Abstract
Abstract The geomagnetic survey at 135 stations in China were carried out in 2003. These stations are with better environmental condition and small magnetic field gradient (<5 nT/m). In the field survey, the geomagnetic declination D, the inclination I and the total intensity F were measured. Ashtech ProMark2 differential GPS (Global Positioning System) was used in measuring the azimuth, the longitude, the latitude and the elevation at these stations. The accuracy of the azimuth is 0.1′. The geomagnetic survey data were reduced using the data at geomagnetic observatories in China. The mean standard deviations of the geomagnetic reduced values are: <1.5 nT for F, <0.5′ for D and I. Using the geomagnetic data which include the data at 135 stations and 35 observatories in China, and the data at 38 IGRF (International Geomagnetic Reference Field) calculation points in China’s adjacent regions, the Taylor polynomial model and the spherical cap harmonic model were calculated for the geomagnetic field in China. The truncation order of the Taylor polynomial model is 5, and its original point is at 36.0°N and 104.5°E. Based on the geomagnetic anomalous values and using the method of spherical cap harmonic (SCH) analysis, the SCH model of the geomagnetic anomalous field was derived. In the SCH model, the pole of the spherical cap is at 36.0°N and 104.5°E, and the half-angle is 30°, the truncation order K= 8 is determined according to the mean square deviation between the model calculation value and the observation value, the AIC (Akaike Information Criterion) and the distribution of geomagnetic field.
Highlights
The geomagnetic survey and the geomagnetic field model are the foundation in geomagnetic research
The distribution characters of various geomagnetic components can be seen from Fig. 2 that: the declination D and the east component Y are basically distributed along the longitude; D decreases from 8◦ in the west to −12◦ in the east; Y decreases from 2,000 nT in the west to −4,000 nT in the east
4.2 Result Using the above geomagnetic data, which include the data at 135 stations and 35 observatories in China, and the data at 38 International Geomagnetic Reference Field (IGRF) calculation points in China’s adjacent regions, the spherical cap harmonic model is calculated
Summary
The geomagnetic survey and the geomagnetic field model are the foundation in geomagnetic research. The geomagnetic surveys were carried out in some regions of China since the beginning of the 20th century (Chen, 1944; Chen and Liu, 1948). The geomagnetic surveys in the whole China were carried out once every 10 years on the average during 1950∼2000 (Tschu, 1979; An, 2001). In order to compile China geomagnetic chart for 2005.0, the geomagnetic surveys in China were carried out during 2002∼2004. Modern equipments including GPS were used in geomagnetic survey. A lot of geomagnetic survey data with better accuracy and stability were obtained
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