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Several observational programmes were conducted with ISO (Kessler et al., 1996) aiming at the investigation of the near- and far- infrared spectrum of the satellites of the giant planets. Thus, Jupiter's satellites Callisto, Io and Ganymede were explored mainly with the spectrometers, while the spectrum of Titan, Saturn's largest satellite, was investigated thoroughly by all the instruments. The analysis of the data has provided original and precious information on the satellites' surfaces and Titan's atmosphere in particular.

A series of far infrared (FIR) spectra of Mars between 43 and 196 μm was taken with the Long Wavelength Spectrometer (LWS) on board the European Space Agency's Infrared Space Observatory (ISO). Analysis of these medium-resolution data reveals a rotational modulation of the disk-averaged FIR brightness temperature. The observed variability of ±1.5% in the LWS wavelength range compares favorably with the predictions of a thermophysical model of the martian surface. A surface emissivity of ∼0.90 gives good agreement between the measured and the modeled brightness temperatures and leads to an improved estimate of the LWS photometric calibration uncertainty.

Infrared spectra of Mars were taken with the two complementary spectrometers onboard the European Space Agency's Infrared Space Observatory (ISO), in both moderate- and high-resolution mode. From the strengths of the observed water lines we derived information about the vertical distribution of water vapor and on the emissivity of the dust/surface system in the infrared. Assuming atmospheric and surface temperatures derived from the European Martian Climate Database with a slight adjustment to the observed 15-μm CO2 band, the ISO data are consistent with an H2O mixing ratio of (3±1)×10−4 at the surface, a saturation level at 13±2 km, and a total column density of 12±3.5 pr-μm. The mean disk emissivity is found to be close to 1.0 at 6 μm and 0.92±0.02 at 40 μm. At longer wavelengths the emissivity decreases from a value of 0.97±0.03 at 50μm to 0.92±0.03 at 180 μm.

The short-wavelength spectrometer for the Infrared Space Observatory (ISO) is a cryogenic instrument operating at wavelengths from 2.45 to 45 μm, containing a grating spectrometer and a scanning Fabry-Perot interferometer. Some of the techniques used to build and test the instrument are described and some test results are presented, all from the viewpoint of cryoengineering.

We report the results of a series of experiments on the use of an extrinsic silicon photoconductor for heterodyne detection at 10.6 μm. An arsenic-doped sample was for these measurements, having a donor density of 3 × 10 16 cm −3 . The measurements were made at approximately 5 K, with a CO 2 laser providing the local oscillator power, and a calibrated blackbody at 900 K providing the signal. The signal-to-noise ratio was measured as a function of detector bias voltage for local oscillator powers ranging from 30 to 280 mW. The measured signal-to-noise ratio was found to be within 4 dB of the theoretically expected value. The 3 dB roll-off frequency was measured from the signal roll-off and from the laser-induced generation-recombination noise roll-off. Both measurements agreed closely. The detector response time determined from this measurement varied between 4 and 10 nsec, depending on the laser power and bias voltage.

The observation and quantative measurement of optical heterodyne detection at 337 μm using a HCN laser and an epitaxial n-type GaAs photoconductor are reported. The measured NEP amounted 1.4 × 10−14 W Hz−1.