A Multifunctional Fiber Laser Lidar for Measuring Atmospheric CO2 and O2

Author: T. Scott Zaccheo and J.T. Dobler
January 23, 2012
2011 NASA Carbon Cycle & Ecosystems Joint Science Workshop

Jeremy Todd Dobler, James Nagel, Valery L. Temyanko, T. Scott Zaccheo, Edward V. Browell, Fenton Wallace Harrison, Susan A. Kooi, Marta A. Fenn, Yonghoon Choi, & Stephanie A. Vay. A Multifunctional Fiber Laser Lidar for Measuring Atmospheric CO2 and O2. 2011 NASA Carbon Cycle & Ecosystems Joint Science Workshop.

In 2004, ITT Geospatial Systems began development of a multi-functional fiber laser lidar (MFLL) for altimetry and high precision laser absorption of atmospheric CO2. The instrument is based on a unique intensity modulated (IM) continuous wave (CW) measurement technique, which allows simultaneous transmission and collection of multiple wavelengths, and uses an all software correlation technique to separate and quantify signal strength of the individual wavelengths. The MFLL architecture significantly reduces the cost and risk for furture space missions, such as the Active Sensing of CO2 Emissions over Nights, Days and all Seasons (ASCENDS) mission, by exploiting highly robust and reliable telecom components in a unique manner which allows multiple transmitters to be combined in order to meet the power and efficiency requirements with currently available components. The CO2 and altimeter components of the MFLL prototype have been extensively evaluated in conjunction with our partners at the NASA Langley Research Center and Atmospheric and Environmental Research, Inc. through 11 different flight campaigns using 3 different aircraft and totaling more than 70 individual flights. These flights have allowed the instrument performance to be evaluated over an extensive range of atmospheric and surface conditions, and comparisons with highly accurate in-situ instrumentation has shown absolute agreement of the remote measurement to the point measurement to sub parts per million (ppm) with standard deviations of a few ppm. To the authors knowledge this represents the only airborne CO2 measurement technique that has demonstrated this precision and accuracy to date. The MFLL IM-CW approach was recently extended to the measurement of atmospheric O2 through support from a 2008 NASA Earth Science Technology Office (ESTO) Advance Component Technology (ACT) contract awarded to ITT, and the O2 component was flown for the first time in July and August 2011 onboard the NASA DC-8 aircraft. The transmitter for the O2 component is a Raman amplifier and represents the first known high power (1.5 W average) narrow linewidth (<6 MHz) IM laser source at 1262.5 nm. At the time of this abstract only a first look at the O2 measurements were completed, but results are promising. It is expected that with some minor refinements the O2 component will be capable of demonstrating measurements with the same precision and accuracy as have been demonstrated for the CO2 component. Other recent developments include development and implementation of hybrid modulation techniques which enable the CW measurement approach to discriminate against returns from intermittent scatters such as thin cirrus clouds, while maintaining the advantage of lower peak output powers and simultaneous transmission of all wavelengths. This paper will discuss the overall design concept of the MFLL architecture, recent modeling and implementation of thin cloud rejection algorithms, flight results, and details on the O2 component development and evaluation. Also, a brief review of current and ongoing development plans will be discussed.