Researchers review coherent laser radar
Ove Steinvall
LINKÖPING, SWEDEN--The ninth Coherent Laser Radar Conference, held here in June, attracted almost 100 attendees. Nearly 80 papers were presented at the meeting, which was organized by the the Swedish Defence Research Establishment (FOA; Linköping, Sweden) and is held every second year, alternating between venues in Europe and the USA. The technology for coherent laser radar (CLR) has now reached the stage where it is ready for commercial, military, and scientific use. Applications include wind sensing, vibration sensing, long-distance target ranging, imaging, and tracking.
The sparsely covered ocean regions are of special interest for space lidar measurements. Several papers covered efforts by the European Space Agency (ESA), NASA, and Japanese researchers to develo¥space lidar technology and their proposed systems for technology demonstrations as well as for operational units--NASA has one technology demonstrator already approved for a shuttle mission around 2001.
Among the key technology achievements reported at the conference was a single-mode 0.5-J transmitter emitting at 2 µm developed by Upendra Singh and colleagues from NASA Langley (Langley, VA). This grou¥also received the best-paper award at the meeting. In an invited paper Mark Philips from Coherent Technologies Inc. (CTI; Boulder, CO) described a compact 2-µm multimode laser transmitter. Robert Menzies and coworkers from the Jet Propulsion Laboratory (JPL; Pasadena, CA) re ported on widely tunable (4 GHz) local oscillators for 2-µm operation.
Peter Ojala from the Industrial Microelectronics Center (Stockholm, Sweden) reported on distributed-feedback (DFB) semiconductor lasers suitable for CLR systems. Linewidths of less than 300 kH¥and tunability of more than 100 GH¥have been obtained.
Laser and radar techniques for meteorological applications were compared by Madison Post from the National Oceanic and Atmospheric Administration (NOAA; Boulder, CO) and others. This session also included reports on recent ad vances in the edge technique--in which wind measurements are inferred from the directly detected signal change obtained from frequency shifts at the edge of a very-narrow-band optical filter--by Larry Korb and others from NASA/Goddard Space Flight Center (Greenbelt, MD) and Christina Flesia from University of Geneva, Switzerland.
R. D. Callan and others from DERA (Malvern, England) and GEC-Marconi (Southampton, England) showed that room-temperature operation of quantum-noise-limited coherent CO2 receivers is possible. R. M. Jenkins and colleagues, also from DERA, showed a novel integrated optical beam combiner for CO2 laser radar. Rod Frehlich from the University of Colorado (Boulder, CO) discussed experimental verification of velocity estimators from Doppler lidars and showed that signal-to-noise ratios below 0 dB can still give valuable wind data.
Long-range measurements
In another invited talk, Vic Hasson and Francis Corbett from Textron Systems Corp. (Wilmington, MA) discussed long-range CLR systems ranging out to satellite targets at 1500 km and using a kilowatt-level CO2 laser. Applications include precision tracking, imaging, and chemical detection. Meanwhile Monica Minden from Hughes Research Laboratories (Malibu, CA) described a potentially ultra-low-cost laser radar for range-resolved Doppler imaging. The system was based on a passively modelocked fiber-laser transmitter with multiple randomly spaced pulses and a fiber-laser local oscillator.
Sammy Henderson from CTI described a new scheme for simultaneous measurement of range and velocity. Christer Karlsson and others from FOA Sweden and Mike Harris with colleagues from DERA reported on measurements using an ultracompact DFB-diode coherent laser radar system.
In a session on atmospheric targets Victor Banakh from the Institute of Atmospheric Optics (Tomsk, Russia), together with colleagues from DLR (Wessling, Germany), gave an invited talk about the influence of turbulence on CW Doppler lidars and showed the potential of measuring dissipation rate of turbulent energy with such systems. J. Fred Holmes and others from Oregon Graduate Institute (Portland, OR) used the speckle-turbulence interaction to make single-ended measurements of turbulence strength.
A session on wind shear, wake vortex, and air data included invited papers describing the need for and results of optical air-speed measurements for flight applications by E. Kullberg from Saab Military Aircraft (Linköping, Sweden) and Rod Bogue from NASA/Dryden Flight Center (Edwards, CA), respectively. Several papers on wake vortices and turbulence measurements were also presented by groups from DLR, DERA, NASA, and CTI (see photo on p. 54).
Papers from FOA Sweden included reports on target recognition from an airborne laser radar system and on laser tracking using coherent and direct-detection techniques as well as performance calculations for different airborne laser-radar configurations. Duane Smith from CTI and E. A. Watsson of Wright Laboratory described an all-solid-state multifunction laser-radar transmitter based on a solid-state Raman laser.
The next Coherent Laser Radar conference will be held in 1999 in the USA. Conference chair is Michael Kavaya from NASA`s Marshall Space Flight Center ([email protected]).