Geoscience Reference
In-Depth Information
12 of the 39 DART station buoys were nonoperational despite the four-year design lifetime of
the DART II systems.
Maintenance occurs in the summer months, accounting for the annual cycle in Figure 4.7.
The declining trend in performance is emphasized in Figure 4.8 that depicts the median age of
the deployed DART stations as increasing while the median age of failed systems has declined
below the median age of deployed systems and hovers around one to two years. A system
availability of 69 percent is signiicantly below the network performance goal of 80 percent,
which perhaps is not surprising for such a large, new, and admittedly hurriedly-deployed set
of complex systems that are deployed in very harsh environments. (For comparison, the effort
to establish a German Indonesian Tsunami Early Warning System (GITEWS; http://www.gitews.
de/index.php?id=5&L=1) has expended more than €55 million over the past ive years, result-
ing in deployment of a single open-ocean tsunami sensor that has been operational for only
six months to date, in 2007-2008.)
The issue of low network performance is exacerbated by the fact that clusters of nearby
DART stations tend to be nonoperational for many months, leaving large gaps in DART cover-
age. For example, ive stations cover the Aleutian Islands west of the Dateline, past the Kuril
700
653
600
563
529
500
Median Age of
Deployed Moorings
Median Age of
Failed Moorings
496
438
400
410
300
273
274
200
100
0
2006
2007
2008
2009
2006
(15)
(1)
2007
(30)
(4)
2008
(39)
(9)
2009
(39)
(15)
Number of Deployed Stations:
Number of Mooring Failures:
FIGURE 4.8
Median age of deployed DART II moored systems and median age of failed DART II moored
systems. SOURCE: National Data Buoy Center, NOAA.
