Impact of Flight Altitude on Unmanned Aerial Photogrammetric Survey of the Snow Height on Mount Lebanon

Abstract

Abstract. In Lebanon, the seasonal snowpack is poorly monitored despite its importance for water resource supply. The snow accumulates on Mount Lebanon in karstic depressions named “sinkholes.” It is important to monitor the evolution of the snow height inside those “sinkholes”, because of their key role as “containers” for seasonal snow. UAV photogrammetry is a major technological breakthrough which allows an accurate monitoring of the snow height. Because the impact of flight parameters on snow height retrievals is not well documented yet, this research aims to evaluate the impact of UAV flight altitude on the resolution and accuracy of the resulting orthomosaic and DSM. The flight missions were done using the Phantom DJI which generated five DSMs. These are validated using total station measurements.The results indicate that the snow DSMs can be retrieved by adopting a resolution of 8 to 84 cm, a point density between 1.43 and 153 points/sqm and a RMSE of 13 to 41 cm. The testing was done using an elevation varying between 50 and 500 m. The results will be compared to total station observations. These results allow the user to choose the suitable flight altitude for required resolution and points density. We suggest that a flight altitude of 100 m is sufficient for the survey of the snow cover elevation.

Optimising UAV Data Acquisition and Processing for Photogrammetry: A Review

“…They were differentiated in terms of AGL height (30, 40, 50, 60, 70, 80 m), overlap between photographs (40/70%, 50/80%) and the use or absence of GCPs. It was shown that decreasing the flight height has a positive effect on the detail of the obtained products which was also confirmed in the study [100] and increases the accuracy of the RMSE readings. For comparison, the value of the RMSE error when using an altitude of 30 m was 3.8 cm at 80/50% coverage and 5.4 cm at 70/40% coverage, while when using an altitude of 80 m it was 9.5 cm at 80/50% coverage and 10.0 cm at 70/40% coverage.…”

“…Similar conclusions were reached in another study [101]. DEMs generated from images acquired at five different flight heights (50,100,150,200, 250 m AGL) were analysed. The georeferencing was performed using 18 GCPs while the accuracy assessment was based on 385 CPs.…”

“…The effect of pre-calibration on final accuracies of the BA achieved with the application of the non-metric camera installed on board the UAV and a threedimensional test field was analysed in the studies [66]. Data for calibration were acquired at three different cruising altitudes (23, 28, 35 m) with a variable number of GCP (3,14,50,100). The results were compared with studies conducted with selfcalibration.…”

Acquisition of high-resolution topographic information in forest environments using integrated UAV-LiDAR system: System development and field demonstration

“…However, when the flight velocity was 11 m/s, the velocity-driven variation in the point density was the greater: 5 pt/m 2 at 70 m high and 10–12 pt/m 2 at 30–50 m high. Conclusively, it is preferable to fly the UAV at the slower velocity and the lower height, but note that this will reduce the coverage area and increase the flight operation time [ [67] , [68] , [69] , [70] ].…”

Effect of varying UAV height on the precise estimation of potato crop growth

“…Especially during emergence, it is important to determine these parameters to precisely determine the sprout rate and their traits. It has been shown that increased flight altitude results in decreased resolution of the densified surface model (DSM) which is used to extract height and related parameters ( Abou Chakra et al., 2020 ). While increasing the UAV flight height reduces the time taken to take mages in the same field, the lesser number of images captured reduces the processing time.…”