Dear Colleagues, I am currently doing some work for an ecologist in our organisation. She is interested in investigating the relationship between ground water depth and vegetation health / moisture content. I am using Landsat 5 TM imagery from 1991 through to 2003. After orthorectification, radiance conversion (using gains - bias), and atmospheric correction (using FLAASH), I have now run a TC transformation. In particular I was thinking of using the 2nd and 3rd TC channels to correlate with depth to ground water. Unfortunately I see that most of TC 3 is made up of negative numbers. Is this normal? If so can convert these to positive numbers by simply adding the min value (e.g. -64) to the imagery? I am not sure how the ecologist will react to negative moisture status values. Many thanks, Wesley