MODAPS PCR 15-028
| PCR Number | 15-028 |
|---|---|
| Date | 2015-08-17 |
| Initiator | Jim Ray |
| Abstract | PGE11 v6.3.15. Better algorithm for recognizing orbital maneuvers, and the conversion of weights for ancillary data from floats to doubles to avoid rounding error. |
| Problem Statement | A bug in the interpolation of ancillary data (AD) was found. GDAS and GFS AD files are made every 6 hours (GDAS) or three hours (GFS) per day. AD is interpolated from two files that bracket the granule time. The interpolation algorithm uses the Julian day value of the AD file, including its fractional day part - e.g., for GDAS, 0.0, 0.25, 0.5, 0.75; for GFS, 0.0, 0.125, 0.25, 0.375, etc. We found errors in casting some Julian day values for GFS files to 4-byte floats. |
| Description of Change | Julian day values in the interpolation algorithm are no longer cast to 4-byte floats, but to 8-byte floats. |
| Products Affected | MxD09, MxD09CMG, in NRT only |
| Software Affected | PGE11 v6.3.15 |
| Processing String to Receive the Change | Terra Reprocessing, Aqua Reprocessing, NRT |
| Downstream Product Effects | None. |
| Data Granules to be Used for Science Testing | Process one global day on the MODAPS test system and the NRT system using PGE11 version 6.3.14 and 6.3.15.2010-059 |
| Justification | This change provides a more accurate interpolation of GFS data. GDAS data aren't affected, since the Julian day values can be accurately represented in either 4-byte floats or 8-byte floats. Therefore, any product improvements would be limited to NRT outputs; and these improvements are slight (e.g., slight improvements in cloud masking). |
| Effective Date for Implementation of Change | Completed. |
| Status | Major algorithm development completed. Sadashiva Devadiga approved approved on 08/18/2015. Michael King approved on 08/19/2015. |
