NDVI anomaly using atmospheric correction

Hello ,

We are computing NDVI anomaly using the script here : https://raw.githubusercontent.com/sentinel-hub/custom-scripts/master/sentinel-2/ndvi_anomaly_detection/ndvi_anomaly_detection_script.js

We tried to use Sentinel 2 L2A but this do not have enough historical data to compute a proper NDVI anomaly.

So we used atmospheric correction (ATMCOR) over Sentinel 2 L1C.

But this give completely different result from without atmospheric correction.

Here is an example without :

And with correction :

Here is the link for the last image :
http://services.sentinel-hub.com/ogc/wms/?SERVICE=WMS&REQUEST=GetMap&SHOWLOGO=false&VERSION=1.3.0&CRS=EPSG:4326&temporal=true&atmFilter=ATMCOR&LAYERS=TRUE_COLOR&MAXCC=100&WIDTH=512&HEIGHT=512&FORMAT=image/jpeg&BBOX=10.083731584377,78.420571584377,10.134968415623,78.471808415623&TIME=2013-01-01%2F2019-08-31&EVALSCRIPTURL=https%3A%2F%2Fraw.githubusercontent.com%2Fsentinel-hub%2Fcustom-scripts%2Fmaster%2Fsentinel-2%2Fndvi_anomaly_detection%2Fndvi_anomaly_detection_script.js

Do we use atmospheric correction correctly ?

Thank you,

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As described here, the ATMCOR is not a “full scale” atmospheric correction but rather a statistical approach, which works OK in some cases and not that OK in other cases. We would not recommend it to be used for such analysis.