PSB - NOAA-16 AVHRR PRT Coefficient Update

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NOAA-16 AVHRR PRT Coefficient Update

On July 31, 2001, the Information Processing Division plans to update the
NOAA-16 PRT Conversion Coefficients (IR Target Temperature Coefficients - as
identified in the NOAA-KLM Users Guide). Jerry Sullivan, Office of
Research and Analysis, provided a brief explanation of the problem and the
impact on the user that is inserted below for your information. Also, below
is a table showing all changes.

Test data is provided for CEMSCS users in datasets named P1S and P1B.*.NL,
where "*" is the instrument (LHRR, HRPT, GHRR, AMAX, AMBX, HIRX, ...). For
other users, subsets of the data will be provided daily on
psbsgi1.nesdis.noaa.gov anonymous ftp site (pub/test1b/NOAA16). After your
initial examination of the changes, please let us know if additional testing
time is required. We believe that this will be a no impact change for all
users except those level 1B structure file users (not 1B*). You will need
to change to a new file as indicated below. If you, are not on the CEMSCS
and need more data than provided on the anonymous ftp site, please contact
us.
Please accept our apologies for any problems this may have caused you.
Please contact us if you have questions, concerns, or need additional time
to test. Thank you.
Emily

THE PROBLEM:
To calibrate the thermal channels on any AVHRR, the temperature of the
internal blackbody must be known. The are four Platinum Resistance
Thermometers (PRTs) imbedded in the blackbody that measure its temperature.
NESDIS calculates the blackbody temperature as the average of these four PRT
temperatures. The PRTs actually send a count value back to the ground
station, so coefficients to convert each PRT count value to temperature are
supplied by ITT, the instrument manufacturer. For AHVRRs in the KLM series,
the coefficients are different for each PRT. These coefficients must be put
into the NESDIS operational computer code that calculates internal
blackbody temperature as the first step in computing calibration
coefficients. For the NOAA-16 AVHRR, the wrong coefficients were put into
the computer code; the NOAA-15 coefficients were put in by mistake.

THE IMPACT of the CHANGE on DATA USERS:
Brightness temperatures were calculated for the same 1,000,000 earth scene
pixels in the test dataset in two ways: using the correct NOAA-16 PRT
coefficients and using the wrong ones (current operational values). The
conclusions were:
Using GAC test data:
1. The difference between brightness temperatures (equivalent blackbody
temperatures) generated by using the correct NOAA-16 PRT coefficients and
the
incorrect NOAA-15 coefficients was nearly constant for all three channels,
3B, 4,
and 5,
2. the difference depends on the Earthscene temperature,
3. the difference was a bias, not a random difference; the temperatures
produced
from the correct coefficients are always lower.

The root-mean-square (RMS) differences between temperatures produced from
the
correct coefficients and temperatures produced from the incorrect
coefficients,
tabulated as a function of scene temperature are:

Scene temperature RMS temperature differences
215 K 0.04 K
240 K 0.05 K
275 K 0.06 K
295 K 0.07 K
320 K 0.09 K

CHANGES:
The changes to the NOAA-16 PRT Conversion Coefficients 4, 5 and 6 scaling
factors resulted in the creation of version 02 of the GAC and HRPT 1B
structure files (no change to the 1B* structure file). The new structure
files are located in:
DEV.PDP.CM.CONVERT.STRUCTUR(GA1BSF02)
DEV.PDP.CM.CONVERT.STRUCTUR(HRPT1B02)

The PRT conversion coefficients are listed in the Level 1B Header beginning
with byte 201 through byte 248 the list below shows the old values provided
in the KLM Users' Guide and the updated values.

OLD New
StartEnd Word ScalingScaling Number GENERAL
OctetOctet DT Size of INFORMATION Old Value New Value
Factor Factor Words
IR Target
Temperature
201 202 i 2 2 2 1 1 Conversion 276.601562 276.354980
Coefficient
1
IR Target
Temperature
203 204 i 2 5 5 1 1 Conversion 0.510450006E-01 0.556199998E-01
Coefficient
2
IR Target
Temperature
205 206 i 2 8 8 1 1 Conversion 0.136327981E-05-0.159000047E-04
Coefficient
3
IR Target
Temperature
207 208 i 2 8 11 1 1 Conversion 0.000000000E+00 0.248600003E-07
Coefficient
4
IR Target
Temperature
209 210 i 2 8 14 1 1 Conversion 0.000000000E+00 -0.119900001E-10
Coefficient
5
IR Target
Temperature
211 212 i 2 8 1 1 1 Conversion 0.000000000E+00 0.000000000E+00
Coefficient
6
IR Target
Temperature
213 214 i 2 2 2 1 2 Conversion 276.142090
Coefficient 276.625244
1
IR Target
Temperature
215 216 i 2 5 5 1 2 Conversion 0.509090014E-01 0.560499988E-01
Coefficient
2
IR Target
Temperature
217 218 i 2 8 8 1 2 Conversion 0.147266019E-05 -0.170699932E-04
Coefficient
3
IR Target
Temperature
219 220 i 2 8 11 1 2 Conversion 0.000000000E+00 0.259500013E-07
Coefficient
4
IR Target
Temperature
221 222 i 2 8 14 1 2 Conversion 0.000000000E+00 -0.122399998E-10
Coefficient
5
IR Target
Temperature
223 224 i 2 8 1 1 2 Conversion 0.000000000E+00 0.000000000E+00
Coefficient
6
IR Target
Temperature
225 226 i 2 2 2 1 3 Conversion 276.674072 275.996094
Coefficient
1
IR Target
Temperature
227 228 i 2 5 5 1 3 Conversion 0.509070009E-01 0.548599996E-01
Coefficient
2
IR Target
Temperature
229 230 i 2 8 8 1 3 Conversion 0.147656010E-05
Coefficient -0.122299998E-04
3
IR Target
Temperature
231 232 i 2 8 11 1 3 Conversion 0.000000000E+00 0.186199998E-07
Coefficient
4
IR Target
Temperature
233 234 i 2 8 14 1 3 Conversion 0.000000000E+00 -0.852999962E-11
Coefficient
5
IR Target
Temperature
235 236 i 2 8 1 1 3 Conversion 0.000000000E+00 0.000000000E+00
Coefficient
6
IR Target
Temperature
237 238 i 2 2 2 1 4 Conversion 276.592529 276.132080
Coefficient
1
IR Target
Temperature
239 240 i 2 5 5 1 4 Conversion 0.509659983E-01 0.549400002E-01
Coefficient
2
IR Target
Temperature
241 242 i 2 8 8 1 4 Conversion 0.147656010E-05 -0.134399997E-04
Coefficient
3
IR Target
Temperature
243 244 i 2 8 11 1 4 Conversion 0.000000000E+00 0.211200017E-07
Coefficient
4
IR Target
Temperature
245 246 i 2 8 14 1 4 Conversion 0.000000000E+00 -0.100099998E-10
Coefficient
5
IR Target
Temperature
247 248 i 2 8 1 1 4 Conversion 0.000000000E+00 0.000000000E+00
Coefficient
6
249 256 i 4 0 0 2 0.000000000E+00 0.000000000E+00

--
*******************************************
* Arlington Morgan/Brenda Hardie phone 301-457-5262
* Emily D. Harrod
* voice 301-457-5247
* fax 301-457-5199
*******************************************

Scene temperature RMS temperature differences
215 K 0.04 K
240 K 0.05 K
275 K 0.06 K
295 K 0.07 K
320 K 0.09 K

The PRT conversion coefficients are listed in the Level 1B Header beginning
with byte 201 through byte 248 the list below shows the old values provided
in the KLM Users' Guide and the updated values.

ppp@nesdis.noaa.gov