Hi everyone, I'm relatively new to envi, so I know, perhaps, the barest minimum of how to make it work, I'm looking at MODIS L1b 500m data of the Baltic sea and Barents sea in order to attempt to crudely quantify algal blooms. I have an issue with NDVI (and every other vegetation index there is) where green algal blooms report back negative values much greater than the surrounding water and and clouds that escaped masking (e.g. water= -0.3, thick algae = -0.6). I understand that algal blooms will be slightly negative anyway in a best case scenario. I've tried masking out land and cloud, using the images raw and georeferenced, converting the images using the MODIS toolkit. I've also attempted Dark Object Subtraction as a way to crudely apply an atmospheric correction and the results are the same. I'm completely out of ideas here! Any help is greatly appreciated Thanks, Nic