Calibration of the Planetary Fourier Spectrometer short wavelength channel

The Planetary Fourier Spectrometer (PFS) experiment on board the Mars Express mission has two channels covering the 1.2–5.5 μ m short wavelength channel (SWC) and the 5.5–45 μ m (LWC). The SWC measures part of the thermal emission spectrum and the solar reflected spectrum of Mars between 1700 and 8200 cm−1 with a spectral resolution of 1.3 cm−1, in absence of apodisation. We present here the calibration of this channel and its performance. The instrument calibration has been performed on ground, before launch, in space during near earth verification (NEV) measurements, and at Mars. Special attention has been given to the problem of microvibrations on board the spacecraft. er to obtain correct results, the source–instrument–detector interaction for the thermal part is studied very accurately. The instrument shows a nonlinear behaviour with source intensity. The SNR increases with amplification, hence high gain factors are usually used. The detector is, in space, cooled by a passive radiator, and works around 210–215 K. The calibration source (an internal lamp) shows variations during a pericentre pass and therefore impose a complex procedure for the SW channel calibration. Mechanical microvibrations strongly affect part of the spectrum. We discuss the validity of the present calibration, and indicate possible future developments. Samples of the calibrated data are given to show the performance of the experiment and its scientific potentialities.