Causes of Errors include positional erros with the GPS/IMU, range, scan angle, boresight angles, lever-arm offsets. These are systematic errors and corrections can be applied over the entire dataset.

Range Errors – Not corrected for, occur due to recording of the time between emission and return of laser – centimeter scale.

Beam Divergence – Common error in places with terrain effects which result in vertical errors.

Scale Error – caused by the rotating mirrors which occasionally have delay. Occurs in across-track profiles near edge of flightline.

Deceleration Error – related to mirror deceleration at the edge of a scan swath.

Encoder Latency – scan lag, timing delay between laser and scan angle measurement

Pitch- Slope Error – Laser head is not exactly perpendicular with mirror (likely needs factory calibration)

Lever-Arm Errors

Lever-Arm Offsets – GPS, IMU and laser head not at same location. Measurements between these features need to be accurate.

Boresight Errors – Fixable Error within Microstation

Boresight Angles – very slight angular differences between IMU and scanning mirror. Visible in profile, looks like a shift in data between lines.

Boresight Roll Error – positions shift across-track. Due to angling of the laser. (parallel to flightline)

Boresight Pitch Error – As you move away from nadir you can increase the position shift (perpendicular to flight line)

Boresight Heading Error – positions rotate around the mirror

 

Calibration methods can be Rigorous (sensor specific, uses range data), Quasi-Rigorous (error specific, no range data) or Non-Rigorous (purely data driven (no trajectory etc).

Terramatch uses a Quasi-Rigorous technique and mostly corrects roll, pitch and heading errors.

All of these methods use geometry of points to minimize discrepancies (such as rooftops).