| Re: Routine for Converting DN to Radiance to Temperature [message #54989] |
Fri, 27 July 2007 15:08 |
James Kuyper
Messages: 425
Registered: March 2000
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Senior Member |
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Paul van Delst wrote:
> Conor wrote:
>> On Jul 26, 5:12 pm, Marsh...@gmu.edu wrote:
>>> Hi dears:
>>> Can someone help me how to write routine for converting Digital Number
>>> to Radiance to Temperature for MASTER bands (HDF format) in IDL?
...
> But, given that the MASTER instrument has been used pretty extensively,
>
> http://master.jpl.nasa.gov/
Following that link, I learned that MASTER data is stored in the same
format as MAS data, and the format is documented at <http://
mas.arc.nasa.gov/reference/hdfread.txt>. The CalibratedData SDS has an
SDS attribute named "scale_factor" which is a 50 element array, and
another one named "units" with a value of "watts/meter2/steradian/
micron". The middle dimension of the CalibratedData array is also 50,
which appears to be the number of bands of data. Therefore, I'd hazard
a guess that, in order to obtain a value with those units for a given
band, you just calculate:
radiance = CalibratedData[*,band,*]*scale_factor[band]
The file specification has many references to temperatures, but they
look like instrument temperatures, whereas I suspect you're interested
in the brightness temperature. However, if you know what the
brightness temperature is, you should know how to calculate it from
the radiance.
If you need help reading HDF data, look in the IDL online help for
HDF_SD_Start()/HDF_SD_Close, HDF_SD_NameToIndex(), HDF_SD_Select()/
HDF_SD_EndAccess, HDF_SD_GetData, HDF_SD_AttrFind(), and
HDF_SD_AttrInfo().
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| Re: Routine for Converting DN to Radiance to Temperature [message #54995 is a reply to message #54989] |
Fri, 27 July 2007 09:52  |
Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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Conor wrote:
> On Jul 26, 5:12 pm, Marsh...@gmu.edu wrote:
>> Hi dears:
>> Can someone help me how to write routine for converting Digital Number
>> to Radiance to Temperature for MASTER bands (HDF format) in IDL?
>>
>> Best Regards,
>
> I think you'll have to be much more specific if you want some help.
> In particular, we don't all have the same science background as you.
> Since not everyone here knows how to convert DNs to radiance to
> temperture in general, we certainly can't help you do it in IDL.
> Provide a little background and someone might be able to help though...
Hello,
Working from scratch, the user will have to be *much* more specific. The questions that
immediately occurred to me were not all language related. Does the OP have the necessary
calibration data for the instrument for the time that they want to calibrate the
earth-viewing data? If they do, do they have the documentation stating how to use that
data to convert the digital counts into physical radiances? Do you also have the channel
frequencies and polychromatic correction coefficients to do the conversion from radiances
to temperatures? If not, do you have the channel spectral response functions so you can
derive them? Once all those sorts of ducks are lined up, the language one chooses to use
to write the calibration+conversion routines in is mostly for convenience.
But, given that the MASTER instrument has been used pretty extensively,
http://master.jpl.nasa.gov/
I'd be quite amazed if the data released to the public, or even researchers, wasn't
already calibrated. Instrument scientists are usually *extremely* picky about their
instrument's calibration.
At any rate, a better place to ask the original question is via the MASTER page above (and
they even have links to ENVI and IDL software to read the hdf datafiles!).
cheers,
paulv
--
Paul van Delst Ride lots.
CIMSS @ NOAA/NCEP/EMC Eddy Merckx
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| Re: Routine for Converting DN to Radiance to Temperature [message #55002 is a reply to message #54995] |
Fri, 27 July 2007 05:30 |
Conor
Messages: 138
Registered: February 2007
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Senior Member |
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On Jul 26, 5:12 pm, Marsh...@gmu.edu wrote:
> Hi dears:
> Can someone help me how to write routine for converting Digital Number
> to Radiance to Temperature for MASTER bands (HDF format) in IDL?
>
> Best Regards,
I think you'll have to be much more specific if you want some help.
In particular, we don't all have the same science background as you.
Since not everyone here knows how to convert DNs to radiance to
temperture in general, we certainly can't help you do it in IDL.
Provide a little background and someone might be able to help though...
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