At a time when a bomb smuggled by trristsis as big a concerm as one from a foreign power, delivered by missile orairplane, an attack at a port is definitely a more likely scenario, says ThomasCartledge, a nuclear engineer with the U.S. Defense Threat Reduction Agency(DTRA) in Fort Belvoir, Virginia. But forensic experts, who rely largely onnuclear test data collected years ago in Western deserts, lack a clear pictureof how energy from a detonation would propagate in the highly saturated geologyof many U.S. port cities. To remedy that, DTRA last October quietly stagedHumming Terrapin: a 2-week test series at the Aberdeen Proving Ground inMaryland that detonated nearly 2 metric tons of conventional explosives tosimulate nuclear blast effects in shallow water.
Since the 9/11 attacks, the U.S. govermment has mounted a major effort toprevent a nuclear bomb from being smuggled into a port. It has ouftitted pointsof entry with radiation detectors, and it is working with foreign ports towarda goal of having all U.S.-bound cargo scanned for nuclear materials beforedeparture. But it's well nigh impossible to track the myriad small craftfitting in and out of the 361 U.S. ports and 153,000 kilometers of openshoreline. "There are a zillion fishing boats that leave U.S. ports andnobody inspects them when they come home," says Matthew Bunn, a specialiston nuclear terrorism at Harvard University's Belfer Center for Science andIntermnational Affairs. "If there is highly enriched uranium metal that'sshielded and below the water line, it's going to be really tough to detect atlong range."
In case the unthinkable happens, a sensor array called Discreet Oculus that isbeing installed in major U.S. cities would capture key forensic information.The array, which DTRA is still developing, would Tecord radiation and seismicwaves emanating from the blast. "Discreet Oculus is up and runningin several U.S. cities now," Cartledge says. A sister system--- a portablearray that runs on battery or solar power called Minikin Echo--will be deployedat major events such as the Olympics or the Super Bowl. Data from Cold War-eranuclear testing and simulations are being used to calibrate the sensors.
Yet past U.S. testing is a poor proxy for detonations at a port, says TamaraVanHoose, a U.S. Army major and nuclear engineer at DTRA. A closer analog is alttle known campaign in 1963-64 in which the U.S. Air Force conducted a seriesof detonations of as much as 10 tons of chemical explosives at the bottom ofLake Superior. The tests offered a wealth of data on how seismic waves traversethe land-water interface, but they "were not instrumented to meet ourneeds," VanHoose says.
Humming Terrapin aims to fill that gap. VanHoose and colleagues set up DiscreetOculus and two Minikin Echo arrays at Aberdeen, adding hydrophones, which arenot currently included in either array. Another set of sensors probed howseismic signals ripple through East Coast rock layers. "These are wet-typegeologies versus the granite geologies that we see out at the typical desertsites where we've done historic testing," VanHoose says.
The word 'myriad' in line 5, para.2, is closest in meaning to_________.
A、unscreened
B、untold
C、unregistered
D、unguided
【正确答案】：B
【题目解析】：myriad无数的；untold数不清的。