A Low-Power Global Positioning System-Acoustic Payload to study the subduction zones offshore the Pacific Northwest and Alaska

巨大的俯冲带地震发生在日本、智利和早期的苏门答腊岛近海，由于地震本身和随之而来的海啸造成了广泛的破坏。类似的俯冲带断层位于太平洋西北部近海，即卡斯卡迪亚俯冲带（CSZ）。它最后一次破裂是在1700年，远早于人口密集社区的广泛建立。从那时起，CSZ以每年几厘米的速度在地壳中建立弹性应变。在未来，这种储存的弹性能量可能会以强烈的地震和海啸的形式释放出来。大部分弹性应变在海岸附近的海底积聚。通过测量这种应变在近海的缓慢积累，可以更好地了解潜在的地震和海啸风险。通过结合海面平台上的全球定位系统和声波测距系统，以及海底的声波应答器，可以测量弹性应变的累积。小型（冲浪板大小）海浪和太阳能平台现在可以取代大型船只进行大量数据收集。然而，这需要重新设计机载电子元件，使其更小，功耗更低，这是该项目的目标。全球定位系统-声学（GPS-A）方法已被应用于波浪滑翔机，这是一种遥控的、波浪和太阳能驱动的海面飞行器。波浪滑翔机的资金将持续到2017年，用于测量卡斯卡迪亚俯冲带三个海底站点的板块变形。2014年9月，我们在俄勒冈州中部90海里的一个3000米深的地点收集了30小时的GPS和声学数据。初步结果证实，在卡斯卡迪亚，波浪滑翔机可以替代高成本的船只，也可能在全球其他地区使用。然而，我们发现，目前的gps -惯性导航系统（GPS-INS）和波浪滑翔机上的计算机的功率需求约为22瓦(W)。这将数据收集限制在24-30小时内，在660瓦时的波浪滑翔机电池耗尽之前。此时，GPS-A的操作必须暂停2-3天，同时太阳能电池板为机载电池充电。我们和日本研究人员的研究表明，厘米级定位需要4-5天的GPS-A测量。由于连续3天充电仅需~24小时就必须暂停数据采集，因此单个站点累积5天的GPS-A数据采集需要16-20天。加上3-5天的过境时间，在卡斯卡迪亚的3个月的夏季天气窗口中，只能访问和测量3到5个GPS-A站点。这使得天气延误、机械问题等的应急时间很少。随着越来越多的海底站点在卡斯卡迪亚近海被提出和增加，低效率被放大了。该项目将用仅消耗6- 8w的低功耗版本取代现有的GPS-INS和板载CPU。GPS-A数据可以连续收集5天。当波浪滑翔机在海底站点之间移动时，机载电池会在几天内充电。这是一种有效的操作方法，可用于卡斯卡迪亚、阿留申群岛和其他潜在地区。

Great subduction zone earthquakes offshore Japan, Chile, and earlier Sumatra caused extensive damage due the earthquake itself and the resulting tsunami. A similar type of subduction zone fault lies offshore the Pacific Northwest, the Cascadia Subduction Zone (CSZ). It last ruptured in 1700 long before the extensive establishment of populated communities. Since then the CSZ has been building up elastic strain in the crust at the rate of a few centimeters per year. In the future, this stored elastic energy will likely be released as a powerful earthquake and tsunami. Much of the elastic strain is accumulating the seafloor offshore the coast. By measuring the slow buildup of this strain offshore, a better understanding of the potential earthquake and tsunami risk can be established. By combining the Global Positioning System and an acoustic ranging system on a sea surface platform, and acoustic transponders on the sea floor, the elastic strain buildup can be measured. Small (surfboard-size) wave- and solar-powered platforms can now replace large ships for much data collection. However, this requires re-engineering the onboard electronic components to be smaller and lower power, which is the goal of this project. The Global Positioning System-Acoustic (GPS-A) approach has been adapted to a Wave Glider, a remotely controlled, wave- and solar-powered sea-surface vehicle. The Wave Glider is funded through 2017 to measure plate deformation at three seafloor sites in the Cascadia Subduction Zone. In Sept. 2014, we collected 30 hours of GPS and acoustic data at a 3000-m-deep site 90 Nm offshore central Oregon. Preliminary results validate the Wave Glider as a replacement for high-cost ships in Cascadia, and likely at other global sites. We found, however, the power requirements of the present GPS-Inertial Navigation System (GPS-INS) and the computer onboard the Wave Glider draw about 22 Watts(W). This limits data collection to 24-30 hours, before the 660 Watt-Hour battery bank aboard the Wave Glider is depleted. At this point, GPS-A operations must be suspended for 2-3 days, while the solar panels recharge the onboard batteries. Our research and that of Japanese researchers demonstrated that 4-5 days of GPS-A measurements are needed for centimeter-level positioning. Because data collection must be suspended after only ~24 hours to charge batteries for 3 days, it takes 16-20 days to collect the cumulative 5 days of GPS-A data at a single site. Adding 3-5 days for transiting between sites, only three to five GPS-A sites can be visited and measured over a 3 month summer weather window in Cascadia. This allows little contingency time for weather delays, mechanical problems, etc. As more seafloor sites offshore Cascadia are proposed and added, the inefficiency is magnified. This project will replace the existing GPS-INS and onboard CPU with low power versions that consume only 6-8 W. GPS-A data could then be collected continuously for up to 5 days. The onboard batteries are recharged over the few days as the Wave Glider transits between seafloor sites. This is an efficient operational approach for use in Cascadia, the Aleutians, and potentially other regions.