b. If satellite zenith angle ∃26
0 but <50
0 , check the four corners and the center
c.
If satellite zenith angle ∃50
0 , check the four corners, center , and the two points equidistant from
the center and the outside edge on the long axis of the target.
If all coordinates checked are sea, process the target. If all are land, do not process. If some coordinates are
coastal interface with high resolution tags available, process. If any are coastal interface with no high
resolution tags available, do not process. (High resolution tags are available globally now).
If no AVHRR data are available, check the HIRS center latitude/longitude against the low resolution land/sea
tag for the nearest ½
0 latitude/longitude intersection. Unless the tag is sea, reject the target.
3.
Select Algorithms
Data input is used to select from 1 to 12 different algorithms to be used on each target. These are:
(1) AVHRR-only day operational
(7) AVHRR-only day test
(2) AVHRR-only night operational
(8) AVHRR-only night test
(3) HIRS-only day operational
(9) HIRS-only day test
(4) HIRS-only night operational
(10) HIRS-only night test
(5) AVHRR & HIRS day operational
(11) AVHRR & HIRS day test
(6) AVHRR & HIRS night operational
(12) AVHRR & HIRS night test
Note: Only algorithms 1, 2, 7 and 8 have been used in the last 15 years.
4. Determine whether it is Day or Night
First the solar zenith angle is checked. If it is less than 75
0 , then it is daytime. If it is greater than 75
0 , then
check the center spot of one of the GAC Visible Channels (or the HIRS visible channel value if GAC is not
available). If the visible channel value (currently channel 2) is greater than or equal to a reflectance threshold
(currently 1%), then do not process. If it is less than the threshold, it is nighttime.
5. Call Retrieval Algorithm
Each selected algorithm will be used if it matches the actual time of the day (i.e., day or night) and if the
Target Rejection Decision Table indicates that this algorithm is to be used for the geographical location of the
target. The algorithm is then called to make one or more SST observations. Then the next algorithm is
selected, and so on until the input list of desired algorithms is exhausted.
AVHRR-Only Nighttime Algorithm Summary
Note: All threshold values reflect current NOAA-14 settings as of 2/22/99.
1.
Nighttime Gross Cloud Test T4 > 268.16 for 30 or more target elements
2.
Unit Array Selection
Find warmest channel 4 elements in the target and construct four 2x2 unit arrays containing the warmest
elements.
3.
IR Uniformity Test
Test each of the four unit arrays until one passes both of the following tests:
Cmax 4 - Cmin 4 # 2
where cmax 1 & cmin 1 are the maximum and minimum counts for channel 1
4.
Average Unit Array Counts
Find the average count for each of five channels for the unit array that passes the IR uniformity Test.
5.
Calibrate the unit array averages.
6.
Channel 4 Test T 4 ∃ 270
0
7. (Not currently used)
3.7-11 IR Cloud Test T3 = -25.0089766 + 1.0916 (T4)
|T3 -T3 | # 3
0 C
8.
Channel 4-Channel 5 Test T 4 - T 5 # 4.0
0
9. (Not currently used)
4-5 IR Cloud Test
T4 = -11.488987 + 1.0439 (T5)
|Td -T3 | # 1
0 C
10. Currently using T 5 -T 3 option in the following (not using T 4 -T 3 )
Nighttime Low Stratus Test or T 5 - T 3 Low Stratus Test (currently this is used)
|T4 -T3 | # 0.7
0 C
T5 -T3 # 0.0
0 C
11. Calculate SST with 3 Equations (SST in
0 C)
Split, Dual, & Triple Window Equations
Currently the equations used for NOAA-14 are the NLSST split-window, the MCSST dual-window, and
the NLSST triple-window equations.
12. Unreasonable SST Test
-2
0 C # T sst # 35
0 C where T sst is currently (2/22/99) the NLSST triple
window equation.
13. SST Intercomparison Test [ Max (Tsst1, Tsst2, Tsst3) - MIN (Tsst1, Tsst2, Tsst3)] # 2.0
0 C
The equations used to compute the three SSTs are those noted in 11.
Where
MAX (A, B, C) is the maximum of A, B, C
MIN (A, B, C) is the minimum of A, B, C
14. Compute Earth Location of Center of Unit Array
15. Climatology Test
|T sst - CLIMO| < 10
0 C
24
Skirving, Strong, Liu, Arzayus, Liu and Sapper
0 but <50
0 , check the four corners and the center
c.
If satellite zenith angle ∃50
0 , check the four corners, center , and the two points equidistant from
the center and the outside edge on the long axis of the target.
If all coordinates checked are sea, process the target. If all are land, do not process. If some coordinates are
coastal interface with high resolution tags available, process. If any are coastal interface with no high
resolution tags available, do not process. (High resolution tags are available globally now).
If no AVHRR data are available, check the HIRS center latitude/longitude against the low resolution land/sea
tag for the nearest ½
0 latitude/longitude intersection. Unless the tag is sea, reject the target.
3.
Select Algorithms
Data input is used to select from 1 to 12 different algorithms to be used on each target. These are:
(1) AVHRR-only day operational
(7) AVHRR-only day test
(2) AVHRR-only night operational
(8) AVHRR-only night test
(3) HIRS-only day operational
(9) HIRS-only day test
(4) HIRS-only night operational
(10) HIRS-only night test
(5) AVHRR & HIRS day operational
(11) AVHRR & HIRS day test
(6) AVHRR & HIRS night operational
(12) AVHRR & HIRS night test
Note: Only algorithms 1, 2, 7 and 8 have been used in the last 15 years.
4. Determine whether it is Day or Night
First the solar zenith angle is checked. If it is less than 75
0 , then it is daytime. If it is greater than 75
0 , then
check the center spot of one of the GAC Visible Channels (or the HIRS visible channel value if GAC is not
available). If the visible channel value (currently channel 2) is greater than or equal to a reflectance threshold
(currently 1%), then do not process. If it is less than the threshold, it is nighttime.
5. Call Retrieval Algorithm
Each selected algorithm will be used if it matches the actual time of the day (i.e., day or night) and if the
Target Rejection Decision Table indicates that this algorithm is to be used for the geographical location of the
target. The algorithm is then called to make one or more SST observations. Then the next algorithm is
selected, and so on until the input list of desired algorithms is exhausted.
AVHRR-Only Nighttime Algorithm Summary
Note: All threshold values reflect current NOAA-14 settings as of 2/22/99.
1.
Nighttime Gross Cloud Test T4 > 268.16 for 30 or more target elements
2.
Unit Array Selection
Find warmest channel 4 elements in the target and construct four 2x2 unit arrays containing the warmest
elements.
3.
IR Uniformity Test
Test each of the four unit arrays until one passes both of the following tests:
Cmax 4 - Cmin 4 # 2
where cmax 1 & cmin 1 are the maximum and minimum counts for channel 1
4.
Average Unit Array Counts
Find the average count for each of five channels for the unit array that passes the IR uniformity Test.
5.
Calibrate the unit array averages.
6.
Channel 4 Test T 4 ∃ 270
0
7. (Not currently used)
3.7-11 IR Cloud Test T3 = -25.0089766 + 1.0916 (T4)
|T3 -T3 | # 3
0 C
8.
Channel 4-Channel 5 Test T 4 - T 5 # 4.0
0
9. (Not currently used)
4-5 IR Cloud Test
T4 = -11.488987 + 1.0439 (T5)
|Td -T3 | # 1
0 C
10. Currently using T 5 -T 3 option in the following (not using T 4 -T 3 )
Nighttime Low Stratus Test or T 5 - T 3 Low Stratus Test (currently this is used)
|T4 -T3 | # 0.7
0 C
T5 -T3 # 0.0
0 C
11. Calculate SST with 3 Equations (SST in
0 C)
Split, Dual, & Triple Window Equations
Currently the equations used for NOAA-14 are the NLSST split-window, the MCSST dual-window, and
the NLSST triple-window equations.
12. Unreasonable SST Test
-2
0 C # T sst # 35
0 C where T sst is currently (2/22/99) the NLSST triple
window equation.
13. SST Intercomparison Test [ Max (Tsst1, Tsst2, Tsst3) - MIN (Tsst1, Tsst2, Tsst3)] # 2.0
0 C
The equations used to compute the three SSTs are those noted in 11.
Where
MAX (A, B, C) is the maximum of A, B, C
MIN (A, B, C) is the minimum of A, B, C
14. Compute Earth Location of Center of Unit Array
15. Climatology Test
|T sst - CLIMO| < 10
0 C
24
Skirving, Strong, Liu, Arzayus, Liu and Sapper