MODAPS PCR 17-023
| PCR Number | 17-023 |
|---|---|
| Date | 2017-10-01 |
| Initiator | Lin, Guoqing (Gary) |
| Abstract | PGE60 v6.1.1. I was instructed to increase the maximum sensor zenith angle to 70°, just to be safe. Testing uncovered a defect in the code that had been hidden by the previously restricted range of the scan: at no point did the code make any attempt to prevent comparison of a landsat scene with the MODIS image from running past the ends of a scan. Previously, chips sufficiently close to the ends of a scan to trigger this bug were filtered out by the sensor zenith limit. The code now explicitly checks whether a given landsat scene would extend past the end, and if so, skips it. |
| Problem Statement | Control points which could have been observed at scan angles greater than ±45 degrees were being ignored. |
| Description of Change | Internally, this is the result of a filter based upon the sensor zenith angle rather than directly on the scan angle. For nominal attitude (roll=0, pitch=0) and a perfectly spherical Earth, there's a direct relationship between those two angles: sin(sensor_zenith)/(Re+h) == sin(|scan_angle|)/Re where Re is the radius of the Earth, and h is the altitude of the satellite. The old limit was sensor_zenith < 52°, which corresponds, for Re=6371km and h = 705km, to |scan_angle| < 45°. Increasing the maximum sensor zenith angle to 67° would allow scan angles up to the maximum of 56°. |
| Products Affected | MODCP |
| Software Affected | PGE60 v6.1.1 |
| Processing String to Receive the Change | Terra Reprocessing, Aqua Reprocessing |
| Downstream Product Effects | There are no downstream products. |
| Data Granules to be Used for Science Testing | |
| Justification | Improve monitoring the quality of geolocation products. |
| Effective Date for Implementation of Change | Completed. |
| Status | Major algorithm development completed. Guoqing (Gary) Lin approved 10/10/2017; Robert Wolfe approved 10/10/2017; Gang Ye approved on 10/11/2017. |
