Tropospheric ozone sensing Fabry-Perot interferometer: I. Space-based feasibility assessment

Abstract

Space-based observation of tropospheric pollution has been identified as a high-priority atmospheric science measurement to be included in Earth science missions of the 21st century. Levels of tropospheric O3 have been increasing and will continue to increase as concentrations of the precursor gases necessary for the photochemical formation of tropospheric O3 continue to rise. A global tropospheric O3 monitoring capability is critical to enhance scientific understanding as well as to potentially lessen the ill-health impacts associated with exposure to elevated concentrations in the lower atmosphere. A measurement technique to enable such a measurement capability utilizing Fabry-Perot interferometry will be presented. It involves a double-etalon series configuration FPI along with an ultra-narrow bandpass filter to achieve single-order operation with an overall spectral resolution of approximately .068 cm-1, sampling a narrow spectral region within the strong 9.6 micrometers ozone infrared band from a nadir-viewing satellite configuration. The Fabry-Perot interferometer (FPI) provides high spectral resolution and high throughput capabilities that are essential for this measurement task. Through proper selection of channel spectral regions, the FPI optimized for tropospheric O3 measurements can simultaneously observe a stratospheric component and thus the total O3 column abundance. A retrieval technique employing the maximum likelihood method has been implemented and will be demonstrated for a tropical atmosphere possessing enhanced tropospheric ozone amounts. An error analysis assessing the impact on retrieved O3 amounts form the most significant uncertainties associated with this particular measurement has been performed for several different types of atmospheres. Emphasis will be placed on a tropical atmosphere, for which sounding data have been used in the a priori information covariance matrix estimation process. An error budget has been formulated by estimating the impact on overall measurement uncertainty of the potential random and systematic component error sources. Results show the proposed instrumentation to enable a good measurement of absolute ozone amounts and an even better determination of relative changes.