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ARVI formula says NIR, so shouldn't use B08? #104

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smaprs opened this issue Jan 21, 2020 · 3 comments
Closed

ARVI formula says NIR, so shouldn't use B08? #104

smaprs opened this issue Jan 21, 2020 · 3 comments

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@smaprs
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smaprs commented Jan 21, 2020

Hi, nice work, just one question, about ARVI:
The present script for ARVI used at
https://github.com/sentinel-hub/custom-scripts/blob/master/sentinel-2/arvi/script.js
states:
let index = (B09 - B04 - y * (B04 - B02)) / (B09 + B04 - y * (B04 - B02));

But, since:

  1. As said in https://www.indexdatabase.de/db/si-single.php?sensor_id=96&rsindex_id=4 :

General Formula: NIR−RED−y(RED−BLUE) / NIR+RED−y(RED−BLUE)
Specific Formula: 9−5−y(5−1) / 9+5−y(5−1)

  1. true NIR is B08, and true RED is B04 (https://en.wikipedia.org/wiki/Sentinel-2#Instruments);
  2. it was already changed in the script "5" for "B04" (so it could be expected to change "9" for "B08");
    So, isn't a mistake in both the "Specific Formula" and the "arvi/script.js"?
    Shouldn't it be used just B08|B04|B02 , like :
    let index = (B08 - B04 - y * (B04 - B02)) / (B08 + B04 - y * (B04 - B02));

?
Thanks in advance

@mslapek
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mslapek commented Jan 24, 2020

Seems to be related to #96 - it also mentions ARVI.

@gmilcinski
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Indeed there is a mistake for this index. Before manually changing this one, we would like to check the issue a bit more systematically so we will need a bit more time.
Thanks for raising this and for your patience.

@jonasViehweger
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This was apparently fixed in #97

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