Harris Multifunctional Fiber-Laser Lidar; The Transition to an Operational Instrument for an Airborne CO2 Lidar in Support of ACT-America

The Multifunctional Fiber-Laser Lidar (MFLL) was built by Harris in 2004 and has been used to support more than 15 flight campaigns led by NASA Langley Research Center since 2005 to evaluate the technique for the Active Sensing of CO2 Emissions over Nights Days and Seasons (ASCENDS).  A lot has been learned and improved through this extensive testing.  MFLL is a concept that uses amplitude modulation to uniquely encode fixed frequency wavelengths of light, allowing simultaneous transmission of multiple wavelengths, low peak power, and the use of robust fiber lasers and photonics components. The initial instantiation of the instrument used pure sinusoidal modulation with a standard lock-in amplifier approach and worked well in clear air environments.  However, this approach could not distinguish between returns from the ground versus returns from clouds and heavy aerosols due to the continuous wave nature of the measurement.  In 2009, Harris demonstrated a swept sinewave modulation version, which enabled ranging while still maintaining the advantages of the continuous wave approach.  Since then, NASA Langley has developed more sophisticated, orthogonal waveforms and improved methods for performing the matched filter to separate the channels in digital space.  Recently (2015), MFLL was selected as one of the primary instruments for the NASA Earth Venture Suborbital mission Atmospheric Carbon Transport – America (ACT-America).  In preparation for ACT-America a number of improvements have been made to the instrument, still largely built out of commercial components, in order to transition from a proof of concept instrument to an operational science instrument.  This paper will review the MFLL measurement approach, discuss the recent upgrades and performance testing of the instrument, and review preliminary results from the first ACT-America science campaign.