Soil moisture experiments 2005 (SMEX05): Passive microwave polarimetric signatures of soil moisture and vegetation

Microwave remote sensing provides a direct measurement of soil moisture; however, there have been many challenges in algorithm science and technology that we have faced on the path to providing global measurements. Field experiments, especially those involving both ground and aircraft measurements, provide the linkage between spatial scales necessary for both algorithm development and validation. Soil Moisture Experiments 2005 (SMEX05) was designed to address algorithm development and validation related to several current and scheduled satellite systems that can provide soil moisture. The Airborne Polarimetric Microwave Imaging Radiometer (APMIR), an aircraft simulator of WindSat, was flown on a P3B aircraft over an agricultural domain (corn and soybean) in Iowa, USA. Early morning flights were conducted for several weeks from late June to early July 2005. Efforts in SMEX05 to focus on the early morning time frame offered an opportunity to understand the effect of dew on microwave emissions, which could contribute to improved microwave soil moisture algorithms for satellites with early morning observation times. From the analysis on the preliminary data it was found that 1) the effect of dew on both H and V is small and 2) as dew evaporates the emissivity increases, which suggests a “standing water” effect. Expected differences between forest and crop sites and between polarizations were observed. These preliminary results will be refined following further calibration of the APMIR data.