FABRY-PEROT CCD ANNULAR-SUMMING SPECTROSCOPY - STUDY AND IMPLEMENTATION FOR AERONOMY APPLICATIONS

The technique of Fabry-Perot CCD annular-summing spectroscopy, with pa rticular emphasis on applications in aeronomy, is discussed. Parameter choices for optimizing performance by the use of a standard format CC D array are detailed. Spectral calibration methods, techniques for det ermining the ring pattern center, and effects imposed by limited radia l resolution caused by superpixel size, variable by on-chip binning, a re demonstrated. The technique is carefully evaluated experimentally r elative to the conventional scanning Fabry-Perot that uses a photomult iplier detector. We evaluate three extreme examples typical of aeronom ical spectroscopy using calculated signal-to-noise ratios. Predicted s ensitivity gains of 10-30 are typical. Of the cases considered, the la rgest savings in integration time are estimated for the day sky thermo spheric (OD)-D-1 case, in which the bright sky background dominates th e CCD read noise. For profile measurements of faint night sky emission lines, such as exospheric hydrogen Balmer-alpha, long integration tim es are required to achieve useful signal-to-noise ratios. In such case s, CCD read noise is largely overcome. Predictions of a factor of 10-1 5 savings in integration time for night sky Balmer-alpha observations are supported by field tests. Bright, isolated night sky lines such as thermospheric (OD)-D-1 require shorter integration times, and more mo dest gains dependent on signal level are predicted. For such cases it appears from estimate results that the Fabry-Perot CCD annular-summing technique with a conventional rectangular format may be outperformed by a factor of 2-5 by special CCD formats or by unusual optical coupli ng configurations that reduce the importance of read noise, based on t he ideal transmission for any additional optics used in these configur ations. (C) 1996 Optical Society of America