NDMI in the past ten years

In the latest Teagasc Map of the Month (https://www.teagasc.ie/rural-economy/rural-economy/spatial-analysis/gis-monthly-maps/) I used MODIS Terra surface reflectance data to calculate the Normalised Difference Moisture Index (NDMI) as a proxy for the spatial variation in the effect of the spring 2020 drought in Ireland. The specific measure I used was the difference in the average NDMI in May 2020 to a long-term May average (2009 to 2019). The map showed well the spatial variation. To better highlight the underlying data I produced an animation of the calculated NDMI averages for May of each year since 2009. Brown tones indicate lower NDMI values (drier) while blue tones indicate higher NDMI (wetter).

The animation draws a very different picture to the map of the NDMI difference, with bogs and upland showing much lower NDMI values than the rest of the country. The reason is that NDMI is an index for leaf water content, based on the near and short-wave infrared reflectance, and in the absence of green vegetation (such as in cut bogs and sparse uplands) will be lower.

Uncategorized Earth Observation & Remote Sensing Research in IrelandRead More