The history of the development of real-time measurements of tsunamis in the deep ocean for the purpose of forecasting coastal tsunami impacts will be presented, with early history to include the various instruments tested to determine IF tsunamis could be measured in the deep ocean. The measurement of pressure changes induced by the tsunami required a high resolution pressure sensor installed on the seafloor, to provide a motionless environment that allowed the ocean to filter out higher frequency ocean waves. Instruments included bourdon tubes and vibrating crystals that rested on the seafloor and used the depth of the ocean as a pressure reference. Once deep ocean measurements were deemed possible, testing and evaluation was used to identify which technology was accurate, affordable, and reliable enough to be used for tsunami forecasting under tsunami warning conditions. National Oceanic and Atmospheric Administration (NOAA) had completed the research and development, including an operational prototype, by October of 2003, when the technology was transferred to NOAA operations. The first generation Deep-ocean Assessment and Reporting of Tsunamis (DART I) array consisted of six stations strategically located off Alaska, Oregon, and near the equator to detect tsunamis originating in the Chile/Peru area. The original DART array demonstrated its value within four months by measuring a small tsunami originating in Alaska and relaying these data to NOAA's Pacific Tsunami Warning Center in real time. The tsunami data indicated a nondestructive tsunami had been generated and evacuation of Hawaii's coastline was unnecessary, saving the cost of a nonessential evacuation. The December 2004 Indian Ocean tsunami, which killed over 235,000 people, led to the development of the second generation system, named DART II because of the two-way communication link from seafloor to desktop. Another impact of this horrific tsunami was the appearance of many technologies that were touted as being able to detect tsunamis in the deep ocean. Satellite-based technologies, radar-based technologies, and acoustic-based technologies were identified as tsunami detection technologies. However, these technologies could not measure tsunamis as accurately, reliably, and within time constraints required to forecast tsunamis in real time. The pressure-measurement-based DART technology prevailed as the most affordable and accurate technology to measure tsunamis for real-time forecasting. By 2008, NOAA had expanded the original DART array from 6 to 39 stations in the Pacific and Atlantic oceans. Because the U. S. wanted to make this technology available to all nations, NOAA licensed the patents for the technology and a commercial DART was manufactured by a U. S. private company that currently provides DART technology to foreign countries. Meanwhile, NOAA continued to make improvements to the original design, reducing operating costs and improving reliability. By 2010, over 40 tsunamis had been measured using DART technology and the third generation DART system had become a part of the operational global array. The DART ETD (Easy to Deploy) is more affordable and does not require large ships or highly specialized crew to deploy and maintain the operational arrays. These new developments in DART technology hold promise for a global network of DART stations supporting a standardized global tsunami warning system.
