Mapping the last frontier
Chapter 2: Flying with double the scanning power
Flying with double the scanning power
A total of 95 lines were flown to cover the entire survey area, where line numbers increased in the westerly direction. The average flight line was approximately 50 km long. To ensure complete coverage, the flight line spacing was set at 160 to 180 m, where the ground laser swath footprint was calculated to be 280 to 290 m wide. To compensate for the changing ground elevation (30 m in the north, 95 m in the south), atmospheric pressure was monitored during flights to maintain a constant flight altitude and swath above the ground.
The Chiroptera uses two LiDAR scanners to acquire topographic and bathymetric data. Data from the topographic LiDAR (red wavelength) was fired at 300 kHz and used to acquire high-resolution 3D positional data on vegetation height and earth topography. Data from the bathymetric LiDAR (green wavelength) was emitted at 35 kHz and used to determine water related statistics, such as depth, volume and area size. We also collected colour-infrared and natural-colour imagery at 400 m and 1,700 m, respectively, for visual reference and ortho-rectification purposes.
“The technological cornerstone of this project was the Chiroptera airborne LiDAR and imaging system,” said John Hupp, a research scientist from the Bureau who was responsible for field data processing and system calibration. “Simultaneously collecting high resolution imagery with the LiDAR data allowed us to easily discriminate water bodies, vegetation characteristics, wetlands and uplands, saving us time and costs compared to any other conventional type of survey.”
For both LiDAR scanners, the average vertical offset was measured at less than 1 cm, while the standard deviation was calculated at approximately 3 cm compared to the ground control points collected at Deadhorse airport runway pavement. Calibration procedures were applied to both scanners individually, where average roll and pitch biases were measured to be less than 2.6 cm.
“We also examined and corrected any evident LiDAR system calibration errors caused mostly by incorrect inertial navigation system (INS) rotation angles of roll, pitch and yaw. These errors can be detected through analysis of adjacent and opposing LiDAR strips,” said Hupp. “In theory, if no rotational misalignments are present, LiDAR points registered from different strips should match each other seamlessly on an unobstructed surface; although not expected to have perfection, we can achieve very close results in practice.”
Explore next chapter: Faster, more accurate data analysis