Two Methods to Solve the Ionospheric Electron Concentration Horizontal Gradient at Chongqing

The electron concentration horizontal gradient vector of the ionosphere and its south-north and east-west components over Chongqing station are analyzed and calculated, using the first approximation, time correlation and space correlation and another approach introduced. And then, the validity of the two methods is analyzed and compared.

A Comparative Structural Study of Southern Region Shallow Basement of the North-Kivu Province (DR Congo) by Gravity and Magnetic Data Analysis

The aim of this study is to characterize the subsoil in the southern region of the North-Kivu province (DR Congo). Gravity and geomagnetic data were used in this study. Five different filters—the horizontal gradient magnitude, the analytic signal, the tilt derivative, the horizontal derivative of tilt derivative and the tilt angle of horizontal gradient—enabled us to delineate the gravity and magnetic anomaly sources present in the shallow subsurface of the study area. The plains of the Rutshuru territory are dominated by sources of weak gravity anomalies and sources of very weak magnetic anomalies located almost in the same places. The southern part of Rutshuru territory and a large part of Masisi territory are underlain by shallow sources of high gravity and magnetic anomalies. Gravity and magnetic anomaly sources are almost identical in the study area. The shallow sources of gravity and magnetic anomalies encountered in our study area are more or less linear and connected. The numerous gravity and magnetic lineaments present in our study region have three major directions: oriented East-West, North-South and North-East-South-West.

An initial investigation of the non-isotropic feature of GNSS tropospheric delay

Tropospheric delay is a significant error source in Global Navigation Satellite Systems(GNSS)positioning.Slant Path Delay(SPD)is commonly derived by multiplying Zenith Tropospheric Delay(ZTD)with a mapping function.However,mapping functions,assuming atmospheric isotropy,restrict the accuracy of derived SPDs.To improve the accuracy,a horizontal gradient correction is introduced to account for azimuth-dependent SPD variations,treating the atmosphere as anisotropic.This study uncovers that,amidst atmospheric dynamics and spatiotemporal changes in moisture content,the SPD deviates from that based on traditional isotropy or anisotropy assumption.It innovatively introduces the concept that SPD exhibits non-isotropy with respect to azimuth angles.Hypothesis validation involves assessing SPD accuracy using three mapping functions at five International GNSS Service(IGS)stations,referencing the SPD with the ray-tracing method.It subsequently evaluates the SPD accuracy with horizontal gradient correction based on Vienna Mapping Function 3(VMF3)estimation.Lastly,the non-isotropic of SPD is analyzed through the ray-tracing method.The results indicate the smallest residual(1.1–82.7 mm)between the SPDs with VMF3 and those with the ray-tracing.However,introducing horizontal gradient correction yields no significant improvement of SPD accuracy.Considering potential decimeter-level differences in SPD due to non-isotropic tropospheric delay across azimuth angles,a precise grasp and summary of these variations is pivotal for accurate tropospheric delay modeling.This finding provides vital support for future high-precision tropospheric delay modeling.

Transformations between Aeromagnetic Gradients in Frequency Domain

Aeromagnetic gradients are often used to enhance details or add new insights for interpretation. The gradients may be measured or derived from the total field or from transformation between horizontal and vertical gradients. At present, vertical, horizontal, and triaxial aeromagnetic gradiometers are in operation throughout the world, while the first two are used more widely. Transformations between horizontal and vertical gradients are needed for acquiring three gradient components or for checking the validity of measured gradients. Transformation of potential field by fast Fourier transform technique in frequency domain is popularly used; however, when applied to transforming between gradients, there is a problem that needs resolving. Because those expressions of transform operators are undefined when u or v is equal to zero or u and v are simultaneously equal to zero （u is the frequency in x-direction, and v is the frequency in y-direction）, the operators cannot be sampled at these frequencies. Consequently, the transformation cannot be implemented by fast Fourier transform technique directly. In this article, shift sampling theory is employed for resolving this problem. Model test results show that the technique has good accuracy, and the real case of transformation indicates that the computed results agree better with the measured gradients; it demonstrates not only the effective- ness of method but also the reliability of the measured gradients.

Structural Setting of the South-West Cameroon Using Satellite Potential Field Derived from SGG-UGM-2 Gravity Data

This study aims to improve knowledge of the structure of southwest Cameroon based on the analysis and interpretation of gravity data derived from the SGG-UGM-2 model. A residual anomaly map was first calculated from the Bouguer anomaly map, which is strongly affected by a regional gradient. The residual anomaly map generated provides information on the variation in subsurface density, but does not provide sufficient information, hence the interest in using filtering with the aim of highlighting the structures affecting the area of south-west Cameroon. Three interpretation methods were used: vertical gradient, horizontal gradient coupled with upward continuation and Euler deconvolution. The application of these treatments enabled us to map a large number of gravimetric lineaments materializing density discontinuities. These lineaments are organized along main preferential directions: NW-SE, NNE-SSW, ENE-WSW and secondary directions: NNW-SSE, NE-SW, NS and E-W. Euler solutions indicate depths of up to 7337 m. Thanks to the results of this research, significant information has been acquired, contributing to a deeper understanding of the structural composition of the study area. The resulting structural map vividly illustrates the major tectonic events that shaped the geological framework of the study area. It also serves as a guide for prospecting subsurface resources (water and hydrocarbons). .