Estimation of the effect of GNSS positioning errors on the dose rate calculation concerning aerial radiation monitoring

Mori, Airi; Seguchi, Eisaku*; Futemma, Akira; Iwai, Takeyuki*; Sanada, Yukihisa   

Four global navigation satellite system (GNSS) receivers were installed in a helicopter to reduce positioning errors in aerial radiation monitoring. The effect of positioning errors on the conversion of the counting rate of the detector to the ambient dose equivalent rate at the ground level was evaluated. The positioning results obtained by receiving the centimeter-class augmentation signal known as the L-band experiment, which the Quasi-Zenith Satellite System generates on an experimental basis for a limited time, were used as the reference values. A comparison between horizontal and vertical positioning errors among four receivers demonstrated that the vertical errors were larger than the horizontal errors. They did not differ among receivers, whereas the horizontal errors varied according to the characteristics of the receivers, particularly in mountainous areas; the errors tended to be larger when the terrain change at the measurement point was larger. The median effects of the vertical and horizontal errors on the calculated values of the radiation dose rate at the ground level were 3%-6% and 1%-5%, respectively, and the maximum possible effect of the positioning error was 20%-32%. The fact that the receiver with the highest number of available satellites had larger errors than the other receivers indicated that the elevation angles of satellites and the augmentation signals play an important role in improving the positioning accuracy when the number of available satellites reduces in mountainous areas. This study has provided insight into selecting a suitable GNSS receiver for surveying by vehicles such as helicopters, aircraft, and drones, which are required to perform 3D positioning in complex terrains.