Laser lidar

Laser-based lidar (light detection and ranging) has also proven to be an

important tool for oceanographers. While satellite pictures of the ocean surface

provide insight into overall ocean health and hyperspectral imaging provides more

insight, lidar is able to penetrate beneath the surface and obtain more specific data,

even in murky coastal waters. In addition, lidar is not limited to cloudless skies or

daylight hours.

“One of the difficulties of passive satellite-based systems is that there is watersurface

reflectance, water-column influence, water chemistry, and also the influence

of the bottom”, said Chuck Bostater, director of the remote sensing lab at Florida Tech

University (Melbourne, FL). “In shallow waters we want to know the quality of the

water and remotely sense the water column without having the signal contaminated by

the water column or the bottom”.

A typical lidar system comprises a laser transmitter, receiver telescope,

photodetectors, and range-resolving detection electronics. In coastal lidar studies, a

532-nm laser is typically used because it is well absorbed by the constituents in the

water and so penetrates deeper in turbid or dirty water (400 to 490 nm penetrates

deepest in clear ocean water). The laser transmits a short pulse of light in a specific

direction. The light interacts with molecules in the air, and the molecules send a small

fraction of the light back to telescope, where it is measured by the photodetectors.