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incidence angle maps for palsar
Submitted by aswanson on Mon, 07/06/2009 - 11:55
Hi,
I'm working with dual-pol palsar level 1.5 data, and need a map of local incidence angle to perform terrain correction. I would happily settle for a map of incidence angle since it is not hard to calculate local incidence angle from this. I can get an incidence angle map usng ASF view for the raw palsar imagery, but this is not geocoded or orthorectified. Is there any way to get a map of (local) incidence angle that is orthorectified and geocoded?
Cheers,
Alan
#1 Re: incidence angle maps
Alan,
We had an e-mail conversation about this, however I did not notice you'd posted a forum question until now. I'd like to summarize the procedure for this for the benefit of anyone who may be searching the forum archives.
There isn't an easy way to get local incidence angles - though this is a good idea and we should add it to our feature request backlog.
To get ellipsoid incidence angles, it can be a little tricky if you want the result to be terrain corrected (because the coregistration part of terrain correction will fail when trying to match an angle map). Here is how you can do it, using the command line tools.
1) Use asf_import to import the data as amplitude: e.g., asf_import LED-ALPSRP112361140-H1.5_UA imported This results in the ASF Internal file "imported.img" (with "imported.meta") 2) Use asf_view to view the data, and save an incidence angle map of the entire image. You might name the saved subset "incidence_angle.img" (with "incidence_angle.meta"). It might take a little time to calculate all those angles. It is important to get the entire image -- in the next step we combine the angle map with the original amplitude data, so they must match in size. If you don't want the entire image, you could save the portion you want twice -- once with the angle data, and again with the amplitude, and then in Step #3/4 use these two subsets. 3) You will have to edit the metadata file manually in order for adjust_bands to work: 3a) Edit "imported.meta" and change the "bands" field in the "general" block from "???" to "AMP" (or something similar) 3b) Edit "incidence_angle.meta" and change the "bands" field in the "general" block from "???" to "ANGLE" (or something similar You shouldn't have to do this step in the next version of MapReady -- this is a bug that should be fixed in 2.2.7 & later versions. 4) Use the adjust_bands tool to combine the amplitude file with the angle file: adjust_bands -bands AMP,ANGLE imported incidence_angle combined This creates "combined.img" and "combined.meta", a 2-band file containing your amplitude data and the incidence angles. These files are still in the azimuth/range geometry. 5) Use MapReady to terrain correct, geocode & export "combined.img". You will need to select "ASF Internal" as the format. You could also use the command-line tools asf_terrcorr, asf_geocode, and asf_export. Terrain correction should succeed because when terrain correcting a multi-band file, the first band is used for co-registration.