Difference between types of Vegetation indices

I am currently comparing different types of Vegetation Indices, in this example I am using a NDVI formula and a TCARI formula. The NDVI result came out as expected with values ranging from +1 to -1. However the TCARI result came out with a different range. Kindly refer to the image below, illustrating the results of the TCARI Index before and after a bergwind hit a citrus farm. These images were obtained through use of an UAV and Micasense Rededge multispectral camera.

My question is, how do you interpret the values presented by TCARI? and how do you compare those values to that of NDVI?

I know the common range for green vegetation of NDVI is between 0.2 and 0.8, higher being more favourable. But how do I interpret TCARI without knowing the common range of values indicative of healthy vegetation?

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• are you working based on top of canopy reflectances ? what do you mean by "strange values" ? – radouxju Aug 23 '17 at 13:42
• I suggest you to snapshot for both of it, so we can know what you were talking about – PROBERT Aug 23 '17 at 16:42
• I update my answer. Check it – aldo_tapia Aug 28 '17 at 11:15

Not all indices are from -1 to 1.

For example, REP (red-edge position) index could start near to 600 and end near to 800 nm. In the other hand, for any Normalized Difference Index, you can expect to be within a range from -1 or 1.

In the case of TCARI, the description is:

This index is one of several CARI indices that indicates the relative abundance of chlorophyll. It is affected by the underlying soil reflecance, particularly in vegetation with a low LAI.

Hence, you can expect values in a range from 0 to ~0.5.

Finally, some indices require a regression analysis (as you said), an example is CCCI index. For this index, you need to determine the NDREmax slope and NDREmin slope:

TCARI calculation

By definition, all values under 0 need to be stretched to 0 (you can have negative chlorophyll content).

Be careful, if you don't use reflectance values, the output will be in a different range, for example:

Using 0-1 reflectance values:

Using 0-10000 reflectance values pre-factor conversion:

Using 0-255 DN 8-bit values: