C. Muller

Simultaneous measurements of No and No2 in the stratosphere

Abstract Simultaneous measurements of NO and NO 2 in the stratosphere leading to an NO x determination have been performed by means of i.r. absorption spectrometry using the Sun as a source in the 5·2 μm band of NO and in the 6·2 μm band of NO 2 . The observed abundance of NO P peaks at 26 km where it is equal to (4·2 ± 1) × 10 9 cm −3 . The volume mixing ratio of NO p was observed to vary from 1·3 × 10 −9 at 20 km to 1·3 × 10 −8 at 34 km.

The study of the martian atmosphere from top to bottom with SPICAM light on mars express

Abstract SPICAM Light is a small UV-IR instrument selected for Mars Express to recover most of the science that was lost with the demise of Mars 96, where the SPICAM set of sensors was dedicated to the study of the atmosphere of Mars (Spectroscopy for the investigation of the characteristics of the atmosphere of mars). The new configuration of SPICAM Light includes optical sensors and an electronics block. A UV spectrometer (118–320 nm, resolution 0.8 nm) is dedicated to Nadir viewing, limb viewing and vertical profiling by stellar occultation (3.8 kg). It addresses key issues about ozone, its coupling with H2O, aerosols, atmospheric vertical temperature structure and ionospheric studies. An IR spectrometer (1.2– 4.8 μm , resolution 0.4–1 nm) is dedicated to vertical profiling during solar occultation of H2O, CO2, CO, aerosols and exploration of carbon compounds (3.5 kg). A nadir looking sensor for H2O abundances (1.0– 1.7 μm , resolution 0.8 nm) is recently included in the package (0.8 kg). A simple data processing unit (DPU, 0.9 kg) provides the interface of these sensors with the spacecraft. In nadir orientation, SPICAM UV is essentially an ozone detector, measuring the strongest O3 absorption band at 250 nm in the spectrum of the solar light scattered back from the ground. In the stellar occultation mode the UV Sensor will measure the vertical profiles of CO2, temperature, O3, clouds and aerosols. The density/temperature profiles obtained with SPICAM Light will constrain and aid in the development of the meteorological and dynamical atmospheric models, from the surface to 160 km in the atmosphere. This is essential for future missions that will rely on aerocapture and aerobraking. UV observations of the upper atmosphere will allow study of the ionosphere through the emissions of CO, CO+, and CO2+, and its direct interaction with the solar wind. Also, it will allow a better understanding of escape mechanisms and estimates of their magnitude, crucial for insight into the long-term evolution of the atmosphere. The SPICAM Light IR sensor is inherited from the IR solar part of the SPICAM solar occultation instrument of Mars 96. Its main scientific objective is the global mapping of the vertical structure of H2O, CO2, CO, HDO, aerosols, atmospheric density, and temperature by the solar occultation. The wide spectral range of the IR spectrometer and its high spectral resolution allow an exploratory investigation addressing fundamental question of the possible presence of carbon compounds in the Martian atmosphere. Because of severe mass constraints this channel is still optional. An additional nadir near IR channel that employs a pioneering technology acousto-optical tuneable filter (AOTF) is dedicated to the measurement of water vapour column abundance in the IR simultaneously with ozone measured in the UV. It will be done at much lower telemetry budget compared to the other instrument of the mission, planetary fourier spectrometer (PFS).

Global results of grille spectrometer experiment on board Spacelab 1

Measurements of atmospheric trace gases have been performed during the first Spacelab mission, on board the Space Shuttle, from 28 November to 8 December 1983. The principle of the observations is absorption spectroscopy, in the infrared, using the sun as a light source during sunset or sunrise periods. The instrumental set-up and the flight operations, already described in previous papers, are briefly summarized. The automatic retrieving method for the processing of the spectra is explained. Finally, all the results, in terms of vertical concentration profiles, are given for NO, NO2, CH4, N2O, CO, CO2 and H2O. Several results have been published (Laurent et al., 1985, Nature315, 126; Muller et al., 1985a, J. Optics (Paris) 16, 155 ; 1985b, Geophys. Res. Lett.12, 667 ; Vercheval el al., 1986, Ann. Geophys.4A, 161 ; Laurent et al., 1986, Planet. Space Sci.34, 1067). This last version may be slightly different, due to recently available and more accurate orbital parameters.

An AOTF-based spectrometer for the studies of Mars atmosphere for Mars Express ESA mission

The SPICAM Light optical package on the ESA Mars Express mission is dedicated to the nadir and limb observations in the UV between 118 nm and 320 nm, and has originally included an IR solar occultation channel, an inheritance of the IR part of the SPICAM solar occultation instrument for Mars 96. Because of severe mass constrains of the mission this channel has been replaced by a lightweight (0.7 kg) near infrared instrument that employs a new technology acousto-optical tuneable filter (AOTF). This channel is dedicated to the nadir measurements of water vapour column abundance in the near infrared between 1 and 1.7 μm simultaneously with ozone measured in the UV. In addition to the measurements of water vapour column abundance in the band of 1.38 μm, the NIR nadir spectrometer will measure the CO2 quantity in the bands of 1.43, 1.57-1.6 μm, and, consequently, the surface pressure (with known topography); and will contribute to the studies of atmospheric aerosols and the surface, by spectro-polarimetry measurements. Fully functional model of the instrument has been assembled, has been undergone a number of tests; the spectra of terrestrial atmospheric transmittance have been recorded. The scientific context of the experiment will be discussed along with the instruments description; current development status and the calibration results will be presented.

Atmospheric Physics and Earth Observations Sample Performance of the Grille Spectrometer

The grille spectrometer observed the setting and rising sun 18 times during the Spacelab 1 mission. In addition to solar absorption lines, many of which had not been observed before, atmospheric spectral absorptions due to carbon monoxide and carbon dioxide were observed at heights tangent to the thermosphere (greater than 85 kilometers), and absorptions due to ozone, water, methane, and nitrous oxide were observed in the mesosphere (greater than 50 kilometers). The strongly coupled molecules NO-NO2 and HC1-HF were observed as pairs in the stratosphere. Methane is presented as an example of the instrumental operations because of the characteristic aspect of the Q branch of its v3 band.

Trace constituents measurements deduced from spectrometric observations on-board spacelab

Abstract The observation of infrared absorption lines by means of a grille spectrometer on board Spacelab 1 allows the determination of Co2 and CO in the low thermosphere and in the middle atmosphere. Equal abundances of CO and CO2 are found at 115 ± 5 km altitude. CO2 is observed to depart from its homospheric volume mixing ratio near 100 km, dropping by a factor of 10,15 km higher. The CO largest number density is observed near 70 km altitude, close to the H Lyman alpha photoproduction peak. The analysis of one run dedicated to the observation of water vapor shows a middle atmospheric mixing ratio of this species within the limits : 3 to 8 ppmv up to 70 km altitude, with the indication of an increase from 30 to 50 km altitude. The H2O mixing ratio drops very rapidly above 70 km. The comparison of the results from strong and weak H2O and CO2 lines shows the need to refine the line profile model.

Sterilisation properties of the Mars surface and atmospheric environment.

The radiative and chemical conditions at the surface and in the lower Martian atmosphere are computed at various latitudes and seasons combining a 2D photochemical model and radiation simulations. In most situations, the solar UV B and C radiations reach the surface however, suspended dust and, in polar cases, ozone can constitute an effective UV shield. The daytime and night time concentrations of the sterilizing oxidants: OH, H2O2 and O3 are determined, as well as the concentration of the substances which could influence the metabolism of microorganisms. The possible habitats of a remaining Mars life as well as the possibilities of contamination by resistant earth life forms will be described.

Middle atmospheric water vapor observed by the Spacelab one grille spectrometer

Two water vapor atmospheric concentration profiles have been obtained, one at 33°N, 59°E and the other at 68°S, 124°W, during the Spacelab One flight respectively on 2 and 1 December 1983. These profiles extend from the middle stratosphere up to mesopause and show significant differences above the altitude of 70 km, the Antarctic profile showing then higher concentrations. This result correlates with Spacelab One carbon monoxide observations and SM E ozone results as far as the hydroxyl radical chemistry is concerned.

Second flight of the Spacelab Grille Spectrometer during the ATLAS‐1 mission

The SPACELAB grille spectrometer on its second space flight during the ATLAS-1 mission (March 24-April 2, 1992) took advantage of the favorable timeline and of the extra day to perform more than 65 successful solar occultation runs. It succeeded in obtaining spectra pertinent to its ten target molecules in the full range of altitudes available to the solar infrared occultation technique. These ten molecules are H[sub 2]O, CO, CO[sub 2], CH[sub 4], NO, NO[sub 2] N[sub 2]O, HCl, HF and O[sub 3]. The preliminary analysis of the sunset observation presented here adds new information to the available database on HCl vertical profiles, for assessing long-term trends of this important stratospheric species. 11 refs., 4 figs., 1 tab.

SPICAM-light on Mars-Express as a monitor of surface UV radiation and atmospheric oxidants

Abstract The SPICAM-light optical package on the ESA Mars-Express mission includes a UV radiation channel to perform nadir and limb observation between 118 and 320 nm as well as an infrared channel extending between 1 and 1.7 μm . The UV resolution will be 0.5 nm per pixel. This spectral range was chosen for the observation of the total column and vertical distribution of ozone, aerosols and other gases; it is also aimed at the Martian upper atmosphere where the obtained data will help to constrain the escape problem. The associated infrared channel specialises in water vapour. The UV range corresponds exactly to the UV-B and UV-C spectral domains and will be used to determine the solar mid-UV radiation received at the surface and to establish its climatology. Signal simulations are performed using the results of a 2-D Martian model as input (Moreau, Thesis, Universite Libre de Bruxelles, Brussels, Belgium 1995; Moreau, Fonteyn, Two-dimensional study of the atmospheric and surface oxidants on Mars, Proceedings of the Fifth International Conference on Mars, Lunar and Planetary Institute Contribution, Vol. 972, 1999, p. 6093) in order to show the influence of ozone and aerosol distributions on this radiation. Possibility of a UV shield exists during extreme polar ozone maxima as well as during dust storms, due to the UV absorption of Martian dust. In the other more normal cases, the daytime mid-UV radiation between 200 and 320 nm penetrates in sufficient amount to prevent the development of surface micro-organisms. Other life science conclusions could be drawn from the SPICAM-light observations: the direct mapping of water vapour will constrain the possible occurrences of subsurface liquid water that could be a favourable environment for the survival of life. SPICAM-light by its mapping of ozone and water vapour will also allow determining the amount of oxidants and especially OH. These could also affect the survival of Martian or contaminating bacteria. It is also intended to achieve a sufficient signal quality to measure an upper limit of lower atmospheric H2O2 and NO which are also related in diverse ways to living processes.