Multi-component Study Of Air-Ground Transient Electromagnetic Method System

Air-ground transient electromagnetic method system (AGTEM) is an advanced transientelectromagnetic measurement method that can achieve ground emission and air receiving.AGTEM employs a cable transmitter on the ground and an airborne receiver coil flown belowa helicopter or a UAV. Comparing to airborne and ground electromagnetic systems, the mainadvantage of the AGTEM system is that it does not fly a large transmitter loop that makes thepayload heavier and the survey logistics more expensive. The AGTEM system can possibilityto apply at relatively higher flight altitudes (>100m).This article based on the Maxwell’s equations in electromagnetic fields deduces theexpression of Air-ground system in frequency-domain electromagnetic field using large-loopsource device, and gives the expression of the time-domain electromagnetic field. Theexpression of time-domain we got is a double integration which inner integral is Hankelintegral and outer integral is ether sine integral or cosine integral. It can be solved, for thesetwo types of high oscillatory integrals, by conventional numerical methods, but it takes a longtime. In this paper, we use a linear digital filtering method to solve them, and verify that thelinear digital filtering method is an ideal one for its high computing speed and precision bycomparison with the analytical solution of the homogeneous half-space case. I wrote theone-dimensional forward program for the center point of the large-loop source in air-groundsystem to calculate the response in both frequency-domain and time-domain of both thehomogeneous half space and six kinds of typical cross-section of both two and three layers,detail analyzed the shape of different reception height response curve, and got some valuableconclusions, which have important guiding significance in processing and interpretation fortransient electromagnetic data.It shows that the acquisition of low-level, multi-component, multi-parameter,high-resolution, high-density and high-precision in integrated airborne geophysical surveyand interpretation is the direction of the airborne geophysical development based on theexploration and practice both in the country and abroad in recent years. And it should bedeveloped in a variety of geographical achieve large-scale, high-precision, multi-parameter, and multi-component integrated AEM measurements, to offer full-service for regionalgeology, mineral geology, hydrology, engineering, and environmental geology. In this paper,a large-loop source of air-ground system in both homogeneous and layered medium, and thenumerical method for the magnetic field in both vertical component and horizontalcomponent response of different offset are studied. I wrote a program to calculate thefrequency-domain and time-domain response of the non-center point of the loop source ofair-ground system of several typical geoelectric section, detail analyzed the influence betweenchanging of the receiver height and offset and the response curve shape, and summarized anumber of laws provide a theoretical basis for multi-component explanation, and lay thefoundation for follow-up work.