A22C-02
Impact of O2–Based Surface Pressure Uncertainties on Laser Absorption Spectrometer Retrievals of Column CO2 Mixing Ratios (XCO2)

Tuesday, 15 December 2015: 10:40
3012 (Moscone West)
Timothy Pernini1, T Scott Zaccheo1, Rick Pernak2, Chris Botos2 and Edward V Browell3, (1)Atmospheric and Environmental Research Lexington, Lexington, MA, United States, (2)Atmospheric and Environmental Research, Lexington, MA, United States, (3)NASA Langley Research Center, Hampton, VA, United States
Abstract:
In this work we assess the overall impact of surface pressure uncertainties, derived from either laser-based O2 column measurements or numerical weather prediction (NWP) models, and water vapor uncertainties on laser-based retrievals of CO2 column mixing ratios (XCO2). Laser Absorption Spectrometer (LAS) estimates of column XCO2 can be derived from a combination of observed CO2 differential optical depths ( ) and measured/estimated values of temperature (T), pressure (P), and moisture (q) along the viewing path. XCO2 can be related to CO2 as

(equation 1)

where Δτother represents residual observed due to other species, is CO2 differential absorption cross section, psfc is surface pressure, q is local specific humidity and / represent the observation on/off-line wavelengths. The accuracy of retrieved XCO2 values depends on both the error characteristics of the observed and the ability to accurately characterize T, P, and q along the observed path. A radiative transfer (RT)-based simulation framework, combined with representative global upper-air observations and matched NWP profiles, was used to assess the impact of model differences in vertical T, vertical moisture, and surface P on estimates of column CO2 and O2concentrations.

Additionally we characterize the impact of a combined XCO2 retrieval approach based on either O2 LAS measurements or NWP data, as well as the additional impact due to water vapor. These analyses focus on characterizing the errors for a combined retrieval approach for LAS CO2 measurements in the 1.57 and 2.05 µm regions and O2 measurements in the 0.76 and 1.27 µm. The results provide a set of signal-to-noise metrics that characterize the errors in retrieved XCO2 associated with uncertainties in knowledge of the atmospheric state, and provide a method for selecting optimal differential line pairs for both CO2 and O2 measurements to minimize the impact of this noise term.

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