SMART Defringing - Theory

Fringing is a detector effect well known from other infra-red detectors. Its effects during the ISO mission are described here :

1. ISO Fringes 1?
2. ISO Fringes 2?

The first IRS test data taken at BALL Aerospace with 3 neutral density (ND) filters in series showed significant fringing at the 50% level.
Subsequent IRS tests with no ND filters in the beam revealed much weaker fringing at the <10% level,
but the beam in those tests had an unconstrained f-cone.

A detailed description can be found in Fringing in IRS High Resoloution Spectra? by Pat Morris.

Points to note about fringing in IRS :

• Fringing is limited to 1-2 main components but the frequencies varies across orders and even along one order,
  indicating varying thickness of the detector substrate.
• Defringing algorithms have been developed only for the SH and LH modules in which the fringes are resolved,
  and the LL module in which the dominant fringe component originates in the delaminated filter.
• The standard fringing removal (defringing) tool will be a 1-D interactive or batch-mode procedure using sine-wave & cross correlation methods.
  (FFT filtering techniques have been tested as well but found to be inferior.)
• 2-D defringing methods that would work on the 2-D FITS data file before the actual extraction of the spectra are under study.

The basis of the defringer software is described in SIRTF-IRS Defringing? by Fred Lahuis.

Beta testing of the software is described in Report on Tests of the Beta Defringer? by Martin Burgdorf.

On November 1st & 2nd 2001 a meeting was held at Cornell University about defringing.
Those present included Ewine van Dishoeck, Geoff Blake and Russ Shipman.
The minutes of the meeting? provide a summary.

Presentations on defringing were also made :

• Interactive Defringing of IRS High Resoloution Spectroscopy? by Pat Morris.
• An Outlandish IRS De-Fringing Hypothesis? by J.D. Smith.

Beta release of the SIRFT-IRS defringing software was on 4 September 2003.
A short overview is provided at SIRTF IRS SMART Defringing Beta Release? by Fred Lahuis.