Preprints
https://doi.org/10.5194/amt-2020-466
https://doi.org/10.5194/amt-2020-466

  22 Dec 2020

22 Dec 2020

Review status: a revised version of this preprint was accepted for the journal AMT.

Retrieval Algorithm for the Column CO2 Mixing Ratio from Pulsed Multi-Wavelength Lidar Measurements

Xiaoli Sun1, James B. Abshire1,2, Anand Ramanathan3, S. Randy Kawa1, and Jianping Mao2 Xiaoli Sun et al.
  • 1NASA Goddard Space Flight Center, Code 698/690/614, Greenbelt, Maryland, USA
  • 2University of Maryland, College Park, Maryland, USA
  • 3Audible, Inc., Newark, New Jersey, USA

Abstract. The retrieval algorithm for the column mixing ratio of CO2 from the measurements of a pulsed multi-wavelength integrated path differential absorption (IPDA) lidar is described. The lidar samples the shape of the 1572.33 nm CO2 absorption line at 15 or 30 wavelengths. The algorithm uses a least-squares fit between the CO2 line shape computed from a layered atmosphere model to that sampled by the lidar. In addition to the column average CO2 dry air mole fraction (XCO2), several other parameters are also solved simultaneously from the fit. These include the Doppler shift in the received laser signal wavelengths, the product of the surface reflectivity and atmospheric transmission and a linear trend in the lidar receiver's spectral response. The algorithm can also be used to solve for the average water vapor mixing ratio, which causes a secondary absorption in the wings of the CO2 absorption line under high humidity conditions. The least-squares fit is linearized about the expected XCO2 value which allows the use of a standard linear least-squares fitting method and software tools. The standard deviation of the retrieved XCO2 is obtained from covariance matrix of the fit. An averaging kernel is defined similarly to that used for passive trace-gas sounding. Examples are presented of using the algorithm to retrieve XCO2 from the measurements from NASA Goddard's airborne CO2 Sounder lidar made at a constant altitude and during spiral-down maneuvers.

Xiaoli Sun et al.

 
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

Xiaoli Sun et al.

Xiaoli Sun et al.

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Short summary
The manuscript gives a detailed and complete description of the retrieval algorithm used in the multi-wavelength lidar for average column carbon dioxide mixing ratio measurements. The algorithm is similar to that used in passive trace-gas sounding and simultaneously solves for several parameters and provides the associate averaging kernel. The algorithm has been successfully used with the airborne lidar measurements. It can also be used with similar lidar for other trace-gas measurements.