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5.4 Aperture Calibration

For a given filter of the PHT-P subsystems, the FCS calibration was obtained from observations always taken with the same standard apertures or default apertures:

The applicability of the calibration to any given aperture is based on the following assumptions:

  1. the apertures are perfectly circular or rectangular,
  2. the effective solid angle of an aperture is proportional to its area,
  3. the solid angle of an aperture is independent of filter,
  4. the FCS in-band power is proportional to the area of an aperture.

The physical dimensions of the apertures were measured on ground and are given in Section A.1.2. From available calibration measurements deviations from these simple assumptions are clearly indicated:

For a subset of PHT04 observations the PHT off-line processing provides an analysis based on an empirical calibration scheme (Müller 2000a, [41]; Müller 2000b, [42]). In the analysis the normalised source signals of an aperture sequence are compared with the normalised signals of a calibration (point) source. Subsequently, the algorithm determines whether the source is point-like or extended, see Section 7.9.


next up previous contents index
Next: 5.5 PHT-S Wavelength Calibration Up: 5. Photometric Calibration Previous: 5.3 Point Sources Versus
ISO Handbook Volume IV (PHT), Version 2.0.1, SAI/1999-069/Dc