A Study On The Key Parameters Of Airborne Transient Electromagnetic Synthetic Aperture Imaging Method

The exploration in the mountain areas and ocean is becoming a research hotspot inGeophysics. Airborne transient electromagnetic has been widely used in the exploration of oreresources, regional geological mapping, hydrogeological investigation and environmentalexploration due to its fast speed, wide capability and feasibility in ocean prospecting. Thereare mainly two classes of interpreting method about the airborne transient electromagneticdata, and they are: Conductivity-depth transformations and Layered-earth inversion method.The thin-plate method belongs to the first class, this method uses a conductive thin plateto replace the homogeneous underground media and it’s an approximate simple and fastinterpreting method which uses apparent longitudinal conductance curves to divide earth layer.Starting from the basic theory of thin-plate model method, the definition of apparentlongitudinal conductance is given in this paper and the second derivative which is alsocalculated. Its second derivative curve will produce sharp peak at the interface of two earthlayer with different conductivity and it will form an event figure similar to the seismic event ifthe peaks of different curve is linked together. We call this process as apparent verticalconductance differential imaging, it can reflect the distribution of underground conductivityfaster and clearer than the traditional method.For the further optimization of the apparent vertical conductance differential imagingmethod, this paper introduced the conception of transient electromagnetic synthetic apertureimaging. It is derived from synthetic aperture radar. It overlies the signal of adjacent surveypoints by signal processing according to the fact that the signal of adjacent survey point hascorrelation over a same geology body for the purpose of raising signal to noise ratio andhighlighting the response of anomaly body hence improving distinguishability. Thisprocessing method developed the traditional interpreting method which is based on singlepoint data into a multi-coverage one which is based on all the data centered of the surveypoint.Different kinds of models are designed in this paper, and the data processing result isanalyzed and compared. An empirical formula calculating the maximum aperture length is also proposed which can be referred to when selecting an aperture boundary at practical work.A flume experiment is also accomplished simulating the working pattern of airborne transientelectromagnetic at the very last, and the result of the experiment demonstrated that thesynthetic aperture method can efficiently improve the precision of transient electromagneticimaging.