Laser Air Motion Sensor (LAMS)

The LAMS measures airspeed in a region of undisturbed airflow via the Doppler shift in the frequency of laser light returned from a laser beam focused ahead of the aircraft. The coaxial laser system uses optical heterodyning to detect the Doppler shift in light backscattered from atmospheric aerosols.

The system uses fiber-based components and a laser producing 4W at a wavelength of 1.56 um. The beam is focused about 15 m ahead of the aircraft and is capable of producing high-rate data (up to about 100 Hz). Because the system relies on backscatter from atmospheric aerosols, its performance is sometimes limited when aerosol concentrations are low, but it has performed in tests up to 90% of the time at flight altitudes exceeding 40,000 ft. For details of the test results, see the publication by Spuler et al. (2011) referenced in the "Documentation" section at the end of this page.

Measurements Provided: Speed of the relative wind in the direction of the instrument axis (single beam) or, for the multiple-beam system, the relative wind vector.

Measurement Characteristics: 

• Overall estimate of uncertainty: 0.1m/s
• Response time: 0.02s
• Precision: 0.1m/s
• Other measurement characteristics ( comments on signal/noise, bias limits, etc): sometimes limited by low aerosol backscatter

History of Significant Changes: 

Aug 2009: Flown as a single-axis, proof-of-concept prototype on the NCAR GV during the first test flight for the ADELE/SPRITE project

Jan 2010: During the HEFT 10 project the instrument configured with the beam in-line with the fuselage.  Wing motion measured with a global position system (GPS) and Inertial Navigation System (INS) unit attached to the same wing strut.  Sufficient signal-to-noise to measure wind speeds at altitudes up to 7 km in clear air.  Able measure winds speeds in elevated aerosol layers and/or clouds at higher altitudes.  At aircraft speeds < 200 m/s the differences between the LAMS and fuselage pitot tube are less than 1 m/s.  At aircraft speeds over 200 m/s differences up to 2m/s from the pitot tube measurements.  It is believed that these differences are caused by errors in the pitot tube measurements.

Aug 2010: Flight tests conducted in (PREDICT) with a new 4W laser amplifier system. The prototype system had reliable performance for 14 test flights. Wind speed measurements at 50 Hz within the boundary layer and 1-Hz in clear-air up to 12.5 km altitude were demonstrated.  Frequency response of the system to turbulence was shown to match the theoretical Kolmogorov inertial subrange.

November 2011: During IDEAS4 installed on the NCAR C-130 aircraft and flown as a single forward pointing instrument to test the new wing-pod subsystem and temperature-resilient fiber-based circulators. Collected data from several flights, including a five hour flight designed for wind calibration.  The circular flight tracks offered the opportunity to measure an integrated quantity vorticity.  Additionally, a new method to measure temperature was demonstrated with this data set utilizing the LAMS true airspeed combined with information from the pressure sensors

October 2013: The 3-beam system was flown in IDEAS on the GV 

September 2015: The 4-beam system was flown in ARISTO2015 on the C-130