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This project is funded by NASA grant NAG5-11107
To develop and implement an optimal procedure to merge the AMSR-E brightness temperatures with legacy or precursor SMMR and SSM/I data
In order to accomplish this it was first necessary to identify ground targets with suitable temporal and spatial brightness temperature stability.
Onboard satellite instrument calibration systems allowed ground-based processing to derive brightness temperatures of the Earth. However, a variety of post-launch artifacts, such as uncorrected attitude errors, instrument misalignment, thermal gradients, and component degradation, created a need for fine-tuning of the calibration in the data production system.
The challenge of post-launch tuning was finding suitable targets. Reference targets should be homogenous over a large enough surface to resist nonlinear averaging and antenna pattern effects, while remaining stable and well-known in their brightness temperature characteristics. Calm ocean scenes were used to cross-calibrate the SSM/I, TRMM Microwave Imager (TMI), and AMSR-E sensors at the cold end (80 to 150 Kelvin) of the typical Earth-view brightness temperature range. However, even with excellent cold end calibration, such that ocean geophysical products are accurate, the warmer temperature calibration may be inaccurate, causing errors in the geophysical retrievals over land. Some previous studies have investigated suitable targets at the mid-range (~200 Kelvin) and warm end (250 to 300 Kelvin) of the Earth's emission range. The optimal locations and dimensions of such targets have not been studied adequately from a satellite sensor viewpoint.
This study investigated specific ice sheet locations for the mid-range, and tropical forest locations for the warm end, using AMSR-E EASE-Grid TBs. The investigators developed a systematic method to evaluate the spatial and temporal variability of brightness temperatures over these land targets. Targets with minimal variability will be selected as optimal sites for long-term spaceborne radiometer system calibration monitoring over land.
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