Differential Laser Absorption Spectrometry for Global Profiling of Tropospheric Carbon Dioxide: Selection of Optimum Sounding Frequencies for High-Precision Measurements

Abstract

We discuss the spectroscopic requirements for a laser absorption spectrometer (LAS) approach to high-precision carbon dioxide (CO2) measurements in the troposphere. Global-scale, high-precision CO2 measurements are highly desirable in an effort to improve understanding and quantification of the CO2 sources and sinks and their impact on global climate. We present differential absorption sounding characteristics for selected LAS transmitter laser wavelengths, emphasizing the effects of atmospheric temperature profile uncertainties. Candidate wavelengths for lower-troposphere measurements are identified in the CO2 bands centered near 1.57, 1.60, and 2.06 microm.

The air-broadened, near-infrared CO2 line shape in the spectrally isolated regime: Evidence of simultaneous Dicke narrowing and speed dependence

“…3 Of particular importance are higher order effects such as collisional narrowing, speeddependent effects and line mixing which are yet to be incorporated into the vast majority of atmospheric retrievals which often employ the Voigt line profile. These effects will play an even greater role in next generation, active sensing missions [4][5][6][7][8][9][10][11] (including NASA's Active Sensing of CO 2 Emissions over Nights Days and Seasons, ASCENDS) where individual transitions in the near-infrared spectral region will be interrogated rather than entire bands, and where precise measurements of CO 2 concentrations will require exquisite knowledge of the spectral line shape.…”

Investigations on frequency and energy references for a space-borne integrated path differential absorption lidar

“…The quantity of scientific interest is the weighted average of the CO 2 dry-air volume mixing ratio along the probed column, XCO 2 , which is given by [8]. The denominator in (1) is the integral of the so-called weighting function (IWF) along the probed column down to surface pressure (p SFC ), determined solely by the temperature and pressure dependent differential absorption cross-section for the considered wavelengths and atmospheric parameters such as air density and humidity that can be obtained from NWP model results.…”

A New Laser Based Approach for Measuring Atmospheric Greenhouse Gases

“…The literature describing these various approaches is vast and spans both ground and space concepts. A good general reference can be found in [17] and a few additional selected examples for the interested reader can be found in references [18][19][20][21][22][23][24]. Only a brief overview of the concepts is provided here, as needed for clarification of the LAnTeRN measurement concept.…”