Download MOD13A2, Convert, Graph NDVI using NCL scripts.


It’s been a while since I have started using the NCAR Command Language (NCL). To my opinion it is indeed a great tool to process data in geoscience and automate batch processing.

Quite recently, couple of my friends asked me if I can assist them with processing some data from MODIS. Even on LinkedIn, one person from Brazil was interested in the same procedure. After sending the scripts to all these people separately, I told myself, why not just upload the code here and let every one using it.

Here is what this script does:

  1. It downloads the MOD13A2 data for a given tile and year. You can read the information about the MODDownload script separately here.
  2. This script retrieves the NDVI data out of all of the MODIS files downloaded (23 per year) and scales the data by the proper scale factor and store the results in a NetCDF file with (time,lat,lon) dimensions. So it is ready for further time series analysis.
  3. It graphs all the time series using NCAR graphics generating PS or PNG files.

You can download the script from here. After downloading edit PrepTile and set the tile number and the year of your choice, (currently it is set to download tile h09v05 for the year 2008). Set the locations were you want the files to be stored and then run the script.

Feel free to make any changes that you like to the code in order to make it more suitable for your own needs, and if you thought the changes that you made, can be helpful to others, you can let me know and I will include it in the file for future distribution.

What you need to run the script?

  1. I have tested the code under Linux and Mac; however, there shouldn’t be any problem on cygwin on windows machine.
  2. You need to have NCL installed properly and in the PATH. You can get NCL from here.
  3. You must have wget installed on the system. On ubuntu you just type “sudo apt-get install wget” and on mac you type “sudo port install wget”, (well, if you have mac port installed, you can get mac port from here).
  4. To generate PNG graphics, you need ImageMagick. If you don’t have ImageMagick you can only generate PS graphics using this script. (although if you change the script you might be able to generate other types of graphics, but currently I just made it that way). You can get ImageMagick from here.

Ok, hope you like the script and enjoy using NCL.

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