Algorithms

The empirically derived equations used in CoastWatch are Nonlinear SST (NLSST) and Multi-channel SST (MCSST) equations.

NLSST=A₁ (T₁₁) + A₂(T₁₁-T₁₂)(MCSST) + A₃(T₁₁-T₁₂)(Secq -1)-A₄

MCSST= B₁ (T₁₁) + B₂(T₁₁-T₁₂) + B₃(T₁₁-T₁₂)(Secq -1) - B₄

Where, T₁₁ and T₁₂ are the AVHRR 11 and 12 µm channel temperatures in Kelvin; Secq is the secant of the satellite zenith angle q; NLSST and MCSST are the non-linear and linear multi-channel SST, respectively, in Centigrade; A₁-A₄ and B₁-B₄ are constant coefficients.

The CoastWatch equations differ from the global SST equations in four respects:

(1) The CoastWatch equations are applied to AVHRR local area coverage (LAC) data at approximately 1KM, whereas the global equations are applied to global area coverag (GAC) data at approximately 4KM resolution.

(2)The CoastWatch equations use the MCSST value in the non-linear term rather than a priori SST estimate obtained from an analysis of past satellite SST data. This means that there is somewhat more noise in the CoastWatch observations. Both the global operation and CoastWatch constrain the value of the a priori SST or the MCSST to the range 0^oC to 28^oC.

(3) In the Great Lakes, the MCSST value is used as the final SST value during the day; i.e., a linear equation is used as the operational equation rather than a non-linear equation.

(4) The NLSST split-window equation is used for CoastWatch rather than the triple-window equation (employing all three infrared channels) which is used in the global operation.

Information on algorithms is maintained by: