Two Approaches for Inter-Satellite Radiometer Calibrations between TMI and WindSat(3. TRMM Microwave Imager (TMI),<Special Issue>Precipitation Measurements from Space)

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概要

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• This paper presents recent progress in inter-satellite microwave radiometric cross-calibration to eliminate brightness temperature measurement biases between a pair of radiometer channels operating at slightly different frequencies and incidence angles. The motivation of this research is to develop robust analytical cross-calibration techniques for inter-calibration of various satellite radiometer instruments, with the first projected application being the multi-satellite Global Precipitation Measurement (GPM) constellation to be launched in 2013. The significance of this work is that it will allow the formation of consistent multi-decadal time series of geophysical measurements for multiple satellite microwave radiometers that are free of instrumental biases and other long-term changes in radiometric calibration, which will allow researchers to study global climate change. Descriptions are given for two independent calibration techniques: a Taylor series expansion of the oceanic brightness temperature (T_b) spectrum between dissimilar radiometer channels and a non-linear regression among multi-channel T_b measurements. In the first approach, predictions were made of T_b's at a destination frequency from T_b's of a close by source frequency by expansion of the oceanic brightness temperature spectrum in a Taylor series centered at the source frequency. The relationships between T_b's and frequencies were derived from simulations using a radiative transfer model (RTM), which accounts for the total collected emissions from the ocean surface and the atmosphere. Further, earth incidence angle differences between radiometer channels were transformed in a similar manner using the partial derivatives of T_b with incidence angle derived from RTM simulations. In the second approach, we used a prediction algorithm that relies on the correlation between radiometer T_b's at various frequencies and polarizations and which uses a regression on the T_b's and their non-linear transformations developed using an independent radiative transfer model. As a demonstration, near-simultaneous pair-wise ocean T_b comparisons are presented between the TRMM Microwave Imager (TMI), which is not sun synchronous, and the sun-synchronous polar orbiting WindSat, using oceanic T_b observations from 2003-04. The corresponding results between these two intersatellite calibration techniques are highly correlated, and results demonstrate that fixed channel-by-channel differences, of order 1-2K exist between TMI and WindSat. These are significant radiometric calibration differences, which can be removed prior to forming joint data sets of geophysical parameter retrievals.

• 2009-03-31

著者

• HONG Liang

  Central Florida Remote Sensing Laboratory, University of Central Florida

• JONES W.

  Central Florida Remote Sensing Laboratory, University of Central Florida

• WILHEIT Thomas

  Brazos Earth System Science, Inc.

• KASPARIS Takis

  Central Florida Remote Sensing Laboratory, University of Central Florida

• Hong Liang

  Central Florida Remote Sensing Laboratory University Of Central Florida

• Wilheit Thomas

  Brazos Earth System Science Inc.

• Kasparis Takis

  Central Florida Remote Sensing Laboratory University Of Central Florida

• Jones W.

  Central Florida Remote Sensing Laboratory University Of Central Florida

関連論文

• Two Approaches for Inter-Satellite Radiometer Calibrations between TMI and WindSat(3. TRMM Microwave Imager (TMI),Precipitation Measurements from Space)

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