Spherical cap harmonic analysis of regional magnetic anomalies based on CHAMP satellite data

We used CHAMP satellite vector data and the latest IGRF12 model to investigate the regional magnetic anomalies over China's Mainland. We assumed satellite points on the same surface （307.69 km） and constructed a spherical cap harmonic model of the satellite magnetic anomalies for elements X, Y, Z, and F over Chinese mainland for 2010.0 （SCH2010） based on selected 498 points. We removed the external field by using the CM4 model. The pole of the spherical cap is 36N° and 104°E, and its half-angle is 30°. After checking and comparing the root mean square （RMS） error of AX, AY, and AZ and X, Y, and Z, we established the truncation level at Kmax = 9. The results suggest that the created China Geomagnetic Referenced Field at the satellite level （CGRF2010） is consistent with the CM4 model. We compared the SCH2010 with other models and found that the intensities and distributions are consistent. In view of the variation off at different altitudes, the SCH2010 model results obey the basics of the geomagnetic field. Moreover, the change rate of X, Y, and Z for SCH2010 and CM4 are consistent. The proposed model can successfully reproduce the geomagnetic data, as other data-fitting models, but the inherent sources of error have to be considered as well.

Influence of higher-order ionospheric delay correction on GPS precise orbit determination and precise positioning

At present, Global Navigation Satellite Systems（GNSS） users usually eliminate the influence of ionospheric delay of the first order items by dual-frequency ionosphere-free combination. But there is still residual ionospheric delay error of higher order term. The influence of the higher-order ionospheric corrections on both GPS precision orbit determination and static Precise Point Positioning（PPP） are studied in this paper. The influence of higher-order corrections on GPS precision orbit determination, GPS observations and static PPP are analyzed by neglecting or considering the higher-order ionospheric corrections by using a globally distributed network which is composed of International GNSS Service（IGS） tracking stations. Numerical experimental results show that, the root mean square（RMS） in three dimensions of satellite orbit is 36.6 mme35.5 mm. The maximal second-order ionospheric correction is 9 cm, and the maximal third-order ionospheric correction is 1 cm. Higher-order corrections are influenced by latitude and station distribution. PPP is within 3 mm in the directions of east and up. Furthermore, the impact is mainly visible in the direction of north, showing a southward migration trend, especially at the lower latitudes where the influence value is likely to be bigger than 3 mm.

Autonomous navigation algorithm based on AUKF filter about fusion of geomagnetic and sunlight directions

Purpose-The geomagnetic field vector is a function of the satellite’s position.The position and speed of the satellite can be determined by comparing the geomagnetic field vector measured by on board three-axis magnetometer with the standard value of the international geomagnetic field.The geomagnetic model has the disadvantages of uncertainty,low precision and long-term variability.Therefore,accuracy of autonomous navigation using the magnetometer is low.The purpose of this paper is to use the geomagnetic and sunlight information fusion algorithm to improve the orbit accuracy.Design/methodology/approach-In this paper,an autonomous navigation method for low earth orbit satellite is studied by fusing geomagnetic and solar energy information.The algorithm selects the cosine value of the angle between the solar light vector and the geomagnetic vector,and the geomagnetic field intensity as observation.The Adaptive Unscented Kalman Filter(AUKF)filter is used to estimate the speed and position of the satellite,and the simulation research is carried out.This paper also made the same study using the UKF filter for comparison with the AUKF filter.Findings-The algorithm of adding the sun direction vector information improves the positioning accuracy compared with the simple geomagnetic navigation,and the convergence and stability of the filter are better.The navigation error does not accumulate with time and has engineering application value.It also can be seen that AUKF filtering accuracy is better than UKF filtering accuracy.Research limitations/implications-Geomagnetic navigation is greatly affected by the accuracy of magnetometer.This paper does not consider the spacecraft’s environmental interference with magnetic sensors.Practical implications-Magnetometers and solar sensors are common sensors for micro-satellites.Near-Earth satellite orbit has abundant geomagnetic field resources.Therefore,the algorithm will have higher engineering significance in the practical application of low orbit micro-satellites orbit determination.Originality/value-This paper introduces a satellite autonomous navigation algorithm.The AUKF geomagnetic filter algorithm using sunlight information can obviously improve the navigation accuracy and meet the basic requirements of low orbit small satellite orbit determination.

Characteristics of the crustal magnetic anomaly and regional tectonics in the Qinghai-Tibet Plateau and the adjacent areas

Study of the characteristics of the crustal magnetic anomaly in the Qinghai-Tibet Plateau and the adjacent areas helps better understand the lithospheric structure and evolution, as well as the regional geodynamic processes. Here we analyze the distri- bution laws of the crustal magnetic anomaly and its vertical gradient, the decay characteristics of the anomaly, the contribu- tions from different wavelength bands to the anomaly, and the relationship between the anomaly and the crustal regional tec- tonics in the plateau and nearby, based on a new and higher degree geomagnetic model NGDC-EMM-720-V3 constructed from the surface, aeromagnetic, marine and satellite survey data. The results reveal that the positive and negative anomalies in the Qinghai-Tibet Plateau are weak, while those of the surrounding areas are strong. The boundary agrees well with the border of the plateau regional tectonics. The anomaly is nearly east-west in the central and western plateau, arc-shaped in the south- western and eastern, and nearly north-south in the southeastern, consistent with the tectonic trends. There are strong negative anomaly loci in the east and west syntaxis, whereas no significant differences exist among the Cenozoic blocks in the plateau interior. No direct correspondence exists between the anomaly and the crustal depth. On the background of a weak magnetic anomaly in the plateau, relatively stronger short wavelength fields from the shallower crust are overlapped in the Lhasa, Qilian, Qaidam, and Sichuan-Yunnan rhombic blocks. A strong negative anomaly in the east-west direction is distributed along the Himalayas, mainly caused by the middle and long wavelength bands in the deep and central crust. The magnetic structural lay- ers are stable in the Sichuan and Tarim basins. The anomalies at different altitudes over the southern plateau vary strongly, showing a drastic variation in the magnetic structure from the deep crust to the shallow crust.