Integration Of Remote Sensing And Ground Penetrating Radar For Prospection Of Underground Archaeological Objects

In recent years,the space archaeology has been gradually developed and established with the dramatic development of space information technology.Noninvasive prospection of cultural relics is one important research topic of space archaeology.The non-invasive prospection techniques,such as geophysics,remote sensing(RS),Light Detection and Ranging(Li DAR),has been increasingly applied to for measuring and mapping characteristics of the soil and the archaeological remains therein,which provides solid technique support for archaeological prospection.Among these,ground penetrating radar(GPR)can effectively cover the shortages of RS which are limited prospection depth and inadequate spatial resolution for some cases,because it can produce successive and high-resolution data for imaging subterranean archaeological objects.In return,the broad view of RS can designate target survey areas for GPR.Therefore integration of GPR and RS for archaeological prospection is a significant trend in non-invasive prospection of cultural relics.However,like other noninvasive techniques they both have a major drawback: they do not give us any direct information about what is in the ground.What does a geophysical anomaly tell us about soil conditions at a certain depth? And how should we interpret the features recognized on a GPR image.So final verification by invasive techniques(direction observation of soil and archaeological remains found in it)is necessary.Some important issues about GPR archaeological prospection and integration with RS were researched in this paper,and the main research results are shown in the following:1.Response anomaly patterns on GPR profiles of archaeological objects with different geometric characteristics.In simulation experiment and prospection of the two true cultural relics,response anomaly patterns on GPR profiles of archaeological objects with different geometric characteristics were analyzed and summarized.According to the relative sizes of archaeological objects to antenna beam width of GPR,they can be grouped into point object,line object and plain object.If an archaeological object is relatively very small to antenna beam width,it can be regarded as a point object,and its anomaly on GPR profile is typically hyperbolic shape.If an archaeological object is relatively very large to antenna beam width,it can be regarded as a plain object.The anomaly often present as multi-layer texture,and the two edges of the plain object can raise respectively two branches of a hyperbolic anomaly.If the long axis of an archaeological object is much larger than antenna beam width and the short axis is smaller than or almost same with antenna beam width,it can be regarded as a line object.Its anomaly will represent as multi-layer texture or hyperbolic shape which is transition stage between point object and plain object.2.The effects of burial depths,materials of underground archaeological objects and soil water content to GPR prospection results.In order to test effects of burial depths,materials of underground archaeological objects and soil water content on GPR prospection,the simulation prospection experiment of underground archaeological objects was designed and carried out,and two cultural relics in different environment were prospected by GPR.A high soil water content not can decline not only the maximum penetrating depth of GPR but also eccentricity of hyperbolic anomaly raised by the archaeological object,which means narrower opening and more sharpen peak.The deeper an archaeological object is buried,the longer the real axis of its response hyperbola anomaly becomes.Therefore the deeper bury depth will lead to wider opening and less sharpen peak.In extreme cases,the hyperbola will transform into a straight line.The reflection signal intensity is related to the contrast of relative permittivity between archaeological objects and around media.Since the difference between metal archaeological objects and around soil is usually significant,a strong reflection signal especially will be generated.3.Working procedure of archaeological prospection integrating GPR,RS and traditional invasive field survey.The working procedure of archaeological prospection integrating GPR,RS and traditional invasive field survey was applied in investigating Longcheng site and it has been proved that the three techniques can complement each other and this working procedure can balance effectiveness and efficiency well in prospecting large ancient city sites.The working procedure is listed as the following:1)Remote sensing interpretation and extraction of archaeological objectsThe main aim of remote sensing interpretation and extraction is to recognize potential archaeological remains,and map their spatial distribution,which can designate target region for GPR prospection.2)GPR surveyBased on the spatial distribution and surrounding environment of potential archaeological objects,GPR survey can be planned scientifically in order to derive their information about shape,burial depth,and orientation and so on.These information is very useful for design of traditional field survey plan.3)Final verification by traditional field survey including core sampling,test pitting and trial trenchingCore sampling,test pitting and trial trenching should be carried out at the spot where anomalies are raised on GPR profile in order to observe and analyze soil samples according to their color,compactness,and inclusion.Sequentially the RS and GPR prospection results can be verified.