Laser Mapping

Lasers, nasty space weapon or another tool?

Equipped with a laser system, a plane collected highly precise images of New York city, its rooftops, trees, wetlands and much of what lies in between. In only four days, a twin engine aircraft equipped with an advanced version of lidar (light detection and ranging) flew back and forth over the jungle of Belize and collected data surpassing the results of decades of torturous ground mapping. After three weeks of laboratory processing, the almost 10 hours of laser measurements showed topographic detail over an area of 80 square miles, notably settlement patterns of grand architecture and modest house mounds, roadways and agricultural terrace. Such a tool can quickly measure environmental areas of concern as well as urban areas.

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LIDAR (Light Detection And Ranging) is an optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target. The prevalent method to determine distance to an object or surface is to use laser pulses. Like the similar radar technology, which uses radio waves, the range to an object is determined by measuring the time delay between transmission of a pulse and detection of the reflected signal.

Lidar can be and is used in a number of interesting applications such as archaeology, meteorology, atmospheric concentrations (Ozone and Carbon Dioxide for example), forest heights, mountain heights, biomass concentrations, and even wind speed for some wind power applications.

The New York data will be used to create up-to-date maps of the areas most prone to flooding, the buildings best suited for the installation of solar power and the neighborhoods most in need of trees.

Rohit T. Aggarwala, the director of the city’s Office of Long-Term Planning and Sustainability, said the effort would result in a picture of New York’s physical space “in far more detail than what we had before.”

The current flood plain maps used by the Federal Emergency Management Agency date to the 1980s and were based on aerial photography and ground surveys. The maps are not as accurate or precise as they should be for the density of the city, Mr. Aggarwala said, and the new data could lead to zoning changes and stricter building codes, among other adjustments.

The rooftop count can then be used to create an online solar map that will help assess the city’s capacity for solar power and even allow New Yorkers to check if the buildings they work or live in are suitable for solar panels.

Cities like San Francisco have already developed solar maps, and the new Lidar technology is increasingly being adopted by coastal regions around the nation, FEMA officials said.

Meanwhile Lidar was used to investigate a Mayan ruined city called Caracol. There Lidar was helpful in determining that Caracol extended over a wide area in its heyday, between A.D. 550 and 900. From a ceremonial center of palaces and broad plazas, it stretched out to industrial zones and poor neighborhoods and beyond to suburbs of substantial houses, markets and terraced fields and reservoirs.

This picture of urban sprawl led the Chases to estimate the city’s population at its peak at more than 115,000. But some archaeologists doubted the evidence warranted such expansive interpretations.

For further information: http://en.wikipedia.org/wiki/LIDAR or http://www.nytimes.com/2010/05/10/science/earth/10mapping.html?partner=rss&emc=rss or http://www.nytimes.com/2010/05/11/science/11maya.html?partner=EXCITE&ei=5043