1、機載探地雷達探測地下目標體的數值仿真和成像研究        【中文摘要】機載探地雷達用于探測地雷區、被未爆炸武器污染的地區等方面的研究在國外已經有很多成功的實例,在國內該方面的研究還未幾,尚處于起步階段。本論文的主要研究目的就是通過仿真的手段來驗證機載探地雷達探測地下目標體的有效性,從而為實際探測提供依據,起到指導性作用。本論文首先是采用FDTD方法,對二維情況下水平地表及起伏地表下的單一目標體以及多目標體分別進行了正演模擬,并對結果進行了解釋和分析,然后對測得的共偏移距剖面數據進行繞射掃描疊加偏移的成像研究,并

2、對該偏移方法的適用性進行了更深一步的討論。最后考慮了影響因素:儀器的動態范圍、飛機飛行速度的影響。本文的創新點:一、給出了利用高斯頻譜產生起伏界面的方法,并將這一程序與GPR正演模擬軟件Gprmax聯系起來。二、通過模擬分析,可知機載探地雷達用于地下探測是有效的。三、在繞射掃描疊加偏移方面,本文根據論文的需要對其進行了擴展,發展了分層偏移以及已知地表位置情況下的偏移方法。');【Abstract】 Ground Penetrating Radar is a kind of near-su*ce geophysical methodusing high-frequency electro

3、magnetic waves to determine the laws ofcomposition of su*ce. Because of its excellent resolution, * operation,the advantages of speed, it has been applied in various engineering problems.The operation platform of GPR can be separated into airborne, in-vehicle, holeunderground and multi-holes explora

4、tion, we often meet the latter fourcategories, but the airborne GPR is mainly used in surveying large areas or ininaccessible regions, for example, desert areas, permafrost areas or highmountain ranges. In addition, the airborne GPR could survey hydrogeologicalresource, map subsu*ce geomorphologic c

5、haracteristics, detect buriedobjects and underground installations. Specially needs to be pointed, theairborne GPR is related to the detection of martial objects, such as areas oflandmine and unexploded ordnance.Airborne GPR came into existence in the 1960s with the development ofice profiling radar

6、s by the Technical University of Denmark, and the ScottPolar Research Institute of Cambridge. The primary interest at the time was inthe profiling of ice layers at depths of several thousand feet. Ultra-widebandradars were developed slightly later when the goal moved to producingprofiles and imagery

7、 of the near sub-su*ce in normal soils. Afterward more institutes manufactured GPR in abroad, for example, the GPR system thatHamburg-harburg technical university operated was used by The FederalInstitute for Geosciences and Natural Resource, The system was successfullyemployed during various campai

8、gns in Antarctica, it was a successful trial thatproved the validity of airborne GPR.I use numerical simulation to simulate the mechanism of airborne GPRexploring underground objects, simulation is model experiment, when theresearchful system is expensive or there is big hazard in the experiment or

9、thesystem needs more time to be understood with the changed parameters,simulation is an effective method. Using airborne GPR to detect undergroundobjects needs expensive cost, so I select the method of simulation. Thenumerical simulation method is FDTD, its main idea is to discrete the Maxwellrotati

10、on equation in time and space domain, then the partial differentialequations is replaced by the differential, and solve the differential equation, thevalue of the EM field of each cell could be calculated. It can be used widely,almost the entire electromagnetic and microwave technology in all fields

11、 aswell as other technological and industrial fields. For the sake of the need ofresearch, I simulate single and multi-objectsairborne GPR response underdifferent irregular topography, The simulation model include the cavity modelunder 2D horizontal and irregular topography, the model of multi-objec

12、ts under2D horizontal and irregular topography.Later I deal with the common offset profile using migration imaging,because radar imaging is the focus of the reflected wave method, and it is readyfor obtaining geological image exactly. I use diffraction scan stacking migrationin the article, the diff

13、raction scan migration founds the base of ray theory, and itcan let reflected wave return to real position automatically. According toHuyghensprinciple, every reflection point underground is regarded as awavelet source, the diffracted wave that these wavelets sources bring could get to the topograph

14、y and be received by the receiver, and the time-distance curvesare hyperbola. When we use diffraction scan migration, we compartmentalizethe underground space to grid, and regard every grid point as a reflection point.When there are reflection inte*ces or reflection points, every traces amplitudeis

15、contiguous and in-phase stacking, the amplitude after stacking is increscent;Contrariwise, when there are no reflection inte*ces or reflection points, everytraces amplitude isnt contiguous and in-phase stacking, their amplitudescounteract one another, the amplitude after stacking is decrescent.First

16、ly, I use matlab code to produce the procedure of the irregulartopography, in order to integrate it with the numerical simulation software ofFDTD, thereby it produces the inner file that Gprmax can identify, these canfound base of the following irregular topography. Secondly, I simulate that theairb

17、orne GPR explores the model of cavity under the horizontal topography, theresult indicates that the common offset profile is clear, the following step ismigration imaging, first of all, suppose the medium is homogeneous mediumand the homogeneous medium is air, we can see the result, but the position

18、 ofthe cavity is errorless compare to the real position, then I use layered migration,and regard the air portion and the soil portion as homogeneous mediumrespectively, adopting the speeds of air and soil, the outcome arrivesanticipation aim, this model mainly proves the validity of the airborne GPR

19、exploring. Thirdly, I simulate that the airborne GPR explores the model ofcavity under the big relief and small relief respectively, and complete migrationimaging, it indicates when the relief becomes big, even if we adopt layereddiffraction scan stacking migration, the position of the object is wro

20、ng, and theoutcome has false interferer, so I decide to adopt the migration after savvyingthe position of the irregular topography, apropos of how to know the position ofthe irregular topography, as the article refers, we may utilize pulsed laserranging or aerophotogrammetry,. When we use this metho

21、d to complete migration, we arrive to anticipative effect, but compiling procedure is alsotroublesome. Fourthly, the article has a brief summary aims at the diffractionscan stacking migration: When we carry through the migration under thehorizontal topography, the divisiory grid and velocity are the

22、 most importantinfection factors. When we carry through the migration under the irregulartopography, in addition to the infection factors of the divisiory grid and velocity,the irregular topography also influences the result of imaging. If thetopographys fluctuant degree is big, the object imaging positions