The EUMETSAT Polar System - Second Generation (EPS-SG) Visible/Infrared Imaging mission supports the optical
imagery user needs for Numerical Weather Prediction (NWP), Nowcasting (NWC) and climate in the timeframe beyond
2020. The VII mission is fulfilled by the METimage instrument, to be flown onboard the Metop-SG-A satellite series.
The instrument itself is a cross-purpose medium resolution, multi-spectral optical imager, measuring radiation emitted
and reflected by the Earth from a low-altitude sun synchronous orbit with a swath width of 2700 km. Measurements will
be made in 20 spectral channels ranging from 443 nm in the visible up to 13.345 μm in the thermal infrared at a spatial
sampling distance of 500 m at nadir.
This paper focuses on the Calibration and Validation (Cal/Val) activities planned for the METimage level 1B products to
ensure that the calibrated and geolocated radiances meet the performance specifications for the lifetime of the mission.
Such methods include cross-calibration with instruments on the same platform e.g. IASI-NG and Sentinel-5
measurements, inter-comparisons with other missions during simultaneous nadir overpasses, comparisons with ground
based observations and lunar calibration. The level 1B product performance will be validated with respect to geometric,
spectral, and radiometric requirements for all geographic regions including their seasonal variability. In particular the
following specific activities are described:
• Calibration verification
• Validation of radiometry
• Geometric verification
• Image quality verification
As the commissioning phase is limited in time, the products from METimage have to be confidence checked and
validated with a concise focus on essential tests. The Cal/Val activities will extend to routine operations in order to
ensure long term stability of the calibrated radiances and continually improve the calibration throughout the lifetime of
the mission.
In-orbit verification of the coregistration of channels in a scanning microwave or infrared radiometer can in principle be done during normal in-orbit operation, using the regular events of lunar intrusion in the instrument cold space calibration view. A technique of data analysis based on best fit of data across lunar intrusions has been used to check the mutual alignment of the spectral channels of the microwave humidity sounder (MHS) instrument. MHS is a cross-track scanning radiometer in the millimeter-wave range flying on EUMETSAT and NOAA polar satellites, used operationally for the retrieval of atmospheric parameters in numerical weather prediction and nowcasting. This technique does not require any special operation or maneuver and only relies on the analysis of data from the nominal scanning operation. The coalignment of sounding channels and window channels can be evaluated by this technique, which would not be possible using Earth landmarks, due to the absorption effect of the atmosphere. The analysis reported shows an achievable accuracy below 0.5 mrad against a beam width at 3 dB and spatial sampling interval of about 20 mrad. In-orbit results for the MHS instrument on Metop-B are also compared with the prelaunch instrument characterization, showing a good correlation.
In-orbit verification of the co-registration of channels in a scanning microwave or infrared radiometer can in principle be done during normal in-orbit operation, by using the regular events of lunar intrusion in the instrument cold space calibration view. A technique of data analysis based on best fit of data across lunar intrusions has been used to check the mutual alignment of the spectral channels of the MHS instrument. MHS (Microwave Humidity Sounder) is a cross-track scanning radiometer in the millimetre-wave range flying on EUMETSAT and NOAA polar satellites, used operationally for the retrieval of atmospheric parameters in numerical weather prediction and nowcasting. This technique does not require any special operation or manoeuvre and only relies on analysis of data from the nominal scanning operation. The co-alignment of sounding channels and window channels can be evaluated by this technique, which would not be possible by using earth landmarks, due to the absorption effect of the atmosphere. The analysis reported in this paper shows an achievable accuracy below 0.5 mrad against a beam width at 3dB and spatial sampling interval of about 20 mrad. In-orbit results for the MHS instrument on Metop-B are also compared with the pre-launch instrument characterisation, showing a good correlation.
The EPS-SG Visible/Infrared Imaging (VII) mission is dedicated to supporting the optical imagery user needs for Numerical Weather Prediction (NWP), Nowcasting (NWC) and climate in the timeframe beyond 2020. The VII mission is fulfilled by the METimage instrument, developed by the German Space Agency (DLR) and funded by the German government and EUMETSAT. Following on from an important list of predecessors such as the Advanced Very High Resolution Radiometer (AVHRR) and the Moderate resolution Imaging Spectro-radiometer (MODIS), METimage will fly in the mid-morning orbit of the Joint Polar System, whilst the early-afternoon orbits are served by the JPSS (U.S. Joint Polar Satellite System) Visible Infrared Imager Radiometer Suite (VIIRS). METimage itself is a cross-purpose medium resolution, multi-spectral optical imager, measuring the optical spectrum of radiation emitted and reflected by the Earth from a low-altitude sun synchronous orbit over a minimum swath width of 2700 km. The top of the atmosphere outgoing radiance will be sampled every 500 m (at nadir) with measurements made in 20 spectral channels ranging from 443 nm in the visible up to 13.345 μm in the thermal infrared. The three major objectives of the EPS-SG METimage calibration and validation activities are: • Verification of the instrument performances through continuous in-flight calibration and characterisation, including monitoring of long term stability. • Provision of validated level 1 and level 2 METimage products. • Revision of product processing facilities, i.e. algorithms and auxiliary data sets, to assure that products conform with user requirements, and then, if possible, exceed user expectations. This paper will describe the overall Calibration and Validation (Cal/Val) logic and the methods adopted to ensure that the METimage data products meet performance specifications for the lifetime of the mission. Such methods include inter-comparisons with other missions through simultaneous nadir overpasses and comparisons with ground based observations, analysis of algorithm internal diagnostics to confirm retrieval performance for geophysical products and vicarious calibration to assist with validation of the instrument on-board calibration. Any identified deficiencies in the products will lead to either an update any auxiliary data sets (e.g. calibration key data) that are used to configure the product processors or to a revision of algorithms themselves. The Cal/Val activities are mostly foreseen during commissioning but will inevitably extend to routine operations in order to take on board seasonal variations and ensure long term stability of the calibrated radiances and geophysical products. Pre-requisite to validation of products at scientific level is that the satellite and instrument itself have been verified against their respective specifications both pre-launch and during the satellite in-orbit verification phase.
The evolving needs of the meteorological community concerning the EUMETSAT Polar System follow-on satellite
mission (Post-EPS) require the development of a high-performance multi-spectral imaging radiometer, the so-called
Visible-Infrared Imager (VII). Recognizing these needs, Jena Optronik GmbH proposed an innovative instrument
concept, METimage. METimage is the candidate instrument to fulfill the VII mission on Post-EPS.
Core item of the METimage instrument is a rotating telescope scanner covering the large swath width of about 2800 km,
which is needed for a global coverage by a polar platform. The de-rotated image facilitates in-field spectral channel
separation, which allows tailoring individual channel GSD (ground sampling distance) and features like TDI (time delay
and integration). State-of-the-art detector arrays and read-out electronics will be employed. The reflecting telescope
design is able to support demanding requirements on image quality and ground resolution.
The chosen instrument concept covers a spectral range from 443 nm to 13.345 μm and provides 20 to 22 spectral
channels. The ground sampling distance is 500 m and 250 m for selected high-resolution channels from low Earth orbit.
The METimage instrument development is currently in phase B and has undergone its System Requirements Review in
summer 2010.
The Microwave Humidity Sounder (MHS) is the high-frequency microwave radiometer of the ATOVS
(Advanced TIROS Operational Vertical Sounder) instrument suite of the IJPS (Initial Joint Polar
System), the current joint EUMETSAT-NOAA programme for operational satellite meteorology. Five
MHS models have been built by Astrium Ltd under EUMETSAT contract, two of which are currently
operational on the NOAA-18 and Metop-A satellites. The MHS instrument replaces the former
AMSU-B in the operational microwave sounder suite. This paper provides a summary description of
the MHS instrument and describes in some detail its in-orbit performance and functionality, along with
a comparison with similar instruments. The in-orbit performance has been extensively assessed during
the SIOV (Satellite In-Orbit Verification), the first part of the commissioning phase aimed at activating
the payload and verifying its operation, and is periodically monitored throughout the mission life. The
performance relevant to the SIOV and operational phase of the MHS instruments on both NOAA-18
and Metop-A are presented. With respect to its predecessor AMSU-B, the MHS instrument constitutes
a sensible improvement in terms of radiometric sensitivity and calibration accuracy, while allowing
full continuity of the acquired data and relevant processing.
The definition and preliminary design of a thermal imager for earth observation applications has been performed, justified by a thorough analysis of user requirements. A survey of international programmes and other sources have been used to derive the radiometric requirements at ground level. Then instrument requirements at top of atmosphere have been obtained by means of the usual split-window techniques for land and sea. Preliminary instrument radiometric performances have been estimated on the basis of a review of possible instrument concepts (detectors and scan modes). A trade-off analysis between instrument requirements and performances led to the identification of two classes of instruments - the first based on high performance, cooled infrared detectors, and the second relying on microbolometer technology, with lower performance but not constrained by the need for a cryocooler. The applications feasible by means of each of them have been identified. The chosen instrument baseline was that using uncooled microbolometers, for which the best spatial and radiometric resolution achievable has been assessed, in order to cover as many applications as possible in view of the analysis of requirements. The selected baseline has been further detailed, up to a complete outline of the instrument, in order to confirm the achievable performance and assure its feasibility.
The REFIR (Radiation explorer in the far infrared) project is a study, funded by European Union, of feasibility of a novel space-borne instrument that will measure the atmospheric spectral radiance of the Earth in the broad spectral range 100-1100 cm-1 from space with sufficient spectral resolution (0.5 cm-1) and signal-to-noise ratio (SNR > 100). The main scientific objectives of the REFIR experiment are the measurement of the outgoing FIR radiation at the top of the atmosphere and the improvement of our knowledge of the principal drivers of this flux, e.g. temperature structure, water vapor, and clouds throughout the troposphere-surface system. The REFIR concept consists of a far infrared Fourier transform spectrometer (FTS) as the core instrument, of an embedded imager operating in an infrared 'window', sharing the same bore-sight as FTS, for scene/cloud signature identification in the FIR, of an add-on imager to provide multi-channel imagery, and of an absolute single-pixel radiometer with a single broad-band channel, used to measure the emitted radiation contextually with the spectral measurements. The integration of all the systems leads to a very compact satellite instrumentation, working at room temperature, with an estimated overall mass of 70 kg and a power consumption of 80 W, including electronics. The overall data rate toward the ground station is foreseen to be of 170 kbps before on-board data compression. This work highlights the main technical results at the end of phase-B0 study. The technical solutions adopted for the instrument are outlined and an accurate analysis of performances is shown.
The paper focuses on the aliasing phenomenon that may produce distortions on remotely sensed images acquired by hyper-spectral push-broom sensors and that arises because of its sampling rate. The analysis is performed on images recorded over different targets at a resolution that is high for the sensor under investigation. A model for the system modulation transfer function of PRISM hyper-spectral push- broom sensor is developed by taking into account the different contributions due to optical layout, electronics, detector, satellite motion. By using the sensor model, the high resolution images are pre-filtered and spatially re- sampled in order to obtain simulated images of the sensor. Such images are compared with those obtained by an ideal pre-filtering and re-sampling process in order to evidence possible aliasing effects. Quantitative indexes are adopted in order to assess the presence of aliasing. Filtering procedures are utilized to mitigate aliasing effects; to this aim multi-resolution filtering and a fuzzy filtering scheme are evaluated by means of the adopted indexes and by visual inspection. Quantitative and qualitative results show that, due to the efficacy of the proposed filters, aliasing mitigation is obtained with negligible penalties on spatial resolution.
12 The VISIR instrument has been designed as a lightweight facility to be embarked on future low Earth orbit operational satellites whose mission requirements include monitoring of open oceans, coastal zones and land surface areas. The instrument consists of an imaging spectrometer working in the visible range, dual-band thermal infrared radiometer and a single-band imager in the short-wave infrared. The instrument provides two operational modes, namely the global mode (ground pixel 1200 m, swath 1200 km) and the regional mode (ground pixel 300 m, swath 100 km) with steering capability. The high radiometric performances achieved in both operational modes show the capability to detect very small radiometric changes such as those induced by typical variations of the water quality parameters (chlorophyll, suspended sediments, yellow substance) and surface temperature anomalies. VISIR can achieve many of the MERIS and ATSR/AVHRR performance characteristics within a considerable smaller envelope that can lead to a more affordable instrument. The performances are achieved thanks to a newly designed high-performance (f/2.0 optical spectrometer based on a double-Schmidt configuration, the use of hybrid CMOS detectors for the VNIR and uncooled microbolometers for the TIR, and a hybrid whiskbroom scanning technique. This solution is an excellent compromise as regards the cost/benefit ratio, achieving many of the performances required for a coastal zone earth watching mission, with considerable simplifications with respect to equivalent existing instruments that can lead to much more affordable budgets in terms of mass, power and cost. The spectrometer has the potential to match other type of applications in different spectral bands and/or with different spatial and spectral resolution.
CLOUDS is a project co-funded by the EC under FP-4 (Environment and Climate), conducted by 12 European partners (7 scientific institutes and 5 industrial companies), also cooperating with NOAA/ETL. It is the mission study of a monitoring satellite to perform measurements necessary to describe cloud-radiation interaction in operational models for climate and long-term weather prediction. Complementary to missions for process study (Picasso-Cena, CloudSat, .. . ), CLOUDS addresses the monitoring aspect. As such, it has to comply with requirements of sufficiently frequent observing cycle, and operational sustainability. This prevents using active systems (radar and lidar) and leads to consider passive radiometry only, however exploiting as much as possible of the e.m. spectrum, with more polarisations and more viewing geometries. The paper reports on the instruments and system concepts developed to comply with the mission requirements. Six instruments are described, operating, respectively, in narrow channels of the UV/VIS/NIRISWIR, the TIRIFIR, the Sub-mm waves and the MW, in broad-band channels from UV to FIR, and in a relatively large-band channel of VIS/NIR. Several channels have three or four polarisations, all take images fore- and aft- (conical scanning), one has multi-angle-viewing capability. The overall system size is estimated as 900 kg mass, 1600 W power, 1 .1 Mbps data rate for real-time S-band transmission and 30 Mbps data rate for global data recovery in X-band.
SkyMed/Cosmo is a research project aimed to the realization of a space-borne observing system devoted to the monitoring of the Earth surface in the optical and microwave ranges. The project, which is supported by the Italian Space Agency, foresees the utilization of a group of satellites, each of which equipped with a set of instruments allowing different spatial resolutions. The entire system is realized for operational purposes over regional scale (i.e.: disaster monitoring, observation of marine and terrestrial ecosystems), that require a very short re-visitation time. The phenomena to be taken into account for the disaster monitoring are mainly earthquakes, landslides and marine emergencies. The SkyMed/Cosmo system promises to become a useful tool both for the analysis of risks and assessment of damages, and in any case where rapidly changing features (days or weeks) should to be observed. The system will be able to monitor the ground, marine and coastal environments, and to provide useful information about water circulation, water quality, sea bottom vegetation, soil coverage, geology, coastline monitoring, archaeology and cartography. Some of these applications, like those related to marine environment, will require a very high signal to noise ratio as well as accurate radiometric calibration. This work describes the outgoing feasibility study devoted to regional scale environmental applications of remote sensing by the SkyMed/Cosmo optical payload. The analysis of the SkyMed/Cosmo performance and diagnostic capabilities is given and discussed in comparison with those allowed by other satellite instruments.
An evaluation model of a high precision mirror drive, based on the parallelogram principle, has been designed and manufactured at Officine Galileo so as to meet the instrumental requirements of the high resolution Fourier Transform Spectrometer (FTS for the Spectroscopy of the Atmosphere using Far InfraRed Emission (SAFIRE) project. Mechanical and optical tests, carried out on the scanning mechanism evaluation model, provided measurements of the stability and uniformity of the movement and showed that the selected mirror drive concept meets the required tolerances.
KEYWORDS: Comets, Sensors, Navigation systems, Stars, Space operations, Cameras, Data processing, Laser range finders, Control systems, Optical tracking
This paper describes the overall configuration and performance of a comet approach and landing system (CALS), a space-borne sensor package for navigation toward a low-gravity celestial body in an interplanetary environment. The sensor system is aimed at satisfying the requirements of the Rosetta/CNSR (comet nucleus sample return) mission, whose objective is to land on a cometary surface and to retrieve samples that will be analyzed on the ground after Earth re-entry. Several constraints at the mission and spacecraft level make the configuration of a suitable sensor package a quite complex problem. The baseline system includes the following sensors, all mounted on a high-precision gimballed platform: (1) high-resolution camera, for detection of the comet at large distance and mapping at medium/short distance for ground-assisted landing site selection; (2) wide-angle camera with data processing equipment (star and target tracker), able to track simultaneously the irregular comet image and the surrounding stars for autonomous navigation; (3) laser topographic mapper for autonomous topography-assisted navigation in the final descent phase; (4) multitask radar altimeter for the on-board measurement of range, attitude, 3-axis velocity and surface roughness, with a microwave sounder section for the determination of subsurface structure and composition.
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