[GIS] Calculating 2-bands EVI from Sentinel-2

arcgis-desktoparcmapeviremote sensingsentinel-2

I have been trying to calculate Enhanced Vegetation Index (EVI) using Sentinel-2 Level 1C imagery. I have atmospherically corrected the imagery (so the imagery is in BOA) but I can't seem to derive EVI in ArcGIS.

I have been calculating EVI using Raster Calculator using the following formula (2-band EVI):

(2.5 * ("Band 8" – "Band 4")) / ("Band 8" + (2.4 * "Band 4") + 1)

The range of the values are between 2.4 and -1.8 and the theoretical range is between 1 and -1.

Is there anyway that I can correct this?

Best Answer

Sentinel 2 L1C reflectances are multiplied by 10000. Therefore you should adapt your equation in order to take the into account (or you can divide all values by 10000, but I wouldn't do this). On the other hand, it is worth noting that, while most values will ly between -1 and 1, EVI could mathematically be out of this range.

(2.5 * float("Band 8" - "Band 4")) / ("Band 8" + (2.4 * "Band 4") + 10000)

As a remark, I don't see the reason to use "2 bands" EVI when you have a multispectral sensor with NIR, red and blue bands available at the highest spatial resolution (in this case of S2, 10 m). According to Huete et al 1997, the original EVI is 2.5 * ((NIR − R)/(1 + NIR + 6R − 7.5B)). The B(lue) band correspond to band 2 of Sentinel-2 MSI, NIR to Band 8 and R(ed) to band 4. As far as I know, no empirical study tried to adjust these parameters for the specific spectral response of the Sentinel-2 MSI bands, but they re "useable" like this.

Related Solutions

[GIS] Calculating EVI from Sentinel 2 imagery gives difference in results between ArcMap & QGIS

Please stick to one question per post in the future. It makes answering significantly easier.

Question 1 - How to calculate EVI:
The formula that you are using is "correct", in the sense that you are using the constants calculated for MODIS.

Question 2 - Why does QGis and ArcGIS provide different results:
Minuscule differences in results most likely originate from different resampling methods used when combining the spectral bands. It is a difficult discover the reason for the differences, without having the data available.

Question 3 - How to remove extreme values from a raster calculation:
Removing those values is best done by adjusting your raster calculation. One approach would be to simply add a parenthesis around the entire equation and multiply it by a pair of 'greater than' and 'less than' calculations.
Example:

(EVI) * (EVI > -1) * (EVI < 1) + (EVI > 1)*1 + (EVI < -1)*(-1)

The above outlined calculation would set all the values below -1 and above 1 to -1 and 1, respectively.

Question 4 - When to apply the scale factors:
The scale factors should be applied when you are using the bands. If you applied them afterwards, to the EVI, then the effect of the constants in the equation would be changed, and your calculations would become incorrect. As such, you use is currently the right one.

[GIS] Calculating EVI in Sentinel 2-2A

Because you map maskS2clouds onto your image collection after addEVI, you end up dividing your EVI band by 10000. Decide whether you want to re-scale your images earlier in your script or on a case-by-case basis (e.g. when calculating EVI).

Best Answer

Related Solutions

[GIS] Calculating EVI from Sentinel 2 imagery gives difference in results between ArcMap & QGIS

[GIS] Calculating EVI in Sentinel 2-2A

Related Question