ARC - Algorithm Specification |

Algorithm Specification of the science processors

### Saharan Dust Detection

Dust aerosol can be a problem for some satellite SST products as infrared SST retrievals are biased cold in the presence of dust. While very high dust loadings are often (incorrectly) flagged as "cloud", more moderate amounts are passed as "clear" and impact the resulting SST fields. This is a particular problem over the Atlantic in the summer months when desert dust is lifted from the Saharan desert and transported west over the ocean.

Desert dust is detected using the ATSR Saharan Dust Index (ASDI) method described in
Good et al. (2011)
. This functions as a dual-view retrieval of dust index using the 11 and 12 micron channels which can therefore be used both day and night.

### SST Retrieval

ARC SSTs are estimated using a coefficient-based retrieval scheme (
Embury and Merchant 2011
) which is robust to the presence of stratospheric aerosol from the Mount Pinatubo eruption in 1991. The coefficients are banded by: total column water vapour (TCWV) to reduce the effects of atmospheric variability on the nadir and day-time retrievals; satellite zenith angle to reduce viewing angle dependent biases from the dual-view geometry.

### SNAP implementation

TCWV data is provided in SLSTR inputs; however, it is not included with ATSR L1b files. As a result the user must supply the TCWV data when processing ATSR scenes.