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I’m trying to generate NWI images from the Planet 4 band imagery in QGIS. Should I use

NDWI = (Band 2 - Band 4) / (Band 2 + Band 4)

or as a QGIS tutorial (Viewing a Flood Event with the Planet Explorer QGIS Plugin) suggests

NDWI = ((Band 2 * Band 2 coefficent) - (Band 4 * Band 4 coefficient)) / ((Band 2 * Band 2 coefficent) + (Band 4 * Band 4 coefficient))

The first option seems to give results closer to downloaded Sentinel 2 NDWI imagery, and I’ve not seen option 2 published outside of that tutorial.

NDWI = (Band 2 - Band 4) / (Band 2 + Band 4)

Hi @Gillian,

Based on our investigation, it’s recommended to use the standard formula NDWI = (Green - NIR) / (Green + NIR). 

Thank you for flagging the discrepancy! We’ll check it out. 

Let us know, if you have any further questions!

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