Satellite HotSpots & SSTs

[Al Strong]

AVHRR SST Calibration Problems (August 2000 to present)

AVHRR SST appears to be too cool (0.2 - 0.8C depending on
the time and location) compared to ship and buoy
observations in parts of the equatorial regions and southern
hemisphere.

An in-depth analysis of AVHRR aerosol optical depths has
revealed slightly enhanced aerosols over the global
latitudinal band -5 to -10S, likely due to increased biomass
burning over the period.  These do not appear significant
enough to be the sole cause of the AVHRR SST bias.

During the past two months the calibration channel 3 on the
NOAA-14 AVHRR (which is used in the NLSST equations) appears
to be negatively effected by stray light occasionally
contaminating the blackbody (probably due to the geometry of
the satellite compared to the sun) over the tropical
latitudes. This happened with NOAA-11 at the end of its
lifetime as well.  Although there is an "automatic"
threshold
fix in the processing stream to fix the drops in counts due
to stray light, based on NOAA-11, it appears to be
insufficient to correct our current negative SST offset (we
are in "uncharted territory.").

We will attempt to develop corrections for this negative
offset, but they may have to be carried out manually for
several months until NOAA-16 is producing our "new/improved"
SSTs.  We hope to go operational with NOAA-16 in December
2000.

...therefore, NOAA's satellite-derived "HotSpot" coral
bleaching charts have not been correctely identifying
regions of potential bleaching since August, since we are
"seeing" SSTs that are somewhat below the in-situ
values...AND...NOAA's satellite-derived SST Anomaly charts
are showing considerably more "below-normal" (blue) SSTs
than correct...

AES and SST Cal/Val Team

October 17, 2000


--
**** <>< ******* <>< ******* <>< ******* <>< *******
Alan E. Strong
Phys Scientist/Oceanographer
  NOAA/NESDIS/ORA/ORAD -- E/RA3
  NOAA Science Center -- RM 711W
  5200 Auth Road
  Camp Springs, MD 20746-4304
        Alan.E.Strong at noaa.gov
             301-763-8102 x170
      FAX: 301-763-8108
  http://orbit-net.nesdis.noaa.gov/orad