Dear Prof. Nayak,

There are a number of ways for accessing freely available Landsat Imagery. I've mentioned some of the websites here which I usually use. I'm sure there are more out there. You just need to create an account and start exploring/downloading the data sets.

• http://earthexplorer.usgs.gov/
• http://reverb.echo.nasa.gov/reverb/#utf8=%E2%9C%93&spatial_map=satellite&spatial_type=rectangle
• http://glovis.usgs.gov/

Of course you need to perform pre-processing before doing classification like radiometric, geometric, atmospheric corrections etc. although in the case of Landsat you may not need a geometric correction because it is already corrected geometrically and uses a projected coordinate system (UTM). There are a number of sources on the web for the steps involved before doing a satellite image classification. Nevertheless, for me these two books by John R Jensen were quite helpful in cementing an understanding of the whole concept.

Hope this helps a bit. Good luck with your Research.

Hi

they usually provide them in GeoTif, but as archive with each band stored in separate file. So, if you want to use multispectral image - you need to ctack bands first into a single file. you can do this by GDAL for example, or any other RS software, quite a standard operation.

Dear Sir,

the one more website: http://glcfapp.glcf.umd.edu/ for download Landsat images. From this site, you can download data under data and product option.

Landsat MSS, TM and ETM Images available from 1979-2003 without SLC error. Rest of recent images have SLC error. Off course you can correct it using mask file which available with it. 

Most of them in Geotiff format only.

Before classification you should process them for atmospheric correction.

See one of my paper suspended sediment analysis using multi-spectral image which is available with my RG profile.

All the best

Thank you dear @ Varghase, Kaliraj and Evgenia Gurova for kind information.

Please see the link below. In some dataset, you do not need to any pre-processing step. it might be required but not obligatory.

http://landsat.usgs.gov/descriptions_for_the_levels_of_processing.php