Terra MODIS PWA Failure - Update

December 21, 2020
By: LP DAAC

UPDATE 12/21/2020: On November 8, 2020 Terra MODIS acquisitions switched to a flexible schedule for alternating orbits to enable greater daytime coverage over polar regions. The alternating schedule is an improvement over the day/night coverage ratio of 44.2/55.8 that was initially used following the PWA failure.


Previous Announcement for the Terra MODIS PWA Failure

On October 5, 2020 at 15:21:12, Terra MODIS experienced a Printed Wire Assembly (PWA) failure that caused partial to full science data loss where the data could not be played back because of recording on the faulty PWA. The image below shows the data gaps for the global browse image of the night time orbits for October 6, 2020.

Terra MODIS data gaps for night time acquisitions for 2020-10-06

MOD02SSH, BAND 29, night time orbits
Data gaps for night time acquisitions for 2020-10-06

To minimize the overflow of onboard buffers and reduce the chance of buffers being filled and data overwritten, the day/night coverage ratio was shifted from 50/50 to 44.2/55.8 on October 7, 2020. This minimized the chance of unscheduled and unrecoverable data loss. The new day/night ratio resulted in an observed reduction in the overall Terra daytime coverage over Greenland and portions of Northern Russia as well as North America and Alaska.

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