基于岩性光谱特征的雄安新区地面古河道识别研究

A Study of Paleochannels Interpretation by the Spectrum of Lithology in Xiongan New Area

雄安新区地面古河道与河漫滩岩性分别以砂土和黏性土为主,两种岩性所含矿物成分对电磁波的反射率不同。将地表岩性调查与光谱采集分析相结合,捕捉了这两种岩性在遥感影像中反射光谱的差异,在此基础上识别了古河道,并利用钻孔数据加以验证分析。结果表明:雄安新区表层砂土和黏性土在TM影像B5波段的DN值差值最大,该波段可作为识别河道砂体的必选波段;综合考虑波段信息量、波段之间信息重复程度,R(4)G(5)B(1)组合下河道砂体的形迹清晰可辨;钻孔数据与遥感解译结果吻合,岩心揭露的古河道发育深度在3.2~8.7 m之间;研究区古河道总体较发育,河道宽度多在0.5~2.0 km之间,多处分叉和汇聚后呈辫状河形态,河网密度约0.26 km/km^2;钻孔剖面显示河道地势高于河漫滩,属条状高地型古河道,河道有"游荡"痕迹;古河道的发育位置控制着区内居民地的分布。

The paleochannels and floodplains in Xiongan New Area are mainly composed of sand and clay,respectively.Mineral composition of the two kinds of lithology shows difference in their spectral reflectance.In this paper,the approaches of field survey and spectral analysis were combined to detect the difference of spectral reflectance of sand and clay.On such a basis,paleochannels were interpreted and were proved by boreholes.According to results obtained,Landsat TM B5 has the largest difference of DN value between sand and clay,so it could be the preferred band to identify channel sand body.Considering the amount and repeatability of spectral information,optimal bands combination for identifying paleochannel is R(4)G(5)B(1);The boreholes show that the surface sand layer is 3.2~8.7 m thick in the interpreted paleochannel area,which fit together with the RS interpretation;On the whole,paleochannels in the study area are well developed in the form of braided river,the density of paleo river system is about 0.26 km/km2,and the width of them ranges from 0.5 to 2.0 km;Borehole profile shows that the terrain of paleochannels is higher than that on both sides,so they could be classified as striped highland paleochannels;There are obvious traces of migration and diversion between rivers.The development of ancient rivers controls the distribution of residential areas.