I want to perform Tasseled cap transformation on Landsat 5 and Landsat 8 Images to get forest Disturbance Index. And I want to compare the forest Disturbance of Different Years ( before 2011 by using Landsat 5 and After 2013 using Landsat 8). What things should I take in consideration before comparing the Indices obtained from both sensors? And what image processing are required to get those images eligible of comparison?