| ndvi color table [message #21678] |
Wed, 13 September 2000 19:44  |
Sylvain Carette
Messages: 19
Registered: May 2000
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Junior Member |
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<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
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Anybody know where I can find a good ndvi color table that could be applyed
on global avhrr 10 days composites?
<br> Here the link to edcdaac: <a href="http://edcdaac.usgs.gov/1KM/1kmhomepage.html">1km
homepage</a>
<br>Band 6 on this dataset is the ndvi channel - (ch1-ch2)/(ch1+ch2) -
8 bit pixel
<br>and here from the doc:
<blockquote TYPE=CITE>
<pre>3.4 Computation of NDVI
The NDVI is the difference of near-infrared (NIR, channel 2) and visible (VIS, channel 1) reflectance values normalized over the sum of channels
1 and 2 ((NIR-VIS)/(NIR+VIS)). The NDVI equation produces values in the range of -1.0 to 1.0, where increasing positive values indicate
increasing green vegetation and negative values indicate nonvegetated surface features such as water, barren, ice, and snow or clouds. To obtain
the most precision, the NDVI is derived from calibrated channels 1 and 2 data in 16-bit precision, prior to geometric registration and resampling.
It is recommended to scale the computed NDVI results to 8- bit range to minimize the volume and optimize analysis and display. This is
acceptable because there is very little quantitative understanding of the relationship between excessive mathematical precision in the NDVI and
physical measurements of the vegetation condition. If greater precision is required, the NDVI can be computed from the calibrated channel 1 and
2 values that are stored with 10-bit precision.
The scaling method is chosen to emphasize different types of vegetation or vegetation condition. The EDC routinely uses a formula that scales the
NDVI from -1.0 to 1.0 as 0 to 200, where each value represents 1.0 percent of the total possible range.</pre>
</blockquote>
<p>Any cues welcome, thanks
<p>Sylvain Carette
<br>VRML designer-composer</html>
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