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I’m doing phenological study using a threshold method in IDL. I have a twelve-band image in 2005 (format is in .tiff not ENVI format). Twelve-band means that monthly images (Jan to Dec) have been stacked in ARCGIS.

I know how to set threshold value on a single image. But I don’t know how to set a threshold value on multiband image to determine the date when growing season starts and ends. Start of the season is determined as the day when the NDVI value is return to threshold value in a given year.

So what I’d like to ask:

  1. Can the stacked image be in .tiff format to be imported into IDL via the envi_open_data_file procedure. Or is an ENVI-formatted file required as input?

  2. What kind of procedure and function should I use to extract start and end of season using threshold method on multiband image? The start/end date of season varies by vegetation type. Basically I want one image showing different places are different phenological date. Is there anyone who can help me for this?

Thanks a lot

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Please provide more information on your data and files (what kind of data exactly each pixel contains, bit depth, floating point/int, IDL version). – Sceptical Jule May 18 '13 at 22:18

for your first question, you can use one "envi meta file" to stack your 12 bands.

for your second question, note that it could be done with map algebra in arcgis , something like Con(b1>threshold, 1, Con(b2>theshold, 2, Con(b3>threshold, ....))) for the start of vegetation, and the same starting from b12 for the end of vegetation period. The images do not need to be stacked in this case.

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