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地球信息科学学报 >

2018 , Vol. 20 >Issue 4: 489 - 495

DOI: https://doi.org/10.12082/dqxxkx.2018.170442

全国激光雷达大会特约稿件

基于LiDAR数据特征的湖相层三维地理信息提取

  • 刘强 , 1, 2, 3 ,
  • 傅学庆 2, 3 ,
  • 黄华芳 2, 3 ,
  • 党海燕 2 ,
  • 于国超 2 ,
  • 李仁杰 2, 3 ,
  • 张军海 , 2, 3
展开
  • 1. 河北师范大学 地理学博士后科研流动站,石家庄 050024
  • 2. 河北师范大学资源与环境科学学院, 石家庄 050024
  • 3. 河北省环境演变与生态建设实验室,石家庄 050024
*通讯作者：张军海（1964-）,男,硕士,教授,主要从事地理信息可视化理论及应用研究。E-mail:

作者简介：刘 强（1985-）,男,博士,讲师,主要从事泥河湾环境考古三维古环境重建理论及应用研究。E-mail:

收稿日期: 2017-09-21

  要求修回日期: 2018-02-26

  网络出版日期: 2018-04-20

基金资助

河北省高等学校自然科学青年基金项目(QN2016251)

河北师范大学博士启动基金

河北师范大学地理学博士后启动基金项目

收起

Three-dimensional Geographic Information Extraction of Nihewan Lacustrine Sediments Based on LiDAR Data

  • LIU Qiang , 1, 2, 3 ,
  • FU Xueqing 2, 3 ,
  • HUANG Huafang 2, 3 ,
  • DANG Haiyan 2 ,
  • YU Guochao 2 ,
  • LI Renjie 2, 3 ,
  • ZHANG Junhai , 2, 3
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  • 1. Postdoctoral research station of geography, Hebei Normal University, Shijiazhuang 050024, China
  • 2. College of Resources and Environment Science, Hebei Normal University, Shijiazhuang 050024, China
  • 3. Hebei Key Laboratory of Environmental Change and Ecological Construction , Hebei Normal University, Shijiazhuang 050024, China
*Corresponding author: ZHANG Junhai, E-mail:

Received date: 2017-09-21

  Request revised date: 2018-02-26

  Online published: 2018-04-20

Supported by

Natural Science Youth Fund Project of Hebei Education Department No.QN2016251

Doctor Start-up Fund of Hebei Normal University

Postdoctoral Startup Fund for Geography of Hebei Normal University.

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《地球信息科学学报》编辑部 所有
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摘要

泥河湾盆地的化石和旧石器遗址与泥河湾古湖、古河道有极强的相关性,如果发现了湖滨相和河流阶地的沉积地层,那么下一步很可能发现古人类活动留下来的化石和旧石器遗址。本文按照广义DEM的定义,将DEM的表达对象“地形表面”改为“泥河湾更新世湖相沉积层”称为湖相层DEM,泥河湾更新世湖相层DEM的建立可以大大推进泥河湾地区的古人类活动及古地理环境的研究。本文通过提取湖相层的三维地理信息,以禾尧庄剖面为例,研究了露头信息的泥河湾更新世湖相层三维地理信息提取方法。采用三维激光扫描仪采集剖面的三维地理信息,基于LiDAR点云的数据特征设计滤波方法,针对剖面采集点的距离近似相等,采用回波强度进行区分植被及土质,得到了一定的效果。在回波强度滤波后的结果基础上,进一步利用RGB信息设置阈值,区分植被和土质,得到了较好的效果。最后,经过手动去噪,得到干净、地层信息完整的剖面三维地理信息数据,可以做为湖相层DEM建模的基础数据。

关键词： 湖相沉积地层; 地面三维激光扫描; 点云特征; 禾尧庄遗址剖面; 泥河湾

本文引用格式

刘强 , 傅学庆 , 黄华芳 , 党海燕 , 于国超 , 李仁杰 , 张军海 . 基于LiDAR数据特征的湖相层三维地理信息提取[J]. 地球信息科学学报, 2018 , 20(4) : 489 -495 . DOI: 10.12082/dqxxkx.2018.170442

Abstract

The fossil and Paleolithic sites are strongly related to the ancient lakes and ancient rivers of Nihewan Basin. If the sedimentary formations of the lakeside facies and river terraces were discovered, then the next step is likely to find the fossils and Paleolithic sites of ancient human activities. The generalized definition of DEM as "terrain surface" is changed to " lacustrine sedimentary layer of the Nihewan basin" and named as Pleistocene lacustrine layer DEM. The establishment of the Pleistocene lacustrine layer DEM of Nihewan Basin can greatly promote the study on the ancient human activities and paleogeography in Nihewan area. In this paper, the first step of establishing the Pleistocene lacustrine layer DEM in Nihewan was studied. The three-dimensional geographic information of the lacustrine layer was extracted and the geological information of the Pleistocene lacustrine layer at the outcrop section of Heyaozhuang was studied as an example. The three-dimensional laser scanner was used to collect the three-dimensional geographic information of profile, and the filtering method was designed based on the LiDAR point cloud data. The distance between the sampling points was approximated and the echo intensity was used to distinguish the vegetation and the soil. On the basis of the result of the echo intensity filtering, the RGB information is used to set the threshold to further distinguish between the vegetation and the soil quality, and the better effect was obtained. After the final manual removal of noise, a clean and complete three-dimensional geographic information data of formation integrity can be obtained which can be used as the basic data for DEM modeling of lacustrine sediments.

Key words： lacustrine sediments; terrestrial 3D laser scanning; characteristics of point cloud; Heyaozhuang Site profile; Nihewan

1 引言

泥河湾盆地位于华北平原与内蒙古高原的过渡地带,在更新世期间所经历的大湖、萎缩、峡谷开通、侵蚀、冲积和风积的环境变迁过程与非洲东部著名的奥杜威峡谷（Olduvai Gorge）的环境变迁过程非常相似[1,2]。这一环境变迁过程使得泥河湾盆地沉积了自更新世早期以来的河湖相地层,含有丰富的哺乳动物化石和旧石器遗址[3,4]。泥河湾盆地因与古人类活动相关的化石、完整时间序列的旧石器和华北地区的第四纪地层而被世界知名[5,6]。泥河湾盆地被发现的遗址中的旧石器可以拼合[1],说明遗址中旧石器基本没被搬运过。这些化石和旧石器遗址位于湖积台地或残丘边缘被侵蚀出的冲沟或形成陡崖的剖面,分布于湖滨或河流阶地的沉积中,说明泥河湾盆地的古人类是依水而居。为此可以认为泥河湾盆地的化石和旧石器遗址与泥河湾古湖、古河道有极强的相关性,如果发现了湖滨相和河流阶地的沉积地层,那么下一步很可能发现古人类活动留下来的化石和旧石器遗址。
通常认为数字高程模型（Digital Elevation Model,DEM）是对地形表面的数字化表达,是经滤波除去植被、人造地物等之后的结果,表达的是出露于现代地表的地形高程和地层几何信息。本文按照广义DEM的定义[7],将DEM的表达对象“地形表面”改为“泥河湾更新世湖相沉积层”称为湖相层DEM。泥河湾盆地被发现的旧石器的时间序列连续,但是古人类的化石却发现的较少,湖相层DEM可以作为寻找古人类活动的湖滨相沉积地层的基础,也可以作为进一步排除构造、剥蚀影响后测量不同沉积相地层地理信息的基准数据,因此确定泥河湾盆地的湖相层DEM可以大力推进泥河湾地区的古人类活动及古地理环境的研究,泥河湾更新世湖相层DEM的确定工作具有重要意义。
泥河湾盆地更新世湖相层DEM与一般地形表面的DEM的建立方式不同,在盆地中部为湖积冲积平原,大部分湖相层直接暴露于地表,受剥蚀、人类活动等影响较大;在距离盆地中心较远的盆地边缘,由于山前堆积较厚,湖相层被冲洪积黄土、马兰黄土及表土覆盖,为此泥河湾盆地更新世湖相层DEM的建立需要在滤除植被、人造地物之后,进一步考虑剥蚀和沉积的影响。图1为泥河湾禾尧庄遗址附近某自然剖面地层,红色线部分为长期处于无氧状态下、细颗粒、灰绿色的湖相沉积地层,红色线以上为洪积黄土及表土。对于直接暴露于地表的湖相层,往往受剥蚀和人类活动的影响较大,且难以判断沉积地层序列间的接触关系。对于其他地区的湖相层,由于泥河湾盆地山前堆积较厚,宜利用盆地内因河流发育下切形成的自然剖面和170余处人工挖掘的遗址剖面[8]直接测量泥河湾更新世湖相层的地理信息,在排除构造及剥蚀的影响后,辅以电阻率测深数据确定泥河湾盆地更新世湖相层DEM。由于该项工作需要沉积学、第四系地质和测绘科学等理论和方法的综合应用,难度较大,本文仅考虑剖面处的泥河湾更新世湖相层地理信息提取。
Fig. 1 Demarcation between lacustrine sediments of Nihewan and Diluvial loess

图1 泥河湾湖相层与洪积黄土分界示意

传统测绘手段对于普通区域的地理信息采集具有良好的操作性,而剖面处的泥河湾更新世湖相层地理信息提取比较特殊,需提取的地理信息都位于剖面的侧面部分如图1所示。为了获得准确的地理信息,不破坏剖面原始形态,确保地理信息采集人员安全,地理信息采集宜使用摄影测量或三维激光扫描的方法。其中,三维激光扫描可以直接对剖面侧面进行三维密集采样,可快速获取具有三维坐标（X,Y,Z）和一定属性（反射强度等）的海量、不规则空间分布三维点云,是最直接和重要的三维地理空间数据获取手段[9]。在LiDAR硬件方面,激光发射方式分单点、线阵和面阵;激光源有双波长偏振高光谱分辨率激光雷达;载体为手持、地面、车载、机载、星载[9]。在数据处理方面,激光雷达点云数据分割与分类[10,11]、点云数据滤波[12]、LiDAR与多源数据配准/融合技术[13,14]、卫星激光雷达数据处理等[15]。在应用方面,文化遗产保护与修复、三维建模、森林冠层高度、胸径提取、植被生化组分垂直分布、电力巡线、隧道断面提取、交通标示识别与分类、路沿识别与车道估计等[16,17,18,19]。然而,基于LiDAR数据进行地层沉积层序界限识别以进一步确定某一沉积层的DEM的研究尚是空白,只能借鉴点云数据分割与分类、文化遗产保护、建筑物建模等其他研究的方法和技术。为解决剖面处的泥河湾更新世湖相层三维位置采集问题,本文基于地面三维激光扫描仪的点云数据特征,以泥河湾的禾尧庄遗址剖面[20]为例,研究湖相层、河流相层及覆盖表土的分布及纹理特征,并提取这些地层的地理信息。

2 研究区概况

2.1 泥河湾禾尧庄剖面地质地层特征

泥河湾禾尧庄遗址剖面（图2）是2013年考古挖掘的主探坑剖面,位于泥河湾盆地内的阳原县境内经纬度为40°04'18＂ N, 113°59'01＂ E,该地区曾经发现了大量的牛类化石,有人类猎取牛为食物的证据。剖面揭露地层总厚度为3.9 m,自上而下层序为：
Fig. 2 Pit profile of Heyaozhuang site

图2 禾尧庄遗址探坑剖面

（1）上更新统（Qp3）是厚1 m左右的冲洪积相沉积层,为土黄色、黄褐色含烁黄土、亚砂土夹粉砂沉积,具水平层理,与下伏地层不整合接触[20]。
（2）中更新统（Qp2）为2层,分别是河流相沉积层和泥河湾湖相沉积层。河流相沉积层为厚2.4 m的灰黄色、浅灰色、黄褐色及杂色含细烁的中细砂、粉砂和泥质薄层沉积,夹灰色泥河湾湖相粉砂质、泥质沉积团块或透镜体,具水平层理。该沉积层中含有大量云母碎片、炭屑和腐烂植物根系及少量火山碎屑颗粒,与下伏泥河湾湖相地层呈不整合接触。该层出土了上千件的石制品和哺乳动物化石,是重要的旧石器中期古人类文化层。泥河湾湖相沉积层,为浅灰色、灰色、灰绿色粉砂、含粉砂泥质沉积层。该剖面在该层的挖掘厚度为0.5 m,没有挖到该层底部[20]。
纵横向追踪这套河流相沉积层呈周边弯曲的不规则矩形大范围分布于禾尧庄遗址周围区域,南北长约1.2 km,东西宽0.7 km;在厚度变化上,其北、西、南三边的边部较薄,约2~2.5 m,向中东部逐渐加厚到4~5 m;从其顶、底界高度变化来看,边部比中东部高5~8 m。根据沉积物结构、厚度变化和顶底界高程变化等特征以及古人类文化遗存的分布位置推断,这套沉积层应为古河流发育过程中强烈侧蚀而形成的河湾相泥沙沉积物[20]。

2.2 点云数据采集

本文在2016年8月24日至30日对泥河湾侯家窑、马圈沟、油坊、禾尧庄等多处遗址进行了地理信息数据采集实验,并携带GNSS接收机一台、河北CORS卡一张,Riegl VZ-1000型地面三维激光扫描仪一台,Nikon D610相机一台。其中GNSS接收机与CORS卡一起确定所测点位的CGCS 2000坐标框架下的三维坐标,主要是三维激光扫描仪的三维坐标;三维激光扫描仪采集剖面处的点云数据,相机用来采集彩色纹理。Riegl VZ-1000型地面三维激光扫描仪为脉冲型扫描仪,水平方向扫描角度为360°,竖向扫描角度为从天顶30°到130°,幅度为100°。将Nikon D610相机采集的彩色纹理与三维激光扫描仪采集的点云数据进行矫正和配准,可以使点云与影像信息一一对应。图3为禾尧庄遗址剖面的赋色点云数据,图中心圆柱形标志为扫描仪所在工作位置。对比图2、3可知,经过3年自然侵蚀,禾尧庄遗址剖面某些部位生长出了杂草,由于雨水侵蚀的原因导致部分地层间分界发生轻微错乱,整体的地层接触关系仍然可以分辨。
Fig. 3 3D point cloud data acquisition of Heyaozhuang profile

图3 禾尧庄遗址剖面三维点云数据采集

3 数据处理与分析

本文使用的三维激光扫描仪可以获得的禾尧庄遗址剖面各点的三维坐标、回波强度（Amplitude）、反射率（Reflectance）,将点云数据与GNSS接收机和CORS卡测量的三维激光扫描仪的仪器坐标进行配准和转换后,可以得到CGCS2000坐标系下的三维点云,与相机配准后可以得到各点的影像颜色信息（RGB）。采集禾尧庄遗址剖面的三维地理信息的意义为：① 保留现在的遗址剖面三维信息,避免进一步的侵蚀破坏而损失信息;② 提取各地层的三维地理信息以进一步建立各地层DEM,尤其是湖相层DEM。

3.1 禾尧庄遗址剖面三维赋色点云数据预处理

禾尧庄遗址剖面含有现代沟谷塌垮堆积、黄土、河湾相沉积层和湖相沉积层,这4种地层在地质地貌学上有其自己的意义,而对于采集的点云数据来讲,都是对介质特性为土质的目标进行的采集。由于三维激光扫描仪是一种基于扫描头的射线型数据采集方式,在距离较近处采集的点比较密,在距离较远处采集的数据较稀疏。为了使数据分布均匀,首先应当对点云数据进行预处理,本文采用0.01 m等间隔取点的方式将原始点云数据进行重采样,得到图4的均匀分布的点云结果。
Fig. 4 Preprocessing results of Heyaozhuang 3D point cloud

图4 禾尧庄遗址剖面三维点云数据预处理结果

3.2 回波强度（Amplitude）滤除植被

Riegl VZ-1000型地面三维激光扫描仪提供的回波强度（Amplitude）是一个校准之后的值,是目标接收激光后反射信号的强度特性,定义为实际探测到的光幅值与检测阈值的比值,单位为分贝（dB）。当测量到在不同距离上的大的、平面目标时,回波强度随距离的变化而减少1/R2。例如,如果距离为50 m的回波强度为A,在100m处回波强度将减少A/4,1/4相当于6 dB,所以100 m处的回波强度比50 m处的回波强度低6 dB。点云回波强度除了与距离有关之外,与地物的介质属性也有较强的对应关系,不同的地物介质其回波强度不同。
由于禾尧庄遗址剖面的点云数据采集距离相差较小,本文将距离对回波强度的影响暂时忽略。禾尧庄遗址剖面的点云数据可以分为2类：植被数据和剖面土质数据。经测算可得该剖面的回波强度的值域为0.23~43.49 dB。本文采用反复试验的方式进行阈值选择,当选择阈值为33.5 dB时,小于33.5 dB的数据如图5中青色所示数据,可以看出滤除的基本是植被数据;当选择阈值为34 dB时,小于34 dB大于33.5 dB的数据如图5黄色所示数据,可以看出滤除的数据中有一定的剖面土质数据,这种现象可能是土质含水量的不同导致。
Fig. 5 Threshold selection of return wave amplitude

图5 回波强度阈值选择

设定阈值为33.5 dB,将33.5 dB以下的数据全部滤除（图6）。由图6可看出,经过回波强度阈值滤波后,部分植被数据已经滤除,然而仍然有一些植被数据没有滤掉,所以对于该剖面回波强度的阈值滤波只能滤除一定量的植被数据,不能将所有的植被数据滤除。
Fig. 6 Threshold filtering results of return wave amplitude

图6 回波强度阈值滤波结果

3.3 基于影像颜色信息（RGB）进一步处理

从图6可得出,使用回波强度的阈值进行滤波还不够将植被与土质区分开,而人眼可以直接判断出植被与土质的区别,人眼判断的重要信息依据是影像颜色信息,对黄土、河湾相沉积层和湖相沉积层进行随机采样分析。图7中列出了采样后的3种地层的RGB信息结果。
Fig. 7 RGB sampling of loess, fluvial facies sediments and lacustrine sediments

图7 黄土、河湾相沉积层和湖相沉积层的RGB采样

以采样得到的RGB信息,分别进行设置阈值范围,按照红、绿、蓝的顺序进一步滤波得到图8。图8中红色部分为使用红色阈值滤波去除的结果,绿色部分为使用绿色阈值滤波去除的结果,蓝色部分为使用蓝色阈值滤波去除的结果。
Fig. 8 Pluvial loess and river facies Nihewan formation contrast sampling

图8 RGB阈值滤波

由滤除之后的结果图（图9）可知,大部分的植被信息已经被滤除,然而仍然有一些噪点数据散乱分布。这些噪点中有一部分是由于采样的RGB阈值未能全部覆盖所有植被噪点,另一部分是由于在扫描物体边缘,由于多次回波和散射等造成的结果。
Fig. 9 Results of RGB threshold filtering

图9 RGB阈值滤波结果

显然仅使用阈值的方法综合回波强度、RGB信息进行滤波可以去除大部分的植被噪点,阈值的设置非常重要,阈值范围设置的比较大时,则会滤掉太多重要的信息,而阈值范围设置比较小时又会遗留很多噪点。经过手动编辑将图9中的散列噪点进行删除得到最终的剖面结果（图10）。
Fig. 10 Final result of Heyaozhuang profile

图10 最终的剖面结果

4 结语

为了确定泥河湾盆地更新世湖相层DEM推进泥河湾地区的古人类活动及古地理环境的研究,本文对泥河湾盆地的禾尧庄遗址剖面进行地理信息采集,旨在确定一种剖面处地理信息采集方案,以采集足够的泥河湾各地层的三维地理信息,进一步确定泥河湾地区的各地层的DEM,其中重点是更新世湖相层的DEM。基于植被与地层LiDAR点云数据的回波强度和影像颜色信息,设置合理的阈值,滤除了植被噪点。阈值滤波可以去除大量的噪点信息,结果基本可靠,而少量噪点主要由物体边缘多次回波和散射造成。经过手动进一步编辑,可去除散列噪点,得到最终的剖面三维模型。该模型含有各地层的三维坐标、回波强度、RGB的信息,可以作为进一步确定地层的接触关系,建立各地层的DEM的基础数据。确定泥河湾盆地更新世湖相层DEM的工作非常艰难,不过科学意义重大,提取湖相层的三维地理信息是确定泥河湾更新世湖相层DEM的第一步;确定泥河湾更新世湖相层DEM对于研究泥河湾地区的古地理环境、古人类迁徙,人类演化具有重大的推进作用。

The authors have declared that no competing interests exist.

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