The Sentinel-3 (S3) is a Global Land and Ocean Mission  currently in development as part of the European Commission’s Copernicus programme (former: Global Monitoring for Environment and Security (GMES) ).
The multi-instrument Sentinel-3 mission measures sea-surface topography, sea- and land-surface temperature, ocean colour and land colour to support ocean forecasting systems, as well as environmental and climate monitoring with near-real time data.
The recently launched SENTINEL-3 mission measures sea surface topography, sea/land surface temperature, and ocean/land surface colour with high accuracy. The mission provides data continuity with the ENVISAT mission through acquisitions by multiple sensing instruments. Two of them, OLCI (Ocean and Land Colour Imager) and SLSTR (Sea and Land Surface Temperature Radiometer) are optical sensors designed to provide continuity with Envisat's MERIS and AATSR instruments. During the commissioning, in-orbit calibration and validation activities are conducted. Instruments are in-flight calibrated and characterized primarily using on-board devices which include diffusers and black body. Afterward, vicarious calibration methods are used in order to validate the OLCI and SLSTR radiometry for the reflective bands. The calibration can be checked over dedicated natural targets such as Rayleigh scattering, sunglint, desert sites, Antarctica, and tentatively deep convective clouds. Tools have been developed and/or adapted (S3ETRAC, MUSCLE) to extract and process Sentinel-3 data. Based on these matchups, it is possible to provide an accurate checking of many radiometric aspects such as the absolute and interband calibrations, the trending correction, the calibration consistency within the field-of-view, and more generally this will provide an evaluation of the radiometric consistency for various type of targets. Another important aspect will be the checking of cross-calibration between many other instruments such as MERIS and AATSR (bridge between ENVISAT and Sentinel-3), MODIS (bridge to the GSICS radiometric standard), as well as Sentinel-2 (bridge between Sentinel missions). The early results, based on the available OLCI and SLSTR data, will be presented and discussed.
The Sea and Land Surface Temperature Radiometers (SLSTRs) are high-accuracy radiometers selected for the Copernicus mission Sentinel-3 space component to provide sea surface temperature (SST) data continuity with respect to previous (Advanced) Along Track Scanning Radiometers [(A)ATSRs] for climatology. Many satellites are foreseen over a 20-year period, each with a 7.5-year lifetime. Sentinel-3A will be launched in 2015 and Sentinel-3B at least six months later, implying that two identical satellites will be maintained in the same orbit with a 180-deg phase delay. Each SLSTR has an improved design with respect to AATSR affording wider near-nadir and oblique view swaths (1400 and 740 km) for SST/land surface temperature global coverage at a 1-km spatial resolution (at SSP) with a daily revisit time (with two satellites), appropriate for both climate and meteorology. Cloud screening and other products are obtained with 0.5 km spatial resolution [at sub-satellite point (SSP)] in visible and short wave infrared (SWIR) bands, while two additional channels are included to monitor high temperature events such as forest fires. The two swaths are obtained with two conical scans and telescopes combined optically at a common focus, representing the input of a cooled focal plane assembly, where nine channels are separated with dichroic and are focalized on detectors with appropriate optical relays. IR and SWIR optics/detectors are cooled to 85 K by an active mechanical cryo-cooler with vibration compensation, while the VIS ones are maintained at a stable temperature. The opto-mechanical design and the expected electro-optical performance of the focal plane assembly are described and the model predictions at system level are compared with experimental data acquired in the vacuum chamber in flight representative thermal conditions or in the laboratory.
The European Union-ESA Global Monitoring for Environment and Security (GMES) programme decided to develop the
Sentinels as first series of operational satellites in order to meet specific Earth observation user needs. The series of
Sentinel-3 satellites will provide global, frequent and near-realtime ocean, ice and land monitoring. It continues Envisat's
altimetry, the multispectral, medium-resolution visible and infrared ocean and land-surface observations of ERS, Envisat
and Spot, and includes enhancements to meet the operational revisit requirements and to facilitate new products and
evolution of services. The first launch is expected in 2013.
In this paper an outline of the Sentinel-3 satellite and optical payload is presented. Dedicated calibration and validation
activities regarding the sea and land surface temperature radiometer (SLSTR) and ocean and land colour radiometer
(OLCI) are then reviewed. Calibration and validation (calval) activities are based on the heritage gained from ENVISAT
MERIS and AATSR experience and cover pre-launch, in-orbit commissioning and operational measures for the Sentinel
The Sea & Land Surface Temperature Radiometer (SLSTR) is a high accuracy infrared radiometer selected as optical
payload for the Sentinel 3 component of the GMES mission, to provide climatological data continuity respect to the
previous ERS and ESA Envisat missions, that embarked respectively the ATSR, ATSR-2 and AATSR payloads.
The instrument design follows the dual view concept of the ATSR series with some notable improvements. An increased
swath width in both nadir and oblique views (1400 and 740 km) provides measurements at global coverage of Sea and
Land Surface Temperature (SST/LST) with daily revisit times, which is useful for climate and meteorology (1 Km
Improved day-time cloud screening and other atmospheric products will be possible from the increased spatial resolution
(0.5 Km) of the VIS and SWIR channels and additional SWIR channels at 1.375μm and 2.25μm.
Two additional channels using dedicated detector and electronics elements are also included for high temperature events
monitoring (1 km spatial resolution).
The two Earth viewing swaths are generated using two telescopes and scan mirrors that are optically combined by means
of a switching mirror at the entrance of a common Focal Plane Assembly. The eleven spectral channels (3 VIS, 3 SWIR,
2 MWIR, 3 TIR) are split within the FPA using a series of dichroics. The SWIR, MWIR and TIR optics/detectors are
cooled down to 80 K with an active cryocooler, while the VIS detectors work at a stabilised uncooled temperature.
The paper highlights the technical and programmatic status of the project, which is now in phase C.
Hyperspectral imaging (HSI) sensors suffer from spatial misregistration, an artifact that prevents the accurate acquisition
of the spectra. Physical considerations let us assume that the influence of the spatial misregistration on the acquired data
depends both on the wavelength, and on the across-track position. A scene-based edge detection method is therefore
proposed. Such a procedure measures the variation on the spatial location of an edge between its various monochromatic
projections, giving estimation for spatial misregistration, and allowing also misalignments identification. The method has
been applied to several hyperspectral sensors, either prism, or grating-based designs. Results confirm the dependence
assumptions on &lgr; and &thgr;, spectral wavelength and across track pixel respectively. In order to correct for spatial
misregistration suggestions are also given.
In order to achieve quantitative measurements of the Earth's surface radiance and reflectance, it is important to determine the aerosol optical thickness (AOT) to correct for the optical influence of atmospheric particles. An advanced method for aerosol detection and quantification is required, which is not strongly dependant on disturbing effects due to surface reflectance, gas absorption and Rayleigh scattering features. A short review of existing applicable methods to the APEX airborne imaging spectrometer (380nm to 2500nm), leads to the suggested aerosol retrieval method here in this paper. It will measure the distinct radiance change between two near-UV spectral bands (385nm & 412nm) due to aerosol induced scattering and absorption features. Atmospheric radiation transfer model calculations have been used to analyze the AOT retrieval capability and accuracy of APEX. The noise-equivalent differential AOT is presented along with the retrieval sensitivity to various input variables. It is shown, that the suggested method will be able to identify different aerosol model types and measure AOT and columnar size distribution. The proposed accurate AOT determination will lead to a unique opportunity of two-dimensional pixel-wise mapping of aerosol properties at a high spatial resolution. This will be helpful especially for regional climate studies, atmospheric pollution monitoring and for the improvement of aerosol dispersion models and the validation of aerosol algorithms on spaceborne sensors.
Based on the Matrix-Operator Method the radiative transfer code
STORM (STOkes vector Radiative transfer Model) is introduced,
which was developed in a joint project of DLR and Institut fuer
Weltraumwissenschaften of the Freie Universitaet Berlin. STORM
calculates the Stokes parameters (I, Q, U, V) in a plane parallel,
multi layered atmosphere in the visible and near infrared spectral
range. The scattering characteristics of aerosols are determined
by Mie theory. The surface represents a Lambertian reflector or a
wind ruffled water surface described by Cox-Munk model. The
results of one calculation are the upward and downward directed
Stokes parameters for one wavelength at a desired number of sun
incident and viewing angles at varying altitudes in the principal
plane and other azimuth angles. STORM is applied for an analysis
in view of designing downward looking Earth observing optical
remote sensing systems and values of the degree of polarization
are presented as generic basis for remote sensing system design
and data processing.
ESA currently builds the airborne hyper-spectral push broom imaging spectrometer APEX (Airborne Prism EXperiment) operating in the spectral range from 380 to 2500 nm. In the scope of the APEX project a large variety of characterization measurements will be performed, e.g., on-board characterization, frequent laboratory characterization, and vicarious calibration. The APEX instrument will only achieve its challenging measurement accuracy by regular calibration of the instrument between flight cycles. For that on-ground characterisation, a dedicated characterisation and calibration facility is necessary to enable a comprehensive and accurate calibration of the instrument. In view of the high relevance to scientific objectives, ESA is funding an external "Calibration Home Base" (CHB). It is located at DLR Oberpfaffenhofen and will be operational from 2006 on. The CHB provides all hard- and software tools required for radiometric, spectral and geometric on-ground characterisation and calibration of the instrument and its internal references and on-board attachments, and to perform measurements on polarisation- and straylight-sensitivity. This includes a test bed and the provision of the infrastructure. In this paper the calibration equipment and concept is outlined.
Spectro-directional surface measurements can either be performed in the field or within a laboratory setup. Laboratory measurements have the advantage of constant illumination and neglectable atmospheric disturbances. On the other hand, artificial light sources are usually less parallel and less homogeneous than the clear sky solar illumination. To account for these differences and for determining for which targets a replacement of field by laboratory experiments is indeed feasible, a quantitative comparison is a prerequisite. Currently, there exists no systematic comparison of field and laboratory measurements using the same targets.
In this study we concentrate on the difference in spectro-directional field and laboratory data of the same target due to diffuse illumination. The field data were corrected for diffuse illumination following the proposed procedure by Martonchik . Spectro-directional data were obtained with a GER3700 spectroradiometer. In the field, a MFR sun photometer directly observed the total incoming diffuse irradiance. In the laboratory, a 1000W brightness-stabilized quartz tungsten halogen lamp was used. For the first direct comparison of field and laboratory measurements, we used an artificial and inert target with high angular anisotropy. Analysis shows that the diffuse illumination in the field is leading to a higher total reflectance and less pronounced angular anisotropy.
APEX (Airborne Prism EXperiment) is a project of the European Space Agency ESA focusing on high accuracy simulation, calibration and validation for spaceborne remote sensing instruments. The instrumentation comprises a hyperspectral imager for various standard airborne platforms, a fixed installed calibration home base and a complete facility for data processing and archiving. The pushbroom-type instrument accommodates two spectrometer channels covering a spectral range from 0.38 up to 2.5 micron. The spatial/spectral resolution amounts to 1000 samples at 28-degree field of view with 312 spectral bands. The overall instrument design and its built-in characterization unit will allow excellent performance stability under various flight conditions. The presentation will focus on the design, development and realization phases of the instrument and discuss various highlights of technical achievements, as there are the infrared HgCdTe detector with extended array format for the short wave infrared channel, the thermal/mechanical stabilization of the spectrometer and the realization of the infrastructure for high accuracy characterization and calibration of the instrument.
APEX is a dispersive pushbroom imaging spectrometer operating in the spectral range between 380 - 2500 nm. The spectral resolution will be better than 10 nm in the SWIR and < 5 nm in the VNIR range of the solar reflected range of the spectrum. The total FOV will be ± 14 deg, recording 1000 pixels across track with about 300 spectral bands simultaneously. A large variety of characterization measurements will be performed in the scope of the APEX project, e.g., on-board characterization, frequent laboratory characterization, and vicarious calibration. The retrieved calibration parameters will allow a data calibration in the APEX Processing and Archiving Facility (PAF). The data calibration includes the calculation of the required, time-dependent calibration coefficients from the calibration parameters and, subsequently, the radiometric, spectral and geometric calibration of the raw data. Because of the heterogeneity of the characterization measurements, the optimal calibration for each data set is achieved using a special assimilation algorithm. In the paper the different facilities allowing characterization measurements, the PAF and the new data assimilation scheme are outlined.
Recently, a joint Swiss/Belgian initiative started a project to build a new generation airborne imaging spectrometer, namely APEX (Airborne Prism Experiment) under the ESA funding scheme named PRODEX. APEX is a dispersive pushbroom imaging spectrometer operating in the spectral range between 380 - 2500 nm. The spectral resolution will be better then 10 nm in the SWIR and < 5 nm in the VNIR range of the solar reflected range of the spectrum. The total FOV will be ± 14 deg, recording 1000 pixels across track with max. 300 spectral bands simultaneously. APEX is subdivided into an industrial team responsible for the optical instrument, the calibration homebase, and the detectors, and a science and operational team, responsible for the processing and archiving of the imaging spectrometer data, as well as for its operation. APEX is in its design phase and the instrument will be operationally available to the user community in the year 2006.
The handling of satellite or airborne earth observation data for scientific applications minimally requires pre-processing to convert
raw digital numbers into scientific units. However depending on sensor characteristics and architecture, additional work may be
needed to achieve spatial and/or spectral uniformity. Standard
higher level processing also typically involves providing orthorectification and atmospheric correction. Fortunately some of the computational tasks required to perform radiometric and geometric calibration can be decomposed into highly independent
subtasks making this processing highly parallelizable. Such
"embarrassingly parallel" problems provide the luxury of being
able to choose between cluster or grid based solutions to perform
these functions. Perhaps the most convenient solutions are grid-based, since most research groups making these kinds of measurements are likely to have access to a LAN whose spare computing resources could be non-obtrusively employed in a grid. However, since many higher level scientific applications of earth observation data might be composed of more highly interdependent subtasks, the parallel
computing resources allocated for these tasks might also be made
available for low level pre-processing as well. We look at two
modules developed for our prototype data calibration processor for
APEX, an airborne imaging spectrometer, which have been implemented
on both a cluster and a grid leading us to be able to make observations and comparisons of the two approaches.
The whiskbroom scanner Global Imager (GLI) was launched in December 2002 on the Advanced Earth Observation Satellite 2 (ADEOS-2). The sensor provides remotely sensed data from the Earth surface in the visible to the thermal infrared part of the spectrum. Since the Earth observation data require careful post-launch calibration, different on-board calibration tools have been integrated in the GLI hardware design. For the VIS-SWIR spectral range a special calibration device allows solar and lamp calibration. In this paper we describe first results on solar calibration of GLI.
Besides pre-launch and on-board calibration, the method of vicariously calibrating space sensors became a reliable tool for space sensor calibration. One possibility of vicarious calibration is to inter-calibrate sensors aboard different satellite platforms directly. This leads to a better understanding of differences in global data sets produced these sensors. Recently, ADEOS-2 was launched (14 Dec 2002) successfully and the optical sensor GLI onboard the ADEOS-2 satellite became operational from April 2003. In a first calibration check-up, the radiometric performance of GLI was compared relatively to that of other sensors on different satellites with different calibration backgrounds. As calibration site a large snowfield near Barrow (Alaska, USA) was used, where space sensors in polar orbits view the same ground target on the same day with small differences in the local crossing times. This is why GLI, MODIS (terra, aqua), SeaWiFS, AHVRR (N16, N17) and MERIS data sets were selected for the following clear-sky condition days: April 14th and 26th 2003. At the same time ground-truth experiments, e.g., measurements of ground reflectance, BRDF, aerosol optical thickness (AOT), were carried out. Thereinafter, top-of-atmosphere (TOA) radiance/reflectance was forward calculated by means of radiative transfer code (RTC) for each sensor, each band and each day. Finally, the vicariously retrieved TOA reflectance was compared to TOA sensor L1B data. As a result GLI’s performance is encouraging at this early time of the mission. GLI and the other 6 sensors deliver similar sensor output in the range of about 5-7% around the expected vicariously calculated TOA signal.
The Advanced Earth Observing Satellite-II (ADEOS-II) was launched on 14 December 2002, and its functions were checked until 2003 spring. The Global Imager (GLI) on board ADEOS-II has 36 channels (thirty 1-km resolution, six 250-m resolution) from ultraviolet to thermal infrared to facilitate understanding the global environmental changes in oceans, land and clouds with high accuracy. Ocean algorithms (e.g., ocean atmospheric correction and sea-surface temperature) need highly accurate sensor characterization coefficients because they retrieve sea-surface upward radiance precisely from the top of the atmosphere. The NASDA GLI calibration team includes members of sensor development, ground system integration, and science application groups. The team started investigating GLI characteristics and radio- and geo-correction processes in the initial verification period. In this paper, we will describe the initial results, radiometric accuracy, 12- or 48-detector dependency, scan-mirror surface, incident-angle dependency, and dynamic range related to oceanographic applications.
A primary productivity model for the turbid water is proposed using the remote sensing data. In previous studies, we proposed a time and depth resolved primary productivity model for a global scale, but results indicated significant errors on the East China Sea. A euphotic zone estimated in this model was based on a chlorophyll α concentration in the surface, which made errors on the turbid water. A photosynthetically available radiation and chlorophyll α concentration along the water column are defined as a function of the diffused attenuation coefficient and chlorophyll α concentration in the surface.
To deliver high quality data sets to the user community, space sensors have to be calibrated with high accuracy. Besides pre-launch and on-board calibration, there exists the possibility to inter-compare the sensor data using well-characterized ground sites. To cover different radiometric signal levels, ground sites with high and low spectral reflectance (and surface temperatures) were chosen to allow not only an absolute signal comparison, but also an estimation of the linearity of the sensor signal. This why one ground site is located at in the dark ocean (East china sea), and the other is a fresh snow site in the polar region (alternating: Arctic and Antarctic cal sites). These polar sites have the advantage to compare sensors from different sun-synchronous orbit satellites platforms on the same day, i.e. semi-simultaneous measurements can be performed.
The dark ocean site will be located near Ishigaki Island (Japan) at 24°37'N and 123°27'E using optical buoy data and frequent in-situ measurements. The snow target sites are in the Antarctic and Arctic, where measurements will be carried out in the polar autumn and spring near Syowa Station (East Ongul Island, Lützow-Holm Bay, East Antarctica; 69°S and 39°35'E) and near Barrow (Alaska, USA; 71°16'N, 156°50'W).
In the scope of the project the ground sites will be characterized (depending on logistical and weather conditions), to allow an estimation of the TOA signal, which will be calculated using either developed codes or generated products. After systematic (space sensor and ground-truth) data acquisition and analysis, a comparison between these space sensors will be provided to assess long-term variations and trends in the calibration.
This paper describes the ongoing preparation (e.g., data selection, ground truth measurements and algorithm development) for a systematic inter-sensor comparison of the GLI and MERIS/AATSR sensors, which are onboard of ADEOS-2 and ENVISAT satellites.
The whiskbroom scanner Global Imager (GLI) will be launched on Advanced Earth Observation Satelite 2 (ADEOS-2). It will provide remotely sensed data from the Earth surface from the visible to the thermal infrared. Since the Earth observation data require a careful calibration, different on-board calibration tools have been integrated in the GLI hardware design. For the VIS-SWIR spectral range a special calibration device allows solar and lamp calibration. In this paper a calibration strategy is presented to achieve a high calibration accuracy of the remotely sensed data by means of solar calibration. Therefore the theoretical background, the performed hardware characterization and applied external data basis are presented. Further on it is shown how a stray light simulation analysis using a non- sequential ray-tracing tool will be used to increase the reliability of the solar calibration.
Until now incandescent lamp, sun and moon calibrations have been successfully applied for in-flight calibration of spaceborne Earth observation imaging sensors. The performance development of LEDs in the past decade guided to higher luminous efficiencies, broader spectral coverage, lower degradation of light output over time and lower power consumption. These advantages make LEDs to a candidate for radiometric and spectral calibration of spaceborne spectrometers. For analysing LEDs for space in-flight calibration a set of LEDs has been characterised and a simulation of space radiation quantities (i.e. proton and electron radiation for a polar low-Earth orbit) has been carried out. Additional vacuum tests (outgassing behaviour) demonstrated a possible application of LEDs with epoxy housing for the future space environment. Further on, a concept for long-term temperature stabilisation has been developed for solving the main problem of LED in-flight calibration, i.e. the temperature dependency of the irradiance. Consequently, this study demonstrates that (1) a degradation of LEDs due to space environment is not expected, that (2) long-term temperature stability of LEDs can be ensured, and that (3) the higher blue part of ‘white’ LEDs would best suit ocean-colour scientists needs.
The beginning of the next millennium promises an explosion in the quantity and quality of global data available from imaging remote sensing systems. The scientific and commercial communities become aware of unique hyperspectral imaging data acquisition opportunities. A brief profile of over 80 high resolution spaceborne and airborne earth observation sensor systems (H less than 800 km) planned to be operating in the year 2000 and beyond are presented in this paper. This overview covers multi- and hyperspectral civil, land and ocean nadir viewing observation sensors in the spectral range from the ultraviolet to the thermic infrared. A summary of the performance of each system, from image parameters (spectral and ground resolution) to the image generating procedure (spectral selection mode, image acquisition mode) is presented. At this point some caution is due since not all these concepts and plans will come to pass. The cuts in the government budget and the containment of commercial plans for new sensor systems will affect the realization of the present plans. However, the year 2000 will see at least four large area vegetation and ocean mappers, three landsat-like systems and two commercial high resolution systems in polar orbit simultaneously. A fleet of over 40 airborne sensor systems gives the final polished form of the future data acquisition opportunities.