Tuesday, 3 May 2011

Critical mass, satellite imagery and GIS

Satellite imagery has been around for almost as long as GIS, and the following may just make them so easy they finally gain momentum. The same way Jeeps and Suburbans had been around for a couple of generations, but only the last generation saw Ford legitimize SUVs with its Explorer.

ESRI announced today the availability with the US Department of Interior of Landsat imagery worldwide and for free. In addition these are served up in a cool Change Matters format, a sort of imagery-compare-dot-com. This is not a new idea, but until now it meant collecting imagery, storing massive files on a server, tiling and ortho-rectifying them and stitching them together (say that 100 times)... in other words enough to turn off all but the most ardent imagery enthusiast!

The drainage of marshes is a bit of a feature back home near the East Anglia Fenlands. I jumped on it looking for ecological step-changes in river / coastal environments that proved to be a bit of a challenge. Living through Kuwaiti dust-storms* brought up another episode of marshland drainage, as controversial under Saddam Hussein's Iraq at the turn of this millennium as the Earl of Bedford's East Anglia a quarter of a millennium ago.

*: Iraqi marshlands acted as a buffer against northerly winds sweeping in from Iran, so their dried up state only adds dust instead of absorbing it. They are gradually returning to their original state, of the fabled Gardens of Eden or Hanging Gardens of Babylon (like the fabled Isle of Avalon in East Anglia, marshlands do seem to start a lot of legends!).

Search then for Abu Sabayah on Change Matters and zoom out until the scale bar show 10 km. / 5 mi. 'Keep-it-simple' infra-red covers the entire time span 1975 - 2005 of interest. It's not perfect - variable imagery quality (large swathes of differing hue) and coverage (large blotches of black, apparently no data) or comparison (green highlights both swelling and dried-up river-beds) - but professional image-processing would handle all that and more... and nothing beats the ease of this website!

This comparison of infra-red in 1975 and 1990 clearly shows the mismatch up&down the center, and the left looks like a false-color image. Also the dried river bed at bottom is as green to the right as the existing river at left, again because of a 'false image' at bottom. Clearly seen however are, at bottom the drainage of the Euphrates into the Main Outfall Drain, and at right the drying up of the marsh and urbanization at bottom.

Ignoring the false-color and absent imagery at top left and bottom right, respectively, one sees the Glory River diverting the Tigris - switch the year spans on&off to find which decade it appeared in - and the recovery of the drainage system post-Saddam, which has been well reported in the press.
Such easy map-making will help me explain to my friends and family one more time, some geo-morphology that relates to current weather or events