| 07 Feb 2014 01:40 PM |
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Hi everybody,
I'm a student, just entering the world of remote sensing. Don't even know if anyone can help me about this issue, but I m dialing with envi trying to calculate the Leaf Area Index, can someone give me some tips about how to do it with the software (or maybe some reading to do)? I already know the algorithm I want to use, exploiting the Reduced simple ratio, but I don't know how to use it. Please.Help me.
Thanks a lot.
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Deleted User
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| 07 Feb 2014 04:46 PM |
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If you already know the formula, then dump it straight into ENVI's "Band Math" utility.
A quick search on the RSR equation brought up this paper "www.asprs.org/a/publications/proceedings/portland08/0073.pdf" with
the equation (TM4/TM3) * ((max(TM5) - TM5) / (max(TM5) - min(TM5))
Don't put that straight into band math as ENVI will then be calculating the max and min of every tile block that is read during processing. Rather you want to calculate it over the entire image. Calculate the statistics on the image first, and substitute the max and min into the equation. If your image isn't floating point, either convert it up front or "on the fly" withing band math, i.e. float(b1) * float(b2) etc
Hopefully that can get you started.
Cheers
Josh
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Deleted User
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Posts:59
| 10 Feb 2014 12:42 PM |
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Hi,
ENVI has a "Vegetation Index Calculator" available through the toolbox (version 5 and later) or through the ENVI Classic menu bar (all versions). However, LAI is not an available option. ENVI will have a new Spectral Indices tool in the next service pack of version 5.1, and it will include LAI. For now, Band Math is the best choice as Josh mentioned in the last post.
-Jason
Exelis VIS
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Deleted User
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| 11 Feb 2014 03:20 PM |
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thanks to both of you for the advices!!!
I've tried to do it.. even if I've obtained too high values of LAI. I'll insist.. maybe I made some mistakes.
But I have another doubt, I'm working with coarse/moderate resolution images, specifically SPOT Vegetation datas (1 km spatial resolution), which are already pre-processed.. so if we don't consider additional operations to improve the quality of the image, I can directly use my expression to calculate LAI as it has been said, right??
THANK YOU for your help!
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Deleted User
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| 13 Feb 2014 05:10 AM |
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Factors such as atmosphere and terrain can impact upon you analysis. I'm assuming your SPOT data has been radiometrically corrected (and not simply colour enhanced for a map back drop), in which case you might then want to go one step further and convert to reflectance. If you want to account for atmospheric effects then ENVI's flaash module will help with that.
On the otherhand you can simply drop the formula in and get a result.
There'll be noise regardless of what the data units are :)
Cheers
Josh
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