I downloaded the MODIS band 1 and band 2 files using https://ladsweb.modaps.eosdis.nasa.gov/search/ in tif format.
Then I calculated the NDVI using QGIS. But my NDVI value range is -119 to 141.
Please help me to solve this matter.
- raster calculate step.PNG (50.57 KiB) Not viewed yet
- Capture qgis.PNG (239.75 KiB) Not viewed yet
- User Services
- Posts: 154
- Joined: Mon Sep 30, 2019 12:39 pm America/New_York
- Has thanked: 4 times
We have forwarded your inquiry to our subject matter expert for further assistance. We have not received a reply back from the PI yet on this question.
I was able to replicate what you are seeing in QGIS. I don’t see a problem other than you should be quality filtering these data before you calculate the NDVI. The MODIS granule you downloaded will have a “QC_250m_1” layer in it that you should use to quality filter your data. The QA bit flags for the QC_250m_1 layer is provided in Table 8 of the User Guide (https://lpdaac.usgs.gov/documents/925/MOD09_User_Guide_V61.pdf) on page 19.
To better visualize the data you are working with, open the properties for your NDVI layer (i.e., ndvi in your screenshot), then select “Symbology”. Next…
- Change “Render type” to “Singleband pseudocolor”
- Change “Min” to “0” and “Max” to “1”
- Select a color ramp (I like BrBG for NDVI)
- Under the table, change “Mode” to “Equal Interval” and increase the “Classes” to “11”
- Finally, click “OK”
Hopefully that will give you a better view of the data.