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Space Signals a Modern Tool of Surveyors

November 22, 1987|EVELYN De WOLFE | Times Staff Writer

Space surveying technology, first pioneered for military use, is becoming a viable alternative to conventional surveying methods.

With the aid of satellite radio signals, combined with photogrammetry and electronic mapping techniques, civilian surveyors can enhance their ability to assist city agencies at all levels--from the municipal engineer designing new storm drains to the planner charting an industrial development.

"In each situation, task efficiency and cost reduction may result," said James M. Duffy, vice president at Psomas Associates, a civil engineering firm in Costa Mesa and the first private surveying firm in California to utilize space satellite signals in mapping.

Commissioned by the City of Rancho Cucamonga to chart its maps, Psomas is measuring satellite radio waves in relation to ground monuments, to obtain elevations and horizontal distances for the community. "And they are accurate to within 10 centimeters--a level of precision that even the military does not require," Duffy added.

"When the project is finished, Rancho Cucamonga will have the most complete and accurate map grid of any city in Southern California," he said.

The fast-growing Southern California community, about 50 miles northeast of Los Angeles and about 15 miles west of San Bernardino, consisted of a scattered group of vineyards off Interstate 10 before its incorporation a decade ago.

In Planning Stages

It now has a population of 85,000 and its construction projects, begun last year alone, amount to $350 million. Additional mixed-use communities within Rancho Cucamonga are currently in the planning stages or under construction.

Prior to the Psomas assignment, the city had already purchased a geographic information management system from ESRI Inc. of Redlands, said Blane W. Frandsen, the city's senior civil engineer. "But in the bidding for the survey project, Psomas was the only company that proposed using satellite techniques to enhance the existing ground surveys."

Under a $510,000 contract (the largest consulting contract in Rancho Cucamonga's history), Frandsen said, Psomas is surveying about 42 square miles, which includes 10 square miles north of the city falling within its sphere of influence.

Minimum of 18 Layers

"When the work is completed by Psomas, in about a year, the city will receive 340 map sheets and a digital topographic contour community map that will enable city engineers to design storm drains, sidewalks, traffic flow and provide far greater flexibility and cost reduction.

"The maps will have a minimum of 18 layers of topographic information, and users will have the option to isolate selected elements and choose from 324 map variations," Frandsen said.

"Computerized mapping with all of the traditional topographic data on disks can display information in uncluttered layers. For example, a city staff member may want to create an electronic display showing only roads or streets, water lines, or electrical conduits, trees or location of buildings.

"A task that normally took days, can be accomplished and updated in minutes and saving the cost of countless revisions on paper maps."

Highest Mountain

Surveying from space is so accurate, explained Psomas' vice president, that information gathered from satellite signals and surveying techniques was employed to refute a recent claim that the K2 peak (which straddles the Sino-Pakistani border) might actually be the highest mountain in the world.

Last month, an eight-man Italian expedition led by 90-year-old geologist Ardito Desio, found that Mt. Everest towers at 29,108 feet above sea level, actually 80 feet taller than previously believed, and is 840 feet higher than K2.

Both the Everest/K2 measurements and the Rancho Cucamonga survey work were done with the aid of U. S. Global Positioning Satellites that are the core of the American military radio navigation system, and both projects carried computerized radio receivers to specific locations, Duffy noted.

The GPS system, he said, works from a "constellation" of seven satellites run on atomic clocks, each about the size of an average bathroom and circling the globe at a distance of 22,000 kilometers.

Measure Time Gap

"The military forces need only use one satellite to compute positions; civilian surveyors use a minimum of three satellites because they are not privy to the encrypted codes set by the military," Duffy said.

"The technique we use is to measure the infinitesimal time gap of satellite radio waves at different points to calculate elevation differences. Using signals from four NASA satellites in combination with set ground-based survey references throughout the San Bernardino County community, Psomas has been able to chart vertical and horizontal positions faster and more accurately than traditional surveying techniques that require each survey siting point to be visible from the other siting point."

The surveying firm is currently planning a demonstration of space surveying technology to check for earth crustal movement as a result of the Whittier Fault earthquake and will do this by re-establishing control values on existing first order monuments in Los Angeles, Orange and San Bernardino counties, in conjunction with city and county survey departments.

With the cities of Santa Ana, Bell, Glendale and Fountain Valley, as well as the Long Beach Police Department, Psomas has been involved primarily in computerized mapping projects and is currently creating a mapping data base to assist the City of Whittier in the assessment of earthquake damage.

Wave of Future

"There is a nationwide trend among cities, large and small, moving into computerized mapping for their survey work and someday that work will be further enhanced by satellite assistance," Duffy said.

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