Submitted to: IEEE Transactions on Geoscience and Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2010
Publication Date: 12/1/2010
Publication URL: http://handle.nal.usda.gov/10113/56283
Citation: Narvekar, P.S., Heygster, G., Jackson, T.J., Bindlish, R., Macelloni, G., Notholt, J. 2010. Passive polarimetric microwave signatures observed over Antarctica. IEEE Transactions on Geoscience and Remote Sensing. 48:1059-1075. Interpretive Summary: Satellite observations provided by a new type of microwave radiometer called WindSat were analyzed and responses were found to be related to surface topography, roughness and snow morphology. Spaceborne passive microwave remote sensing have provided valuable information on the Earth’s geophysical features that is used in assessments and prediction models. The WindSat instrument includes the first fully polarimetric observations. It was expected but unproven that these measurements would provide new information that will lead to improved agricultural and hydrologic forecasts. The first step in the evaluation was the examination of the system response to well known targets. Here we explored the Antarctic ice sheet. In addition to providing insights on the new sensor information, the analysis of the Antarctic ice sheet is important to global climate studies. It’s condition and spatial extent are viewed as indicators of global warming. The study demonstrated the potential of spaceborne fully polarimetric passive microwave radiometers in monitoring the thermal and morphological properties of large ice sheets as well as surface structural properties, which will also be useful for other types of surfaces.
Technical Abstract: WindSat satellite-based fully polarimetric passive microwave observations, expressed in the form of the Stokes vector, were analyzed over the Antarctic ice sheet. The vertically and horizontally polarized brightness temperatures (first two Stokes components) from WindSat are shown to be consistent with previous studies. Azimuthal modulations in the 3rd and 4th Stokes components were analyzed and related to surface topography, roughness and snow morphology. A second harmonic sine function of the azimuth angle was used to estimate the orientation angle of snow features, such as topographic slope and sastrugi. The results show good agreement with the orientations derived in a previous study using scatterometer data at similar frequencies. The seasonal variability in the 3rd and 4th Stokes components were also analyzed. A consistent pattern of response emerged for the 10.7 GHz channels. Under winter conditions, the large contribution of multiple volume scattering causes a high and regionally varying 10.7 GHz 4th Stokes signal. Under summer conditions, surface scattering dominates and results in a high 10.7 GHz 3rd Stokes signal. The 3rd and 4th Stokes observations at 37 GHz were found to correspond to the smaller penetration depth at this higher frequency, resulting in a low difference between the amplitudes of summer and winter. The study demonstrates the potential of a spaceborne fully polarimetric passive microwave radiometers in monitoring the thermal and morphological properties of large ice sheets.