Abstract
The Composite InfraRed Spectrometer (CIRS) on-board the Cassini spacecraft has currently returned around three years worth of data from Saturn’s largest moon Titan. One of the unique aspects of CIRS is to take high spatial resolution spectra of the limb of Titan, with sub-scale height (20–40 km) resolutions. This is made possible by the small field-of-view (FOV) of the mid-IR detectors. However, many limb spectra have moderate to large sized FOVs, which introduces bias into retrieved profiles of temperature and abundance unless the finite FOV size is taken into account. The bias can be reduced by calculating a FOV-averaged spectrum comprising a weighted sum of a small number of spectra with infinitesimal FOVs across the FOV. Here we introduce a scheme for incorporating FOV averaging into radiative transfer calculations of CIRS spectra and quantify the errors as a function of number of FOV averaging points, FOV size, tangent altitude, and wavenumber. The optimum number of FOV averaging points for a given observation can then be found by matching the calculated FOV averaging error with the measurement error. This allows for accurate analysis of a vast amount of Cassini-CIRS data.
Similar content being viewed by others
References
Flasar, F.M., Kunde, V.G., Abbas, M.M., et al.: Exploring the Saturn system in the thermal infrared: the composite infrared spectrometer. Space Sci. Rev. 115, 169–297 (2004)
Irwin, P.G.J., Parrish, P., Fouchet, T., et al.: Retrievals of jovian tropospheric phosphine from Cassini/CIRS. Icarus 172, 37–49 (2004)
Kunde, V., Ade, P., Barney, R., et al.: Cassini infrared Fourier spectroscopic investigation. Proc. Soc. Photo-Opt. Instrum. Eng. 2803, 162–177 (1996)
Lacis, A.A., Oinas, V.: A description of the correlated k distribution method for modeling nongray gaseous absorption, thermal emission, and multiple-scattering in vertically inhomogeneous atmospheres. J. Geophys. Res. 96(D5), 9027–9063 (1991)
Nixon, C.A.: Remote sounding of the atmosphere of Titan. Ph.D. thesis, University of Oxford (1998)
Nixon, C.A., Achterberg, R.K., Conrath, B.J., et al.: Meridional variations in C2H2 and C2H6 in Jupiter’s atmosphere from Cassini CIRS infrared spectra. Icarus 188, 47–71 (2007)
Press, W.H., Flannery, B.P., Teukolsky, S.A., et al.: Numerical Recipes, 2nd edn. Cambridge University Press, Cambridge (1992)
Teanby, N.A., Irwin, P.G.J., de Kok, R., et al.: Latitudinal variations of HCN, HC3N, and C2N2 in Titan’s stratosphere derived from Cassini CIRS data. Icarus 181, 243–255 (2006)
Teanby, N.A., Irwin, P.G.J., de Kok, R., et al.: Vertical profiles of HCN, HC3N, and C2H2 in Titan’s atmosphere derived from Cassini/CIRS data. Icarus 186, 364–384 (2007)
Vinatier, S., Bézard, B., Fouchet, T., et al.: Vertical abundance profiles of hydrocarbons in Titan’s atmosphere at 15 °S and 80 °N retrieved from Cassini/CIRS spectra. Icarus 188, 120–138 (2007)
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Teanby, N.A., Irwin, P.G.J. Quantifying the effect of finite field-of-view size on radiative transfer calculations of Titan’s limb spectra measured by Cassini-CIRS. Astrophys Space Sci 310, 293–305 (2007). https://doi.org/10.1007/s10509-007-9519-3
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10509-007-9519-3