Ice Detection in Hudson Bay using VIIRS data from Suomi NPP

 VIIRS visible imagery (0.68 micrometers) (above) over Hudson Bay, 1801 UTC on 2 July.

VIIRS Snow/Ice Band (1.62 micrometers) (above) over Hudson Bay, 1801 UTC on 2 July

Channels on the VIIRS instrument on board Suomi NPP allow easy discrimination between ice and water clouds.  Ice is a very effective absorber of energy at 1.61 micrometers;  thus, if you compare visible imagery (top) with 1.61-micrometer imagery, regions that are very white in the visible (lots of reflection) and very dark at 1.61 micrometers (lots of absorption, not so much reflection) are assumed to be ice, either at the surface, or in clouds.  In the example above, ice is indicated over central Hudson Bay -- it is very white in the visible, and dark in the 1.61 micrometers.  Similarly, ice clouds are indicated over the southwest part of the image, where clouds are indicated as white in the visible, but not white at all in the 1.61 micrometers.  This is a handy method especially in winter to discriminate between surface snow and water-based clouds.

Scott Lindstrom, UW-CIMSS, Steve Hentz, NWS-MKX