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.
Sentinel-4 is an imaging UVN (UV-VIS-NIR) spectrometer, developed by Airbus Defence and Space GmbH under ESA contract in the frame of the joint EU/ESA COPERNICUS program. The mission objective is the operational monitoring of trace gas concentrations for atmospheric chemistry and climate over Europe. Sentinel-4 will provide accurate measurements of key atmospheric constituents such as ozone, nitrogen dioxide, sulfur dioxide, methane, and aerosol properties. The instrument is a hyperspectral imager. It is composed of two imaging spectrometers covering the spectral ranges of 305 – 500 nm and 750 – 775 nm and a telescope which projects an image of the Earth onto the slits of the spectrometers. The instrument will be placed in a geostationary orbit, and a 3D spectral-spatial data-cube will be acquired thanks to the mirror scanning in East-West direction. The Telescope Spectrograph Assembly (TSA) represents the core of the optical system inside the Optical Instrument Module (OIM). It is composed of one common Telescope, two Spectrographs and two Focal Plane Assemblies integrated and aligned into a three-dimensional supporting structure. The TSA is later integrated into the main instrument structure which already includes the Scan Mirror Unit, Calibration Assembly and Front Baffle; thus completing the full optical chain. This paper gives an overview of the TSA integration and alignment activities for the Proto Flight Model (PFM) performed at the Airbus premises in Ottobrunn, Germany. It describes the alignment philosophy developed to meet the challenging optical requirements, including for example, the spatial co-registration between the two spectrometers and the spatial sampling distance on ground, after the transition from ambient laboratory conditions to the instrument operating conditions in geostationary orbit. The results of the optical tests in operating conditions produced by the Optical Ground Support Equipment are also included and discussed in this paper.
KEYWORDS: Contamination, Absorption, Transmittance, Space operations, Sensors, Signal to noise ratio, Signal attenuation, Modeling, Confocal microscopy
ESA Sentinel-4 mission will monitor trace gas concentrations and aerosols in the Earth’s atmosphere with a 1-hour revisit frequency and unprecedented spatial resolution. Initial performance predictions, relying on literature/historical values for optical absorption coefficients, revealed considerable losses at the end of the mission lifetime caused mainly by high levels of absorption of light due to molecular contamination spread over the 39 optical surfaces of the UVIS channel. This publication describes the significant effort undertaken by Sentinel-4 team to establish more reliable and accurate performance predictions, and the importance of performing measurements under representative conditions of the instrument’s contamination environment. The refined performance prediction analysis was the final step of the activity, demonstrating that the end of life performance requirements of Sentinel-4 will be met.
Sentinel-4 is an imaging UVN (UV-VIS-NIR) spectrometer, developed by Airbus Defence and Space as prime contractor under ESA contract in the frame of the joint EU/ESA COPERNICUS program. The mission objective is the operational monitoring of trace gas concentrations for atmospheric chemistry and climate applications. Stray light, which is unwanted light captured by the detectors, is one of the major contributors to such important instrument performance metrics as absolute and relative spectral and spatial radiometric accuracies. Amongst the different sources of stray light, Out-of-Band stray light can not be corrected. It is thus important to ensure its impact is limited. The main scope of this paper is to describe the stray light simulations performed in the frame of the Sentinel-4 project: the models, analysis approach and the results. Also, the technical challenges faced in building the models and performing the analysis and the solutions found to solve them are presented.
Sentinel-4 is an imaging UVN (UV-VIS-NIR) spectrometer, developed by Airbus Defence and Space as prime contractor under ESA contract in the frame of the joint EU/ESA COPERNICUS program. The mission objective is the operational monitoring of trace gas concentrations for atmospheric chemistry and climate applications. This paper gives an overview of the Sentinel-4 system architecture, its design & development status.
Sentinel-4 is an imaging UVN (UV-VIS-NIR) spectrometer, developed by Airbus Defence and Space under ESA contract in the frame of the joint EU/ESA COPERNICUS program. The mission objective is the operational monitoring of trace gas concentrations for atmospheric chemistry and climate applications – hence the motto of Sentinel-4 “Knowing what we breathe”. Sentinel-4 will provide accurate measurements of key atmospheric constituents such as ozone, nitrogen dioxide, sulfur dioxide, methane, and aerosol properties over Europe and adjacent regions from a geostationary orbit (see Fig. 1). In the family of already flown UVN spectrometers (SCIAMACHY, OMI, GOME and GOME 2) and of those spectrometers currently under development (Sentinel-5p and Sentinel-5), Sentinel-4 is unique in being the first geostationary UVN mission. Furthermore, thanks to its 60-minutes repeat cycle measurements and high spatial resolution (8x8 km2), Sentinel-4 will increase the frequency of cloud-free observations, which is necessary to assess troposphere variability. Two identical Sentinel-4 instruments (PFM and FM-2) will be embarked, as Customer Furnished Item (CFI), fully verified, qualified and calibrated respectively onto two EUMETSAT satellites: Meteosat Third Generation-Sounder 1 and 2 (MTG-S1 and MTG-S2), whose Flight Acceptance Reviews are presently planned respectively in Q4 2021 and Q1 2030. This paper gives an overview of the Sentinel-4 system1 architecture, its design and development status, current performances and the key technological challenges.
KEYWORDS: Sensors, Ultraviolet radiation, Charge-coupled devices, CCD image sensors, Signal detection, Spectroscopy, Near infrared, Detector development, Data acquisition, Data modeling
The future ESA Earth Observation Sentinel-4/UVN is a high resolution spectrometer intended to fly on board a Meteosat Third Generation Sounder (MTG-S) platform, placed in a geostationary orbit. The main objective of this optical mission is to continuously monitor the air quality over Europe in near-real time. The Sentinel-4/UVN instrument operates in three wavelength bands: Ultraviolet (UV: 305-400 nm), Visible (VIS: 400- 500 nm) and Near-infrared (NIR: 750-775 nm). Two dedicated CCD detector have been developed to be used in the Focal Plane Subsystems (FPS), one for the combined UV and VIS band, the other covering the NIR band. Being a high resolution spectrometer with challenging radiometric accuracy requirements, both on spectral and spatial dimensions, an effect such the Random Telegraph Signal (RTS) can represent a relevant contribution for the complete system accuracy. In this work we analyze the RTS effect on data acquired during the FPS testing campaign with qualification models for the Sentinel-4/UVN detectors. This test campaign has been performed in late 2016. The strategy for the impact assessment of RTS is to measure the effect at room temperature and then to extrapolate the results to the at instrument operational temperature. This way, very-long lasting data acquisitions could be avoided since the RTS frequency is much lower at cryogenic temperatures. A reliable technique for RTS effect detection has been developed in order to characterize the signal levels amplitude and occurrence frequencies (flipping rate). We demonstrate the residual impact of the RTS on the global In-Orbit Sentinel-4/UVN instrument performance and products accuracy.
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