Atmospheric Remote Sensing: Instruments
The airborne lidar for fisheries surveys is named FLOE (Fish Lidar, Oceanic, Experimental).
How does it work?
LIDAR is an acronym for LIght Detection And Ranging. In its simplest form, a short pulse of laser light is directed toward a target. A receiver is pointed in the same direction and waits for a return signal reflected from the target. The elapsed time indicates the targets range, and the time difference between the sea surface return and the return from a subsurface target indicates its depth. The strength and polarization characteristics of the return provide additional information about the target.
A compact LIDAR system in a small airplane can measure distributions of various targets over large areas of the ocean. Equipping the aircraft with imagers, radiometers, and expert observers provides even more information about targets and the environment. The information obtained from an aerial survey is less detailed than from a surface ship, but can be obtained much more rapidly and at a lower cost. The LIDAR will generally penetrate to a depth of 40 - 50 m in clear, blue waters, 20 - 30 m in productive, green waters, and as little as 10 m in very turbid waters like Chesapeake Bay. More detailed information is provided with instrumentation and field programs, including photographs of aircraft we have used and publications.
What has been measured?
The LIDAR and associated instruments have been used in a number of studies looking at:
The instrumentation is owned and operated by NOAA, but these studies have been partially supported by other organizations and we are always looking for applications and collaborations.
Is the laser safe?
The laser beam is expanded to meet the ANSI standards for occupational laser safety at the surface. We also avoid illuminating boats by momentarily blocking the beam as we pass over. We have also investigated the potential hazard to marine mammals (Zorn et al., 2000) for 13 species of cetaceans and pinnipeds. We found that all of these were considerable less sensitive to laser illumination than humans and therefore not at risk from our lidar. There are no species that are expected to be more sensitive than the ones examined based on available information. Other marine creatures are expected to be even less sensitive than marine mammals from what we know about their visual systems.