Title: Laser Absorption Spectrometer Measurements of Atmospheric O2 in the 1.27 µm Band
Primary Author: Dobler, Jeremy
Organization: ITT Geospatial Systems
Co-Author(s): Mike Braun, ITT Geospatial Systems; James Nagel and Valery Temyanko, TIPD LLC; Bryan Karpowicz and T. Scott Zaccheo, Atmospheric and Environmental Research, Inc.,
Abstract: We report on the development of a Laser Absorption Spectrometer (LAS) instrument for measuring atmospheric O2 in support of the future space mission, Active Sensing of CO2 Emissions over Nights Days and Seasons (ASCENDS), put forth in the National Research Council’s Decadal Survey, 2007. Over the past year a transmitter capable of emitting 1.8 Watts of average power with <3MHz linewidth and at the desired wavelength of 1271 nm has been developed. This transmitter is based on stimulated Raman amplification in a P2O5 doped fiber, designed to minimize Stimulated Brillion Scattering (SBS) while maintaining high Raman gain. The transmitter has been integrated into an ITT Engineering Development Unit (EDU) and has made preliminary measurements of O2 at ITT’s lidar ground test facility. The measurement approach is based on ITT’s flight validated EDU for measuring atmospheric CO2. This technique takes advantage of the high sensitivity measurement method known as lock-in amplification to allow multiple wavelengths to be simultaneously transmitted and received on a single detector, even in the presence of significant background noise. The wavelengths are separated in post processing, are normalized and their ratios taken to yield the differential absorption between the transmitted wavelengths. The differential absorption is then combined with other measurements such as range to the target, temperature and altitude to determine the atmospheric pressure. A Line-By-Line Radiative Transfer Model (LBLRTM), utilizing local weather station data is being used for comparisons with the lidar measurements. Details of the amplifier development to date, methodology of the measurement and retrieval methodology will be presented.