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ENVI

Compute AVHRR Sea Surface Temperature

Compute AVHRR Sea Surface Temperature

  1. From the Toolbox, select Raster Management > Data-Specific Utilities > AVHRR Sea Surface Temperature (SST).
  2. Select an input file and perform optional spatial and spectral subsetting, then click OK. The AVHRR Sea Surface Temperature Parameters dialog appears.
  3. The input file must contain AVHRR bands 3, 4, and 5.

  4. From the Satellite drop-down button, select the satellite name.
  5. From the SST Algorithm drop-down button, select the algorithm.
  6. Select output to File or Memory.
  7. Click OK.

The output sea surface temperature image is in degrees Celsius.

Note: AVHRR data that have been scaled to 8-bit depth cannot be used to compute SSTs because NOAA does not modify the calibration coefficients stored in the file’s Level 1B header.

ENVI computes SST images in degrees Celsius, using AVHRR bands 3, 4, and 5. Currently, it does not use a cloud or land mask in the sea surface temperature calculation. It uses the Multi-Channel Sea Surface Temperature (MCSST) algorithms: one for daytime data and three for nighttime data:

  • Day MCSST Split
  • Night MCSST Split
  • Night MCSST Dual
  • Night MCSST Triple

These algorithms differ by which bands are used to correct for the atmosphere. Split-window uses bands 4 and 5, dual-window uses bands 3 and 4, and triple-window uses bands 3, 4, and 5.

ENVI uses the following SST equations for NOAA-12, -14, and -15:

Day MCSST Split
Ts = a0 + a1*band4 + a2(band4 - band5) + a3(band4 - band5)(sec(f) -1)

Night MCSST Split
Ts = a0 + a1*band4 + a2(band4 - band5) + a3(band4 - band5)(sec(f)-1)

Night MCSST Dual
Ts = a0 + a1*band4 + a2(band3 - band4) + a3(sec(f) -1)

Night MCSST Triple
Ts = a0 + a1*band4 + a2(band3 - band5) + a3(sec(f)-1)

ENVI uses the following SST equations for NOAA-16 through NOAA-18:

Day MCSST Split
Ts = a0 + a1*band4 + a2*band5 + a3(band4 - band5)(sec(f) -1)

Night MCSST Split
Ts = a0 + a1*band4 + a2*band5 + a3(band4 - band5)(sec(f) -1)

Night MCSST Dual
Ts = a0 + a1*band4 + a2(band3 - band4) + a3(sec(f) -1)

Night MCSST Triple
Ts = a0 + a1*band3 + a2*band4 + a3*band5 + a4(band3 - band5)(sec(f) -1)

ENVI uses the following SST equations for NOAA-19:

Day MCSST Split
Ts = a0 + a1*band4 + a2(band4 - band5) + a3(band4 - band5)(sec(f) -1)

Night MCSST Split
Ts = a0 + a1*band4 + a2(band4 - band5) + a3(band4 - band5)(sec(f) -1)

Night MCSST Dual
Ts = a0 + a1*band4 + a2(band3 - band4) + a3(sec(f) -1)

Night MCSST Triple
Ts = a0 + a1*band4 + a2(band3 - band5) + a3(band3 - band5)(sec(f) -1)

ENVI uses the following SST equations for NOAA MetOp-A FRAC data:

Day MCSST Split
Ts = a0 + a1*band4 + a2(band4 - band5) + a3(band4 - band5)(sec(f) -1)

Night MCSST Split
Ts = a0 + a1*band4 + a2(band4 - band5) + a3(band4 - band5)(sec(f) -1)

Night MCSST Dual
Ts = a0 + a1*band4 + a2(band3 - band4) + a3(sec(f) -1)

Night MCSST Triple
Ts = a0 + a1*band4 + a2(band3 - band5) + a3*(band3 - band5)(sec(f) -1)

Sec(f) is the secant of the satellite zenith angle (f), and bands 3 through 5 are the calibrated brightness temperatures of NOAA AVHRR bands (in Kelvins). The “a” coefficients are derived from a regression model based on drifting buoy and tropical Pacific fixed-buoy data. The coefficient values depend on which NOAA satellite was used to collect the AVHRR image. ENVI uses published MCSST coefficients for NOAA-12 through NOAA-17. The following tables show the “a” coefficients for the various NOAA sensors, for each algorithm that is computed.

Day MCSST Split

Satellite

a0

a1

a2

a3

NOAA-12

-263.006

0.963563

2.579211

0.242598

NOAA-14

-278.43

1.017342

2.139588

0.779706

NOAA-15

-261.029735

0.959456

2.663579879

0.570613

NOAA-16

-273.77

3.301267

-2.30195

0.628966

NOAA-17

-271.206

0.992818

-2.49916

0.915103

NOAA-18

-280.43

1.02453

2.10044

0.784059

NOAA-19

-278.74596

1.01922

1.72270

0.80263

MetOp-A FRAC

-273.816

1.00255

2.39451

0.903773

Night MCSST Split

Satellite

a0

a1

a2

a3

NOAA-12

-263.94

0.967077

2.384376

0.480788

NOAA-14

-282.24

1.029088

2.275385

0.752567

NOAA-15

-271.3969724

0.993892

2.7523466369

0.662999

NOAA-16

-273.15

-2.53655

3.5316

0.753291

NOAA-17

-276.59

1.01015

-2.5815

1.000541

NOAA-18

-276.075

1.00841

2.23459

0.736946

NOAA-19

-277.71304

1.01432

1.91798

0.72064

MetOp-A FRAC

-277.447

1.01377

2.52362

1.03056

Night MCSST Dual

Satellite

a0

a1

a2

a3

NOAA-12

-279.846

1.031355

1.288548

2.265075

NOAA-14

-273.914

1.008751

1.409936

1.975581

NOAA-15

-283.5117285

1.041037

1.5875819344

1.67743

NOAA-16

-273.082

1.50825

1.00413

1.52452

NOAA-17

-276.603

1.01805

1.49789

1.96181

NOAA-18

-275.493

1.01463

1.42759

1.68783

NOAA-19

-276.61174

1.01873

1.47374

1.88560

MetOp-A FRAC

-273.235

1.00711

1.49927

1.88373

Night MCSST Triple

Satellite

a0

a1

a2

a3

a4

NOAA-12

-271.971

1.000281

0.911173

1.710028

 

NOAA-14

-275.364

1.010037

0.920822

1.760411

 

NOAA-15

-276.7558563

1.015354

1.0635723508

1.294955

 

NOAA-16

-271.763

0.733532

1.01684

0.344182

-0.753123

NOAA-17

-274.622

1.00903

0.913248

0.440015

 

NOAA-18

-274.398

1.00820

0.841674

0.377061

 

NOAA-19

-275.24563

1.01084

0.81643

0.43235

 

MetOp-A FRAC

-273.044

1.00424

0.894349

0.508159

 



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