Geoscience Reference
In-Depth Information
DART stations in regions with a history of generating destructive tsunamis. The DART technol-
ogy was developed at NOAA's PMEL under the U.S. National Tsunami Hazard Mitigation Pro-
gram (González et al., 1998; http://nthmp-history.pmel.noaa.gov/index.html) to provide early
detection of tsunamis regardless of the source (http://www.ndbc.noaa.gov/dart/dart.shtm). A
DART station comprises an autonomous, battery powered, bottom pressure recorder (BPR) on
the sealoor and a companion moored surface buoy that forwards the data it receives acousti-
cally from the BPR to an onshore receiver via satellite links (Figure 4.5; see González et al., 1998).
The BPR collects and internally stores pressure and temperature data at 15-second intervals.
The stored pressure values are corrected for small temperature-related offsets and converted
to an estimated sea-surface height (the height of the ocean surface above the sealoor). The
BPR water height resolution is 1 mm in water depths to 6,000 m, and the maximum timing
error is 15 seconds per year.
The station has two data reporting modes: standard and event. In standard mode, data are
transmitted less frequently to conserve battery power. Event mode is triggered when internal
detection software in the BPR identiies anomalous pressure luctuations associated with the
passage of a tsunami. During event mode, all 15-second data are transmitted for the irst few
minutes, followed by 1-minute averages. If no further events are detected, the system returns
to standard mode after 4 hours.
There have been two types of operational DART stations: the irst generation DART
stations (DART I) became operational in 2003, but all six were replaced with the second genera-
tion DART stations (DART II) by early 2008. The DART II station has two-way communications
between the BPR and the TWCs/National Data Buoy Center (NDBC) using the Iridium com-
mercial satellite communications system (Meinig et al., 2005). The two-way communication
allows the TWCs to set stations into event mode in anticipation of possible tsunamis or to
retrieve high-resolution (15-second interval) data in 1-hour blocks for detailed analysis, and
allows near-real-time troubleshooting and diagnostics. NDBC receives the data from the DART
stations and distributes the data in near-real time to the TWCs via NWS secure communica-
tions and to other national and international users via the GTS. The data is also available on the
NDBC website, and event data is highlighted when a system has been triggered.
Adequacy of the Geographical Coverage of the DART Network
The NDBC completed, in a little more than two years, an upgrade and expansion of the
DART array from 6 DART I stations to the present 39 DART II stations, as shown in Figure 4.6.
The expansion was supported with funding from the Tsunami Warning and Education Act (P.L.
109-424). In addition, Figure 4.6 shows the locations of 9 DART stations purchased, deployed,
maintained, and operated by Chile, Australia, Indonesia, and Thailand.
Planning for the deployment and siting of the expanded DART network was initiated at a
workshop attended by representatives of NOAA, the USGS, and academia on July 6-7, 2005, in
Seattle (Geist et al., 2005). The central goal of the workshop was to determine an optimal net-
work coniguration that would meet multiple mitigation objectives, while addressing scientiic,
