Search

This paper is devoted to the phenomenological derivation of the vector radiative transfer equation (VRTE) accounting for first-order source terms of rotational Raman scattering (RRS), which is responsible for the in-filling of Fraunhofer and telluric lines by inelastic scattered photons. The implementation of the solution of the VRTE within the framework of the forward-adjoint method is given. For the Ca II and the oxygen A-band (O 2 A) spectral windows, values of reflectance, degree of linear polarization (DOLP) and in-filling, in zenith and nadir geometry, are compared with results given in literature. Moreover, the dependence of these quantities on the columnar loading and vertical layering of non-spherical dust aerosols is investigated, together with their changes as function of two habits of ice crystals, modeled as regular icosahedra and severely rough aggregated columns. Bi-directional effects of an underlying polarizing surface are accounted for. The forward simulations are performed for one selected wavelength in the continuum and one in the strong absorption of the O 2 A, as their combination can be exploited for the spaceborne retrieval of aerosol and cloud properties. For this reason, we also mimic seasonal maps of reflectance, DOLP and in-filling, that are prototypical measurements of the Ultraviolet-Visible-Near Infrared (UVN) sensor, at a nominal spectral resolution of 0.12 nm. UVN is the core payload of the upcoming European Sentinel-4 mission, that will observe Europe in geostationary orbit for air quality monitoring purposes. In general, in the core of O 2 A, depending on the optical thickness and altitude of the scatterers, we find RRS-induced in-filling values ranging from 1.3% to 1.8%, while DOLP decreases by 1%. Conversely, while negligible differences of RRS in-filling are calculated with different ice crystal habits, the severely rough aggregated column model can reduce DOLP by a factor up to 10%. The UVN maps of in-filling show values varying between 1% and 8%. These changes are mainly driven by surface type and seasonal observational geometry. However, accounting for RRS, differences in DOLP do not exceed ± 0.2% within the full instrumental field-of-view. [ABSTRACT FROM AUTHOR]

The Sentinel-4 payload is a multi-spectral camera system which is designed to monitor atmospheric conditions over Europe. The German Aerospace Center (DLR) in Berlin, Germany conducted the verification campaign of the Focal Plane Subsystem (FPS) on behalf of Airbus Defense and Space GmbH, Ottobrunn, Germany. The FPS consists, inter alia, of two Focal Plane Assemblies (FPAs), one for the UV-VIS spectral range (305 nm ... 500 nm), the second for NIR (750 nm ... 775 nm). In this publication, we will present in detail the opto-mechanical laboratory set-up of the verification campaign of the Sentinel-4 Qualification Model (QM) which will also be used for the upcoming Flight Model (FM) verification. The test campaign consists mainly of radiometric tests performed with an integrating sphere as homogenous light source. The FPAs have mainly to be operated at 215 K ± 5 K, making it necessary to exploit a thermal vacuum chamber (TVC) for the test accomplishment. This publication focuses on the challenge to remotely illuminate both Sentinel-4 detectors as well as a reference detector homogeneously over a distance of approximately 1 m from outside the TVC. Furthermore selected test analyses and results will be presented, showing that the Sentinel-4 FPS meets specifications. [ABSTRACT FROM AUTHOR]

The Institute for Optical Sensor Systems was involved in many international space projects in recent years. These include, for example, the fokal plane array (FPA) of the hyperspectral sensors ENMAP or Sentinel-4, but also the FPA for the high resolution FPA for Kompsat-3. An important requirement of the customer is the measurement of the detector MTF for different wavelengths. A measuring station under clean room conditions and evaluation algorithms was developed for these measurements. The measurement setup consist of a collimator with slit target in focus for illumination at infinity, a gimbal mounted detector facing an auxiliary lens in front, a halogen lamp with monochromator or filter, as well as optical and electrical ground support equipment. Different targets and therefore also different measurement and data evaluation opportunities are possible with this setup. Examples are slit, edge, pin hole but also a Siemens star. The article describes the measurement setup, the different measuring and evaluation procedures and exemplary results for Sentinel-4 detector. [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric chemistry observations from space have been made for more than 30years. They have been motivated by the concern about a number of environmental issues. However, most of the space instruments have been designed for scientific research, improving the understanding of processes that govern stratospheric ozone depletion, climate change and the transport of pollutants starting with the BUV instrument on Nimbus-4. Long-term continuous time series of atmospheric trace gas data have been limited to stratospheric ozone and a few related species. According to current planning, meteorological satellites will maintain some of these observations over the next decade. They will also add some measurements of tropospheric climate-relevant gases. As their measurements are motivated by meeting operational meteorology needs, they fall short in meeting requirements for atmospheric chemistry applications. Reliable long-term space-based monitoring of atmospheric constituents with quality attributes sufficient to serve atmospheric chemistry applications still needs to be established. The general framework for this kind of measurements, in synergy with ground-based and airborne measurements and integration with atmospheric models and data assimilation schemes, has been outlined in the IGOS-IGACO Theme Report (Barrie & Langen, 2004). Several other efforts have been made to identify the needs of long-term atmospheric composition data, such as [•] the GMES-GATO report (2004), [•] Report of the GMES atmospheric service (GAS) Implementation Group (GACS, 2009), [•] Global Climate Observing System (GCOS) Implementation Plan (GCOS, 2010), [•] Report of the Protocol Monitoring for the GMES Service Element, Atmosphere Service (PROMOTE, 2009), [•] studies commissioned by EUMETSAT to identify requirements for geostationary platforms in the context of Meteosat Third Generation (MTG) (Lelieveld, 2003), and [•] the position paper of the EUMETSAT post-EPS Application Expert Group on atmospheric chemistry (Kelder et al., 2006). An ESA study on ‘Operational Atmospheric Chemistry Monitoring Missions (CAPACITY)’ (Kelder et al., 2007) had established comprehensive observational requirements by environmental theme, by user group, and by observational system (ground/satellite). The study assessed the contributions of existing missions to the fulfilment of these requirements and identified priorities of future observational capabilities for atmospheric composition. The ESA study on ‘Observation Techniques and Mission Concepts for Atmospheric Chemistry’ (CAMELOT, Levelt et al., 2009) contributed to the definition of the space based monitoring capabilities of GMES for air quality protocol monitoring, air-quality near-real-time applications, and climate protocol monitoring in the time frame 2012–2020: The key objective of the CAMELOT study was to consolidate requirements at radiance level, i.e. Level-1, for the Sentinel-4 and -5 missions. The need for space based atmospheric composition monitoring will be addressed by a variety of instruments. A significant contribution will be provided by the GMES (Global Monitoring for Environment and Security) Sentinel-4 and -5 systems where Sentinel-4 provides a geosynchronous component with a European focus and Sentinel-5 a low Earth orbiting component with global coverage. Sentinel-5p will bridge the gap between existing missions, i.e. Sciamachy on Envisat and OMI on EOS-Aura, and Sentinel-5. [Copyright &y& Elsevier]