Airborne LiDAR is a relatively new land surveying technique, which is based on high precision laser scanners, the Global Positioning System (GPS) and Inertial Navigation Systems (INS). Combined, they allow the positioning and orientation of the footprint of a laser beam as it hits an object, to a high degree of accuracy.
GPS
The Global Positioning System can be used for determining one's precise location and providing a highly accurate time reference almost anywhere on Earth or in Earth orbit. The accuracy of the GPS signal itself is about 5 meters. However, using differential GPS and other error-correcting techniques, the accuracy can be improved to about 1 cm over short distances.
INS
An inertial Navigation System provides the position, velocities and attitude of an aircraft by measuring the accelerations and rotations applied to the system's inertial frame. INS's have angular and linear accelerometers (for changes in position).
Angular accelerometers measure how the aircraft is rotating in space. Generally, there's at least one sensor for each of the three axes: pitch (nose up and down), yaw (nose left and right) and roll (clockwise or counterclockwise from the cockpit).
Linear accelerometers measure how the aircraft is moving in space. Since it can move in three axes (up & down, left & right, forward & back), there is a linear accelerometer for each axis.
A computer continually calculates the aircraft's current position. First, for each of six axes, it integrates the sensed amount of acceleration over time to figure the current velocity. Then it integrates the velocity to figure the current position. |
