Extraction of Illumination Efficiency by Solely Radiometric Measurements for Improved Brightness-Temperature Characterization of Microwave Blackbody Target
Dazhen Gu, Derek A. Houtz, James P. Randa, Dave K. Walker
We report our recent progress towards the deveopment of microwave brightness-temperature (BT) standards. As one of the crucial parameters, the antenna beam efficiencey (BE) was traditionally determined by the relative antenna pattern. We propose a measurement technique to extract the antenna BE with solely passive radiometric measurements for characterizing the BT of the blackbody radiator. Such a technique allows us to skip the complexities that are often encountered during the measurement and calculation of the antenna pattern. Taking advantage of the variable heating capability available on most blackbody targets, we varied the temperature of a heated blackbody target and ran a series of radiometric measurements when the target was set at different distances away from th antenna and the radiometer operated at a few frequencies. Our experimental results show excellent measurement accuracy on the BE with uncertainty of about 1% at close separation distance between the antenna and the target. We further measured and computed the BT of the blackbody target at the locations where we had measured the extracted BE. The BT was slightly lower than the physical temperature of the target and exhibited 0.7K to about 1K uncertainty when the target was located at no ore than 1 m away from the antenna. A measurement uncertainty of 1K already meets the accuracy requirements of some climate variables, and such results reflect a significant step towards the establishment of BT standards at microwave frequencies.
IEEE Transactions on Geoscience and Remote Sensing
, Houtz, D.
, Randa, J.
and Walker, D.
Extraction of Illumination Efficiency by Solely Radiometric Measurements for Improved Brightness-Temperature Characterization of Microwave Blackbody Target, IEEE Transactions on Geoscience and Remote Sensing, [online], https://doi.org/10.1109/TGRS.2012.2193890
(Accessed February 25, 2024)