Roland Meynart

The atmospheric dynamics mission for global wind field measurement

The prime aim of the Atmospheric Dynamics Mission is to demonstrate measurements of vertical wind profiles from space. Extensive studies conducted by the European Space Agency over the past 15 years have culminated in the selection of a high-performance Doppler wind lidar based on direct-detection interferometric techniques. Such a system, with a pulsed laser operating at 355-nm wavelength, would utilize both Rayleigh scattering from molecules and Mie scattering from thin cloud and aerosol particles; measurement of the residual Doppler shift from successive levels in the atmosphere provides the vertical wind profiles. The lidar would be accommodated on a satellite flying in a sun-synchronous orbit, at an altitude of ~400 km, providing near-global coverage; target date for launch is in 2007. Processing of the backscatter signals will provide about 3000 globally distributed wind profiles per day, above thick clouds or down to the surface in clear air, at typically 200-km separation along the satellite track...

APEX: current status of the airborne dispersive pushbroom imaging spectrometer

Over the past few years, a joint Swiss/Belgium ESA initiative resulted in a project to build a precursor mission of future spaceborne imaging spectrometers, namely APEX (Airborne Prism Experiment). APEX is designed to be an airborne dispersive pushbroom imaging spectrometer operating in the solar reflected wavelength range between 4000 and 2500 nm. The system is optimized for land applications including limnology, snow, and soil, amongst others. The instrument is optimized with various steps taken to allow for absolute calibrated radiance measurements. This includes the use of a pre- and post-data acquisition internal calibration facility as well as a laboratory calibration and a performance model serving as a stable reference. The instrument is currently in its breadboarding phase, including some new results with respect to detector development and design optimization for imaging spectrometers. In the same APEX framework, a complete processing and archiving facility (PAF) is developed. The PAF not only includes imaging spectrometer data processing up to physical units, but also geometric and atmospheric correction for each scene, as well as calibration data input. The PAF software includes an Internet based web-server and provides interfaces to data users as well as instrument operators and programmers. The software design, the tools and its life cycle are discussed as well.

FLORIS: phase A status of the fluorescence imaging spectrometer of the Earth Explorer mission candidate FLEX

The Fluorescence Explorer (FLEX) mission is currently subject to feasibility (Phase A) study as one of the two candidates of ESA’s 8th Earth Explorer opportunity mission. The FLuORescence Imaging Spectrometer (FLORIS) will be an imaging grating spectrometer onboard of a medium sized satellite flying in tandem with Sentinel-3 in a Sun synchronous orbit at a height of about 815 km. FLORIS will observe vegetation fluorescence and reflectance within a spectral range between 500 nm and 780 nm. It will thereby cover the photochemical reflection features between 500 nm and 600 nm, the Chlorophyll absorption band between 600 and 677 nm, and the red-edge in the region from 697 nm to 755 nm being located between the Oxygen A and B absorption bands. By this measurement approach, it is expected that the full spectrum and amount of the vegetation fluorescence radiance can be retrieved, and that atmospheric corrections can efficiently be applied. FLORIS will measure Earth reflected spectral radiance at a relatively high spectral resolution of ~0.3 nm around the Oxygen absorption bands. Other spectral band areas with less pronounced absorption features will be measured at medium spectral resolution between 0.5 and 2 nm. FLORIS will provide imagery at 300 m resolution on ground with a swath width of 150 km. This will allow achieving global revisit times of less than one month so as to monitor seasonal variations of the vegetation cycles. The mission life time is expected to be at least 4 years. The fluorescence retrieval will make use of information coming from OLCI and SLSTR, which are onboard of Sentinel-3, to monitor temperature, to detect thin clouds and to derive vegetation reflectance and information on the aerosol content also outside the FLORIS spectral range. In order to mitigate the technological and programmatic risk of this Explorer mission candidate, ESA has initiated two comprehensive bread-boarding activities, in which the most critical technologies and instrument performance shall be investigated and demonstrated. The breadboards will include representative optics and dispersive elements in a configuration, which is expected to be very close to the instrument flight configuration. This approach follows the guideline to reach, before it goes into the implementation phase, a technology readiness level of at least 5. It thereby requires a demonstration of predicted performance in a configuration, where the basic technological components are integrated with reasonably realistic supporting elements such that it can be tested in a simulated environment. We will report, within the limits of the competitive nature of the industrial studies, on the currently running or planned preparatory activities. We will present the mission configuration, the imposed instrument requirements and the identified instrument concepts as derived by the Phase A studies.

Performance modeling for A-SCOPE: a space-borne lidar measuring atmospheric CO2

A-SCOPE (Advanced Space Carbon and Climate Observation of Planet Earth) has been one of the six candidates for the third cycle of the Earth Explorer Core missions, selected by the European Space Agency (ESA) for assessment studies. Earth Explorer missions focus on the science and research aspects of ESAs Living Planet Programme. A-SCOPE mission aims at observing atmospheric CO2 for a better understanding of the carbon cycle. Knowledge about the spatial distribution of sources and sinks of CO2 with unprecedented accuracy will provide urgently needed information about the global carbon cycle. A-SCOPE mission encompasses a new approach to observe the Earth from space based on an IPDA (Integrated Path Differential Absorption) Lidar. Based on the known principle of a differential measurement technique, the IPDA lidar relies on the measurement of the laser echoes reflected by hard targets as the ground or the top of the vegetation. Such a time-gated technique is a promising way to overcome the sources of systematic errors inherent to passive missions. To be fully exploited, it however translates into stringent instrument requirements and requires a dedicated performance assessment. In this paper, the A-SCOPE instrument concept is first presented, with the aim of summarizing some important outcomes from the industrial assessment studies. After a discussion of the mission requirements and measurement principles, an overview is given about the instrument architecture. Then the instrument performance is reported, together with a detailed discussion about sources of systematic errors, which pose the strongest technical challenges.

ALADIN airborne demonstrator: a Doppler Wind Lidar to prepare ESA´s ADM-Aeolus Explorer Mission

The Atmospheric Dynamics/Aeolus mission is the 4th Earth Explorer mission of the Earth Observation Explorer Programme of the European Space Agency (ESA). Its objective is to measure vertical tropospheric profiles of horizontal wind speed components. These global observations of wind profiles from space will improve the quality of weather forecasts and advance our understanding of atmospheric dynamics and climate processes. The 1.3-ton, 1.4-kW Aeolus spacecraft uses an incoherent Doppler Wind lidar (ALADIN) to measure wind speed. It uses a tripled-frequency Nd:YAG laser emitting ultraviolet pulses at a repetition rate of 100 Hz, during a measurement period of 7 sec repeated every 28 sec. The return signal is detected with a double interferometric receiver composed of a Fizeau interferometer to detect the Mie signal scattered by aerosols and a double-edge Fabry-Perot interferometer to detect the Rayleigh signal scattered by atmospheric molecules. A custom-made accumulation CCD is used to detect and integrate the return photons over several laser pulses. The spacecraft has recently passed the CDR level and launch is planned for 2008. An airborne version of the ALADIN instrument has been made with equipment developed during the pre-development phase of the mission. An interferometric receiver with a high-level of representativity to the space receiver and a laser transmitter breadboard have been refurbished and complemented with a telescope, a co-alignment mechanism and custom control and processing electronics to produce the first airborne, direct-detection Doppler Wind lidar worldwide. The lidar was functionally tested in flight in October 2005 and will be used in ground and airborne campaigns in 2006 and 2007 to prepare the exploitation of the Aeolus space mission.

The MetOp second generation 3MI instrument

The MetOp-SG programme is a joint Programme of EUMETSAT and ESA. ESA develops the prototype MetOp-SG satellites (including associated instruments) and procures, on behalf of EUMETSAT, the recurrent satellites (and associated instruments). Two parallel, competitive phase A/B1 studies for MetOp Second Generation (MetOp-SG) have been concluded in May 2013. The implementation phases (B2/C/D/E) are planned to start the first quarter of 2014. ESA is responsible for instrument design of six missions, namely Microwave Sounding Mission (MWS), Scatterometer mission (SCA), Radio Occultation mission (RO), Microwave Imaging mission (MWI), Ice Cloud Imager (ICI) and Multi-viewing, Multi-channel, Multi-polarisation imaging mission (3MI). The paper will present the main performances of the 3MI instrument and will highlight the performance improvements with respect to its heritage derived by the POLDER instrument, such as number of spectral channels and spectral range coverage, swath and ground spatial resolution. The engineering of some key performance requirements (multi-viewing, polarisation sensitivity, straylight etc.) will also be discussed. The results of the feasibility studies will be presented together with the programmatics for the instrument development. Several pre-development activities have been initiated to retire highest risks and to demonstrate the ultimate performances of the 3MI optics. The scope, objectives and current status of those activities will be presented. Key technologies involved in the 3MI instrument design and implementation are considered to be: the optical design featuring aspheric optics, the implementation of broadband Anti Reflection coatings featuring low polarisation and low de-phasing properties, the development and qualification of polarisers with acceptable performances as well as spectral filters with good uniformities over a large clear aperture.

Radiation Effects in InGaAs and Microbolometer Infrared Sensor Arrays for Space Applications

Cobalt60, 60 MeV proton and heavy ion tests have been performed on InGaAs and amorphous silicon microbolometer arrays with CMOS readout circuits. The readout circuits showed latch-up at threshold LETs~14 MeV/mg/cm2, but the total dose and displacement damage effects were negligible for low earth orbit conditions. Effects in a microbolometer array tested, for use in Mercury orbit, to 100 krd(Si) and 3.2 1011 60 MeV p/cm2 showed acceptable performance, though there was a significant increase in power consumption for the CMOS readout circuit when biased during cobalt60 irradiation.

Processes Research by an Imaging Space Mission (PRISM)

PRISM is a spaceborne hyperspectral imager for a future land surface research mission, whose prime objective is the observation of biophysical processes at a local to regional scale. PRISM is designed for a dedicated medium-size satellite in a polar sun-synchronous 11:00 h orbit, and will provide coregistered spectral images in tow spectral regions: from the visible to short-wave IR range with a spectral resolution of about 10 nm and two bands in the thermal IR from 10.3 micrometers to 12.3 micrometers . The presented instrument concept comprises four modules with separate interfaces to the platform: the optical, calibration, cooler and electronics modules. The optics module design is based on a pushbroom type of imaging spectrometer in which the entire field of view is imaged on four detector arrays. The long-wavelength arrays are cooled by tow pairs of Stirling cycle coolers. The instrument layout and platform accommodation are optimized to meet the high radiometric accuracy requirement. The key element of the instrument is the pointing unit, whose mirror is protruding over the platform edge for a wide across track coverage and or access to the three on-board characterization units and to cold space. The pointing unit will provide global accessibility in 3 days. A platform rotation in pitch will enable BRDF measurements of ground test sites by varying along track pointing angles.

Sampling jitter in Fourier-transform spectrometers: spectral broadening and noise effects

The effect of sampling jitter induced by frequency fluctuations of the reference laser is analyzed theoretically. It is shown that the spectral broadening of the lines is small enough to permit the use of single-mode laser diodes in medium-to-high-resolution spaceborne instruments. The same mathematical formalism is used to give a new insight into the analysis of the spectral noise induced by random sampling jitter caused by detector and electronic noise.

The ESA EarthCARE mission: results of the ATLID instrument pre-developments

Due for launch in 2013, EarthCARE (Earth Clouds, Aerosols and Radiation Explorer) has been selected as ESAs sixth Earth Explorer Missions within its Living Planet Programme. Its payload aims at providing measurements, in a radiatively consistent manner, of the global distribution of vertical profiles of clouds and aerosol field characteristics. The EarthCARE payload is composed of four instruments: an Atmospheric backscatter Lidar, a Cloud Profiling Radar, a Multi-Spectral Imager and a Broad Band Radiometer. The EarthCARE mission is a cooperative mission with Japan (JAXA and NiCT), which will provide the Cloud Profiling Radar. ESA will provide the ground segment and the rest of the space segment including the Lidar, the imager and the broadband radiometer. ESA and JAXA have initiated predevelopment activities to reduce technical and programmatic risks for the critical elements of the mission. Following a mission overview, this paper presents results of these pre-development activities mainly related to the ATLID instrument. The activities consist of designing, manufacturing and testing a functional representative model of the ATLID receiver critical units and laser source, of developing and assessing high-power pump laser diodes with extended lifetime and improved efficiency, and of demonstrating the performance of candidate detectors.