Wednesday, 17 October 2001
An aerosol-dependent algorithm for remotely sensed sea surface temperatures from the NOAA AVHRR
For two decades, global measurements of sea surface temperature
(SST) have been produced by the National Oceanic and Atmospheric
Administration (NOAA) using infrared data obtained from the
Advanced Very High Resolution Radiometer (AVHRR) on board NOAA
polar orbiting satellites. The conventional retrieval algorithms
are derived from regression analyses of AVHRR window channel
brightness temperatures against in-situ buoy measurements under
non-cloudy conditions which provide a correction for infrared
attenuation due to molecular water vapor absorption. However for
atmospheric conditions with anomalously high aerosol content
(e.g., arising from dust, biomass burning and volcanic
eruptions), such algorithms lead to significant negative biases
in SST due to unaccounted attenuation arising from aerosol
absorption and scattering. This research presents the derivation
and implementation of a first-phase aerosol-robust daytime
correction algorithm for AVHRR SST. To accomplish this, a
long-term (1990-1998), global AVHRR-buoy matchup database was
created by merging the Pathfinder Atmospheres (PATMOS) and Oceans
(PFMDB) data sets. The merged data set is unique in that it
includes daytime estimates of aerosol optical depth (AOD) derived
from AVHRR channel 1 (0.63 micron) under conditions of significant
aerosol loading. Histograms of retrieved AOD reveal monomodal,
lognormal distributions for both tropospheric and stratospheric
aerosol modes. It is then empirically shown that the SST bias
caused under each aerosol mode can be expressed as a linear
function of observed AVHRR channel 1 slant-path AOD. Based on these
relationships, aerosol correction equations are derived for the
daytime nonlinear SST (NLSST) algorithm. Separate sets of
coefficients are utilized for the two aerosol modes. The elimination
of cold biases in the AVHRR SST, as demonstrated in this work,
will greatly improve its utility for the general user community.
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