This paper presents the results of a study aimed at investigating the potential of Compressive Sensing (CS) technologies for optical space instruments. Besides assessing the pros and cons for a wide set of proposed instrumental concepts for space applications, the study analyzed in further detail two CS-based instrument concepts, each targeting a specific application: an UV-VIS hyperspectral imager on orbiter for stellar spectro-photometry and a MIR camera for sky observation and real-time detection of Near Earth Objects (NEO). The proposed UV-VIS hyperspectral imager relies on a classical CS approach and addresses the CS reconstruction of the full image in order to implement slitless spectrophotometry of stars. The CS-based MIR camera for NEO detection instead explores a novel approach aiming at information extraction without a prior full reconstruction of the image. Besides outlining the optical design of the instruments, its key elements and a pros and cons analysis of the architecture, this paper presents the performance assessment of these instruments for typical application scenarios by means of simulated data. The results showed that, from the point of view of data reconstruction quality, a good performance can be achieved by the designed instruments in terms of compression ratio (CR) and image reconstruction. In terms of system budgets, the CS architecture offered only some marginal benefits with respect to their traditional counterparts, mainly due to the lack of a compression board. Most advantages are instead provided in terms of downlink requirements and memory buffer.
In order to ensure continuity and further enhancement of the European operational meteorological observations in the timeframe of 2020 to 2040, the MetOp-SG programme has been initiated by ESA in collaboration with EUMETSAT. ESA develops the prototype MetOp-SG satellites (including associated instruments) and procures, on behalf of EUMETSAT, the recurrent satellites (and associated instruments). EUMETSAT is responsible for the overall mission, funds the recurrent satellites, develops the ground segment, procures the launch and LEOP services and performs the satellites operations. The corresponding EUMETSAT Programme is termed the EUMETSAT Polar System – Second Generation or EPS-SG.
The FLuorescence Imaging Spectrometer (FLORIS) is the payload of the FLuorescence Explorer Mission (FLEX) of the
European Space Agency. The mission objective is to perform quantitative measurements of the solar induced vegetation
fluorescence to monitor photosynthetic activity. FLORIS works in a push-broom configuration and it is designed to
acquire data in the 500–780 nm spectral range, with a sampling of 0.1 nm in the oxygen bands (759–769 nm and 686-
697 nm) and 0.5–2.0 nm in the red edge, chlorophyll absorption and Photochemical Reflectance Index bands. FLEX will
fly in formation with Sentinel-3 to benefit of the measurements made by the Sentinel-3 instruments OLCI and SLSTR,
particularly for cloud screening, proper characterization of the atmospheric state and determination of the surface
temperature. The instrument concept is based on a common telescope and two modified Offner spectrometers with
reflective concave gratings both for the High Resolution (HR) and Low Resolution (LR) spectrometers. In the frame of
the instrument pre-development Leonardo Company (I) has built and tested an elegant breadboard of the instrument
consisting of the telescope and the HR spectrometer. The development of the LR spectrometer is in charge of OHB
System AG (D) and is currently in the manufacturing phase. The main objectives of the activity are: anticipate the
development of the instrument and provide early risk retirement of critical components, evaluate the system
performances such as imaging quality parameters, straylight, ghost, polarization sensitivity and environmental
influences, verify the adequacy of critical tests such as spectral characterization and straylight, define and optimize
instrument alignment procedures. Following a brief overview of the FLEX mission, the paper will cover the design and
the development of the optics breadboard with emphasis on the results obtained during the tests and the lessons learned
for the flight unit.
The Multi-Viewing, Multi-Channel, Multi-Polarisation Imager (3MI) is an imaging radiometer for the ESA/Eumetsat MetOp-SG programme. Based on the heritage of POLDER/PARASOL, 3MI will collect global observations of the top-of-atmosphere polarised bi-directional reflectance distribution function in 12 spectral bands, by observing the same target from multiple views using a push-broom scanning concept. In order to mitigate any technological risks associated with the 3MI instrument development, an Elegant Breadboard of representative form, function and performance to the 3MI VNIR lens was foreseen in the frame of the Optics Pre- Development (OPD) activity. The optical design and the performance results of the OPD VNIR lens are presented, from the top level requirements flow-down to the optical design solution and concept adopted. The large FOV and image irradiance uniformity, the extended VNIR spectral range, combined with the demanding polarisation and stray-light requirements are the main design drivers. The design concept is based on a Galilean telescope coupled to a focusing group. The aperture stop, placed in between, is located in such a way that the system is telecentric in image space. The system exhibits a fine control of the entrance pupil size as a function of the FOV, low distortion and correction of lateral chromatic aberration. Polarisation related performances are achieved by low polarisation sensitivity and low retardance anti-reflection coatings, as well as by a proper selection of glass material properties.
The Multi-Viewing, Multi-Channel, Multi-Polarisation Imager (3MI) is an imaging radiometer for the ESA/Eumetsat MeteOp-SG programme. Based on the heritage of the POLDER/PARASOL instrument, 3MI is designed to collect global observations of the top-of-atmosphere polarised bi-directional reflectance distribution function in 12 spectral bands, by observing the same target from multiple views using a pushbroom scanning concept. <p> </p>The demanding challenge of the 3MI optical design is represented by the polarisation and image irradiance fall-off (throughput uniformity) requirements. In a generic optical system, the image irradiance fall-off is a function of: target radiance distribution and polarisation, entrance pupil size and optical transmittance variations across the field of view (FOV), distortion and vignetting. In most applications these aspects can be considered as independent; however, when high image irradiance uniformity is required, they have to be considered as linked together. This is particularly true in case of a wide FOV polarimeter as 3MI is.<p> </p> In order to properly account for these aspects, an irradiance fall-off analytical model has been developed in the frame of 3MI Optics Pre-Development (OPD), whose aim is to mitigate any technological risks associated with the 3MI instrument development. It is shown how it is possible to control the image irradiance distribution acting on optical design parameters (e.g. distortion and entrance pupil size variation with FOV). Moreover, the impact of polarisation performances on irradiance fall-off is discussed.
The Centro Nazionale di Meteorologia e Climatologia Aeronautica recently hosted a fellowship sponsored by Galileo
Avionica, with the intent to study and perform a simulation of Meteosat Third Generation - Lightning Imager (MTG-LI)
sensor behavior through Tropical Rainfall Measuring Mission - Lightning Imaging Sensor data (TRMM-LIS). For the
next generation of earth observation geostationary satellite, major operating agencies are planning to insert an optical
imaging mission, that continuously observes lightning pulses in the atmosphere; EUMETSAT has decided in recent
years that one of the three candidate mission to be flown on MTG is LI, a Lightning Imager. MTG-LI mission has no
Meteosat Second Generation heritage, but users need to evaluate the possible real time data output of the instrument to
agree in inserting it on MTG payload. Authors took the expected LI design from MTG Mission Requirement Document,
and reprocess real lightning dataset, acquired from space by TRMM-LIS instrument, to produce a simulated MTG-LI
lightning dataset. The simulation is performed in several run, varying Minimum Detectable Energy, taking into account
processing steps from event detection to final lightning information. A definition of the specific meteorological
requirements is given from the potential use in meteorology of lightning final information for convection estimation and
numerical cloud modeling. Study results show the range of instrument requirements relaxation which lead to minimal
reduction in the final lightning information.