The Oak Ridge National Laboratory distributes global subsets of many MODIS land products. The subsets are spatially limited to a maximum of 200 km X 200 km in size but can cover the entire time of the MODIS program. This is an easy way to obtain a time series of data for you research projects.
The data are available at the ORNL DAAC at:
Begin by entering the scene center coordinates or drag the balloon to your location and click the Continue button. Next select one of the many products available. Note that products beginning with “MOD” are from the Tera sensor and “MYD” are from the Aqua sensor. Next enter the number of kilometers Above and Below (north/south) and Left and Right (east/west) that you want for the spatial coverage and hit the Continue button.
On this third page select the beginning and ending times of your requested series. (You should consider selecting a small temporal subset for initial testing before ordering 400+ layers of data.) You are offered a choice of projections, either MODIS Sinusoidal or Geographic Lat/Lon. You should select the Sinusoidal projection; you can reproject the data to a different coordinate system in ENVI later if necessary. Click on the Review Order button. After reviewing your order you can change parameters or click Create Subset to submit the order. You will get an email when this is completed.
Following the link in the email from ORNL brings you to a page with several charts visualizing the data you have selected. After examining these results, click on the Download Data tab and select the Product GeoTIFF Data link to get your data compressed in a “.tar.gz” file. You can use 7-Zip or another utility to extract the data files for your research. Note that this may result in many more files than you expect. For example, the NDVI/EVI Vegetation Index file consists of 22 datasets for each time period. So an order for a two-year cycle of vegetation indexes will produce 528 separate files.
Finally you need to create a single multi-date file containing all of the desired data layers such as NDVI or Land Surface Temperature, making sure the layers are stacked in date order. This can be done easily using a script written with the ENVI programming interface. The YCEO has developed an script that can perform this task for you. See a member of the YCEO staff for a copy of this ENVI script, along with guidance on how to tailor this for your specific needs and execute the script in the IDL environment.
ENVI has more information about programming in their Help section under Contents | Programming | Programming Guide. Also read the short ENVI Programming FAQ on the YCEO site.