The European Space Agency (ESA), in collaboration with the European Commission (EC) and EUMETSAT, is developing as part of the EC’s Copernicus programme, six new missions to strengthen the already existing family of six Sentinels missions. The six new Sentinel Expansion missions cover four themes: Safeguarding the Artic, Monitoring Land and Natural Resources, Food Security and Management and Combating Climate Change. For this last theme, a space-borne observing system for quantification of anthropogenic carbon dioxide (CO2) emissions is in development. The anthropogenic CO2 monitoring (CO2M) mission will be implemented as a constellation of identical Low Earth Orbit satellites, to be operated over a period of more than seven years. Each satellite will continuously measure CO2 concentration in terms of column-averaged dry air mole fraction (denoted XCO2) along the satellite track on the sun-illuminated part of the orbit, with a swath width of 250 km. Observations will be provided at a spatial resolution of 4 km2, with high precision (⪅0.7 ppm) and accuracy (bias ⪅0.5 ppm), which are required to resolve the small atmospheric gradients in XCO2 originating from anthropogenic activities. The demanding requirements necessitate a payload composed of three instruments, which simultaneously perform co-located measurements: a push-broom imaging spectrometer in the Near Infrared (NIR) and Short-Wave Infrared (SWIR) for retrieving XCO2 and in the Visible spectral range (VIS) for nitrogen dioxide (NO2), a Multi Angle Polarimeter (MAP) and a three-band Cloud Imager (CLIM). Following the Satellite PDR, the industrial activities have concentrated in consolidating the design of the three instruments and the platform as well as completing the different development models. The paper presents the status of these activities which are leading to the Critical Design Review before entering into the flight manufacturing and assembly phase.
Thales Alenia Space has been selected to design and provide the payloads of the European Copernicus CO2M mission, whose main aim is to provide monitoring of the anthropogenic carbon dioxide emissions from space. Each payload is composed of : • The CO2 instrument, which is the instrument dedicated to measuring atmospheric CO2 and CH4. This dispersive instrument measures the spectral radiance in three bands (747-773, 1590-1675 and 1990-2095nm), used as inputs to the inverse models for determining total column concentrations for atmospheric CO2 and CH4. The instrument is designed for high spatial resolution, high spectral resolution, and high thermal and mechanical stabilities. • The CO2 instrument embeds an imaging spectrometer in the VIS 405-490nm band dedicated to measuring atmospheric NO2 content, permitting native nominal co-registration and optimized relative radiometric performances with the CO2 bands. This translates into an accurate tracing of anthropogenic CO2 plumes from power plants and cities while limiting the additional hardware and qualification procedures • This combined CO2 and NO2 instrument is the core of the payload, and two additional instruments of limited mass and volumes are embarked: a multi-angle polarimeter dedicated to aerosols measurement (MAP) to better account for cloud and aerosols scattering effects, and a cloud imager (CLIM) with high spatial resolution to accurately filter the data for cloud-contaminated samples. This article presents the payload design and development status.
The Copernicus missions Sentinel-4 (S4) and Sentinel-5 (S5) will carry out atmospheric composition observations on an operational long-term basis to serve the needs of the Copernicus Atmosphere Monitoring Service (CAMS) and the Copernicus Climate Change Service (C3S). Building on the heritage from instruments such as GOME, SCIAMACHY, GOME-2, OMI and S5P, S4 is an imaging spectrometer instruments covering wide spectral bands in the ultraviolet and visible wavelength range (305-500nm) and near infrared wavelength range (750-775 nm). S4 will observe key air quality parameters with a pronounced temporal variability by measuring NO2, O3, SO2, HCHO, CHOCHO, and aerosols over Europe with an hourly revisit time. A series of two S4 instruments will be embarked on the geostationary Meteosat Third Generation-Sounder (MTG-S) satellites. S4 establishes the European component of a constellation of geostationary instruments with a strong air quality focus, together with the NASA mission TEMPO (to be launched end 2022) [9] and the Korean mission GEMS (launched 19 February 2020) [8]. This paper addresses the result of the final and crucial phase for the end to end performance of the PFM instrument: the extensive on-ground Characterization and Calibration of the instrument that is happening during the summer/fall 2022. The paper presents an overview of the calibration campaign objectives, the main performance verification and calibration measurements and preliminary performances of the PFM as-built instrument.
The European Space Agency (ESA), in collaboration with the European Commission (EC) and EUMETSAT, is developing as part of the EC’s Copernicus programme, a space-borne observing system for quantification of anthropogenic carbon dioxide (CO2) emissions. The anthropogenic CO2 monitoring (CO2M) mission will be implemented as a constellation of identical Low Earth Orbit satellites, to be operated over a period of more than 7 years. Each satellite will continuously measure CO2 concentration in terms of column-averaged dry air mole fraction (denoted XCO2) along the satellite track on the sun-illuminated part of the orbit, with a swath width of 250 km. Observations will be provided at a spatial resolution < 4 km2 , with high precision (< 0.7 ppm) and accuracy (bias < 0.5 ppm), which are required to resolve the small atmospheric gradients in XCO2 originating from anthropogenic activities. The demanding requirements necessitate a payload composed of three instruments, which simultaneously perform co-located measurements: a push-broom imaging spectrometer in the Near Infrared (NIR) and Short-Wave Infrared (SWIR) for retrieving XCO2 and in the Visible spectral range (VIS) for nitrogen dioxide (NO2), a Multi Angle Polarimeter (MAP) and a three-band Cloud Imager (CLIM). Following the kick-off Mid 2020, the industrial activities have now passed the Satellite PDR allowing to enter the phase C/D. The paper summarises the payload activities performed during the phase B2 culminating with the PDR of the instruments and of the payload. The preliminary design of the CO2M mission’s instruments, the progress of the technological activities and the first results of the development models are presented.
SPEXone is a compact five–angle spectropolarimeter that is being developed as a contributed payload for the NASA Plankton, Aerosol, Cloud and ocean Ecosystem (PACE) observatory, to be launched in 2022. SPEXone will provide accurate atmospheric aerosol characterization from space for climate research, as well as for light path correction in support of the main Ocean Color Instrument. SPEXone employs dual beam spectral polarization modulation, in which the state of linear polarization is encoded in a spectrum as a periodic variation of the intensity. This technique enables high polarimetric accuracies in operational environments, since it provides snapshot acquisition of both radiance and polarization without moving parts. This paper presents the polarimetric error analysis and budget for SPEXone in terms of polarimetric precision and polarimetric accuracy. We consider factors that contribute to instrumental polarization and modulation efficiency, which will be calibrated on-ground with high, but finite accuracy. The sensitivity to dynamic systematic effects in a space environment, such as degradation and ageing of components and small variations in the temperature and thermal gradients is addressed and quantified. Finally, the impact of scene dependent error sources, mainly resulting from stray light, are assessed and the total polarimetric error budget is presented. We show that SPEXone complies with the radiometric SNR requirement of 300, yielding a minimum polarimetric precision of 200 (fully polarized light) to 300 (unpolarized light) over the full spectral range for dark ocean scenes at high solar zenith angle. Assuming a stray light correction factor of 5 and considering a moderate contrast scene, the expected in-flight polarimetric accuracy of SPEXone is 1.5 · 10−3 for unpolarized scenes and 2.9 · 10−3 for highly polarized scenes, compliant with the polarimetric accuracy requirement. This performance should enable SPEXone to deliver the data quality that enables unprecedented aerosol characterization from space on the NASA PACE mission.
We have developed a generic physical modeling scheme for high resolution spectroscopy based on simple optical principles. This model predicts the position of centroids for a given set of spectral features with high accuracy. It considers off-plane grating equations and rotations of the different optical elements in order to properly account for tilts in the spectral lines and order curvature. In this way any astronomical spectrograph can be modeled and controlled without the need of commercial ray tracing software. The computations are based on direct ray tracing applying exact corrections to certain surfaces types. This allows us to compute the position on the detector of any spectral feature with high reliability. The parameters of this model, which describe the physical properties of the spectrograph, are continuously optimized to ensure the best possible fit to the observed spectral line positions. We present the physical modeling of CARMENES as a case study. We show that our results are in agreement with commercial ray tracing software. The model prediction matches the observations at a pixel size level, providing an efficient tool in the design, construction and data reduction of high resolution spectrographs.
Hanle echelle spectrograph (HESP) is a high resolution, bench mounted, fiber-fed spectrograph at visible wavelengths. The instrument was recently installed at the 2m Himalayan Chandra Telescope (HCT), located at Indian Astronomical Observatory (IAO), Hanle at an altitude of 4500m. The telescope and the spectrograph are operated remotely from Bangalore,(∼ 3200km from Hanle), through a dedicated satellite link. HESP was designed and built by Kiwi Star Optics, Callaghan Innovation, New Zealand. The spectrograph has two spectral resolution modes (R=30000 and 60000). The low resolution mode uses a 100 micron fiber as a input slit and the high resolution mode is achieved using an image slicer. An R2 echelle grating, along with two cross dispersing prisms provide a continuous wavelength coverage between 350-1000nm. The spectrograph is enclosed in a thermally controlled environment and provides a stability of 200m/s during a night. A simultaneous thorium-argon calibration provides a radial velocity precision of 20m/s. Here, we present a design overview, performance and commissioning of the spectrograph.
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