The best way to compare changes from the images of landscapes is a still image processing in special programs . ENVI, ERDAS Imaging, IDRISI, Definiens (eCognition), etc. For example, in ENVI has a special module which detects changes by comparing satellite images at different times . Selecting Landsat 4-5 Landsat or Landsat 7 or 8 depends on the purpose and scope of research. Spatial resolution Landsat 4-5 - 30m , Landsat 7 , Landsat 8 can be adjusted up to 15 m , due to the panchromatic image. Radiation resolution Landsat 4,5,7 8 bits, and Landsat 8 - 16 bits. Additionally, Landsat 7 , 2003 after a lower quality , due to failure of the scanner and the bands lack of information.

First of all, to compare different images of Landsat 5 and Landsat 7 (and Landsat 8 too), you should correct the images doing an radiometric correction. This procedure is quite time-consuming, but it is necessary to remove the atmosphere effect, to avoid sensor errors or distorsions, and to be able to campare two images of different sensors.

First of all thank you very much for your answers. I Use ENVI 5 to convert landsat images from DN to Radiance and Reflectanse and to apply Dark Substract (The script that has the program). I try to find papers with similar subject, about comparing. I am not sure if I need to execute PCA or something else.

Wht do you want to compare, simply the radiometric data or looking for change detection?

Comparison between remote sensing systems takes the following aspects:

1. Spatial resolution

2. Spectral resolution

3. Radiometric resolution

4. Temporal resolution

5. Areal coverage

but if you want to make change detection between two image dates, it is better to do this after image classification

Dear Ruxanda thanks for the article. I want to compare images and looking process from a theoretical point of view. Also when I do the calibration of images I'm trying to anderstand if it is enough to see the difference between NDVI of both photos and same scater plots of the bands?

Dear Saif yes I would like to compare radiometric data. Change detection I will try in later time (maybe).