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MicroWave Humidity Sounder (MWHS) onboard both FY-3A and FY-3B satellites have three channels (channels 3-5) near 183 GHz water vapor absorption line. These channel frequencies are also used in other instruments such as Advanced Microwave Sounding Unit-B (AMSU-B) and Microwave Humidity Sounder (MHS) onboard MetOp and NOAA satellites. Both MWHS and MHS are cross-track scanners. In this study a comparison between the simulated brightness temperatures with MWHS measurements clearly shows that MWHS observations from the three sounding channels contain a scan angle dependent cohesive noise along the instrument scanline. This noise does not cancel out when a large amount of data over a sufficiently long period of time is averaged, which eliminates the possibility of such a noise to arise from natural variability of the atmosphere and the surface. The noises are around 0.3, 0.2, and 0.2 K for channels 3-5, respectively. A principle component analysis is used for the characterization of this cohesive noise using one-month FY-3B MWHS data. It is shown that the MWHS cohesive noise is contained primarily in the first PC mode, which mainly describes a scan angle dependent brightness temperature variation, i.e., a unique feature of cross-tracking instrument. The 1st PC accounts for more than 99.91% total variance in the three MWHS sounding channels. A five-point smoother is then applied to the first PC, which effectively removes such a data noise in MWHS data. The reconstruction of the MWHS radiance spectra using the noise-filtered first PC component is of good quality. The scan angle dependent bias from reconstructed MWHS data becomes more uniform and is consistent with NOAA-18 MHS data.
A Thesis submitted to the Department of Earth, Oceanic and Atmospheric Sciences in partial fulfillment of the requirements for the degree of Master of Science.
Includes bibliographical references.
Xiaolei Zou, Professor Directing Thesis; Guosheng Liu, Committee Member; Peter S. Ray, Committee Member.
Florida State University
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