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SPEX (Spectropolarimeter for Planetary Exploration) was developed in close cooperation between scientific institutes and space technological industries in the Netherlands. It is used for measuring microphysical properties of aerosols and cloud particles in planetary atmospheres. SPEX utilizes a number of novel ideas. The key feature is that full linear spectropolarimetry can be performed without the use of moving parts, using an instrument of approximately 1 liter in volume. This is done by encoding the degree and angle of linear polarization (DoLP and AoLP) of the incoming light in a sinusoidal modulation of the intensity spectrum. Based on this principle, and after gaining experience from breadboard measurements using the same principle, a fully functional prototype was constructed. The functionality and the performance of the prototype were shown by extensive testing. The simulated results and the laboratory measurements show striking agreement. SPEX would be a valuable addition to any mission that aims to study the composition and structure of planetary atmospheres, for example, missions to Mars, Venus, Jupiter, Saturn and Titan. In addition, on an Earth-orbiting satellite, SPEX could give unique information on particles in our own atmosphere. © 2011 SPIE.

We present the Spectropolarimeter for Planetary EXploration (SPEX), a high-accuracy linear spectropolarimeter measuring from 400 to 800 nm (with 2 nm intensity resolution), that is compact (~ 1 liter), robust and lightweight. This is achieved by employing the unconventional spectral polarization modulation technique, optimized for linear polarimetry. The polarization modulator consists of an achromatic quarter-wave retarder and a multiple-order retarder, followed by a polarizing beamsplitter, such that the incoming polarization state is encoded as a sinusoidal modulation in the intensity spectrum, where the amplitude scales with the degree of linear polarization, and the phase is determined by the angle of linear polarization. An optimized combination of birefringent crystals creates an athermal multiple-order retarder, with a uniform retardance across the field of view. Based on these specifications, SPEX is an ideal, passive remote sensing instrument for characterizing planetary atmospheres from an orbiting, air-borne or ground-based platform. By measuring the intensity and polarization spectra of sunlight that is scattered in the planetary atmosphere as a function of the single scattering angle, aerosol microphysical properties (size, shape, composition), vertical distribution and optical thickness can be derived. Such information is essential to fully understand the climate of a planet. A functional SPEX prototype has been developed and calibrated, showing excellent agreement with end-to-end performance simulations. Calibration tests show that the precision of the polarization measurements is at least 2 • 10-4. We performed multi-angle spectropolarimetric measurements of the Earth's atmosphere from the ground in conjunction with one of AERONET's sun photometers. Several applications exist for SPEX throughout the solar system, a.o. in orbit around Mars, Jupiter and the Earth, and SPEX can also be part of a ground-based aerosol monitoring network.

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.

The TROPOspheric Monitoring Instrument (TROPOMI) is a UV/VIS/NIR/SWIR non-scanning nadir viewing imaging spectrometer that combines a wide swath (110°) with high spatial resolution (8 x 8 km). Its main heritages are from the Ozone Monitoring Instrument (OMI) and from SCIAMACHY. Since its launch in 2004 OMI has been providing, on a daily basis and on a global scale, a wealth of data on ozone, NO 2 and minor trace gases, aeros ols and local pollution, a scanning spectrometer launched in 2004. The TROPOMI UV/VIS/NIR and SWIR heritage is a combination of OMI and SCIAMACHY. In the framework of development programs for a follow-up mission for the successful Ozone Monitoring Instrument, we have developed the so-called TROPOMI Integrated Development Environment. This is a GRID based software simulation tool for OMI follow-up missions. It includes scene generation, an instrument simulator, a level 0-1b processing chain, as well as several level 1b-2 processing chai ns. In addition it contains an error-analyzer, i.e. a tool to feedback the level 2 results to th e input of the scene generator. The paper gives a description of the TROPOMI instrument and focuses on design aspects as well as on the performance, as tested in the end-to-end development environment TIDE. Keywords: TROPOMI, Air Quality, Grid Assist, TIDE, spectrograph

The free-free IR excess and the IR emission lines of H and He I of the Luminous Blue Variable P Cygni are observed with the ISO-SWS instrument. The observed profiles and the free-free emission are compared with predictions from a non-LTE model atmosphere with a stellar wind. The observations agree very well with a model that has the following properties: T_eff_=18100K, R_*_=76Rsun_, He/H=0.30 by number, ˙(M)=3.0x10^-5^Msun_/yr and vinfinity_=185km/s. We observed forbidden emission lines of [Fe II], [Fe III], [Ni II], [Ne II], [Ne III] and [Si II]. From the study of the [Ne II] and [Ne III] lines we find that the Ne abundance is about three times higher than normal. This may be due to clumping in the CS envelope at r=~10^3^R_*_.