Statistical Characterization of Temperature and Pressure Vertical Profiles for the Analysis of Laser Heterodyne Radiometry Data.

Monica M Flores,David S Bomse,J Houston Miller

doi:10.3390/s21165421

Monica M Flores, David S Bomse + Show 1 more

Open Access

https://doi.org/10.3390/s21165421

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Abstract

The statistical analysis of historic pressure and temperature profiles from radiosonde launches for use in the fitting of molecular oxygen line shapes is presented. As the O2 mixing ratio is nearly constant throughout the lower atmosphere, only variations in pressure and temperature profiles will affect the fit of observed O2 features in Laser Heterodyne Radiometry (LHR) spectra. Radiosonde temperature and pressure data are extracted from the Integrated Global Radiosonde Archive (IGRA) for a given station, date, and launch time. Data may be extracted for a single launch, for the same date over several years, and/or within a window centered on a target date. The temperature and pressure profiles are further characterized by the statistical variation in coefficients of polynomial fits in altitude. The properties of the probability distributions for each coefficient are used to constrain fits of O2 line shapes through Nelder–Mead optimization. The refined temperature and pressure profiles are then used in the retrieval of vertically resolved mixing ratios for greenhouse gases (GHGs) measured in the same instrument. In continuous collections, each vertical profile determination may be treated as a Bayesian prior to inform subsequent measurements and provide an estimate of uncertainties.

Highlights

The determination of precise greenhouse gas (GHG) mixing ratios in the lower troposphere, where air is less well-mixed than at higher altitudes, is essential to pinpointing sources of pollution and trace gas species
O2 Laser Heterodyne Radiometry (LHR) spectra are dominated by pressure and temperature effects, allowing retrieval algorithms to emphasize determining those two parameters that can be folded back into GHG and water vapor retrievals
In this study we present a statistical characterization method for the analysis of historic pressure and temperature vertical profiles from radiosonde data obtained from the Integrated Global Radiosonde Archive (IGRA) to inform LHR O2 line shape spectral fitting [16]

Summary

Introduction

The determination of precise greenhouse gas (GHG) mixing ratios in the lower troposphere, where air is less well-mixed than at higher altitudes, is essential to pinpointing sources of pollution and trace gas species. Vertical profile measurements of GHGs include weather balloons (e.g., radiosondes), aircraft, Low Earth Orbiting (LEO) satellites such as NASA’s OCO-2 and JAXA’s GOSAT [1,2], and ground-based measurements such as Laser Heterodyne Radiometry (LHR). Compared with satellite-based instruments, ground-based LHR is less expensive, avoids pathlength ambiguities due to backscattered sunlight, eliminates near-surface pressure uncertainties, and has better response toward gases in the lower troposphere. LHR absorption peaks are the line-of-sight, summed contributions from gases throughout the full atmospheric columns. Retrieval precision can be improved by including LHR spectra of O2 because it has a nearly uniform concentration throughout the troposphere and lower stratosphere. O2 LHR spectra are dominated by pressure and temperature effects, allowing retrieval algorithms to emphasize determining those two parameters that can be folded back into GHG and water vapor retrievals

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