iowa, USA over an agricultural domain (corn and soybean). Ground based measurements of soil moisture and related parameters were made concurrent with the aircraft and satellite observations. A focus on the early morning time frame provided an opportunity to study issues (specifically effect of dew on microwave emission) related to soil moisture retrieval during early morning hours, the observing time for WindSat and other future soil moisture satellites (SMOS, SMAP). Soil moisture estimates made using the aircraft X-band channel had a standard error of estimate of 0.053 m3/m3 for soybean and 0.064 m3/m3 for corn fields. Results of an experiment designed to observe the change in brightness temperature at X-band during the evaporation of dew in corn, soybean, and forest indicated that dew had a measurable impact. The presence of dew decreased land surface emissivity for each type of land cover. The impact of dew in corn was most significant and must be considered in soil moisture retrieval at X-band. Increases in temperature (and differences in canopy and soil temperature) during this period made it difficult to attribute all of the change in emissivity to dew dissipation.