Submitted to: Remote Sensing of Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/29/2005
Publication Date: 7/31/2006
Citation: Bindlish, R., Jackson, T.J., Gasiewski, A., Klein, M., Njoku, E. 2006. Polarimetric scanning radiometer C and X band microwave observations during SMEX02. Remote Sensing of Environment. 103:127-139. Interpretive Summary: The effects of dense agricultural crop conditions on soil moisture retrieval using passive microwave remote sensing were evaluated using ground, aircraft and satellite observations as part of a large scale field campaign in Iowa (SMEX02). The measurement of soil moisture is important for understanding the global hydrologic cycle and its effect on weather and climate. Soil moisture has been difficult variable to measure on a consistent and spatially comprehensive basis in part due to its large spatial and temporal variability. Field campaigns and aircraft observations play an important role in developing and validating algorithms. In SMEX02, aircraft observations were collected using a new version of the Polarimetric Scanning Radiometer (PSR) that provided high spatial resolution measurements at the same low microwave frequencies used by the Advanced Microwave Scanning Radiometer (AMSR-E) on the NASA Aqua satellite. Some of the AMSR-E measurement channels were contaminated with anthropogenic radio frequency interference, which made comparison to the PSR invalid. Aircraft data along with ancillary data were used in a retrieval algorithm to map soil moisture. These soil moisture products provide a validation of the AMSR retrievals and suggest that for vegetation conditions typical of the SMEX02 region that the soil moisture retrieval algorithm can be applied with confidence, however, they also clearly show that vegetation is a very significant factor when interpreting C-band brightness temperatures for soil moisture. These results contribute to the accuracy and reliability of the soil moisture retrievals, which should lead to increased acceptance of the soil moisture products in applications involving hydrology and agriculture.
Technical Abstract: Field experiments (SMEX02) were conducted to evaluate the effects of dense agricultural crop conditions on soil moisture retrieval using passive microwave remote sensing. Aircraft observations were collected using a new version of the Polarimetric Scanning Radiometer (PSR) that provided four C band and four X band frequencies. Observations were also available from the Aqua satellite Advanced Microwave Scanning Radiometer (AMSR) at these same frequencies. SMEX02 was conducted over a three-week period during the summer near Ames, Iowa. Corn and soybeans dominate the region. During the study period the corn was approaching it's peak water content state and the soybeans were at the mid point of the growth cycle. Aircraft observations are compared to ground observations and models to develop appropriate parameterizations to describe the effects of corn and soybeans on soil moisture retrieval are developed. Multiple altitude aircraft brightness temperatures were compared to AMSR-E observations to understand brightness temperature scaling and provide validation. The X-band observations from the two sensors were in reasonable agreement. The AMSR-E C-band observations were contaminated with anthropogenic RFI, which made comparison to the PSR invalid Aircraft data along with ancillary data were used in a retrieval algorithm to map soil moisture. The PSR estimated soil moisture retrievals on a field-by-field comparison had a standard error of estimate of 5.5%. The overall error reduced when high altitude soil moisture estimates were aggregated to 25 km resolution (same as AMSR-E EASE grid product resolution) (SEE ~ 2.85%). These soil moisture products provide a validation of the AMSR retrievals. PSR/CX soil moisture images show spatial and temporal patterns consistent with meteorological and soil conditions. The dynamic range of the PSR/CX observations indicates that reasonable soil moisture estimates can be obtained from AMSR, even in areas of high vegetation biomass content.