SST algorithm

*refer blue book for previous topic for SST processing

i dun think i manage to understand those formulas, however, i'll include it in journal write up.

reference:

http://www.bom.gov.au/sat/SST/sst.shtml

McClain, E. P, et al., 1984, 'Comparative Performance of AVHRR-Based Multichannel Sea Surface Temperatures', J. Geophys. Res., 90, pp11587-11601

NOAA Polar Orbiter Data User's Guide

• http://www2.ncdc.noaa.gov/docs/podug/index.htm

NOAA KLM USER'S GUIDE

• http://www2.ncdc.noaa.gov/docs/klm/

NESDIS SST Equations

• http://manati.orbit.nesdis.noaa.gov/sst/cwIntroduction.html

Links valid at: 26th July 2007

SST Algorithms

If the solar zenith angle is less than or equal to 75° then the day time algorithm is used. Otherwise the night time algorithm is used.

The mean of 3 separate multi channel algorithms are used to compute the SST at night time and three algorithms must be within 2 °C otherwise the pixel is rejected. Only one algorithm is used during the day as channel 3 contains reflected sunlight and can not be used.

Daytime Algorithm

• check satellite zenith angle is less than 53°
• do land/ sea test
• check solar zenith angle - do not process if less than 1°
• gross IR test - if the channel 4 temperature is less than -5° C then do not compute a SST
• visible cloud threshold test - if the corrected albedo (albedo value divided by the cosine of the solar zenith angle) is greater than 10 percent then do not compute a SST
• visible vegetation threshold test - if the vegetation index (corrected channel 2 albedo divided by corrected channel 1 albedo) is greater than 0.75, do not compute a SST
• visible uniformity test - the corrected channel 2 albedos for all pixels in a three by three pixel box centred on the target pixel must be within 0.32 percent of the median value for the box. The maximum and minimum values must be within 0.64.
• daytime IR cloud test - if a calculated channel 4 temperature based on the channel 5 value (channel 5 temp * 1.0439 - 11.49) differs from the actual channel 4 temperature by more than 1.0° C then do not compute a SST. This test is not used by McClain et al. (1984) for daytime data but has been used historically at the BoM. The band widths for NOAA-11, 12, 14 and 15 channels 4 and 5 are the same on each satellite so the coefficients for this equation remain constant.

Multi channel SST calculation

• NOAA-11
  

CPSST Day Split Window Algorithm

sst = (0.19069 * T₅ - 49.16) / (0.20524 * T₅ - 0.17334 * T₄ - 6.78) *
(T₄ - T₅ + 0.7890) + 0.92912 * T₅ + 0.81 * (T₄ - T₅ ) * (sec(ZA) - 1) + 18.98

• NOAA-12
  

MCSST Day Split Window Algorithm

sst = (1.008574 * T₄ ) + 2.452585 * (T₄ - T₅ ) +
0.823990 * (T₄ - T₅ ) * (sec(ZA) - 1) -275.717 + 273.16

• NOAA-14
  

MCSST Day Split Window Algorithm

sst = (1.017342 * T₄ ) + 2.139588 * (T₄ - T₅ ) +
0.779706 * (T₄ - T₅ ) * (sec(ZA) - 1) + -278.43 + 273.16

• NOAA-15
  

MCSST Day Split Window Algorithm

sst = (0.959456 * T₄ ) + 2.663580 * (T₄ - T₅ ) +
0.570613 * (T₄ - T₅ ) * (sec(ZA) - 1) + -261.03 + 273.16

where:

sst - computed SST value in degrees (°) C.

T₄ - channel 4 scene temperature

T₅ - channel 5 scene temperature

ZA - solar zenith angle

Algorithms for NOAA-12, 14 and 15 posted on NOAA/ NESDIS web server. The NOAA-11 algorithm is historical and is no longer operational.

Night time Algorithm

• check satellite zenith angle is less than 53°
• do land/ sea test
• check solar zenith angle, if greater than 75° and if channel 2 reflectance is less than one percent, then use night-time algorithm. If the reflectance is greater than one percent, do not compute a SST
• gross IR test - if the channel 4 temperature is less than -5° C then do not compute a SST
• IR uniformity test - the channel 4 temperatures for all pixels in a three by three pixel box centred on the target pixel must be within 0.2° C of the median value for the box. The maximum and minimum values must be within 0.4° C
• nighttime IR cloud test - if a calculated channel 4 temperature based on the channel 5 value (channel 5 temp * 1.0439 - 11.49) differs from the actual channel 4 temperature by more than 1.0° C then do not compute a SST.
• night time low stratus cloud test - the difference obtained when subtracting the channel 3 temperature from the channel 5 temperature must be less than or equal to -0.6° C.
• Multi channel SST calculation. Three separate algorithms are used. The computed values for the three algorithms must all agree within 2.0° C.

• NOAA-11

MCSST Night Dual Channel Algorithm

sst1 = (0.17079 * T₄ - 58.47) /
(0.17334 * T₄ - 0.07747 * T₃ - 33.74) *
(T₃ - T₄ - 6.440) + 0.98530 * T₄ + 1.97 * (sec(ZA) - 1) + 15.88

MCSST Night Split Window Algorithm

sst2 = (0.19596 * T₅ - 48.61) /
(0.20254 * T₅ - 0.17334 * T₄ - 6.11) *
(T₄ - T₅ + 1.4600) + 0.95476 * T₅ + 0.98 * (T₄ - T₅ ) * (sec(ZA) - 1) + 9.32

MCSST Night Triple Channel Algorithm

sst3 = (0.16835 * T₄ - 34.32) /
(0.20524 * T₅ - 0.07747 * T₃ - 20.01) *
(T₃ - T₅ + 14.86) + 0.97120 * T₄ + 1.87 * (sec(ZA) - 1) - 3.43

• NOAA-12

MCSST Night Dual Channel Algorithm

sst1 = (1.017736 * T₃ ) + 0.426593 * (T₃ - T₄ ) +
1.800916 * (sec(ZA) - 1) - 276.264 + 273.16

MCSST Night Split Window Algorithm

sst2 = (1.013674 * T₄ ) + 2.443474 * (T₄ - T₅ ) +
0.314312 * (T₄ - T₅ ) * (sec(ZA) - 1) - 277.797 + 273.16

MCSST Night Triple Channel Algorithm

sst3 = (1.003194 * T₄ ) + 1.007171 * (T₃ - T₅ ) +
1.174698 * (sec(ZA) - 1) - 273.262 + 273.16

• NOAA-14
  

MCSST Night Dual Channel Algorithm

sst1 = (1.008751 * T₄ ) + 1.409936 * (T₃ - T₄ ) +
1.975581 * (sec(ZA) - 1) - 273.914 + 273.16

MCSST Night Split Window Algorithm

sst2 = (1.029088 * T₄ ) + 2.275385 * (T₄ - T₅ ) +
0.752567 * (T₄ - T₅ ) * (sec(ZA) - 1) - 282.24 + 273.16

MCSST Night Triple Channel Algorithm

sst3 = (1.010037 * T₄ ) + 0.920822 * (T₃ - T₅ ) +
0.067026 * (sec(ZA) - 1) - 275.364 + 273.16

• NOAA-15

MCSST Night Dual Channel Algorithm

sst1 = (1.041037 * T₄ ) + 1.587582 * (T₃ - T₄ ) +
1.677430 * (sec(ZA) - 1) - 283.51 + 273.16

MCSST Night Split Window Algorithm

sst2 = (0.993892 * T₄ ) + 2.752347 * (T₄ - T₅ ) +
0.662999 * (T₄ - T₅ ) * (sec(ZA) - 1) - 271.40 + 273.16

MCSST Night Triple Channel Algorithm

sst3 = (1.015354 * T₄ ) + 1.063572 * (T₃ - T₅ ) +
1.294955 * (sec(ZA) - 1) - 276.76 + 273.16

where:

sst n - computed SST value in degrees ° C.

T₃ - channel 3 scene temperature

T₄ - channel 4 scene temperature

T₅ - channel 5 scene temperature

ZA - solar zenith angle

Algorithms for NOAA-12, 14 and 15 posted on NOAA/ NESDIS web server. The NOAA-11 algorithm is historical and is non-operational.

• the SST value used is the mean of the three values computed.

Climatology test

Computed SST rejected if differs from climatology by more than 10°