It will be enough to look for the data here https://earthexplorer.usgs.gov/ you will have to get an account and download it. A thing that you will have to consider is that this sensor gets an error since roughly 2007 (I am not sure of the exact date), so you will have so much striped data, maybe it could be necessary to run a math model to fulfill gaps.

in earthexplorer u can get

You can download it from https://earthexplorer.usgs.gov/. but to download the data you have to create an account there or you can also download using Google Earth Engine.

You can download the Level 1 data freely from https://earthexplorer.usgs.gov/ and you need to calculate the NDVI using Arcgis, Qgis, Erdas imagine or SNAP.

Henry Arellano Peña thank you for your reply. I do have an earthexplorer account but couldn't find the procedure to download time series data. Is there any related information available? Thanks

Yes, you can download an elaborated mosaic series for whatever world region, you can find it under Landsat legacy and Global Land Survey selection (you can see that in the data set tab); previously, you should have selected your AOI (Area of interest). Unfortunately, I am afraid that you will need a math model to set up your span. If I were you, I would use a blend between Landsat and MODIS or another frequent recovery data sensor in this case. The selection of the sensor would depend on your research goals, spatial resolution selected, and workstation capabilities. I recommend you the GLS because they have already had part of the hard job for you, and I have always considered it an excellent point to start. After that, I can calculate the NDVI for the outcome (stack of images) within a package as GRASS, QGIS, OCTAVE, SCILAB, R, or MATLAB.

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https://earthexplorer.usgs.gov/.