The presentation slides for “Small Optics for Earth Science: Roundtable” are available at <a href="http://doi.org/10.1117/12.2536006">http://doi.org/10.1117/12.2536006</a>, under the Supplemental Content tab.
ESA is currently running two parallel, competitive phase A/B1 studies for MetOp Second Generation (MetOp-SG). MetOp-SG is the space segment of EUMETSAT Polar System (EPS-SG) consisting of the satellites and instruments. The Phase A/B1 studies will be completed in the first quarter of 2013. The final implementation phases (B2/C/D) are planned to start 2013. ESA is responsible for instrument design of five missions, namely Microwave Sounding Mission (MWS), Scatterometer mission (SCA), Radio Occultation mission (RO), Microwave Imaging mission (MWI), Ice Cloud Imaging (ICI) mission, and Multiviewing, Multi-channel, Multi-polarization imaging mission (3MI). This paper will present the instrument main design elements of the 3MI mission, primarily aimed at providing aerosol characterization for climate monitoring, Numerical Weather Prediction (NWP), atmospheric chemistry and air quality. The 3MI instrument is a passive radiometer measuring the polarized radiances reflected by the Earth under different viewing geometries and across several spectral bands spanning the visible and short-wave infrared spectrum. The paper will present the main performances of the instrument and will concentrate mainly on the performance improvements with respect to its heritage derived by the POLDER instrument. The engineering of some key performance requirements (multiviewing, polarization sensitivity, etc.) will also be discussed.
In this paper we present the results obtained within the context of the ESA-funded project Programmable Optoelectronic Adaptive Element (AO/1-5476/07/NL/EM). The objective of this project is the development of adaptive (reconfigurable) optical elements for use in space applications and the execution of preliminary qualification tests in the relevant environment.<p> </p>The different designs and materials that have been considered and manufactured for a 2D beam steerer based on passive matrix liquid crystal programmable blaze grating will described and discussed.
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.
In recent years the European Space Agency (ESA) has been pursuing studies dedicated to Earth imaging from space in the Long Wave Infrared region for applications ranging from monitoring of evapotranspiration, and water resources management to the development of urban heat island and monitoring of high temperature events. Among the various solutions being studied is also that of a low cost instrument with moderate needs in terms of resources. . One potential enabler for such type of mission could be the technology of microbolometer detectors. The latest generation of microbolometer arrays now available offer large formats (XGA) and small pixel sizes which are favourable for keeping the instrument size within reasonable limit while addressing larger swath compared to VGA format. A major concern however, in using commercial microbolometers in space is their ability to sustain the radiation environment of space but also the harsh mechanical environments. COTS microbolometers are potentially susceptible to SEE (single even effects) because of the use of commercial CMOS technology/libraries and no implementation of specific design rules (i.e. space tailored rad hardened). In the past, and in the context of their national program, CNES has performed a space evaluation of COTS microbolometer arrays of 640x480 with 25 μm pitch. Despite successful gamma irradiations and vibration tests; degradation of the ROIC has been evidenced during the heavy ions tests, which makes the full qualification of COTS microbolometers for future space programmes mandatory. Similar tests have been performed on an even earlier device (384x288 with a pitch of 35 μm) under the ESA EarthCARE programme. ESA and Thales Alenia Space have recently run an activity with the objective to validate a third-generation COTS microbolometer offered by ULIS (France) against the relevant environment for a candidate Thermal InfraRed (TIR) space mission. The micro-bolometer selected is the PICO 1024E, which offers 1024x768 pixels of size 17 μm square. The validation sequence included the main types of irradiation tests required by a space application as well as vibration and shock tests. Ageing tests are included and synergetic effects are also investigated. The detector performances were tested before, after and during any test sequence. In this paper, the results of this activity achieved in the beginning of 2017 are reported.
Optical instrumentation on space platforms, typically needs to adhere to high quality standards, in particular as far as robustness to the applicable environment is concerned. The term ‘environment’ typically encompasses all types of loads that a system or component might encounter and is required to survive during its lifetime in space without loss of performance.
Only a small set of radiation hardened optical glasses are currently offered in the market, thus drastically limiting the optical design choices available to the engineers at the early phases of an instrument development. Furthermore, availability of those glasses cannot be easily guaranteed for the long term horizon of future space instrument developments. Radiation tests on conventional glasses on the other hand have shown significant sensitivity to high radiation levels but such levels are not necessarily representative of typical low Earth (LEO) orbits. We have conducted irradiation campaigns on several different types of conventional, non-radiation hard glasses, selected from the wider pool of the Schott “new” arsenic and lead free series (N-*) and characterized their spectral transmission properties before and after ionizing dose deposition. We report our first findings here.
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 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 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.
Liquid-crystal variable retarders (LCVRs) are an emergent technology for space-based polarimeters, following its
success as polarization modulators in ground-based polarimeters and ellipsometers. Wide-field double nematic
LCVRs address the high angular sensitivity of nematic LCVRs at some voltage regimes. We present a work
in which wide-field LCVRs were designed and built, which are suitable for wide-field-of-view instruments such
as polarimetric coronagraphs. A detailed model of their angular acceptance was made, and we validated this
technology for space environmental conditions, including a campaign studying the effects of gamma, proton
irradiation, vibration and shock, thermo-vacuum and ultraviolet radiation.
The use of Liquid Crystal Variable Retarders (LCVRs) as polarization modulators are envisaged as a promising novel
technique for space instrumentation due to the inherent advantage of eliminating the need for conventional rotary
polarizing optics hence the need of mechanisms. LCVRs is a mature technology for ground applications; they are wellknow,
already used in polarimeters, and during the last ten years have undergone an important development, driven by
the fast expansion of commercial Liquid Crystal Displays.
In this work a brief review of the state of the art of imaging polarimeters based on LCVRs is presented. All of them are
ground instruments, except the solar magnetograph IMaX which flew in 2009 onboard of a stratospheric balloon as part
of the SUNRISE mission payload, since we have no knowledge about other spaceborne polarimeters using liquid crystal
up to now. Also the main results of the activity, which was recently completed, with the objective to validate the LCVRs
technology for the Solar Orbiter space mission are described. In the aforementioned mission, LCVRs will be utilized in
the polarisation modulation package of the instruments SO/PHI (Polarimetric and Helioseismic Imager for Solar Orbiter)
and METIS/COR (Multi Element Telescope for Imaging and Spectroscopy, Coronagraph).
We report the use of an experimental ferroelectric liquid crystal material called CDRR8 in bistable optically addressed spatial light modulators for both amplitude- and phase-modulating devices. First, the methods used to improve the alignment and obtain truly bistable switching with CDRR8 are described. The diffraction efficiency and switching characteristics of a bistable CDRR8 optically addressed spatial light modulator used as an amplitude-modulating device and then as a phase-modulating device for encoding high-resolution patterns are compared. The CDRR8 devices exhibit bistability when driven by alternating monopolar pulses. The results show that the use of a device as a phase-modulating rather than an amplitude-modulating device, increases the diffraction efficiency by 10 times. Resolution is better than 100 lp/mm, as measured by the fall in diffraction efficiency by 50% compared with the diffraction efficiency at low spatial frequencies.