By adapting code from Getting Image with highest max Scene NDVI from Image collection using Google Earth Engine I have been able to make a script that gives me the date and mean highest NDVI for each polygon in my collection in a CSV: https://code.earthengine.google.com/72168c350ff039fb7abe24e9fcfe55a8?noload=true
Now, I want to do the same thing again, but to show the mean highest NDWI with dates. I would have thought this would be as simple as changing the Band 4 (Red) to Band 11 (SWIR) in my NDVI function:
function toNdvi(image) {
var newImg = image
.normalizedDifference(['B8', 'B11'])
.rename('ndvi')
.updateMask(
image.select('QA60').not()
)
return newImg.updateMask(
newImg.select('ndvi').gte(0.1)
)
}
However, upon making the one change, the exported CSV no longer provides a column with mean NDWI. This remains the case even when I remove the lower threshold (0.1). Why has highest mean been removed from my output and how can I restore it?
Best Answer
First of all, I searching for NDWI formula by using Sentinel-2 products and bands are B3, B8; not B8, B11. However, I used your provided formula for following modifications in your code (as your asset geometry was not accessible by me, I used an arbitrary polygon in USA).
Running complete code, the exported CSV provides a column with mean NDWI as expected; corroborated in following image for opened CSV (I deleted some columns for better visualization).