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In the current operational system, a simple data thinning is applied to IMS by "bufr_filter" (select 1 from every 36 raw observations). However, it leads to inhomogeneous coverage of IMS, especially in some areas. In order to improve it, new data thinning has been tested by using "bufr_grid_screen_parallel" as same as other satellite observations. The thinning selects nearest observations on a gaussian grid of 31km. As a result, the coverage becomes homogeneous and number of observations is reduced from 251926 to 109223.
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