How to extract MODIS Time Series Normalized Difference Vegetation Index (NDVI) data and plot it on a graph?
Just following Richard, the MODIS product MOD13Q1 already includes two bands, one is the NDVI values of the scene and the other is the EVI values. So, from the NDVI band all pixel values are already NDVI calculated values. All you need is to transfer the digital numbers (in Ascii format) from the images you select (in the time frame that you want) to a spreadsheet of your preference. Or use, as Richard suggests, a georreferenced package, such as R, to produce the comparison results you want.
I have taken only one image for the time being and converted it into ASCII format using ArcGIS. when i open this file in Excel, i am unable to make sense of it... I have attached a txt file. please guide me as to how to use this to extract and plot the ndvi values
Dear Valijayanti,
Based on your txtx file, it appears to me that the problem is in the way that you are processing the data in your software package. I just did a similar procedure using ENVI and the result is in the file attached. You can see that all NDVI values range from 0 to 1. In your file it seems that pixel values correspond to decimal numbers after 0. So, what is missing is "0." before all values. Except -9999 that correspond to the pixels with no NDVI value (the background of our image).
thanks Nelson..
I have another question......
do i stack up all the layers in the time series and then extract values for a particular point over the years?
The most important tip I can give you is: "make sure that you can keep track of what you are doing with your data". That is ... don't loose track of the data structure and data values as you do the necessary steps toward building your data bank. If you choose using one package, make sure that you know how this specific software manipulates your data. Some times is better to do things step-by-step in order to follow every single change that happens along the way. It becomes a learning process that builds your confidence on the results you get.
Hello Everyone
Thank you very much for the information very helpful indeed. Idham what did you mean by "ypu use Sample" is that a softwear? is available?
Hello Everyone
Thank you very much for the information very helpful indeed. Idham what did you mean by "ypu use Sample" is that a softwear? is available?
May be this website will help - http://glam1.gsfc.nasa.gov/
You might need to convert it into a vector (?) to get tabular values. I am just guessing, not sure about it.
Do you have any matlab code to extract NDVI value from MODIS images? if you have please share with me if there is no objection.
Thanks in Advance