ISO Callibration

ISO Calibration Documents

List of contents:

The calibration of ISO data. I (General)
The calibration of ISO data. II (per instrument)
Other documents

The calibration of ISO data. I (General)

Definition of ISO calibration standards


The absolute flux calibration of three of the four ISO instruments (CAM, SWS, and PHT in the 2.5 to 45 micron range) is based primarily on results obtained on stars selected from the ISO Ground-Based Preparatory Programme (GBPP) and from the Cohen, Walker, Witteborn et al. (CWW) absolute calibration programme. The confidence in the absolute flux level of the calibration stars is about 3% in the 2.5 to 35 microns wavelength range and better than 10% at longer wavelengths up to 300 microns.


Asteroids are used to cover the 35 to 200 microns wavelength range in ISO calibration since stars are usually too faint to be used in this wavelength range. An extensive ground and airborne based calibration programme was carried out to quantify the fluxes and to monitor the light curves of the prime asteroids 1 Ceres, 2 Pallas, 4 Vesta, and 10 Hygiea, and other asteroids that have been observed with ISO. For the current calibration the absolute fluxes of the asteroids were derived using a thermophysical model (Mueller and Lagerros 1998). The accuracy of the predicted asteroid fluxes is in general 10% in the wavelength range from 24 to 500 microns.


The outer planets Neptune and Uranus were used for calibration at the longer wavelengths in the high flux density range up to 1000 Jy. The model SED's for a given time in the mission were provided by M. Abbas. Currently, the absolute flux calibration of LWS is based on an updated Uranus model as primary source provided by Griffin and Orton (1993). Comparison with independent model predictions for Uranus showed a consistency of better than 20% in the wavelength range between 30 and 240 microns. At shorter wavelengths the models become less certain.

Photometric and spectral data

  • Results from the ISO Ground-Based Preparatory Programme (GBPP). They consist of near and mid-IR photometry of a wide sample of stars observed from La Palma (P. Hammersley) and ESO-La Silla (N. van der Bliek, J. Manfroid and P. Bouchet) observatories.

  • Results from M. Cohen et al., including calibrated spectra and extrapolations to 300 microns for a few stars.


  • Models of Uranus and Neptune

  • Model spectra of stars in the Ground Based Preparatory Program. The visible magnitudes and near-infrared photometry observed in the GBPP have been fitted with a Kurucz model to provide the flux densities at longer wavelengths. The overall spectral energy distribution is believed to be correct within 5% .

  • Model spectra assembled from ground-based and KAO observations from M Cohen et al.

    Definition of the system zero-points

  • The model spectra of Vega (1-300 microns, R = 4000 throughout, 400 kB) provides the definition of the system zero points (by adoption of the ideal [i.e. model] Vega as zero magnitude in every passband) so that long wave measurements can be quoted in magnitudes or at least with reference to a common context as measurements at other shorter wavelengths.

  • The model spectral energy distribution of Sirius (1-300 mic, R = 1000 up to 35 microns) is also available. This star was also considered a primary reference star for calibration purposes.

    The calibration of ISO data. II (per instrument)

    Absolute Flux Calibration of CAM

  • Absolute Flux Calibration of LWS

    Absolute Flux Calibration of PHT

    Absolute Flux Calibration of SWS

    Other documents


    Page maintained by Pedro Garcia-Lario
    (Last update: 19-07-2000)