Accuracy of Flight Altitude Measured with Low-Cost GNSS, Radar and Barometer Sensors: Implications for Airborne Radiometric Surveys

TL;DR

This study evaluates the accuracy of low-cost GNSS, radar, and barometric sensors for measuring flight altitude in airborne radiometric surveys, highlighting their performance at different heights and implications for radionuclide measurement precision.

Contribution

It provides a comparative analysis of various low-cost altimeters' performance during airborne surveys, informing sensor selection for UAV-based radiometric measurements.

Findings

Radar and barometric altimeters perform best below 70 m altitude.

GNSS improves data quality at heights above 80 m after post-processing.

Uncertainty in flight height measurement impacts radionuclide activity estimation by less than 1.3% at 50 m.

Abstract

Flight height is a fundamental parameter for correcting the gamma signal produced by terrestrial radionuclides measured during airborne surveys. The frontiers of radiometric measurements with UAV require light and accurate altimeters flying at some 10 m from the ground. We equipped an aircraft with seven altimetric sensors (three low-cost GNSS receivers, one inertial measurement unit, one radar altimeter and two barometers) and analyzed $\sim$ 3 h of data collected over the sea in the (35-2194) m altitude range. At low altitudes (H $<$ 70 m) radar and barometric altimeters provide the best performances, while GNSS data are used only for barometer calibration as they are affected by a large noise due to the multipath from the sea. The $\sim$ 1 m median standard deviation at 50 m altitude affects the estimation of the ground radioisotope abundances with an uncertainty less than 1.3%. The GNSS double-difference post-processing enhanced significantly the data quality for H $>$ 80 m in terms of both altitude median standard deviation and agreement between the reconstructed and measured GPS antennas distances. Flying at 100 m the estimated uncertainty on the ground total activity due to the uncertainty on the flight height is of the order of 2%.