
Bernd JähneHeidelberg University · Interdisciplinary Center for Scientific Computing (IWR) and Institute of Environmental Physics (IUP)
Bernd Jähne
Prof. Dr.
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Publications (438)
In order to illustrate the broad application range of the new version of the EMVA standard 1288, its basic concepts will be outlined and illustrated with measurements from standard monochrome industrial cameras, VIS-SWIR cameras and an automotive HDR camera with a dynamic range of 120 dB.
Event-based sensors asynchronously measure pixel brightness changes, and output a stream of events that encode the time, location and sign of the brightness changes instead of capturing images at a fixed rate, as conventional area-scan sensors do. Advantages of event-based sensors include: high temporal resolution and dynamic range (120 dB), low po...
Characterization of materials at interfaces includes also transfer processes taking place there. This is an ubiquitous phenomenon in the environment, technical processes, and living species. Because at least one of the two phases at the interface is mobile, these processes are characterized by a complex interplay between molecular diffusion and tur...
Techniques based on thermography are well-established for destruction-free material inspection. A similar technique was invented independently in environmental sciences to explore exchange processes at air-water interfaces. The analysis was, however, limited to one-dimensional vertical transport assuming a horizontally homogeneous and stationary ex...
Sulfur dioxide is an ideal tracer to study the partitioning of the resistance of gas transfer across the water interface between air and water because the pH value in water controls the effective solubility of sulfur dioxide. Friman and J¨ahne [1] already demonstrated that it is possible to measure sulfur dioxide concentration profiles with laser i...
An almost lossless compression method for images is introduced adapted to the temporal noise of image sensors. In a first step, a non-linear gray value transform is applied to generate an image with a gray value independent temporal noise and less bits than the original image. The chosen value for the standard deviation of the temporal noise in the...
Coherent vortices in the aqueous surface layer beneath wind waves manifest themselves by inducing elongated high‐speed streaks on the interface. Analyses of thermal images taken in the wind‐wave flume reveal that the mean streak spacing scaled by the viscous length, λ+¯, depends strongly on the wind‐wave condition. This contradicts the wall‐bounded...
In 1983 Ed Monahan presented the paper “The role of oceanic whitecaps in air-sea gas exchange” at the first International Symposium on Gas Transfer at Water Surfaces. He predicted a steep increase in the gas transfer velocities once the whitecaps can act as low impedance vents. He also postulated that the main role of bubbles is not their additiona...
Gas transfer velocities were measured in two high-speed wind-wave tanks (Kyoto University and the SUSTAIN facility, RSMAS, University of Miami) using fresh water, simulated seawater and seawater for wind speeds between 7 and 85 m s-1. Using a mass balance technique, transfer velocities of a total of 12 trace gases were measured, with dimensionless...
Due to miscommunication during the proofing process, in 16 occasions throughout the text variables are shown in parentheses in the text, which should not be the case. As one example in the first sentence in section 4.5 “The setup allows for a direct comparison of three methods to determine the transfer velocity (k)” should read: “The setup allows f...
Gas transfer velocities were measured in two high-speed wind-wave tanks (Kyoto University and the SUSTAIN facility, RSMAS, University of Miami) using fresh water, simulated seawater and seawater for wind speeds between 7 and 80 m s−1. Using a mass balance technique, transfer velocities of a total of 12 trace gases were measured, with dimensionless...
Today's camera systems used for machine vision and scientific applications have intra-scene dynamic ranges up to 16 bit and therefore A/D converters with up to 16 bit resolution per pixel. Unfortunately, the linear amplification of electrons also forces a linear or even quadratic increase of the image noise variance with the signal. Based on a meth...
A laser-induced fluorescence technique to measure vertical concentration profiles of the tracer sulfur dioxide above the air–water interface is presented. The imaging technique is capable of recording profiles at a rate of up to 40 Hz with a sufficiently high spatial resolution to resolve the profile within the viscous boundary layer in the air at...
In 1983 Ed Monahan presented the paper "The role of oceanic whitecaps in air-sea gas exchange" at the first International Symposium on Gas Transfer at Water Surfaces. He predicted a steep increase in the gas transfer velocities once the whitecaps can act as low impedance vents. He also postulated that the main role of bubbles is not their additiona...
Heat transfer velocities measured during three different campaigns in the Baltic Sea using the active controlled flux technique (ACFT) with wind speeds ranging from 5.3 to 14.8 m s-1 are presented. Careful scaling of the heat transfer velocities to gas transfer velocities using Schmidt number exponents measured in a laboratory study allows us to co...
Heat transfer velocities measured during three different campaigns in the Baltic Sea using the Active Controlled Flux Technique (ACFT) with wind speeds ranging from 5.3 to 14.8ms−1 are presented. Careful scaling of the heat transfer velocities to gas transfer velocities using Schmidt number exponents measured in a laboratory study allows to compare...
The exchange of trace gases such as carbon dioxide or methane between the atmosphere and the ocean plays a key role for the climate system. However, the investigation of air–sea gas exchange rates lacks fast and accurate measurement techniques that can also be used in the field, e.g., onboard a ship on the ocean. A promising way to overcome this de...
The exchange of inert and sparingly soluble gases including carbon dioxide, methane, and oxygen between the atmosphere and oceans is controlled by a thin about 10–350 μm thick boundary layer at the top of the ocean. The hydrodynamics in this layer are significantly different from boundary layers at rigid walls since the orbital motion of the waves...
This paper tackles the problem of relative pose estimation between two monocular camera images in textureless scenes. Due to a lack of point matches, point-based approaches such as the 5-point algorithm often fail when used in these scenarios. Therefore we investigate relative pose estimation from line observations. We propose a new algorithm in wh...
Disparity estimation using the structure tensor is a local approach to determine orientation in Epipolar Plane Images. A global extension would lead to more precise and robust estimations. In this work, a novel algorithm for 3D reconstruction from linear light fields is proposed. This method uses a modified version of the Progressive Probabilistic...
Camera calibration, crucial for computer vision tasks, often relies on planar calibration targets to calibrate the camera parameters. This work describes the design of a planar, fractal, self-identifying calibration pattern, which provides a high density of calibration points for a large range of magnification factors. An evaluation on ground truth...
Laboratory experiments on studying the structure of the turbulent air boundary layer over waves were carried out at the Wind-Wave Flume of the Large Thermostratified Tank of the Institute of Applied Physics, Russian Academy of Sciences (IAP RAS), in conditions modeling the near water boundary layer of the atmosphere under strong and hurricane winds...
Das Heidelberger Bildverarbeitungsforum ist seit 20 Jahren auf dem Gebiet der Weiterbildung und des Informationsaustauschs zwischen Forschern und Anwendern aktiv. Aus Anlass dieses Jubiläums kamen im April Wissenschaftler sowie Vertreter der Bildverarbeitungsindustrie an der Universität Heidelberg zusammen, um Rückschau zu halten und künftige Entwi...
This paper tackles the problem of relative pose estimation between two monocular camera images in textureless
scenes. Due to a lack of point matches, point-based approaches such as the 5-point algorithm often fail
when used in these scenarios. Therefore we investigate relative pose estimation from line observations. We
propose a new approach in whi...
Gas and heat exchange between the ocean and the atmosphere are a key process in the earth system. Active thermography is a tool that can be used to estimate heat and gas transfer rates with unprecedented temporal and spatial resolution compared to other measurement techniques. In this paper recent technical progress of this method is described: a)...
Modern high-end image sensors require up to 16 bit
quantisation. Uniform quantisation is, however, not well adapted to the
signal, because the temporal noise strongly increases with the grey
value. Here a non-linear transform h(g) is proposed, which yields an image
sensor signal with an adjustable, grey-value independent temporal noise. The
number...
A new optical instrument for the study of ocean waves, the Reflective Stereo Slope Gauge, has been developed. Its purpose is to measure ocean wave field parameters that are crucial to the air–sea exchange of momentum, heat and gases. The instrument combines a statistical wave slope measurement method similar to Cox and Munk’s sun glitter technique...
Results from measurements of wave slope statistics during the R/V Meteor M91 cruise in the coastal upwelling regions off the coast of Peru are reported. Wave slope probability distributions were measured with an instrument based on the reflection of light at the water surface and a method very similar to the Cox and Munk (1954b) sun glitter techniq...
Light-field imaging is a research field with applicability in a variety of imaging areas including 3D cinema, entertainment, robotics, and any task requiring range estimation. In contrast to binocular or multi-view stereo approaches, capturing light fields means densely observing a target scene through a window of viewing directions. A principal be...
Phosphorescence quenching is a common optical method for oxygen sensing where quenching is described by the Stern–Volmer equation. Here, we present a modified Stern–Volmer equation for high laser irradiance regarding quenching of phosphorescence. The Stern–Volmer equation is only an appropriate estimate in the case of low laser irradiance. The modi...
Mehr als zwei Drittel der Erdoberfläche ist mit Wasser bedeckt. Das ist eine gigantische Kontaktfläche mit dem zweiten großen Klimasystem: der Atmosphäre. Forscher wie der Heidelberger Umweltphysiker Bernd Jähne wollen herausfinden, wie der Austausch zwischen Ozean und Atmosphäre genau funktioniert.
Der Beitrag erschien in der Sendereihe "Campus-...
A comparative study of simultaneous heat and gas exchange measurements was
performed in the large annular Heidelberg Air–Sea Interaction Facility, the
Aeolotron, under homogeneous water surface conditions. The use of two gas
tracers, N2O and C2HF5, resulted not only in gas transfer
velocities, but also in the measurement of the Schmidt number expon...
In this study we present gas-exchange measurements conducted in a large-scale
wind–wave tank. Fourteen chemical species spanning a wide range of solubility
(dimensionless solubility, α = 0.4 to 5470) and diffusivity
(Schmidt number in water, Scw = 594 to 1194) were examined under
various turbulent (u10 = 0.73 to 13.2 m s−1)
conditions. Additional e...
From ancient times, science has always used images to document observations and results. In the beginning, people made sketches and drawings, but in the mid-19th century, the advent of photography revolutionised the way we use visual documentation. For the first time, images could be recorded objectively. The quantitative analysis of the photograph...
Creating stereo ground truth based on real images is a measurement task. Measurements are never perfectly accurate: the depth at each pixel follows an error distribution. A common way to estimate the quality of measurements are error bars. In this paper we describe a methodology to add error bars to images of previously scanned static scenes. The m...
We propose a new camera configuration for automotive surround view systems where the criteria for which the camera mountings are optimized is derived not from visualization, but optimal depth measurements. We show that based on special algorithmic processing [1] it is feasible to achieve 3D reconstruction in almost the complete surrounding of the c...
We propose a new approach to achieve 3D environment reconstruction based on automotive surround view systems with fisheye cameras. In particular, we demonstrate that stereo vision techniques can be applied in overlapping areas of adjacent cameras, which are up to 90 degrees per camera pair in the current setup. Lateral limitations are mainly due to...
Assessing atmospheric visibility conditions is a challenging and increasingly important task not only in the context of video-based driver assistance systems. As a commonly used quantity, meteorological visibility describes the visual range for observations through scattering and absorbing aerosols such as fog or smog.
We present a novel algorithm...
In this study we present gas exchange measurements conducted in a large scale windwave
tank. Fourteen chemical species spanning a wide range of solubility (dimensionless
solubility 0.4 to 5470) and diffusivity (Schmidt number in water, Scw = 594
to 1194) were examined under various turbulent (u10 = 0.8 to 15ms−1) conditions.
Additional experiments...
A comparative study of simultaneous heat and gas exchange measurements was performed
in the large annular Heidelberg Air–Sea Interaction Facility, the Aeolotron, under
homogeneous water surface conditions. The use of two gas tracers, N2O and
C2HF5, 5 resulted not only in gas transfer velocities, but also in the measurement of
the Schmidt number exp...
In a pilot study conducted in October and November 2011, air–sea gas transfer velocities of the two sparingly soluble trace gases hexafluorobenzene and 1,4-difluorobenzene were measured in the unique high-speed wind-wave tank at Kyoto University, Japan. This air–sea interaction facility is capable of producing hurricane strength wind speeds of up t...
A novel 2-D fluorescence imaging technique has been developed to visualize the thickness of the aqueous mass boundary layer at a free water surface. Fluorescence is stimulated by high-power LEDs and is observed from above with a low noise, high resolution and high-speed camera. The invasion of ammonia into water leads to an increase in pH (from a s...
This paper introduces the first high-speed system for slope imaging of wind-induced short water waves. The imaging slope gauge method is used, which is based on the shape from refraction principle. The downward looking camera with a telecentric lens observes the refraction of light rays coming from a high power custom telecentric LED light source t...
In a pilot study conducted in October and November 2011, air-sea gas
transfer velocities of the two sparingly soluble trace gases
hexafluorobenzene and 1,4-difluorobenzene were measured in the unique
High-Speed Wind-Wave Tank at Kyoto University, Japan. This air-sea
interaction facility is capable of producing hurricane strength wind
speeds of up t...
We present a computational imaging approach to estimate the depth from
a single image using axial chromatic aberrations. It includes
a co-design of optics and digital processing to select the optimal
parameters of a lens such as focal length, f-number, and chromatic
focal shift according to the performance of a depth estimation
algorithm on the dig...
Image sensors come with a spatial inhomogeneity, known as Fixed Pattern Noise, that degrades the image quality. In this paper a known maximum likelihood estimation method is extended in a way that it allows to estimate the two parameters DSNU and PRNU of a sensor's fixed pattern noise. The method's input are the averaged sensor responses and the co...
Hautière et al. [8] presented a model to describe the road surface luminance curve. Fitting this model to the reality allowed them to measure atmospheric parameters and, in turn, the meteorological visibility. We introduce a more complex and appropriate model based on the theory of radiative transfer. Through modeling the inscattered light by Kosch...
Purpose:
In image-guided surgery (IGS) intraoperative image acquisition of tissue shape, motion, and morphology is one of the main challenges. Recently, time-of-flight (ToF) cameras have emerged as a new means for fast range image acquisition that can be used for multimodal registration of the patient anatomy during surgery. The major drawbacks of...
Image sensors come with a spatial inhomogeneity, known as Fixed Pattern Noise, that degrades the image quality.
In this paper a known maximum likelihood estimation method [1] is extended in a way that it allows to estimate the two parameters DSNU and PRNU of a sensor's fixed pattern noise.
The method's input are the averaged sensor responses and th...
Eine Beschreibung einer 3D-Szene mittels Lichtfeldern führt nicht nur zu einer umfassenden
Theorie ALLER möglichen optischen 3D-Aufnahmesysteme, sondern ermöglicht auch
neue Ansätze, die auch die Schätzung der optischen Eigenschaften der Oberflächen integrieren.
Weiterhin werden damit die Grenzen bisheriger optischer Messtechniken gesprengt.
Am Bei...
In diesem Beitrag werden kurz die Grundprinzipien des Standards EMVA 1288 beschrieben: offen, nicht einschränkend, modellbasiert und Kamera als Komponente. Wenige Parameter
sind notwendig, um flexibel und applikationsspezifisch eine optimale Kameraauswahl zu treffen. Dies wird an vergleichenden Beispielen illustriert. Weiterhin werden verfügbare Te...
In this work, we systematically analyze how good ground truth (GT) datasets for evaluating methods based on Time-of-Flight (ToF) imaging data should look like. Starting from a high level characterization of the application domains and requirements they typically have, we characterize how good datasets should look like and discuss how algorithms can...
Gaseous and volatile chemical species reside not only in the atmosphere. Because they dissolve in water, they are also distributed in the hydrosphere. The by far largest part of the hydrosphere is the ocean. Therefore, the exchange between atmosphere and oceans is the most important process for the fate of gaseous and volatile chemical species (Tab...
Image sensors come with a spatial inhomogeneity, known as Fixed Pattern Noise, that degrades the image quality. Especially the dark signal non uniformity (DSNU) component of the FPN drifts with time and depends highly on temperature and exposure time. In this paper we introduce a cellular neural network (CNN) to estimate the DSNU from a given set o...
Active thermography is a non-contact instrumentation that can be used to investigate small-scale air-sea interaction processes at a footprint of a square meter and with time constants of minutes. It can be used also in large wind/wave facilities. Therefore it is a very useful instrument to investigate the mechanisms of air-sea gas transfer. The pri...
Das noch junge Forschungsgebiet der „Computational Photography” besetzt die Schnittstelle zwischen technischer Optik, Computer Graphik, Bildverarbeitung und Bildanalyse. Grundlegendes Ziel ist, mittels algorithmischer („computation”) Ansätze die physikalischen Grenzen der traditionellen projektiven Kamera, wie begrenzte Tiefenschärfe, Auflösung und...
In this report we describe a high-performance stereo camera system to capture image sequences with high temporal and spatial resolution for the evaluation of various image processing tasks. The system was primarily designed for complex outdoor and traffic scenes which frequently occur in the automotive industry, but is also suited for other applica...
3D Time-of-Flight (ToF) cameras are capable to acquire dense depth maps of a scene by determining the time it takes for light to travel from a source to an object and back to the camera. Determining the depth requires multiple measurements. Current ToF system are not able to acquire all these measurements simultaneously. If the observed scene is ch...
In this paper, we present a novel method for the generation of Epipolar-Image (EPI) representations of 4D Light Fields (LF) from raw data captured by a single lens “Focused Plenoptic Camera”. Compared to other LF representations which are usually used in the context of computational photography with Plenoptic Cameras, the EPI representation is more...
Zusammenfassung
Der neue EMVA-Standard 1288 vereinfacht einem Anwender die Auswahl einer geeigneten Kamera entscheidend. Neben den Inhomogenitätsparametern ist das Signal-Rausch-Verhältnis die wichtigste Größe für die Sensorqualität. Sie hängt nur von der Quantenausbeute und dem Dunkelrauschen ab, wenn das Quantisierungsrauschen vernachlässigt werd...
Recently, the notion of "Light Fields" (LF) has become a very useful tool for the parameterization and theoretical analysis of problems at the intersection of the research areas Computer Graphics, Computational Photography and Computer Vision. In this context, HCI research is focusing on several related topics, such as LF theory and simulation, LF...
Recently, the notion of "Light Fields" (LF) has become a very useful tool for the parameterization and theoretical analysis of problems at the intersection of the research areas Computer Graphics, Computational Photography and Computer Vision. In this context, HCI research is focusing on several related topics, such as LF theory and simulation, LF...
Literally thousands of articles on optical flow algorithms have been published in the past thirty years. Only a small subset of the suggested algorithms have been analyzed with respect to their performance. These evaluations were based on black-box tests, mainly yielding information on the average accuracy on test-sequences with ground truth. No th...
3D Time-of-Flight cameras are able to deliver robust depth maps of dynamic scenes. The frame rate, however, is limited because today's systems utilizing two-tap sensors need to acquire the required raw images in multiple instances in order to compute one depth map. These multiple raw images allow canceling out systematic errors introduced by asymme...
A framework for the visualization and classification of multi-channel spatio-temporal data from water wave imaging is presented. Our interactive visualization tool, WaveVis, allows a detailed study of the water surface shape in reference to additional data streams, like thermographic images or classification results. This facilitates an intuitive a...