Wednesday, 25 January 2012: 4:00 PM
Geolocation and Scan Asymmetry Correction for the Passive Microwave Instruments
Room 257 (New Orleans Convention Center )
Microwave (MW) satellite data play a very important role in hydrological analysis, weather forecasting, and climate monitoring and assessment. They are extensively used for retrieving geophysical variables like temperature, rainfall, snowfall, humidity etc. One of the most important sources of the MW data comes from the satellites operated by the National Oceanic and Atmospheric Administration (NOAA). Current passive microwave sounder data, used in hydrological applications, are derived from POES satellites for which the primary mission is operational weather prediction. These data are not calibrated with sufficient stability for climate and hydrological applications. A properly calibrated Fundamental Climate Data Record (FCDR) needs to be developed to enable the utilization of these data for Thematic CDRs (TCDR) and Climate Information Records. Once developed, TCDR's for water cycle applications (precipitation, water vapor, clouds, etc.) will be developed for use as key components in international programs such as GEWEX, CEOS and GPM. In this study, we investigate the geolocation error and scan asymmetry bias of AMSU-A, -B and MHS sensors, onboard NOAA15-19 and MetOp-A. For AMSU-A the study is limited to the Window Channels, i.e. Channels 1, 2, 3, and 15. Some potential sources of the geolocation errors are 1) the time difference between satellite clock and UTC time, 2) systematic misalignment of the instrument so that the nadir position does not point to the satellite subpoint and/or the scanning is not perpendicular to the velocity direction, 3) inaccuracy in the ephemeris data that are used to predict the satellite position, and 4) the time dependent satellite attitude errors including pitch, roll and yaw error. Long term monitoring of the geolocation errors is vital to develop CDRs from instruments like AMSU. We focus on the correction of satellite and sensor attitude errors. The scan asymmetry is affected by the geolocation error, especially the roll angle error, therefore the asymmetry is analyzed after geolocation correction. The asymmetry can be determined using either radiative transfer calculations or subtracting left and right sides of the scan lines. The later approach is just applicable if the surface does not affect the outgoing radiance. Therefore it can be applied to the AMSU-B and MHS water vapor channels as they are not sensitive to the surface emissivity, except in very cold and dry conditions.
Supplementary URL: http://cics.umd.edu/~imoradi/index.html