Application of GPS in geomagnetic survey

Abstract

When measuring the geomagnetic declination, the azimuth of the reference mark must be measured. This paper briefly describes the principle of measuring the azimuth by the differential GPS (Global Positioning System), several test observations of GPS and the results. In geomagnetic survey in China during 2002∼2003, GPS was used in measuring the azimuth. Field observations by GPS were carried out during the period that satellite signals were better received. The statistical results of the GPS data at 135 stations in China show that the difference of the azimuths between 2 GPS measurements at various stations is 0.0 ∼5.9 and the average is 1.6 . The azimuthal accuracy measured by GPS in this paper is 0.1 , and it is much better than the azimuthal accuracy 1.0 given by Newitt et al. (1996). The observation results show that the azimuths measured by GPS are accurate and reliable; they are not related to the time-space changes. The geomagnetic declinations D at various stations were obtained based on the azimuths measured by GPS, and the standard deviation of the reduced value of D was < 0.4 . Using the reduced values, the 8-order spherical cap harmonic model and the 5-order Taylor polynomial model in China for D were obtained. In geomagnetic survey, GPS is also used in measuring the longitude, the latitude and the elevation at various stations.

Geomagnetic survey and geomagnetic model research in China

“…D I magnetometer is used for measuring the declination D and inclination I , the resolution is 0.1 and the accuracy is 0.2 . GPS is used for measuring the azimuth of the reference mark so as to determine the geomagnetic declination, as well as to measure the longitude, the latitude and the elevation at the station (Newitt et al, 1996;Gu et al, 2006), its vertical locating accuracy is 10 mm + 1 ppm and the horizontal locating accuracy is 5 mm + 1 ppm. The magnetometers are calibrated before and after the survey in order to determine the differences between these magnetometers and the standard one, and the differences were corrected in data processing.…”

Chinese Geomagnetic Reference Field 2020 by the Revised Surface Spline Method

“…A GSM-19T proton magnetometer with a sensitivity of 0.05 nT and an accuracy of 0.2 nT was used to measure F. A CTM-DI magnetometer was used to measure D and I with a sensitivity of 0.1 and an accuracy of 0.2 [35]. A PM-100 GNSS system was used to measure the longitudes, latitudes, and elevations of stations and also provide the direction of geographical north, which is needed to determine the geomagnetic declination [36]. All geomagnetic elements (F, D, and I) of each station were measured in 6 sets.…”

“…• N, 103-112 • E, with the amplitude up to 100 nT for F and Z. There is also a positive anomaly(35)(36)(37)(38)(39)(40)(41)(42) • N, 75-88 • E) near Tarim Basin, with the amplitude up to 150 nT for F and 200 nT for Z. There are three significant negative anomalies, the first one located in Qinling Mountains(30)(31)(32)(33)(34)(35) • N, 103-115 • E), the second one located in Tianshan Mountains (38-42 • N, 75-90 • E), and the last one located in the south of Tibet (27-30 • N, 78-100 • E).…”

Short-term Tests of Potassium dIdD Vector Magnetometer

“…For D and I measurements a null-method was used (Newitt et al 1996). Two high precision GPS receivers in differential mode were used for the determination of the azimuth of the reference mark (Gu et al 2006). One GPS was used as a reference mark, about 120 m away from the DI tripod (due to practical reasons), and a second GPS receiver was set on the tripod.…”