I try to create an NDVI from Landsat and ASTER satellite images using Erdas Imagine. In Erdas, the satellite images have a nodata value of 0.
After creating an NDVI, the nodata value is still 0, but obviously there are also file pixels with the value 0 now (NDVI ranges from -1 to +1). So if I reset the NoData value to 0 (it is not done automatically), some pixels in my raster are missing since they are now classified as "nodata"
Any suggestions?
I have found a workaround, but I hope there are better options. Before creating the NDVI, use Spatial Analyst/ IsNull tool with the satellite image to create a raster with two classes: data (=0), nodata (=1). Then create the NDVI and use the tool Spatial Analyst/ Con with the data/ nodata raster created before to change the nodata value to a number other than zero.
explanation in German: http://help.arcgis.com/de/arcgisdesktop/10.0/help/index.html#//009z000000ms000000
This works, but there must be better options!
What kind of version are you using ERDAS ? I worked on ASTER and performed NDVI from it and from what I see that ERDAS automatically sets its as BANDS 2 as red and 3 as Near Infrared and selected the SPOT XS/XI as the sensor because it has the function that you wanted and the output set to float single and should be able to produce with -1 min and +1 max result. BTW, I use ERDAS 2013 most of the ASTER that worked and one of them had a problem so I use ENVI and corrected it from there.
