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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 "bufr_grid_screen_parallel" as same as other satellite observations. The thinning selects nearest observations on a reduced gaussian grid of 31km (TL639). As a result, the coverage becomes homogeneous and number of observations is reduced from 251926 to 109223.
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