MODAPS PCR 21-014
| PCR Number | 21-014 |
|---|---|
| Date | 2021-03-25 |
| Initiator | Sudipta Sarkar |
| Abstract | PGE11 6.4.10 --The bug was in a routine for compositing L2 data to L3 (routine transfer_sds(), file ids.c); the bug was in an assumption that the numbers of composited L2 pixels (N) for each resolution (1km, 500m, 250m) would all be either zero or nonzero. The bug is expressed when N is zero for 1km and nonzero for other resolutions - because the processing at that step in the algorithm would only take place if the 1km N was nonzero. The algorithm was fixed to process each resolution separately. |
| Problem Statement | In MOD_PR09.exe?s MOD09IDT/N/S products (and the MOD09CMGs made from them), there were found to be regions in which pixels along a scan had slightly lower values than in neighboring scans. While these lower values were still within a normal range, their linearity (along a scan) suggested they were artifactual. The problem turned out to be in the compositing of L2 data into CMG intermediate files (MOD09IDT/N/S files), for Terra data (only). |
| Description of Change | Code generating this artifact was debugged, and a better algorithm was developed; and this algorithm is included in PGE11 v6.4.10 |
| Products Affected | C61 L3 Land Surface Reflectance Intermediate files for Terra (MOD09IDT, MOD09IDS, MOD09IDN). |
| Software Affected | PGE11 6.4.10 |
| Processing String to Receive the Change | Terra and Aqua Forward Processing. Terra and Aqua Reprocessing. NRT |
| Downstream Product Effects | C61 L3 Land Surface Reflectance Intermediate files for Terra (MOD09IDT, MOD09IDS, MOD09IDN), and subsequent MOD09CMG files, will be improved by this fix. |
| Data Granules to be Used for Science Testing | As this change is restricted to the IDT/N/S products with no impact on the L2 science products, no science test was conducted for this change. |
| Justification | While ordinary use of MOD09CMGs (e. g., timeseries analysis) will be improved by this fix only slightly, if at all, software which aggregates several years' worth of CMG data will probably see improvements. |
| Effective Date for Implementation of Change | The PGE11 V6.4.10 has been inducted for C61 forward processing for Terra+Aqua at the leading edge and the same will also be inducted for C61 re-processing from early 2008 onwards. |
| Status | Major algorithm development completed. Sadashiva Devadiga approved on 3/30/2021. Gang Ye approved on 3/30/2021. |
