Atmospheric correction with ATCOR

This page contains some basic processing instructions for atmospherically correcting ARSF data using ATCOR. Note try and do everything in the correct order - if you do later parts of the process first it sometimes resets them when you do the earlier ones (depending on exactly which ones). This is a basic guide only, you may well be able to get better/more accurate results using more advanced bits of ATCOR.

1. If you don't have one already, create a sensor geometry file. This is currently beyond the scope of this guide (should be added in later).
2. Run ATCOR. Currently you need to ssh to either gridnode36 or pmpc1071 (Peter Land's machine) to do this.
3. Select Tools > Solar Zenith and Azimuth. Enter the approximate flightline time and position and click "DO Calculation". This will give you solar azimuth, elevation and zenith values - note these down.
4. Convert the level 1 BIL file to BSQ by whatever means. You can use Tools > BIL to BSQ Conversion, but I recommend you use the similar option under Basic Tools in ENVI - that way you can get on with using ATCOR on a different line while it's running.
5. Select Atm. Correction > ATCOR4f: flat terrain.
6. Click INPUT IMAGE FILE and select your level 1 BSQ file.
7. Click "Date" and enter the date when the flightline you are correcting was collected.
8. Ensure the OUTPUT IMAGE FILE is something sensible.
9. Use logwriter.py <sbet_file> <specim_dir> to get information about the flight altitude and heading.
10. Work out the approximate elevation of the target site in metres (possibly by inspecting the DEM using GRASS or ENVI)
11. Click "Flight and Solar Geometry". Enter the flight altitude and heading, ground elevation and solar elevation and azimuth (all as determined in previous steps) in the appropriate boxes.
12. Click "Selected SENSOR". Click the button with the sensor name and select the sensor appropriate to the bandset used for the flight (check the header file for the number of bands). Select the appropriate calibration file when prompted.
13. Change the nadir pixel size as appropriate (see pixel size calculator at ​http://arsf-dan.nerc.ac.uk/pixelsize/pixelsize.html)
14. Click "Select" next to "ATMOSPHERIC FILE". Select an atmosphere model as appropriate to the flight location and altitude.
15. Click "VISIB. ESTIMATE". Enter the given visibility value in the "Visibility" box.
16. Click "IMAGE PROCESSING". Leave all the options as default and click OK.
    1. Leave all the water vapour options as default and click DONE
    2. Click "RUN Atmospheric Correction" - wait for it to complete.

You should now have an atmospherically corrected version of your level 1 file (ie. it is now at level 2). This can be converted back to BIL format using ENVI and then substituted for the level 1 BIL file as input to azgcorr to be geocorrected.