Remote sensing from satellite imagery can be a challenge in cloudy Ireland, with the wealth of images offered freely on NASA and ESA portals often ending up a white mess of fascinating cloudscape. Fortunately clouds do not affect the Synthetic-Aperture Radar (SAR) products provided from ESA’s Sentinel-1 mission. And there are a lot of exciting things to do with them.
When crossing the Rhine in my German hometown of Neuss recently, I saw the effects of this year’s hot summer in the lowest water-levels I’ve seen in a long time, just about enough space for the cargo liners to pass each other. That got me an idea: SAR has proven a great product in flood-mapping, so why not turn it around?
The result is a map of water-levels for the Poulaphouca Reservoir (or Blessington Lake), one of the main reservoirs for the Greater Dublin area (superimposed on one of the rare cloud-free Sentinel-2 images). The map shows the extent of the water surface on the 4th August 2018 (1378 ha, dark blue) and the 2nd August 2017 (1447 ha, light blue), nicely visualising the retreat of the water following this year’s drought compared to a more normal summer (a difference of roughly 60 GAA pitches). Without the lakes bathymetry this of course does not tell us anything about changes in water volume. But it still is a nice showcase for the possibilities of SAR data for mapping water bodies.