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The ESA (European Space Agency) Sentinel-5 Precursor (S-5 P) is a low Earth orbit polar satellite to provide information and services on air quality, climate and the ozone layer in the timeframe 2015-2022. The S-5 P mission is part of the Global Monitoring of the Environment and Security (GMES) Space Component Programme. The payload of the mission is the TROPOspheric Monitoring Instrument (TROPOMI) that will measure key atmospheric constituents including ozone, NO2, SO2, CO, CH4, CH2O and aerosol properties. TROPOMI has heritage to both the Ozone Monitoring Instrument (OMI) as well as to the SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY). The S-5 P will extend the data records of these missions as well as be a preparatory mission for the Sentinel-5 mission planned for 2020 onward. The mission is pre-operational and is the link between the current scientific and the operational Sentinel-4/-5 missions. This contribution describes the science and mission objectives, the mission and the instrument, and the data products. While building on a solid foundation of the heritage instruments, the S-5P/TROPOMI mission is an exciting step forward with a strong focus on the troposphere. This is achieved by a combination of a high spatial resolution and improved signal-to-noise, as well as dedicated data product development. It is anticipated that the S-5 P mission will make a large contribution to the monitoring of the global atmospheric composition, as well as to the scientific knowledge of relevant atmospheric processes. © 2012 Elsevier Inc.

SPEX (Spectropolarimeter for Planetary EXploration) is an innovative, compact instrument for spectropolarimetry, and in particular for detecting and characterizing aerosols in planetary atmospheres. With its ∼1-liter volume it is capable of full linear spectropolarimetry, without moving parts. The degree and angle of linear polarization of the incoming light is encoded in a sinusoidal modulation of the intensity spectrum by an achromatic quarter-wave retarder, an athermal multiple-order retarder and a polarizing beam-splitter in the entrance pupil. A single intensity spectrum thus provides the spectral dependence of the degree and angle of linear polarization. Polarimetry has proven to be an excellent tool to study microphysical properties (size, shape, composition) of atmospheric particles. Such information is essential to better understand the weather and climate of a planet. The current design of SPEX is tailored to study Martian dust and ice clouds from an orbiting platform: a compact module with 9 entrance pupils to simultaneously measure intensity spectra from 400 to 800 nm, in different directions along the flight direction (including two limb viewing directions). This way, both the intensity and polarization scattering phase functions of dust and cloud particles within a ground pixel are sampled while flying over it. We describe the optical and mechanical design of SPEX, and present performance simulations and initial breadboard measurements. Several flight opportunities exist for SPEX throughout the solar system: in orbit around Mars, Jupiter and its moons, Saturn and Titan, and the Earth. © 2010 SPIE.