APEX: Current Status of the Airborne Dispersive Pushbroom Imaging Spectrometer

ABSTRACT 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 400 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

APEX: Current Status of the Airborne Dispersive Pushbroom Imaging Spectrometer

ABSTRACT 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 400 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

A new laboratory for the characterisation of hyperspectral airborne sensors

A new facility designed to characterize the spectral, radiometric and geometric properties of hyperspectral airborne sensors was established at the German Aerospace Center (DLR) in Oberpfaffenhofen. This laboratory will serve as Calibration Home Base (CHB) for the airborne imaging spectrometer APEX (Airborne Prism Experiment), which is currently being developed under the authority of the European Space Agency (ESA). In APEX configuration (wavelength range: 380 to 2500 nm, instantaneous field of view: 0.48 mrad, field of view: ±14°) spectral measurements can be performed to a wavelength uncertainty of ±0.15 nm, geometric measurements at increments of 0.0017 mrad across track and 0.0076 mrad along track, and radiometric measurements to an uncertainty of ±3 % relative to national standard. Computer control of major laboratory equipment allows automation of time consuming measurements. The facility can be adapted to similar sensors including such with thermal infrared detectors

Canister free videogrammetry system for thermal vacuum and space applications

The development of a canister-free videogrammetry system is presented. Applications in view, are coordinate measurements during thermal vacuum test and on-baord space flight metrology of mechanical structures, reflectors and antenna's. The paper presents the breadboard system architecture. Two breadboards have been developed. One is based on a space-qualified micro-imager camera. Lenses and flashers are all commercial components and have been made vacuum compatible. Results of accuracy (typically 50ppm) and resolution (typically 25 ppm) tests, in ambient and in vacuum are also presented

Calibration Facility for Airborne Imaging Spectrometers

ESA currently builds the airborne hyper-spectral push broom imaging spectrometer APEX (Airborne Prism EXperiment) operating in the spectral range from 380 to 2500 nm. The APEX instrument will only achieve its challenging measurement accuracy by regular calibration of the instrument between flight cycles. In view of the high relevance to scientific objectives, ESA is funding an "Calibration Home Base" (CHB) for APEX. It is located at DLR Oberpfaffenhofen and will be operational from 2006 on. The CHB provides all hard- and software tools required for radiometric, spectral and geometric on-ground characterisation and calibration of the instrument and its internal references and on-board attachments, and to perform measurements on polarisation- and straylight-sensitivity. This includes a test bed and the provision of the infrastructure

Qualification de grands réflecteurs en environnement spatial

Les nouvelles générations de télescopes spatiaux dans le domaine infrarouge nécessitent des réflecteurs de grandes dimensions et de haute qualité. Ceux-ci, pour des raisons de poids, sont basés sur les technologies des matériaux composites dont les comportements aux basses températures sont mal connus. Une méthode par interférométrie holographique de vérification et de validation en environnement spatial de ce type de réflecteurs est présentée. Elle est basée sur l'utilisation d'une caméra holographique dynamique observant un dépoli sur lequel est projeté le faisceau objet venant de la surface réfléchissante. Outre une augmentation de la dynamique de mesure, cette méthode offre l’avantage principal, par rapport aux techniques d’interférométrie optique, de ne pas nécessiter de système optique d’adaptation du front d’onde au réflecteur à mesurer et donc un gain de flexibilité majeur pour des formes exotiques de réflecteurs (types asphériques). Le système de mesure a été calibré avec un interféromètre ponctuel à effet Doppler. L'influence des différentes sources d’erreur du système sur la mesure a été évaluée. Cette évaluation a porté principalement sur des aspects vibratoires et thermiques. Ces réflecteurs devant être testés sous vide et à basses températures, le système de mesure a été rendu compatible à ces conditions. Des éléments de la caméra holographique (objectifs, CCD, cristal, fibre optique) ont été adaptés et testés sous vide. La certification métrologique de l’ensemble du système sera réalisée par la mesure d'une antenne parabolique, de 1.1 m de diamètre de comportement connu et placée dans un environnement spatial simulé. Le test consistera à mesurer les déplacements et déformations de l'antenne entre un état initial à la température ambiante, et un état final à une température d'environ 130K.Optical Ground Verification Metho

Development of optical ground verification method for mu m to sub-mm reflectors

Large reflectors and antennas for the IR to mm wavelength range are being planned for many Earth observation and astronomical space missions and for commercial communication satellites as well. The challenging tasks of on-ground testing are to achieve the required accuracy in the measurement of the reflector shapes and antenna structures and to verify their performance under simulated space conditions (vacuum, low temperatures). A small number of infrared interferometers have been commercially developed over the last 10 years but their applications have also been limited due to poor dynamic range and the restricted spatial resolution of their detectors. It has therefore been considered essential, from the viewpoint of supporting future ESA exploration missions, to develop and realise suitable verification tools based on infrared interferometry and other optical techniques for testing large reflector structures, telescope configurations and their performances under simulated space conditions. Two methods and techniques are developed at CSL. The first one is an IR-phase shifting interferometer with high spatial resolution. This interferometer shall be used specifically for the verification of high precision IR, FIR and sub-mm reflector surfaces and telescopes under both ambient and thermal vacuum conditions. The second one presented hereafter is a holographic method for relative shape measurement. The holographic solution proposed makes use of a home built vacuum compatible holographic camera that allows displacement measurements from typically 20 nanometres to 25 microns in one shot. An iterative process allows the measurement of a total of up to several mm of deformation. Uniquely the system is designed to measure both specular and diffuse surfacesOptical Ground Verification Method

γ-2 and GSG1L bind with comparable affinities to the tetrameric GluA1 core.

BACKGROUND: The AMPA-type ionotropic glutamate receptor mediates fast excitatory neurotransmission in the brain. A variety of auxiliary subunits regulate its gating properties, assembly, and trafficking, but it is unknown if the binding of these auxiliary subunits to the receptor core is dynamically regulated. Here we investigate the interplay of the two auxiliary subunits γ-2 and GSG1L when binding to the AMPA receptor composed of four GluA1 subunits. METHODS: We use a three-color single-molecule imaging approach in living cells, which allows the direct observation of the receptors and both auxiliary subunits. Colocalization of different colors can be interpreted as interaction of the respective receptor subunits. RESULTS: Depending on the relative expression levels of γ-2 and GSG1L, the occupancy of binding sites shifts from one auxiliary subunit to the other, supporting the idea that they compete for binding to the receptor. Based on a model where each of the four binding sites at the receptor core can be either occupied by γ-2 or GSG1L, our experiments yield apparent dissociation constants for γ-2 and GSG1L in the range of 2.0-2.5/µm2. CONCLUSIONS: The result that both binding affinities are in the same range is a prerequisite for dynamic changes of receptor composition under native conditions