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ExoMars Trace Gas Orbiter Instruments

NOMAD - Nadir and Occultation for MArs Discovery

Nadir and Occultation for MArs Discovery, or NOMAD, is part of the ExoMars Trace Gas Orbiter payload, launched in March 2016.

NOMAD proto-flight model.
Credit: ESA – B. Bethge
NOMAD flight spare model.
Credit: Belgian Institute for Space Aeronomy

NOMAD is a spectrometer suite that can measure the spectrum of sunlight across a wide range of wavelengths (infrared, ultraviolet and visible). This broad coverage of the instrument enables the detection of the components of the Martian atmosphere, even in low concentrations. In addition to identifying the constituents of the Martian atmosphere, NOMAD will also map their locations.

The measurements will be carried out in solar occultation, i.e. the instrument points toward the Sun when the Orbiter moves at the dark side of Mars, as well as in nadir mode, i.e. looking directly at the sunlight reflected from the surface and atmosphere of Mars. The inclination of the Orbiter has been chosen to optimise the science that can be done with the instrument suite.

NOMAD structural-thermal model.
Credit: Belgian Institute for Space Aeronomy
Schematic representation of NOMAD.
Credit: Belgian Institute for Space Aeronomy

NOMAD covers the infrared (2.2-4.3 µm) and the ultraviolet-visible (0.2-0.65 µm) spectral regions, using the following three operational modes:

  • The Solar Occultation mode (SO) operates by observing up to six small slices of the full spectral range each second. This allows observing several different target molecules that absorb at different wavelengths, whilst maximising the signal-to-noise ratio for each. During a solar occultation, which lasts about 5 minutes, 300 spectra at each wavelength can be taken providing a profile of the atmospheric composition from the top of the atmosphere down to almost the surface, depending on dust levels.

  • The Limb, Nadir and Occultation mode (LNO) is sensitive to the lower light levels during nadir observations on Mars. The nadir coverage will facilitate the study of the atmospheric composition in addition to examining Martian surface features, such as ice and frost. This measurement will be carried out on average every 3 to 4 sols (a solar day on Mars, or sol, is 24 hours and 39 minutes) with varying local times across the planet.

  • The Ultraviolet and Visible mode (UVIS) will image the wavelength domain between 200 and 650 nm, every second, covering and providing more information about several interesting molecules, such as ozone, sulphuric acid and aerosols in the atmosphere.


NOMAD participants
Principal Investigator
Ann Carine Vandaele, Belgian Institute for Space Aeronomy, Belgium

Co-Principal Investigators
José Lopez Moreno, Instituto de Astrofísica de Andalucía, Spain
Giancarlo Bellucci, Istituto Nazionale di Astrofisica, Italy
Manish Patel, The Open University, United Kingdom
Participating countries
Belgium, Spain, Italy, United Kingdom, United States of America, Canada
ESA contact
ExoMars instrument system engineer
André Debus, Directorate of Science and Robotic Exploration, European Space Agency


Last Update: 04 November 2016

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