Volume 3, Issue 3 April 2003

2003
2002
2001

Sensor Networks from the Silk Road to the Dead Sea by David Pescovitz Printer-friendly version The painted walls and ceilings in China's Cave Temples of Mogao are slowly crumbling. Courtesy Steven D. Glaser A pair of thousand-year-old historic sites in Israel and China will soon be home to some of the most futuristic technology developed by UC Berkeley engineers. Professor Steven D. Glaser of the Department of Civil and Environmental Engineering and the Center for Information Technology Research in the Interest of Society (CITRIS) is preparing to deploy peer-to-peer networks of tiny sensors in Israel's Masada hilltop fortress and the Buddhist cave temples near Dunhuang in Chinese Central Asia. The goal is to help prevent these ancient sites from crumbling into the dustbin of history. Over the next few months, Glaser and his team will visit the distant locales to install arrays of UC Berkeley Smart Dust Motes, tiny sensors outfitted with wireless radios and sensors that keep a constant vigil on temperature, barometric pressure, humidity, and vibration. Professor Kris Pister, inventor of the Motes, recently founded a company, Dust Inc., to commercialize the technology. Outfitted with the TinyOS operating system, also developed at Berkeley in Professor David Culler's laboratory, the matchbox-sized sensors self-organize into ad hoc wireless networks and pass their readings from mote to neighboring mote until the data reaches a central computer for processing. (See this issue's "A Big Radio in a (Very) Small Package.") Glaser's first stop, tentatively slated for June, is a desert oasis along China's Silk Road. The town of Dunhuang is located where the Gobi and Lop Nor Deserts meet in northwestern China. Beginning in the 4th century, Buddhist monks began digging out the cliffs surrounding the town and transforming them into stunning temples lined with massive wall paintings and statues. Today, the nearly five hundred Cave Temples of Mogao, a World Heritage Site, hold one of the grandest collections of Buddhist art on the planet. Steven D. Glaser with wireless sensing equipment in one of the Mogao caves. Courtesy Steven D. Glaser The problem is that over the centuries, the adhesion between the rock and the clay plaster walls has lost its strength. As a result, the painted plaster is slowly flaking away. Glaser believes that the problem is due in part to the salt-rich groundwater evaporating in the arid climate. The remaining salt crystals have a larger volume than the original groundwater inside the caves. While Dunhuang only receives a couple of centimeters of precipitation per year, there is plenty of ground water flowing in from the snow-covered Tibetan mountains, he explains. "I think the silty rock wicks the ground water," says Glaser, who is collaborating on the project with Osaka University professor Chik Tanimoto, a former Berkeley post-doctoral researcher. The Getty Conservation Institute is spearheading a project to preserve the caves. The first step to preservation though is identifying the causes of the deterioration. Until now, mobile weather stations the size of office refrigerators have been used to gain insight into the Mogao interior. According to Glaser, the devices don't perform well in the high humidity of the caves. Glaser's plan is to drop the inexpensive battery-operated Motes throughout the caves to help preservationists create a high-resolution picture of the environmental conditions. Understanding the day-to-day environmental conditions would likely lead to better preservation measures. The Snake Path leading up to Masada was stabilized with steel rods and bolts after Glaser's colleague Yossef Hatzor determined that several massive rocks were at risk of falling. Courtesy Steven D. Glaser "It'd be nice if a guy with a laptop could walk by once a week and gather the data from the sensor network without unlocking and entering the caves," Glaser says. "That way, we could look at how the groundwater changes throughout the year and tie that with the humidity inside the caves." Glaser's next port-of-call is Masada, on the Western shore of Israel's Dead Sea. The elaborate mountaintop palace complex was built by the Roman King Herod in the first century B.C. Then, in the first century A.D., Jews revolting against Rome's rule bunkered down in Masada for three years before choosing suicide over surrender. In recent times, as many as two million tourists a year have visited the World Heritage Site. Meanwhile, the elements have been taking their toll. "The peak and buildings are made from limestone building blocks," Glaser says. "But the blocks move around and pieces are falling off." Glaser became involved in the Masada project through his friend and Berkeley alum Professor Yossef Hatzor, a rock mechanics researcher at Ben-Gurion University of the Negev in Israel. Hatzor had been called in to design retaining structures to prevent some of the large cliff rocks from tumbling down, potentially onto the tramway that carries visitors to the top of the mountain. In the next few months, the two hope to determine what causes the massive blocks to shift in the first place. Until now, the blame has been placed on seismic movement in the area. But Glaser is not convinced. What other civil engineering applications can you think of for the Motes? We want to hear from you... "It is a seismic zone, but not a strong one," he says. "People in California wouldn't even notice earthquakes of the magnitude they've recorded." Glaser's theory is that the dramatic cycles between the blazingly hot days and the chill of night strain the cross joints of the rock blocks. Along with environmental conditions, the Motes will measure the opening of cracks to help pinpoint what's causing them. Unfortunately, the war in Iraq has put Glaser's visit to Masada on indefinite hold. But he says he's patient. And understandably so. "It will be pretty cool to work on historic sites like these instead of a retaining wall at a strip mall or some ugly development somewhere," Glaser says. Steven D. Glaser's Home Page The Getty Conservation Institute's "Wall Paintings at Mogao Grottoes" project "Dynamic rock slope stability analysis at Masada national monument using Block Theory and DDA" by Y.H. Hatzor Israel Nature & National Parks Protection Authority's Masada page "Smart Buildings Admit Their Faults" (Lab Notes) Lab Notes is published online by the Public Affairs Office of the UC Berkeley College of Engineering. The Lab Notes mission is to illuminate groundbreaking research underway today at the College of Engineering that will dramatically change our lives tomorrow. Editor, Director of Public Affairs: Teresa Moore Writer, Researcher: David Pescovitz Designer: Robyn Altman Subscribe or send comments to the Engineering Public Affairs Office: lab-notes@coe.berkeley.edu. © 2003 UC Regents. Updated 4/4/03.