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We present preliminary experimental results, sensitivity measurements and discuss our new CO2
lidar system under development. The system is employing an erbium-doped fiber amplifier (EDFA),
superluminescent light emitting diode (SLED) as a source and our previously developed Fabry-Perot
interferometer subsystem as a detector part.
Global measurement of carbon dioxide column with the aim of discovering and quantifying
unknown sources and sinks has been a high priority for the last decade. The goal of Active Sensing of CO2
Emissions over Nights, Days, and Seasons (ASCENDS) mission is to significantly enhance the
understanding of the role of CO2 in the global carbon cycle. The National Academy of Sciences
recommended in its decadal survey that NASA put in orbit a CO2 lidar to satisfy this long standing need.
Existing passive sensors suffer from two shortcomings. Their measurement precision can be compromised
by the path length uncertainties arising from scattering within the atmosphere. Also passive sensors using
sunlight cannot observe the column at night. Both of these difficulties can be ameliorated by lidar
techniques.
Lidar systems present their own set of problems however. Temperature changes in the atmosphere
alter the cross section for individual CO2 absorption features while the different atmospheric pressures
encountered passing through the atmosphere broaden the absorption lines. Currently proposed lidars require
multiple lasers operating at multiple wavelengths simultaneously in order to untangle these effects.
Our current goal is to develop an ultra precise, inexpensive new lidar system for precise column
measurements of CO2 changes in the lower atmosphere that uses a Fabry-Perot interferometer based system
as the detector portion of the instrument and replaces the narrow band laser commonly used in lidars with
the newly available high power SLED as the source. This approach reduces the number of individual lasers
used in the system from three or more to one-considerably reducing the risk of failure. It also
tremendously reduces the requirement for wavelength stability in the source putting this responsibility
instead on the Fabry-Perot subsystem.
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