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

Diffraction halo in speckle photography

SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Speckle measurements of convection in a liquid cooled from above

Buoyancy-driven recirculation in a liquid-filled rectangular cavity cooled from above is shown to be locally modulated by an unstable thermal layer at the surface. Interferometric observations suggest that fluctuations that occur in a plume descending through the upper liquid layers are of the type described by Howard (1964) and by Krishnamurti & Howard (1981). Temperature measurements across the surface layer are in reasonable agreement with the diffusive heat-conduction model, but indicate that near the plume the fluid is cooler than elsewhere. Quasi-steady measurements of the velocity distribution in the upper regions of the cavity were made using multiple-exposure laser speckle velocimetry. Interrogation of the specklegrams with a Young's fringe technique yields a velocity-vector field of about two thousand elements. These data are used to calculate the corresponding velocity components and estimates of the vorticity distribution. The results compare favourably with measurements recorded directly from Fourier filtering methods. © 1987, Cambridge University Press. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Equal velocity fringes in a Rayleigh-Benard flow by a speckle method

SCOPUS: le.jinfo:eu-repo/semantics/publishe

Flow velocity measurement by a speckle method

An application of the multiple-exposure speckle photography to the Rayleigh-Benard flow is described. A fluid seeded with a minute concentration of diffusing particles is illuminated by a laser light sheet. The multiple-exposure photograph of this sheet is analysed by the well-known techniques of speckle photography to obtain a bidimensional map of the instantaneous velocities. © 1980 SPIE.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Digital image processing for speckle flow velocimetry

A new method is given for the analysis, by digital acquisition and processing, of speckle fringes in fluid mechanics.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Mesure de champs de vitesse d'écoulements fluides par analyse de suites d'images obtenues par diffusion d'un feuillet lumineux

Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe

Speckle velocimetry study of vortex pairing in a low-Re unexcited jet

Application of speckle velocimetry in a round jet (Re = 2300) provides instantaneous 2-D velocity fields and vorticity maps of the interaction between unstable vortices. Detailed descriptions of the pairing process and of the large-scale structures observed near the end of the potential core are obtained without excitation of the jet and without the smearing effects of the conditional sampling method. © 1983 American Institute of Physics.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Non-Gaussian statistics of speckle noise of Young’s fringes in speckle velocimetry

In speckle velocimetry, Young’s fringes observed during analysis of the multiple-exposure photographs of tracer particles seeding a fluid flow are embedded in a speckle noise that renders their analysis difficult. Some first- and second-order statistical properties of this speckle background are considered in this paper. A simple model shows that, because of the small and fluctuating number of scatterers contained in the probe, beam, the intensity fluctuations are enhanced, leading to a contrast greater than one. The same model also shows that the speckle grains are not completely independent because of the existence of long-range intensity correlations. © 1985 Optical Society of America.SCOPUS: ar.jinfo:eu-repo/semantics/publishe