Umberto Del Bello

The FLuorescence EXplorer Mission Concept—ESA’s Earth Explorer 8

In November 2015, the FLuorescence EXplorer (FLEX) was selected as the eighth Earth Explorer mission of the European Space Agency. The tandem mission concept will provide measurements at a spectral and spatial resolution enabling the retrieval and interpretation of the full chlorophyll fluorescence spectrum emitted by the terrestrial vegetation. This paper provides a mission concept overview of the scientific goals, the key objectives related to fluorescence, and the requirements guaranteeing the fitness for purpose of the resulting scientific data set. We present the mission design at the time of selection, i.e., at the end of project phase Phase A/B1, as developed by two independent industrial consortia. The mission concepts both rely on a single payload Fluorescence Imaging Spectrometer, covering the spectral range from 500 to 780 nm. In the oxygen absorption bands, its spectral resolution will be 0.3 nm with a spectral sampling interval of 0.1 nm. The swath width of the spectrometer is 150 km and the spatial resolution will be

Remote sensing of solar-induced fluorescence of vegetation

300 \times 300~\text{m}^{2}

Processes Research by an Imaging Space Mission (PRISM)

. The satellite will fly in tandem with Sentinel-3 providing different and complementary measurements with a temporal collocation of 6 to 15 s. The FLEX launch is scheduled for 2022.

Requirements and design of a thermal high-resolution Earth mapper (THEMA) based on uncooled detectors

The fluorescence signal emitted from vegetation is directly linked to the photosynthesis and as such may be used as an indicator for plant functioning, stress and vitality. Observation of solar induced fluorescence from space is proposed by measuring the weak signal contribution in the Fraunhofer line wavelengths. In an ESA funded study various aspects of measuring the fluorescence signal from space have been analysed for its feasibility. Both scientific and instrumental aspects have been considered in the analysis. The scientific requirements have been studied in detail, looking to aspects such as the selection of Fraunhofer lines, the solar induced fluorescence radiance, measurement accuracy, spatial resolution, atmosphere influence, etc. This has resulted in instrument requirements, that are the basis for a trade off study of optical observation techniques. The main choice was between applying a grating spectrometer or a filter spectrometer, each having advantages and disadvantages for Fraunhofer line detection (FLD). From both spectrometer types a preliminary optical design has been made. Besides a model has been developed to evaluate the different configurations for S/N, integration time, radiance level etc. For these calculations it appeared, that the information about solar excited fluorescence intensity of vegetation is minimal. In the study of feasibility of Fraunhofer line detection from space is demonstrated, albeit, that the observation strategy will depend on the real amount of the solar excited fluorescence intensity. The results of the study are a good basis for further development of a spaceborn Fraunhofer line detector.

Design of the infrared imaging chain for the PRISM hyperspectral imager

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.

Design and development of the Sentinel-2 Multi Spectral Instrument and satellite system

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.

ESA Earth Explorer Land Surface Processes and Interactions mission

ALCATEL has recently studied an infrared imaging chain, in the frame of phase A studies for the Land Surface Processes and Interactions Mission (LSPIM), which was one of the four candidate Core Missions for the European Space Agency Earth Explorer Program. The LSPIM satellite carries a single optical payload named PRISM (Processes Research by an Imaging Space Mission). PRISM is a multispectral imager based on the push broom imaging principle, operating at approximately 679 km altitude with a NADIR swath of 50 km associated to a 50 m spatial resolution. The paper presented herewith summarizes the results of the IR imaging chains study: composed of two IR focal planes (SWIR and TIR) integrated in dedicated ALCATEL dewars (one for each FPA), two proximity electronic modules and a common analog processing unit delivering digital video data to the one board mass memory unit (MMU). The main specifications of the detectors and electronic units are presented, a baseline of the imaging chain architecture complying with the requirements is then proposed with the main achieved trades off. The concept and associated performances of cutting-edge cooling systems are also introduced in this paper.

Visible imaging spectrometer and infrared radiometer (VISIR) for coastal zones and land applications

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.

Hyperspectral Imager Survey and Developments for Scientific and Operational Land Processes Monitoring Applications

The European Space Agency (ESA) is defining candidate missions for Earth Observation. In the class of the Earth Explorer missions, dedicated to research and pre-operational demonstration, the Land Surface Processes and Interactions Mission (LSPIM) will acquire the accurate quantitative measurements needed to improve our understanding of the nature and evolution of biosphere-atmosphere interactions and to contribute significantly to a solution of the scaling problems for energy, water and carbon fluxes at the Earths surface. The mission is intended to provide detailed observations of the surface of the Earth and to collect data related to ecosystem processes and radiation balance. It is also intended to address a range of issues important for environmental monitoring, renewable resources assessment and climate models. The mission involves a dedicated maneuvering satellite which provides multi-directional observations for systematic measurement of Land Surface BRDF (Bi-Directional Reflectance Distribution Function) of selected sites on Earth. The satellite carries an optical payload: PRISM (Processes Research by an Imaging Space Mission), a multispectral imager providing reasonably high spatial resolution images (50 m over 50 km swath) in the whole optical spectral domain (from 450 nm to 2.35 micrometer with a resolution close to 10 nm, and two thermal bands from 8.1 to 9.1 micrometer). This paper presents the results of the Phase A study awarded by ESA, led by ALCATEL Space Industries and concerning the design of LSPIM.

Hyperspectral imager for the future ESA land surface processes earth explorer mission

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.