Extended-range optical televiewer imaging of the NEEM deep ice borehole, Greenland

2010年8月，北格陵兰Eemian （NEEM）冰钻探项目钻孔到达冰盖底部，到达地表以下2438米的深度。因此，NEEM岩心是迄今为止钻取的最长的岩心之一，人们希望它能提供一个高分辨率的记录，记录贯穿最后（Eemian）间冰期的过去气候。通过观察岩心移除后留下的钻孔，可以提供有关岩心和当地冰盖物理组成的额外补充信息。罗伯逊地质有限公司（RGL）最近开发了一种用于采矿业的先进测井技术（光学电视观测；OPTV）。与之前的（定向）井眼视频技术相比，OPTV具有许多优势，因为它可以以非常高的分辨率（每像素小于1毫米）提供整个井眼壁的几何精确图像（即井眼周围和全长360度）。在过去三年中，申请人一直与RGL合作，使该设备适应在冰上使用，并将其应用于冰川和冰盖上的几个试验点。这些试点研究的结果完全改变了可以从冰井中恢复的信息，包括识别不同的冰类型，识别不同的层和结构，识别和表征井壁内的气泡和碎屑包裹体，尤其是提供从井壁中移除的岩心的定向虚拟图像（通过“滚动”和反转钻孔壁图像）。尽管OPTV在冰钻研究方面具有革命性的潜力，但由于探空仪本身的压力等级以及相对较轻（因此可运输）的电缆的信号通信等问题，该技术目前仅限于在深度小于1000米的地方使用。前一个问题现在已经解决，RGL目前正处于解决信号处理挑战的后期阶段，并将在2011年底开发一种扩展范围的OPTV系统（EOPTV）（见支持函）。这项小额拨款申请是为了将新的EOPTV系统应用于NEEM深井的整个长度（约2.5公里），既要评估新系统的性能，又要解决几个具体的科学问题（列在目标下）。

The North Greenland Eemian (NEEM) Ice Drilling Project borehole reached the base of the ice sheet in August 2010, hitting the bed at a depth of 2438 m beneath the surface. The NEEM core is therefore one of the longest ever drilled, and it is hoped that it will provide a high-resolution record of past climate extending through the last (Eemian) interglacial period. Additional complementary information relating to the core and the physical makeup of the local ice sheet can be provided by viewing the borehole that has been left following the removal of the core. An advanced technique for such logging (optical televiewing; OPTV) has recently been developed by Robertson Geologging Ltd (RGL) for use in the mining industry. OPTV has many advantages over previous (directional) borehole video technology in that it provides a geometrically accurate image of the entire borehole wall (i.e., 360 degrees around the borehole and along its full length) at a very high resolution (less than 1 mm per pixel). The applicant has, over the past three years, worked with RGL to adapt this equipment for use in ice and applied it to several test sites on glaciers and ice sheets. The results of these pilot studies have completely transformed the information that can be recovered from ice boreholes - including identifying different ice types, identifying different layers and structural generations, identifying and characterizing bubble and debris inclusions held within the borehole wall and, not least, providing orientated virtual images of the core removed from the borehole (by 'rolling' and inverting the image of the borehole wall). Despite the potential of OPTV to revolutionize ice drilling research, the technique is currently restricted to use at depths of less than 1000 m by issues relating to the pressure rating of the sonde itself and signal communications along an extended length of relatively lightweight (and therefore transportable) cable. The former issue has now been resolved, and RGL is currently in the late stages of solving the signal-processing challenges and will have an extended-range OPTV system (EOPTV) developed by the end of 2011 (see Letter of Support). This small-grant application is to apply this new EOPTV system to the full (~2.5 km) length of the NEEM deep borehole, both to evaluate the performance of the new system and to address several specific science questions (listed under Objectives).