Study On Full-waveform Imaging And Processing Of Time-domain Airborne Electromagnetic Data

Time-domain airborne electromagnetic method (AEM) is one geophysical surveymeans, which is based on the law of electromagnetic induction.The Aircraft is as ameans of delivery. AEM is high speed, low cost, has been widely used in mineralresources prospecting, oil and gas survey, geological mapping, environmentalmonitoring, engineering, hydrology and other fields.This article rely on the national863major projects “airborne geophysicalexploration technology system” sub-topics “study on the theory and design of systemof the time-domain helicopter airborne electromagnetic exploration research andpractice”, the time-domain airborne electromagnetic data full-wave imagingtechnology and data processing, the main research content and structure is as follows:First, the article describes the basic principles of time-domain airborneelectromagnetic method, contrast cited the structural characteristics and the range ofapplications of helicopter and fixed-wing time-domain airborne electromagneticdetection system. The full-wave time domain airborne electromagnetic response ofthe off-time response and on-time response. Step pulse waveform as the basis forcalculating the induced electromotive force is generated by off-time section shuts offthe receiving coil of the emission current with time of the attenuation curve. Using thecalculation results of the frequency domain to the time domain calculation method,based on the frequency-domain electromagnetic field the Hankel represents thetransient response of the form in the Laplace transform domain computation timedomain electromagnetic field, and then with GS transform do pull the Plath inversetransform, to calculate the transient process of the receiving coils within the inducedelectromotive force. Formula and Fourier transform, convolution theorem tear downthe on-time response formula to calculate any off-time response of the transmittedwaveform and on-time response calculated according to the frequency-domainvertical magnetic dipole electromagnetic response.Second, the article study full-wave imaging of the time-domain airborneelectromagnetic data and removal of the primary field.The response of the on-time and off-time exist binary problems with the changesin the conductivity, forward calculation response of a full wave in the case of differentflying height and conductivity, and then α-τ transform data, normalizedprocess,constructing a data table to calculate the conductivity through a look-up table method,through the depth of the formula to calculate depth results conductivity changes withdepth. Data the simulation construct three earth model, off-time response and on-timeresponse of the conductivity depth imaging, found that on-time response can indeedreflect the presence of shallow earth conductor.Rely on the calculation of the magnetic field of the energized circle coil tocalculate induced voltage of the transmitting coil in the three directions of X, Y, Z. Comparative analysis of the impact of the changes in the location of the transmittingand receiving coils of an induction voltage. Application predictive filtering algorithmto remove the first induction, using a flight, the flight parameters of structure matrix, afilter coefficient obtained by the least squares, then calculate the primary field and thecalculated primary field subtracted i.e. removal of a field-responsive.Third, the aiticle study on the data noise suppression technology of thetime-domain airborne electromagnetic.By comb filtering technology, removal of the early oscillations technology,removal of high-altitude background technology and polygon stacking technique tosuppress the noise of airborne electromagnetic data. Comb filtered by data filtering inthe frequency domain and then inverse Fourier transform to remove noise, and toeffectively remove the noise of the late channel data. The early oscillations removaltechnology First, the use of high-altitude flight emission current per channel data tocalculate the coefficient of each channel, each channel coefficient with currentinduced electromotive force detection under the flight altitude less took theopportunity to remove the oscillation. Trapezoid superimposed superimposed data,different time periods with different window width, the relative rectanglesuperimposed for both early data resolution and improved signal-to-noise ratio of thedata of the late.Fourth, image and suppres noise the data of the time-domain airborneelectromagnetic simulation of flight test data. Instrument Science and ElectricalEngineering, Jilin University, independent research and the JLATEM helicopter timedomain airborne electromagnetic exploration system simulation in Changchun Citysuburb Airlines flight experiments, the data processing flow, noise suppressionprocessing and imaging results, the results show that the noise suppression techniqueis superior to conventional data processing methods.