| Re: ENVI: AVHRR Calibration for Old NOAA Platforms [message #22596 is a reply to message #22592] |
Wed, 22 November 2000 00:00  |
Paul van Delst
Messages: 364
Registered: March 1997
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Senior Member |
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wcapehar@my-deja.com wrote:
>
> Has anyone figured out a way to get ENVI (3.4 or previous releases) to
> calibrate the older NOAA plaform's AVHRR data? I am assuming that the
> thermal data ramp calibrations (DN -> Radiance) is taken from the scene
> but the wave-number insertion to get it into Tempreratures requires the
> Plaform-specific values.
I would argue that the former quantity also must be (satellite/instrument) platform
specific also. Each instrument channel's spectral response functions are slightly
different thus the radiometric calibration and polychromaticity correction coefficients
are instrument/channel specific. My experience is with NOAA HIRS and GOES IR instruments
but if you're talking about thermal AVHRR channels, then what I said applies (I have no
idea how to calibrate visible channel data).
The calibration and polychromaticity correction coefficients as well as the channel
central frequencies for just about every satellite that's flown are available from
NOAA....somewhere....I know there is a NOAA website with all this info somewhere. I have
the latter numbers from NOAA-5 (TIROS-N!) to NOAA-15 (minus NOAA-13 which futzed out in
orbit I believe) but it's not officially sanctioned data.
e.g.: Note the difference between NOAA-5, NOAA-14, and NOAA-15 AVHRR. These differences
are significant when it comes to calculating temperatures from measured radiances:
AVHRR PLANCK-FUNCTION CONSTANTS FOR TIROS-N ("NOAA-05")
CHANNEL CENT-WN FK1 FK2 BC1 BC2
3 2651.105 .22193E+06 .38144E+04 1.81578 .99757
4 920.615 .92933E+04 .13246E+04 .46051 .99841
5 920.615 .92933E+04 .13246E+04 .46051 .99841
AVHRR PLANCK-FUNCTION CONSTANTS FOR NOAA-14
CHANNEL CENT-WN FK1 FK2 BC1 BC2
3 2659.515 .22405E+06 .38265E+04 1.98132 .99734
4 929.383 .95613E+04 .13372E+04 .43272 .99852
5 834.606 .69244E+04 .12008E+04 .24104 .99909
AVHRR PLANCK-FUNCTION CONSTANTS FOR NOAA-15
CHANNEL CENT-WN FK1 FK2 BC1 BC2
3 2694.853 .23310E+06 .38773E+04 1.58348 .99781
4 925.715 .94486E+04 .13319E+04 .36698 .99874
5 839.502 .70469E+04 .12079E+04 .21465 .99919
As for the calibration coefficients, depending on the calibration scheme, some are
calculated pre-launch and others calculated in-flight. In some cases time-averaged
coefficients are used. I, personally, would not rely on a commercial package to calibrate
correctly since calibration schemes have improved over time and are still being worked on
to get the most out of satellite data. The NOAA NESDIS research and operational folks that
do this stuff day-in/day-out are a bunch of smart cookies.
Have a lookee at:
http://www2.ncdc.noaa.gov/docs/klm/html/d/app-d.htm
for some of the later NOAA satellite numbers. Maybe it will lead you to the older
instruments' data.
Anyway, sorry for the brain-dump, but satellite radiance calibration is a subtle business.
cheers,
paulv
--
Paul van Delst Ph: (301) 763-8000 x7274
CIMSS @ NOAA/NCEP Fax: (301) 763-8545
Rm.207, 5200 Auth Rd. Email: pvandelst@ncep.noaa.gov
Camp Springs MD 20746
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