for my Master-Thesis in marine ecology I will map changes in mangrove-distribution over a period of 30 years in BCS, Mexico, using Landsat MSS, TM and ETM+ data provided by GLCF. To compare the images of different time periods I need to correct them radiometrically. My question now is: is it necessary to do the calibration using this algorithm, which involves gain, bias, sun elevation,...? Because I cant find this information in the Metadata of the images of 1990. I read papers, where there was simply done radiometric correction by doing Normalization processes through linear regression. Would that technique be enough for my purposes? I am not a remote sensing student, but a biologist, so I try to keep my analysis simple but - of course- appropriate. Thank you very much for your help.