Abstract

Knowledge of the global scale distribution of atmospheric ozone and its temporal variability can only be achieved through implementation of a satellite-based remote sensing technique. Development of a space-based tropospheric ozone remote sensor has remained a difficult task to accomplish due to the challenges associated with such a measurement. Nevertheless, the ability to monitor the global distribution of tropospheric ozone is of much interest for enhancement of scientific understanding as well as to potentially lessen the ill-health impacts associated with exposure to elevated concentrations in the lower atmosphere. Such a capability can be achieved using a satellite-based nadir-viewing device making high spectral resolution measurements with high signal-to-noise ratios;¹ this would enable observation in the pressure-broadened wings of strong O₃ lines while minimizing the impact of undesirable signal contributions associated with, for example, the terrestrial surface and interfering species. The Fabry-Perot interferometer (FPI) provides high spectral resolution and high throughput capabilities that are essential for this measurement task. The periodic nature of the Fabry-Perot instrument function can be advantageous when observation of periodic spectra is desired.² However, for most applications, additional optical elements are necessary to reduce the effect of unwanted passbands. This is frequently accomplished using additional Fabry-Perot etalons in a series configuration³ in conjunction with a bandpass filter. This paper will discuss a Fabry-Perot interferometer conceptual instrument design to achieve tropospheric and total ozone monitoring capability from a satellite-based nadir-viewing geometry. The design involves a double-etalon fixed-gap 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. The impact of inter-etalon reflections has been reduced to acceptable levels by placement of a slightly attenuating medium in between the etalons. A passive device is selected for low power consumption; and continuous day/night coverage, independent of solar zenith angle, is enabled by observing within the strong 9.6 μm ozone infrared band. The IR-FPI detection will be performed through implementation of the new Circle to Line Interferometer Optical (CLIO) system⁴ (U.S. patent #4893003, 1990), developed by researchers at the Space Physics Research Laboratory (SPRL) of the University of Michigan, to accomplish focal plane fringe detection; the CLIO system converts the circular interferometric fringes into a linear pattern which then can be detected by conventional linear array detectors. A multiplex signal advantage is achievable as all necessary frequencies can be measured simultaneously using a multichannel configuration. 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. Details of the preliminary instrument design are given by Larar¹.

© 1995 Optical Society of America