Airborne Laser Scanner (ALS) processing

General Processing with a settings (.reg) file

1. Start ALS PP (possibly using Linux)
2. Load in the reg file to set the specific settings for the project.
   • Reg files under ~arsf/calibration/lidar. Usually, pick the calibration that's the most recent prior to your project day. However, sometimes calibration flights are flown AFTER data is collected. Check with someone if unsure.
   • File > Load Settings
3. For Wine, Go to Inputs > Range Correction and for Intensity Based Range Correction browse to \users\rsg\arsf\calibration\lidar\... and select the relevant SN089_IBRC*txt file for the flight day you are processing
4. Set the Goto Folder to the main project directory
   • File > Set Goto Folder
5. Check the settings are appropriate for the project before proceeding (see below). This is important if using a reg file for a different project.
6. Select POS filename
   • Click Browse and add the .sol file (posatt/ipas_honeywell/proc/)
7. Select the Output directory
   • Click Select > Goto Folder and select <projname>/processing/als50/las. You should create directory if it doesn't exist.
8. If the project is not in the UK, you will need to change the projection (File -> Output Options -> Change output format), change: zone, height and width
9. Save settings for future re-processing purposes.
   • File > Save Settings (e.g. aux_files/2009280b.reg)
10. Add the raw SCN data
    • Click Add and browse to the parent raw data directory. This will add all flight lines in the immediate child directories. liar->als50->RawLaser
11. Run the processing
    • Run > Run

Setup of the system

• Hardware options. Once set these should never change (unless the system is modified etc) Should be supplied when the system is delivered. Can view/set these from File > Processing Options.
• Output file options. Set the projection details (usually OSGB36), LAS file format, and whether want GeoTIFF or ASCII output awswell. Also contains options for debugging.

• Input options
  • Atmospheric Correction. Need values of the altitude, temperature and pressure for a low altitude and high altitude. With these values a correction gradient will be produced.
  • Range Correction. A time-distance delay in metres of the ALS system, in the measurement of range data. (This is complicated...see user manual for details)
  • Scanner Correction. These do not need to be changed after the calibration/boresighting of the system.
  • POS errors. Angular difference between the IMU and the ALS optics reference frames. Needs to be known accurately.
  • Elevation offset. This needs to be set if we have ground control points: is normally non-zero. It is identified using the TScan Control Report (eh?). The LIDAR is then reprocessed using the opposite of the DZ offset.
  • Intensity. Use the Raw intensity.

Possible errors

• ALSPP.EXE on Linux

1. If a Windows crash message appears when trying to 'Run', ensure the POS file is pointed to on the Linux filesystem and not the Windows hard drives (D:,.. etc.).