Hi I have been using Modis level 1b images (MOD02QKM and HKM) to create true colour images of areas of the Greenland Icesheet, with the aim of classifying surface lake areas.  I have been georeferencing both products using Envi into UTM format.  MOD02QKM has a 250m resolution and HKM has a 500m resolution.  After georeferencing I resize  the HKM file to 250m.  When both images are opened and the displays are linked, they do not match up exactly, there appears to be an offset of a few pixels in the N and E direction.  In order to correct for this offset I manually change the lat and long in the header file of the HKM to match the QKM.  However by doing this I realise I am losing the geospatial information - when a number of images over a period of time are compared they no longer match up.  I am georeferencing both QKM and HKM in exactly the same way, I just dont undertsand why they dont match up exactly? Am I doing something wrong? Any help would be much appreciated. Thanks Andrew