Algorithms

The NOAA Office of Satellite Data processing and Distribution generate sea surface temperature (SST) retrievals on an operational basis from the GOES-11 and 12 satellite Imagers. The algorithm retrieval schemes are based on Radiative Transfer Modeling (RTM), generating skin temperatures not bulk temperatures. The Imager channels are listed below.

Radiative-transfer-based SST retrieval algorithms are used to generate the GOES-11/12 SST retrievals. The form of the current GOES operational SST equation is:

SST=a₀ + a₀‘S + Σ_i (a_i + a_i‘S)T_i

where i is GOES-Imager channel number (2, 4, 5),
S = sec (satellite zenith angle) – 1 and Ti is channel brightness temperature in Kelvin.

Coefficients (for Kelvin brightness temperatures)
a₀, a₀‘, a₂, a₂‘, a₄, a₄‘, a₅, a₅‘

GOES-11 (day)
Two channel
Modeled RMS error = 0.68364262
-18.01 -6.52 0.0000 0.0000 3.3188 0.1466 -2.2588 -0.1174

GOES-11 (night)
Three channel
Modeled RMS error = 0.30877404
-5.46 -2.93 0.9449 -0.0384 0.5698 0.3328 -0.4905 -0.2775

As shown in the table, channel 5 of the Imager on the GOES-12 platform is centered at 13.3 microns and is therefore not used in the SST retrieval. While SSTs can still be retrieved at night using the 3.9 and 11 micron channels (2 and 4), daytime retrievals are complicated by the contribution of reflected and scattered solar radiation to the channel 2 brightness temperature. Three extra steps are performed:

• the region affected by sun glint is estimated using NCEP model winds, the Cox and Munk (1954) slope distribution and the satellite-solar geometry;
• the clear-sky scattered solar radiation contribution is estimated for a typical value of aerosol optical depth;
• channel 2 brightness temperatures are adjusted to compensate for the solar contributions estimated in the previous steps, with the exception that sun glint corrections >1 deg. K are flagged as insufficiently reliable to be used for SST retrieval. SSTs are retrieved for the remaining clear-sky pixels using the adjusted channel 2 brightness temperatures along with the channel 4 data, using the same retrieval equation form described above.

GOES-12 (day and night)
-2.10, -1.15, 1.177, 0.073, -0.162, -0.069, 0.0, 0.0
(Coefficients for channel 5 are zero because channel 5 (13.3 µm) is not used.)

Channels	Wavelength(µm)	Resolution
1 (visible)	0.52-0.72	1 km
2 (infrared)	3.78-4.03	4 km
3 (infrared)	6.47-7.02	4 km
4 (infrared)	10.2-11.2	4 km
5 (infrared)	11.5-12.5 (GOES-11) 13.0-13.7 (GOES-12)	4 km

GOES-SST 8-bit data conversion (0-255)

Value	Use
0	Space
1	Screened SST below cloud probability threshold
2	Land
3	Sun Glint
4	Cloud Mask (Gross Cloud Screening)
5	Twilight/ High Zenith Angle
6	Land Contaminated Radiative Transfer Model
7-255	Scaled SST values SST(degrees K) = 270.0 degrees K + (0.15*SST scaled)