Submitted to: IEEE Transactions on Geoscience and Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 29, 2000
Publication Date: N/A
Interpretive Summary: This investigation attempted to understand the relationship between L band brightness temperature and spatial resolution and how it might impact soil moisture retrievals using this type of data. Satellite based passive microwave remote sensing over land involves large footprints that will typically include a mixture of physical characteristics that influence the measurement. Aircraft based 1.4 GHz radiometer data were collected at several altitudes over test sites where soil moisture was measured concurrently. A substantial effort was required to calibrate and normalize the data set. Images developed by merging the flightlines clearly reflected the surface characteristics, both soil moisture and vegetation. As the spatial resolution was degraded these characteristics were retained but generalized in the images. For brightness temperature the results showed that the coarse resolution value is the arithmetic average of higher resolution observations. Emissivity or normalized TB and soil moisture dat were compared to model relationships verified in previous investigations. Relationship between emissivity and soil moisture applied at all resolutions. These results support the extrapolation of soil moisture retrieval techniques developed and verified using high resolution ground and aircraft data to coarser resolutions. The results of this investigation provide important information to support future satellite programs under development in the U.S. for global soil moisture monitoring for agriculture, hydrology and climate applications.
Technical Abstract: Passive microwave Earth observing systems provide coarse resolution data. Heterogeneity in physical characteristics will typically be present within footprints, especially over land. How this affects the development and validation of methods of retrieving soil moisture has not been verified. In this study aircraft based 1.4 GHz (L band) radiometer data were collected at several altitudes over test sites where soil moisture was measured concurrently. The use of multiple flightlines at lower altitudes allowed the direct comparison of different spatial resolutions using independent samples over the same ground location. Results showed that the brightness temperature data from 1.4 GHz sensor in this study region provides the same mean values for an area regardless of the spatial resolution of the original data. The relationship between brightness temperature and soil moisture was similar at different resolutions. These results suggest that soil moisture retrieval methods developed using high resolution data can be extrapolated to satellite scales.