| 11 Dec 2012 11:12 AM |
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Hi,
I have got 10 of rapideye images lvl 1B.
I want to calculate NDVI and to compare NDVI.
Please help me, this is correct?
Step 1-Convert DN to Radiance
Formula :Each band*0.01
Result for example:
pixel value DN – 4485
pixel value rad -47.969997
Step 2-Convert to reflectance, compute TOA,
for example date 18/05/2011, blue band
(3.14159* b1 * 1.01629*1.01629) /(1997.8 * 0.5425)
Result for example:
pixel value DN = 4924
pixel value rad =51.759998
pixel value refl =0.154963
if i click on road on image 18/05/2011 px value reflectance 0.238456
on image 07/07/2012 px value on road 0.328456
its this is normal??? values ??should be equal , or not??
this is spectral profile health vegetation, all correct?
https://docs.google.com/open?id=0ByTBdQJSbYwwdGh1Y3AtVGVYd3M
Step 3Layer Stack
I get a very large file (24 gb)… can I convert floating data to integer?? Its correct?? How a can do it in ENVI??
Step 4
Ortorectification with ground control point
Step 5
compute NDVI
*********
all correct???thx.....
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MariM
Veteran Member
Posts:2396  
| 12 Dec 2012 10:03 AM |
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Your workflow looks reasonable. Radiance is not the same as reflectance so you should not expect the values to be the same. The only step that you may need to check is the orthorectification. Does your RapidEye come with one RPC file (which is used for orthorectification) for all bands or an RPC file for each band? If there is an RPC file for each band, you would need to orthorectify each band separately, then Layer Stack the bands into one file.
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Deleted User
New Member
Posts: 
| 12 Dec 2012 08:36 PM |
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Hi MariM
thanks for the ansver...orthorectification is not problem for ENVI ))
Can i orthorectification how first step??? its correct?? then radiometric correction..??
Could you help me, please with:
1-After convert to reflectance if i clicking on road on image 18/05/2011 px value in reflectance 0.238456
on image 07/07/2012 px value reflectance on road 0.328456
its this is normal??? values ??should be equal , or not?? I thought after reflectance values ??should be approximately equal??
2-this is spectral profile health vegetation, all correct?
https://docs.google.com/open?id=0ByTBdQJSbYwwdGh1Y3AtVGVYd3M
3-after layer stacking I get a very large file (24 gb)… can I convert floating data to integer?? Its correct?? How a can do it in ENVI??
sorry, my english is terrible...
thx..
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MariM
Veteran Member
Posts:2396
| 13 Dec 2012 07:50 AM |
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1- you are performing top-of-the-atmosphere correction to reflectance. This does not take into account the atmosphere which is likely different on those dates. But in any case, even if you do an atmospheric correction, I would not expect the values to be exactly the same. They should be similar for something like a road.
2. Your spectral profile looks normal as far as I can tell. It does not look unusual for vegetation. However, you should have wavelength values on the x-axis. Did you open the file as File ->Open External File ->RapidEye? This will assign wavelengths to the bands and provide a more accurate plot.
3. You can convert your floating point data to integer if you like. It is very common. You can use Basic Tools ->Stretch data to specify exactly the range you want.
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Deleted User
New Member
Posts:
| 13 Dec 2012 08:28 PM |
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Thx a lot MariM
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