| 10 Mar 2010 11:13 AM |
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Hello,
I want to use TIFF files with ENVI. They have a correction level called "L1T Standard Terrain Correction", and are provided by the USGS. It is said in the guidelines of the USGS place, that this correction level provides systematic and radiometric accuracy by incorporating ground control points.
I need to classify the images and my question is, I need to correct them radiometric and geometrically before starting or all of this corrections are already applied when you open the images with ENVI, and you don't need to do anything to them?.
Thanks for your help.
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MariM
Veteran Member
Posts:2396  
| 11 Mar 2010 08:23 AM |
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Landsat L1T means they have already been terrain corrected (orthorectified) so you do not need to do a geometric correction. Landsat is delivered in byte scaled radiance, so it is common to do a calibration on the data to either radiance or top of the atmosphere reflectance. You can use ENVI's Landsat Calibration tool to do this. It is located under Basic Tools ->Preprocessing ->Calibration Utilities.
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Deleted User
New Member
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| 11 Mar 2010 11:33 AM |
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Thanks!!
I'm using Landsat TM images.
So, I think that I need the sun elevation, the date when it was taken, and other things.
You said that I have to choose "radiance", not "reflectance" in the TM Calibration Parameters but...what about Scale min. and max. I couldn't find those numbers in the metadata file, what I have to put?
Thanks!
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MariM
Veteran Member
Posts:2396
| 11 Mar 2010 11:37 AM |
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What version of ENVI are you using? ENVI 4.7 now allows you to select the metadat file (_mtl.txt) to open the TIFF files together into one file and then calibrate by pulling out the necessary paramters from this file. If you are using ENVI 4.6, you should contact the Technical Support group to get the patch that will give you this functionality in 4.6.
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Deleted User
New Member
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| 12 Mar 2010 02:36 AM |
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I'm using ENVI 4.3
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Deleted User
New Member
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| 15 Mar 2010 03:44 AM |
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I found in the metadata file a section called: "Min/max radiance" with a minimum and maximum value for each one of the seven bands that I have.
On the other hand I saw another section in the metadata file called: " Min/max pixel value" where the minimum and the maximum values are the same for all the seven bands (1 -255).
Which numbers do you think that I have to use for the Scale Min/Max section if I have to use one of those? I remember you that I'm working with ENVI 4.3.
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MariM
Veteran Member
Posts:2396
| 15 Mar 2010 08:44 AM |
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You use the LMIN/LMAX for your particular band in the dialog. The min/max value is taken care of internally in the code.
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Deleted User
New Member
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| 15 Mar 2010 09:32 AM |
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Ok!! thanks for the info!!
WIth those number it doesn't matter if I choose the radiance or reflectance option?
That's all,
thank you so much!
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MariM
Veteran Member
Posts:2396
| 15 Mar 2010 09:44 AM |
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No, it does not matter if you choose radiance or reflectance. Those values are used to convert the data to radiance which is always calculated prior to reflectance.
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Deleted User
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| 15 Mar 2010 09:55 AM |
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Thanks!!
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