Possible Fringe Removal Methods

When a spectrum with fringes is ploted against wavenumber [cm^-1] rather than wavelength, the fringes are of a very constant period amplitude. They may show up in some detectors more obviously in others due to signal and noise present at each wavelength.

The Fourier component of the fringe waveform however is very narrow, traced by only two FFT components. When the presence of the fringe is noticed on one detector it may be removed in all detectors by zeroing the Fourier components responsible in all detectors. The components may then be reestablished at these frequencies by maximum entropy considerations.

This form of glitch removal has proven quite successful in tests, and is likely to become part of ISAP, the post-pipeline science analysis package (ISO Spectroscopic Analysis Package).

A second possible way to eliminate the problem is through calibration using a spectral response function that has the appropriate fringes "built-in." The following SRF's have fringes by virtue of the fact that they were prepared while observing an extended source. Different sets of such functions could be provided to users. This idea is under consideration.

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Last update: August 1998

Steve Lord -- lord@heaven.ipac.caltech.edu