Last week monsoon rainfall caused flooding in areas across India and Pakistan. Srinagar experienced severe flooding and relief efforts are now underway. Satellite imagery offers a first response look at the flooded area and shows when flood lines increase or recede.

We recently released landsat-util, a tool for easily processing open Landsat imagery. Using landsat-util and some additional processing we can quickly process imagery to view flood extent from above.

Swipe between August 25 and September 10 Landsat images for a quick first glance at the geographic extent of the flood. View larger

We used Landsat-util to identify, download, and process Landsat imagery before and immediately after the floods. (The left image is Scene LC81490362014237LGN00 from August 25, 2014. The right image is Scene LC81490362014253LGN00 from September 10, 2014.)

With additional processing we can get a clearer view of the floodlines. Water reflects infrared light diffirently than land. We can use this to clearly distinguish muddy water from muddy land. Working from the images we just downloaded, we created a false color composite by combining different near-infrared and mid-infrared bands (also known as a 5,6,4 band composite). The processed image clearly highlights flood lines.

A 5,6,4 false color image clearly distinguishes waters from land to derive a flood line. View larger

First response

Timely response is vital in disaster scenarios. When ground information is limited, satellite imagery can provide first responders with a clear picture of an area. With landsat-util we hope to make landsat imagery accessable to more organizations. For more on image processing, see this great tutorial by the Mapbox satellite team and view the code for the false color comparison here.

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