Submitted to: IEEE Transactions on Geoscience and Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2007
Publication Date: 7/30/2007
Citation: Narvekar, P.S., Jackson, T.J., Bindlish, R., Li, L., Heygster, G., Gaiser, P. 2007. Observations of land surface passive polarimetry with the WindSat instrument. IEEE Transactions on Geoscience and Remote Sensing. 45:2019-2028. Interpretive Summary: Polarimetric passive microwave measurements may provide new information that can be used to estimate or describe land surface features. Data from the WindSat instrument were used in this study to determine if this was possible. Four large and homogenous regions were identified that represented unique land surface features (forest, deserts, agriculture). The results of this study clearly show that when aligned land surface features are present, then there will be a response in the U channel. This is the first time this has been observed at satellite footprint scales. Further controlled condition studies of vegetation features are needed to refine our understanding. How to use this new information in application such as soil moisture retrieval is the next challenge. 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: WindSat provides an opportunity to explore the passive microwave polarimetric signatures of land surfaces. In order to accommodate the large sensor footprint, large homogeneous regions with unique features were used. These included forest, rangeland, desert and agricultural conditions. WindSat observations at horizontal and vertical polarizations over land surfaces were found to be well calibrated and consistent with other passive microwave sensors. Isotropic regions (e.g. Amazon Rainforest) had no polarimetric response at all azimuth angles. Results showed that land surfaces with aligned features (topography or row structured vegetation) produced systematic variations in the 3rd and 4th Stokes parameters. These responses were found to be in good agreement with previous sea surface studies. Analysis of temporal trends of the variation in polarimetric measurements for a specific azimuth angle could be attributed to crop growth cycle in the agricultural region. Further analyses will seek to isolate specific features that could be used in applications such as soil moisture retrieval.