Ah yes, good question. As I understand it, based on working with a few people who do their own LiDAR flights, the airplane has 2 positioning components: a GPS, and an IMU (inertial measurement unit). The IMU is a super accurate system of multiple gyroscopes that is fixed to the same solid plate as the observation equipment and constantly monitors the transverse and rotational acceleration of the instrument. This isn't just used for XYZ positioning--the IMU data are also critical for figuring out the look-direction of the scanner at any given moment so that shots can be accurately located on the ground. (For instance, what happens when the plane is slightly banking? The shots are skewed more to one side.) The general position of the aircraft is updated based on onboard GPS, BUT there's a trick: they simultaneously use a base station GPS unit positioned at well-known coordinates (say, a benchmark) to track the actual effect of the atmosphere and other noise on the GPS signal at a certain time in a certain general area. This is called Differential GPS, and combining the two GPS records with the IMU measurements yields extremely accurate positioning.RadioJay wrote: ↑Sun Jan 02, 2022 8:31 amCan Eli or someone address the accuracy of the aircraft’s elevation? I imagine it uses a combination of GPS and INS but super accurate elevation estimates usually require a long observation time and the airplane is moving and is subject to turbulence.seano wrote: ↑Sun Jan 02, 2022 6:44 am Thanks for the tutorial! QGIS is pretty overwhelming and clumsy at first, as one might expect from an expert tool. Unfortunately LiDAR data does not seem to be available for the Sierra yet. When it is, it's very possible Mount Barnard (between Whitney and Williamson, currently 13,990') will become another 14er.
Read more:
IMU and GPS positioning for remote sensing
Differential GPS
By the way, here's what a LiDAR scanner looks like from inside and outside the airplane.
Updated: looks like Ben was answering the same way while I was typing haha!