SUBSURFACE VALLEYS AND GEOARCHEOLOGY OF THE EASTERN SAHARA REVEALED BY SHUTTLE RADAR
SUBSURFACE VALLEYS AND GEOARCHEOLOGY OF THE EASTERN SAHARA REVEALED BY SHUTTLE RADAR
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DOI：
10.1126/science.218.4576.1004
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发表时间：
1982-01-01
期刊：
影响因子：
56.9
通讯作者：
BLOM, R
中科院分区：
文献类型：
--
作者：
MCCAULEY, JF;SCHABER, GG;BLOM, R
1981年11月，哥伦比亚号航天飞机上搭载的航天飞机成像雷达（SIR-A）穿透了撒哈拉东部极其干燥的塞利马沙丘、沙丘和流沙，揭示了以前未知的埋藏山谷、地质结构和可能的石器时代占领地点。从几厘米到几米厚的风吹沙下的基岩和砾石表面的雷达反应描绘了充满沙子和冲积物的山谷，有些山谷几乎和尼罗河谷一样宽，也许和第三纪中期一样古老。现在已经消失的主要河流系统雕刻这些大山谷可能完成了大部分的侵蚀剥离这个非常平坦，极度干旱的地区。欠适合和切割干河谷，许多叠加在大山谷，代表间歇性流水的侵蚀，可能在第四纪洪积。与冲积层中的土壤有关的石器时代文物表明，干谷附近的地区可能是早期人类居住的地点。古老的排水网络的存在下，砂层提供了地质解释的位置，许多干盐湖和现今的绿洲，已成为中心的插曲人类居住。干砂和土壤的雷达穿透力随入射信号的波长（SIR-A系统为24厘米）、入射角和材料的电特性而变化，这在很大程度上取决于含水量。根据实验室对Selima Sand Sheet样本的电特性测量，计算得出的干砂和颗粒的雷达穿透深度至少为5米。最近（1982年9月）在埃及进行的实地研究证实，SIR-A信号在Selima沙丘和流沙中的穿透深度至少为1米，在沙丘中的穿透深度至少为2米或更深。
The shuttle imaging radar (SIR-A) carried on the space shuttle Columbia in November 1981 penetrated the extremely dry Selima Sand Sheet, dunes, and drift sand of the eastern Sahara, revealing previously unknown buried valleys, geologic structures, and possible Stone Age occupation sites. Radar responses from bedrock and gravel surfaces beneath windblown sand several centimeters to possibly meters thick delineate sand- and alluvium-filled valleys, some nearly as wide as the Nile Valley and perhaps as old as middle Tertiary. The now-vanished major river systems that carved these large valleys probably accomplished most of the erosional stripping of this extraordinarily flat, hyperarid region. Underfit and incised dry wadis, many superimposed on the large valleys, represent erosion by intermittent running water, probably during Quaternary pluvials. Stone Age artifacts associated with soils in the alluvium suggest that areas near the wadis may have been sites of early human occupation. The presence of old drainage networks beneath the sand sheet provides a geologic explanation for the locations of many playas and present-day oases which have been centers of episodic human habitation. Radar penetration of dry sand and soils varies with the wavelength of the incident signals (24 centimeters for the SIR-A system), incidence angle, and the electrical properties of the materials, which are largely determined by moisture content. The calculated depth of radar penetration of dry sand and granules, based on laboratory measurements of the electrical properties of samples from the Selima Sand Sheet, is at least 5 meters. Recent (September 1982) field studies in Egypt verified SIR-A signal penetration depths of at least 1 meter in the Selima Sand Sheet and in drift sand and 2 or more meters in sand dunes.