The Ocean Biology Processing Group detected a notable decline in the scientific accuracy of MODIS-Aqua Ocean Color data products since 2023. This decline stems from challenges in monitoring and adjusting for changes in instrument calibration using solar diffuser and fixed ground targets. The Aqua platform has begun to drift away from the standard orbit node crossing time of 13:30 mean local time. This change in orbit affects the ground track, which in turn impacts the viewing geometry for the fixed desert locations used to track the degradation of the blue bands. The change in orbit also affects the angle of incidence on the on-board solar diffuser, complicating the analysis of those data as well. It was determined that these impacts, though subtle early on in the orbit change, can be traced back as far as July 2021. A revised temporal calibration has been derived and applied to the data collected since 01 July 2021.
The impact to large-scale regional means in the ocean color time-series is shown below. The plot shows the averages of the MODIS Aqua Rrs in global deep water as a function of time both for R2022.0 (blue lines) and R2022.0.1 (red lines).
