SPICAM IR acousto‐optic spectrometer experiment on Mars Express

Abstract

[1] The SPICAM IR spectrometer on Mars Express mission (1.0-1.7 mm, spectral resolution 0.5-1.2 nm) is dedicated primarily to nadir measurements of H 2 O abundance. It is one of two channels of SPICAM UV-IR instrument. In this spectrometer we applied for the first time in planetary research the technology of an acousto-optic tunable filter (AOTF) that allowed unprecedented mass reduction for such an instrument: 0.75 kg. SPICAM IR is a point nadir-looking spectrometer with sequential scanning of the spectrum by the AOTF. Sun occultations are performed with a help of dedicated solar port. We describe instrumentation, calibrations, and the modes of operations of the device and discuss its in-flight performances. A brief overview of the scientific measurements includes water vapor measurements and the mapping of intensity of the O 2 (a 1 D g ) emission at 1.27 mm, described in detail in separate papers. Measurements in reflected solar light allow clear detection of H 2 O and CO 2 ices on the surface or in the atmosphere of Mars. We discuss solar occultation measurements by SPICAM and present resulting vertical profiles of aerosol optical depth.

Mars’ water vapor mapping by the SPICAM IR spectrometer: Five martian years of observations

“…Hence, we will present the results for the first detector. The standard observation mode of SPICAM IR in nadir takes 6 s and contains several gaseous absorption bands including the 1.38 lm band of H 2 O, the 1.43 lm band of CO 2 , and the 1.27 lm O 2 emission (see Korablev et al, 2006b;Fedorova et al, 2006). This mode has been used from Mars Express orbit 200 up to the time of this writing.…”

“…The calibration procedure for SPICAM IR related to water vapor is described in Korablev et al (2006b) and Fedorova et al (2006). The relatively low abundance of water vapor measured by SPICAM IR compared to other Mars-Express experiments, raised questions about the AOTF spectral leakage, or stray light, which may reduce the apparent depth of gaseous features and alter the retrieved water vapor value.…”

“…The general description, operating modes, and observations of the SPICAM IR spectrometer on Mars Express can be found in Korablev et al (2006b). SPICAM IR is a very light (0.8 kg) spectrometer based on the principle of acousto-optic filtration (AOTF) of light in the wavelength range of 1-1.7 lm.…”

“…To measure water absorption lines SPICAM does not record a complete spectrum but a limited spectral window in the range of 1.348-1.44 lm (see Korablev et al, 2006b;Fedorova et al, 2006 for detailed explanation). As a result, when retrieving the water vapor abundance one needs to separate the absorption due to water vapor band from the spectral continuum.…”

AOTF spectrometers in space missions and their imaging capabilities

“…For the Mars Express mission by ESA SPICAM (Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars) was out of the model payload of the Mars Express project. Only an extremely lightweight near-IR spectrometer for the range of 0.9-1.7 µm based on AOTF technology was accepted by ESA as the IR channel of SPICAM [10][11][12]. The Mars Express orbiter has started science operations in January 2004.…”