GLIMS Working group on algorithms

[Frank Paul]

Dear Niels

I have no experience with ice sheets but for alpine glaciers I use
the following procedure:

1. Divide TM 4 by TM 5 (the raw DN !).
2. Threshold the ratio image with a value of about 2.2
   (greater=snow and ice -> black, lower=other  ->white).
3. Apply a 3*3 median filter to the black and white glacier mask.

and perhaps:
4. Export as geotiff and conversion with "imagegrid" and "gridpoly"
    to a polygon coverage within Arc/Info.

Ice with thin debris cover is included with this method, also areas
within cast shadow if they are covered by snow. Also proglacial lakes
with turbid water were assigned to the ice/snow class. The median filter
reduces misclassification without changing the glacier area remarkable
(glacier size > 0.1 km2). 

A summary of available methods is presented at the home page of the
Swiss Glacier Inventory 2000: http://www.geo.unizh.ch/~fpaul/SGI2000

Follow the link (click blue button) Algorithms / References.

Best regards, Frank Paul.