Detailed Description

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Case #:PM_MOD_20280   Opening date: 10/13/20   Last update: 11/18/20
Status: Note
On DOY 2020.279 (10.05.20) MODIS Terra experienced a PWA failure that affected the PWA-41 (supersets 80 and 81), bringing down the total number of MODIS PWA to 14 with only 28 supersets. Given this, there is an increased chance of buffers being filled and data overwritten, resulting in unscheduled and unrecoverable data loss. So, FOT and MODIOT have decided to change the day/night coverage ratio from current 50/50 to 44.2/55.8 to minimize the overflow of onboard buffers. This ratio change occurred on October 7th (2020.281) at 20:00z. Due to this change there is an observed reduction in the overall Terra daytime coverage, specifically at the end of orbits in the northern latitudes. Below is a global browse image of DOY 2020.280, prior to the implementation of the ratio change. The second image on the right shows DOY 2020.282, where the ratio change has been implemented for the full day, and has impacted retrieval over high latitude. In this second image you can observe the reduced daytime coverage over Greenland and portions of Northern Russia as well as North America and Alaska. For comparison, the same DOY 282 from 2019 is shown in the third image, which verifies the difference is not due to seasonal affect.


MOD09, DAILY LAND SURFACE REFLECTANCE BANDS 1,4,3
day A2020280 (2020-10-06), 006
Global Browse image.

MOD09, DAILY LAND SURFACE REFLECTANCE BANDS 1,4,3
day A2020282 (2020-10-08), 006
Global Browse image.

MOD09, DAILY LAND SURFACE REFLECTANCE BANDS 1,4,3
day A2019282 (2019-10-08), 006
Global Browse image.




*** UPDATE 11.18.20 *** MODIOT switched to a Short Term Schedule (STS) for Terra on 11/8/2020 (2020-313), allowing for more flexibility for scheduling alternating orbits, enabling greater Day Rate collection over the poles. This will be an improvement over the 44.2/55.8 ratio that was being followed before, for day/night coverage, immediately following the Terra PWA failure. The global browse image from 11.15.20 (2020.320) below shows the impacts of these changes. Coverage of greater polar areas every alternating orbit results in some increased gaps over the northern high latitude regions.

MOD09, DAILY LAND SURFACE REFLECTANCE BANDS 1,4,3
day A2020320 (2020-11-15), 006
Global Browse image.

Occurrence: TERRA C6 / C61 L1B and all Downstream products DOY 2020281 and forward.
PGE:


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