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1280 KiB

Open AccessArticle

APEX - the Hyperspectral ESA Airborne Prism Experiment

by Klaus I. Itten, Francesco Dell’Endice, Andreas Hueni, Mathias Kneubühler, Daniel Schläpfer, Daniel Odermatt, Felix Seidel, Silvia Huber, Jürg Schopfer, Tobias Kellenberger, Yves Bühler, Petra D’Odorico, Jens Nieke, Edoardo Alberti and Koen Meuleman

Sensors 2008, 8(10), 6235-6259; https://doi.org/10.3390/s8106235 - 1 Oct 2008

Cited by 89 | Viewed by 17347

Abstract

The airborne ESA-APEX (Airborne Prism Experiment) hyperspectral mission simulator is described with its distinct specifications to provide high quality remote sensing data. The concept of an automatic calibration, performed in the Calibration Home Base (CHB) by using the Control Test Master (CTM), the [...] Read more.

The airborne ESA-APEX (Airborne Prism Experiment) hyperspectral mission simulator is described with its distinct specifications to provide high quality remote sensing data. The concept of an automatic calibration, performed in the Calibration Home Base (CHB) by using the Control Test Master (CTM), the In-Flight Calibration facility (IFC), quality flagging (QF) and specific processing in a dedicated Processing and Archiving Facility (PAF), and vicarious calibration experiments are presented. A preview on major applications and the corresponding development efforts to provide scientific data products up to level 2/3 to the user is presented for limnology, vegetation, aerosols, general classification routines and rapid mapping tasks. BRDF (Bidirectional Reflectance Distribution Function) issues are discussed and the spectral database SPECCHIO (Spectral Input/Output) introduced. The optical performance as well as the dedicated software utilities make APEX a state-of-the-art hyperspectral sensor, capable of (a) satisfying the needs of several research communities and (b) helping the understanding of the Earth’s complex mechanisms. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Switzerland)

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945 KiB

Open AccessArticle

Mid-Infrared Tunable Resonant Cavity Enhanced Detectors

by Niels Quack, Stefan Blunier, Jurg Dual, Ferdinand Felder, Martin Arnold and Hans Zogg

Sensors 2008, 8(9), 5466-5478; https://doi.org/10.3390/s8095466 - 4 Sep 2008

Cited by 15 | Viewed by 12437

Abstract

Mid-infrared detectors that are sensitive only in a tunable narrow spectral band are presented. They are based on the Resonant Cavity Enhanced Detector (RCED) principle and employing a thin active region using IV-VI narrow gap semiconductor layers. A Fabry-Pérot cavity is formed by [...] Read more.

Mid-infrared detectors that are sensitive only in a tunable narrow spectral band are presented. They are based on the Resonant Cavity Enhanced Detector (RCED) principle and employing a thin active region using IV-VI narrow gap semiconductor layers. A Fabry-Pérot cavity is formed by two mirrors. The active layer is grown onto one mirror, while the second mirror can be displaced. This changes the cavity length thus shifting the resonances where the detector is sensitive. Using electrostatically actuated MEMS micromirrors, a very compact tunable detector system has been fabricated. Mirror movements of more than 3 μm at 30V are obtained. With these mirrors, detectors with a wavelength tuning range of about 0.7 μm have been realized. Single detectors can be used in mid-infrared micro spectrometers, while a detector arrangement in an array makes it possible to realize Adaptive Focal Plane Arrays (AFPA). Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Switzerland)

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1013 KiB

Open AccessArticle

Neuromorphic VLSI Models of Selective Attention: From Single Chip Vision Sensors to Multi-chip Systems

by Giacomo Indiveri

Sensors 2008, 8(9), 5352-5375; https://doi.org/10.3390/s8095352 - 3 Sep 2008

Cited by 22 | Viewed by 11721

Abstract

Biological organisms perform complex selective attention operations continuously and effortlessly. These operations allow them to quickly determine the motor actions to take in response to combinations of external stimuli and internal states, and to pay attention to subsets of sensory inputs suppressing non [...] Read more.

Biological organisms perform complex selective attention operations continuously and effortlessly. These operations allow them to quickly determine the motor actions to take in response to combinations of external stimuli and internal states, and to pay attention to subsets of sensory inputs suppressing non salient ones. Selective attention strategies are extremely effective in both natural and artificial systems which have to cope with large amounts of input data and have limited computational resources. One of the main computational primitives used to perform these selection operations is the Winner-Take-All (WTA) network. These types of networks are formed by arrays of coupled computational nodes that selectively amplify the strongest input signals, and suppress the weaker ones. Neuromorphic circuits are an optimal medium for constructing WTA networks and for implementing efficient hardware models of selective attention systems. In this paper we present an overview of selective attention systems based on neuromorphic WTA circuits ranging from single-chip vision sensors for selecting and tracking the position of salient features, to multi-chip systems implement saliency-map based models of selective attention. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Switzerland)

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880 KiB

Open AccessArticle

The Improved Dual-view Field Goniometer System FIGOS

by Jürg Schopfer, Stefan Dangel, Mathias Kneubühler and Klaus I. Itten

Sensors 2008, 8(8), 5120-5140; https://doi.org/10.3390/s8085120 - 28 Aug 2008

Cited by 30 | Viewed by 12903

Abstract

In spectrodirectional Remote Sensing (RS) the Earth’s surface reflectance characteristics are studied by means of their angular dimensions. Almost all natural surfaces exhibit an individual anisotropic reflectance behaviour due to the contrast between the optical properties of surface elements and background and the [...] Read more.

In spectrodirectional Remote Sensing (RS) the Earth’s surface reflectance characteristics are studied by means of their angular dimensions. Almost all natural surfaces exhibit an individual anisotropic reflectance behaviour due to the contrast between the optical properties of surface elements and background and the geometric surface properties of the observed scene. The underlying concept, which describes the reflectance characteristic of a specific surface area, is called the bidirectional reflectance distribution function (BRDF). BRDF knowledge is essential for both correction of directional effects in RS data and quantitative retrieval of surface parameters. Ground-based spectrodirectional measurements are usually performed with goniometer systems. An accurate retrieval of the bidirectional reflectance factors (BRF) from field goniometer measurements requires hyperspectral knowledge of the angular distribution of the reflected and the incident radiation. However, prior to the study at hand, no operational goniometer system was able to fulfill this requirement. This study presents the first dual-view field goniometer system, which is able to simultaneously collect both the reflected and the incident radiation at high angular and spectral resolution and, thus, providing the necessary spectrodirectional datasets to accurately retrieve the surface specific BRF. Furthermore, the angular distribution of the incoming diffuse radiation is characterized for various atmospheric conditions and the BRF retrieval is performed for an artificial target and compared to laboratory spectrodirectional measurement results obtained with the same goniometer system. Suggestions for further improving goniometer systems are given and the need for intercalibration of various goniometers as well as for standardizing spectrodirectional measurements is expressed. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Switzerland)

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292 KiB

Open AccessArticle

Performance and Transient Behavior of Vertically Integrated Thin-film Silicon Sensors

by Nicolas Wyrsch, Gregory Choong, Clément Miazza and Christophe Ballif

Sensors 2008, 8(8), 4656-4668; https://doi.org/10.3390/s8084656 - 8 Aug 2008

Cited by 5 | Viewed by 10344

Abstract

Vertical integration of amorphous hydrogenated silicon diodes on CMOS readout chips offers several advantages compared to standard CMOS imagers in terms of sensitivity, dynamic range and dark current while at the same time introducing some undesired transient effects leading to image lag. Performance [...] Read more.

Vertical integration of amorphous hydrogenated silicon diodes on CMOS readout chips offers several advantages compared to standard CMOS imagers in terms of sensitivity, dynamic range and dark current while at the same time introducing some undesired transient effects leading to image lag. Performance of such sensors is here reported and their transient behaviour is analysed and compared to the one of corresponding amorphous silicon test diodes deposited on glass. The measurements are further compared to simulations for a deeper investigation. The long time constant observed in dark or photocurrent decay is found to be rather independent of the density of defects present in the intrinsic layer of the amorphous silicon diode. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Switzerland)

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807 KiB

Open AccessArticle

Textile Pressure Sensor Made of Flexible Plastic Optical Fibers

by Markus Rothmaier, Minh Phi Luong and Frank Clemens

Sensors 2008, 8(7), 4318-4329; https://doi.org/10.3390/s8074318 - 25 Jul 2008

Cited by 164 | Viewed by 19653

Abstract

In this paper we report the successful development of pressure sensitive textile prototypes based on flexible optical fibers technology. Our approach is based on thermoplastic silicone fibers, which can be integrated into woven textiles. As soon as pressure at a certain area of [...] Read more.

In this paper we report the successful development of pressure sensitive textile prototypes based on flexible optical fibers technology. Our approach is based on thermoplastic silicone fibers, which can be integrated into woven textiles. As soon as pressure at a certain area of the textile is applied to these fibers they change their cross section reversibly, due to their elastomeric character, and a simultaneous change in transmitted light intensity can be detected. We have successfully manufactured two different woven samples with fibers of 0.51 and 0.98 mm diameter in warp and weft direction, forming a pressure sensitive matrix. Determining their physical behavior when a force is applied shows that pressure measurements are feasible. Their usable working range is between 0 and 30 N. Small drifts in the range of 0.2 to 4.6%, over 25 load cycles, could be measured. Finally, a sensor array of 2 x 2 optical fibers was tested for sensitivity, spatial resolution and light coupling between fibers at intersections. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Switzerland)

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1921 KiB

Open AccessArticle

Sensor for Measuring Strain in Textile

by Corinne Mattmann, Frank Clemens and Gerhard Tröster

Sensors 2008, 8(6), 3719-3732; https://doi.org/10.3390/s8063719 - 3 Jun 2008

Cited by 409 | Viewed by 22675

Abstract

In this paper a stain sensor to measure large strain (80%) in textiles is presented. It consists of a mixture of 50wt-% thermoplastic elastomer (TPE) and 50wt-% carbon black particles and is fiber-shaped with a diameter of 0.315mm. The attachment of the sensor [...] Read more.

In this paper a stain sensor to measure large strain (80%) in textiles is presented. It consists of a mixture of 50wt-% thermoplastic elastomer (TPE) and 50wt-% carbon black particles and is fiber-shaped with a diameter of 0.315mm. The attachment of the sensor to the textile is realized using a silicone film. This sensor configuration was characterized using a strain tester and measuring the resistance (extension-retraction cycles): It showed a linear resistance response to strain, a small hysteresis, no ageing effects and a small dependance on the strain velocity. The total mean error caused by all these effects was +/-5.5% in strain. Washing several times in a conventional washing machine did not influence the sensor properties. The paper finishes by showing an example application where 21 strain sensors were integrated into a catsuit. With this garment, 27 upper body postures could be recognized with an accuracy of 97%. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Switzerland)

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1277 KiB

Open AccessArticle

Reflectance Modeling for Real Snow Structures Using a Beam Tracing Model

by Dominik Bänninger, Claude Saskia Bourgeois, Margret Matzl and Martin Schneebeli

Sensors 2008, 8(5), 3482-3496; https://doi.org/10.3390/s8053482 - 26 May 2008

Cited by 12 | Viewed by 11528

Abstract

It is important to understand reflective properties of snow, for example for remote sensing applications and for modeling of energy balances in snow packs. We present a method with which we can compare reflectance measurements and calculations for the same snow sample structures. [...] Read more.

It is important to understand reflective properties of snow, for example for remote sensing applications and for modeling of energy balances in snow packs. We present a method with which we can compare reflectance measurements and calculations for the same snow sample structures. Therefore, we first tomograph snow samples to acquire snow structure images (6 x 2 mm). Second, we calculated the sample reflectance by modeling the radiative transfer, using a beam tracing model. This model calculates the biconical reflectance (BR) derived from an arbitrary number of incident beams. The incident beams represent a diffuse light source. We applied our method to four different snow samples: Fresh snow, metamorphosed snow, depth hoar, and wet snow. The results show that (i) the calculated and measured reflectances agree well and (ii) the model produces different biconical reflectances for different snow types. The ratio of the structure to the wavelength is large. We estimated that the size parameter is larger than 50 in all cases we analyzed. Specific surface area of the snow samples explains most of the difference in radiance, but not the different biconical reflectance distributions. The presented method overcomes the limitations of common radiative transfer models which use idealized grain shapes such as spheres, plates, needles and hexagonal particles. With this method we could improve our understanding for changes in biconical reflectance distribution associated with changes in specific surface area. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Switzerland)

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1581 KiB

Open AccessArticle

From Hearing to Listening: Design and Properties of an Actively Tunable Electronic Hearing Sensor

by Ruedi Stoop, Tom Jasa, Yoko Uwate and Stefan Martignoli

Sensors 2007, 7(12), 3287-3298; https://doi.org/10.3390/s7123287 - 14 Dec 2007

Cited by 25 | Viewed by 10957

Abstract

An important step towards understanding the working principles of the mammalian hearing sensor is the concept of an active cochlear amplifier. Theoretical arguments and physiological measurements suggest that the active cochlear amplifiers originate from systems close to a Hopf bifurcation. Efforts to model [...] Read more.

An important step towards understanding the working principles of the mammalian hearing sensor is the concept of an active cochlear amplifier. Theoretical arguments and physiological measurements suggest that the active cochlear amplifiers originate from systems close to a Hopf bifurcation. Efforts to model the mammalian hearing sensor on these grounds have, however, either had problems in reproducing sufficiently close essential aspects of the biological example (Magnasco, M.O. Phys. Rev. Lett. 90, 058101 (2003); Duke, T. & Jülicher, F. Phys. Rev. Lett. 90, 158101 (2003)), or required complicated spatially coupled differential equation systems that are unfeasible for transient signals (Kern, A. & Stoop, R. Phys. Rev. Lett. 91, 128101 (2003)). Here, we demonstrate a simple system of electronically coupled Hopf amplifiers that not only leads to the desired biological response behavior, but also has real-time capacity. The obtained electronic Hopf cochlea shares all salient signal processing features exhibited by the mammalian cochlea and thus provides a simple and efficient design of an artificial mammalian hearing sensor. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Switzerland)

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Review

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726 KiB

Open AccessReview

Bacterial Biosensors for Measuring Availability of Environmental Pollutants

by Robin Tecon and Jan Roelof Van der Meer

Sensors 2008, 8(7), 4062-4080; https://doi.org/10.3390/s8074062 - 10 Jul 2008

Cited by 81 | Viewed by 21242

Abstract

Traditionally, pollution risk assessment is based on the measurement of a pollutant’s total concentration in a sample. The toxicity of a given pollutant in the environment, however, is tightly linked to its bioavailability, which may differ significantly from the total amount. Physico-chemical and [...] Read more.

Traditionally, pollution risk assessment is based on the measurement of a pollutant’s total concentration in a sample. The toxicity of a given pollutant in the environment, however, is tightly linked to its bioavailability, which may differ significantly from the total amount. Physico-chemical and biological parameters strongly influence pollutant fate in terms of leaching, sequestration and biodegradation. Bacterial sensorreporters, which consist of living micro-organisms genetically engineered to produce specific output in response to target chemicals, offer an interesting alternative to monitoring approaches. Bacterial sensor-reporters detect bioavailable and/or bioaccessible compound fractions in samples. Currently, a variety of environmental pollutants can be targeted by specific biosensor-reporters. Although most of such strains are still confined to the lab, several recent reports have demonstrated utility of bacterial sensing-reporting in the field, with method detection limits in the nanomolar range. This review illustrates the general design principles for bacterial sensor-reporters, presents an overview of the existing biosensor-reporter strains with emphasis on organic compound detection. A specific focus throughout is on the concepts of bioavailability and bioaccessibility, and how bacteria-based sensing-reporting systems can help to improve our basic understanding of the different processes at work. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Switzerland)

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