Comparison of Microwave and Infrared SST
in the Eastern North Pacific
John Ryan (MBARI), Ken Casey (USNA) and Tim Mavor (NOAA)
The image below shows the mean difference of TMI (microwave) minus Pathfinder (infrared) SST for the period December 1997 through November 1999. The TMI data are version-2, 0.25° gridded SST obtained from Remote Sensing Systems. The original Pathfinder data were 9 km declouded images to which an additional erosion filter was applied to remove pixels near clouds (a conservative approach to avoid cloud contaminated pixels). Pathfinder data were then spatially and temporally binned to match the 0.25 degree, 7-day TMI grid. The means calculated for each were limited to only the times when both sensors could provide an SST estimate. So, this is comparing apples and apples (almost, although the N for each weekly mean is higher for TMI).
Over most of the region, TMI is higher, and there is a strong "near-land" difference between the two with TMI higher by ~0.5 to 2 degrees. Further, the difference increases toward the land.
Possibilities:
- Pathfinder SST is biased low near land
- TMI SST is biased high near land
- Some combination of the above
MBARI moored observations at the location of the gray circle on the map above (near 122.4W, 36.7N) indicate that TMI is biased high in the region where this difference is pronounced. Further, there is some suggestion that the TMI-mooring difference increased with time (seasonal dependence or calibration drift?). In contrast, Pathfinder SST is consistently closer to the mooring data.
This site will be updated as the comparison develops with further analyses including an examination of GOES Geostationary SST data.