There is several ways to calibrate LiDAR Data wheather it is from a Optech, Leica or Reigl system. The two most common ways are by flying a mission calibration over the base of operation or a cross flight over the project area during the mission. The calibration issues can be resolved using both. The common elements that need to be examined are the Pitch, Roll, Scan factor and heading. The heading usually holds but in some cases it doesn’t but this is rare. The roll and Scan factor or torsion can vary and are directly related. Some refer to torsion or Scan factor as Mirror scale. The roll and mirror scale are directly related and can be preceived as the same thing so it is important to understand these. The mirror scale reflects a smile or frown in the data when profiling across a scan and a roll is inidcated as a uniform linear offset at each end of a scan when two scans are flown in opposite directions of eachother. Mirror Scale seems to be less frequent in the Leica systems. The pitch error is usually represented but offsets in flight direction. The easiest way to identify a pitch error is to profile a builing in overlapping scan areas or in two opposing overlapping flight lines. The pitch error will be indicated when a building in one of the scans is offset from the same building in another scan. This should not be confused with Pitch slope error which is when the pitch is correct at nadir of a scan and offset at the edge of a scan. The pitch slope error doesn’t occur with the Optech systems and is something that needs to be addressed in the Leica systems. The heading is a rotational error between scans and is about the vertical axis of the sensor. Heading can be confused with pitch slope error in the leica systems but not with the optech systems. If someone understands more about the reigl systems that information will be welcome.