Lidar Helps Unravel Environmental Mysteries

Barbara Grant, Contributing Editor

From coastal waterways to Alpine summits, light detection and ranging technology demonstrates how photonics helps to unravel the mysteries of complex environmental processes while sharpening our vision of seas and skies.
In Sweden, for example, researchers at the Defense Research Establishment, Linkoping, are using a frequency doubled Nd:YAG lidar system to map subsurface depths in coastal regions for safer marine navigation. "We have a jagged coastline in the Baltic," said Ove Steinvall laser systems division head in the institute's department of sensor technology, adding that lidar information compares well with that obtained from conventional acoustic sounding.
Steinvall said that the 532 nm green beam of the laser, manufactured by Big Sky Laser Technologies Inc., Bozeman, Mont., penetrates the ocean surface while a 1.06-µm beam provides a surface reference that can correct for wave heights. By investigating the backscattered signal as a function of water depth, researchers studying pollution in the coastal region also can gain information on the water's turbidity.
For determining the concentrations of chemical species such as ozone, water vapor, or pollutants researchers can turn to differential absorption spectroscopy (DAS) lidar or differential absorption lidar (DIAL). Both rely on the ability of molecules to absorb specific wavelengths of light. These systems direct beams of different wavelengths to the target, with one wavelength specifically selected for minimum absorption by a particular molecule. The returned signals from the target allow calculation of molecular concentration because of differential changes in absorption.