The first Sentinel-2 satellites, which constitute the next generation of operational Earth observation satellites for optical
land monitoring from space, are undergoing completion in the facilities at Astrium ready for launch end 2014. Sentinel-2
will feature a major breakthrough in the area of optical land observation since it will for the first time enable continuous
and systematic acquisition of all land surfaces world-wide with the Multi-Spectral Instrument (MSI), thus providing the
basis for a truly operational service. Flying in the same orbital plane and spaced at 180°, the constellation of two
satellites, designed for an in-orbit nominal operational lifetime of 7 years each, will acquire all land surfaces in only 5
days at the equator. In order to support emergency operations, the satellites can further be operated in an extended
observation mode allowing to image any point on Earth even on a daily basis. MSI acquires images in 13 spectral
channels from Visible-to-Near Infrared (VNIR) to Short Wave Infrared (SWIR) with a swath of almost 300 km on
ground and a spatial resolution up to 10 m. The data ensure continuity to the existing data sets produced by the series of
Landsat and SPOT satellites, and will further provide detailed spectral information to enable derivation of biophysical or
geophysical products. Excellent geometric image quality performances are achieved with geolocation better than 16 m,
thanks to an innovative instrument design in conjunction with a high-performance satellite AOCS subsystem centered
around a 2-band GPS receiver, high-performance star trackers and a fiberoptic gyro. To cope with the high data volume
on-board, data are compressed using a state-of-the-art wavelet compression scheme. Thanks to a powerful mission data
handling system built around a newly developed very large solid-state mass memory based on flash technology, on-board
compression losses will be kept to a minimum. The Sentinel-2 satellite design features a highly flexible operational
concept, allowing downlink of all mission data to a nominal X-band core ground stations network. In addition, users
could receive mission data sets at selected X-band local user ground stations or through an Optical Communication
Payload (OCP) via an inter-orbit optical link to a geostationary EDRS relay satellite at Ka-band user ground stations.
Different priority schemes can be selected in flight to allow transmission of critical image data with the shortest possible
latency. The system is designed for high system autonomy allowing for pre-programming of the operational schedule for
15 days in advance without interference from ground. Apart from the nominal and extended imaging modes, the satellites
also feature a calibration mode to support regular in-orbit radiometric calibration of the instrument. Overall, the Sentinel-
2 satellites are designed to provide in-orbit availability for the instrument data greater than 97%, which fulfills the
requirements of a fully operational system for multispectral Earth observation.
2A and Sentinel-2B satellites currently under development will ensure systematic global acquisition of all land and
coastal waters in the visible and short-wave infrared spectral domain with a 5 day revisit time at the equator.
The Multi Spectral Instrument is a push-broom imager providing imagery in 13 spectral channels with spatial resolutions
ranging from 10 m to 60 m and a swath width of 290 Km, larger than SPOT and Landsat. The instrument features a full
field of view calibration device, a silicon carbide Three Mirror Anastigmat telescope with mirror dimensions up to 600
mm, specific filter stripe assemblies, newly developed Si-CMOS and HgCDTe detectors and a low noise wavelet
compression video electronics. The 1.4 Tbits/s raw image date rate is reduced down to 490 Mbits/s at the output of the
instrument to cope with the overall system transmission capability.
The Sentinel-2 program has entered in the CD phase in 2009. Launch of Sentinel-2A satellite is scheduled for 2013.
The Medium Resolution Imaging Spectrometer (MERIS), developed under European Space Agency (ESA) contract, for the ENVISAT 1 Polar Orbit Earth Mission belongs to a new generation of Ocean Color sensors which aim is to improve the knowledge of some crucial processes of our planet. The instrument development is currently carried out by an international team led by AEROSPATIALE under the ENVISAT prime contractor ship of DORNIER. MERIS is a pushbroom instrument measuring the radiance of the Earth in 15 programmable spectral bands between 390 nm and 1040 nm over a 1150 km swath width. The wide spatial extent is obtained by 5 cameras with a field of view of 14 degrees each located in a fan shape configuration. This paper presents MERIS FM instrument performance verification plan, some of the involved test set ups an the measured performances.
The medium imaging spectrometer (MERIS), developed by the European Space Agency (ESA) for the ENVISAT-1 polar orbit Earth mission, belongs to a new generation of ocean color sensors which will yield a major improvement in the knowledge of such a crucial processes as the ocean contribution to the carbon cycle. MERIS measures the radiance reflected from the Earth's surface in the visible and near infrared part of the spectrum. Data are transmitted in fifteen spectral bands of programmable width and location. The instrument features tow spatial resolution and several observation and calibration modes selectable by ground command. The instrument development is currently carried out by an international team led by AEROSPATIALE under ENVISAT prime contractor ship of DORNIER. The development of the instrument has now reached a status where the instrument has been proven to be compliant with the scientific requirements. This paper gives an overview of the instrument, its design with emphasis given to the acquisition and on-board processing chains. A summary of the major performance sand interface budgets is also provided.
A fiber optic sensor system based on the photothermal effect has been developed and applied to very low concentration measurements in solutions. The sensor head comprises three closely spaced optical fibers for excitation, probe, and reflected probe light. A combination of reflective and refractive miniature optics is used to focus the respective beams into the probe volume. If an absorbing substance is present, the absorbed light power from the modulated excitation beam generates a refractive index gradient in the probe volume, which can be observed via deflection measurements of the non-absorbing cw probe beam. The reflective probe beam signal detected after phase synchronous demodulation is proportional to the substance concentration. Using a monochromatic lightsource with variable wavelength it is possible to discriminate different substances. With this system, we have analyzed Cu-II concentrations in galvanic solutions from 1000 ppm down to concentrations below 1 ppm, thus reaching the sensitivity for waste-water control. Applications for this chemical sensor system are in-line environmental and pollution control of water due to its very high sensitivity. The large dynamic range also makes it suitable for various in-line process control tasks.
Results of a detailed design study for an advanced optical communication system based on diode-pumped Nd:YAG laser technology performed within the framework of an ESA contract are presented. Emphasis is placed on reaching a low mass/low power design with sufficient maturity to develop space-qualified systems by the middle of this decade. The systems employ coherent PSK homodyne Costas loop receiver technology on the high data rate links, while QPPM modulation and direct detection is foreseen on the 25-Mb/s link. For the intersatellite duplex link, the same communication laser line is used for both directions, thus allowing multiple connections within a given satellite network. With 15-cm aperture telescopes on both terminals, maximum transmitter power is 500 mW for the 650 Mb/s link. Overall communication terminal mass is in the 70-80 kg range, and typical power consumption is 120-160 W.
The SILEX experimental program is concerned with demonstrating the technologies of an optical communications link between two satellites; in order to expand system capabilities to the high data rates required for future LEO-GEO interorbit links, a detailed design study has been conducted for a system predicated on diode-pumped Nd:YAG laser technology. Even with telescopes whose apertures are less than 10 cm on the LEO satellite, and transmitter powers of less than 1 W, system transmission performance is greater than 1 Gbit/sec.
Germany's Solid State Laser Communications in Space, or 'SOLACOS' program has undertaken the terrestrial verification of coherent laser communications systems based on Nd:YAG lasers, giving attention to the evaluation and breadboarding of critical components and subsystems. These components encompass the pointing/acquisition/tracking subsystem breadboard, an optical Costas-loop receiver, and advanced Nd:YAG transmitter technology. Results are presented for subsystem components developed to date.
A fast optical fiber based tracking detector has been developed, tested and characterized as a cmponent for a coherent Nd:YAG laser space communication system. A freely suspended and conductively coated single-mode fiber end is excited to a fast small amplitude conical motion when electrostatically deflected close to its mechanical resonances by the capacitive action of one or two electrodes. The induced intensity modulation of the laser light coupled into the fiber is phase-sensitively detected (optionally after coherent amplification) and used for spatial input coupling optimization in a servo loop steering the laser beam. Modulation frequencies higher than 10 kHz are feasible in a very compact, rugged device at low power consumption. The device can also be modified for scanning of a transmitter beam.
An experimental coherent communication link has been realized to investigate various aspects of a diode-pumped Nd:YAG laser space communication system. The breadband 500 Mb/s link is based on low power monolithic ring lasers and a balanced receiver PSK homodyne detection scheme. Fiberoptic components are being investigated and a novel fiber-nutator device for coherent tracking has been developed.