scholarly journals Cloud Photogrammetry with Dense Stereo for Fisheye Cameras

2016 ◽  
Author(s):  
Christoph Beekmans ◽  
Johannes Schneider ◽  
Thomas Läbe ◽  
Cyrill Stachniss ◽  
Clemens Simmer
Keyword(s):  
Large Field ◽  
Cloud Base ◽  
Strong Wind ◽  
Real World Data ◽  
First Case ◽  
Dense Matching ◽  
Cloud Dynamics ◽  
Stereo Reconstruction ◽  
3D Information ◽  
Fisheye Lenses

Abstract. In this paper, we present our approach for dense 3D cloud reconstruction using two hemispheric sky imagers with fisheye lenses in a stereo setup. Fisheye lenses follow a different projection function than classical pinhole-type cameras, which provide a large field of view with a single image, but also renders the computation of dense 3D information more complicated, such that we cannot rely entirely on standard implementations for dense 3D stereo reconstruction. In this work, we examine the epipolar rectification model, which allows the use of dense matching algorithms designed for classical perspective cameras to search for disparity information at every pixel. Together with an appropriate camera calibration, which includes internal camera geometry and global position and orientation of the stereo camera pair, we can use the disparity information for dense 3D stereo reconstruction of the a cloud and thus estimate its shape. From the obtained 3D shapes, cloud dynamics, size, motion, type and spacing can be derived and used e.g. for radiation closure under cloudy conditions. We implemented and evaluated the proposed approach using real world data and present two case studies. In the first case, we validate the quality and accuracy of the method by comparing the stereo reconstruction of a stratocumulus layer with the reflectivity observations measured by a cloud radar and the cloud base height estimated from a Lidar-ceilometer. The second case analyzes a rapid cumulus convection in the presence of strong wind shear.

scholarly journals Cloud photogrammetry with dense stereo for fisheye cameras

2016 ◽  
Vol 16 (22) ◽  
pp. 14231-14248 ◽  
Author(s):  
Christoph Beekmans ◽  
Johannes Schneider ◽  
Thomas Läbe ◽  
Martin Lennefer ◽  
Cyrill Stachniss ◽  
...  
Keyword(s):  
Stereo Matching ◽  
Geometric Constraints ◽  
Large Field ◽  
Cloud Base ◽  
Strong Wind ◽  
Real World Data ◽  
First Case ◽  
Novel Approach ◽  
Stereo Reconstruction ◽  
Fisheye Lenses

Abstract. We present a novel approach for dense 3-D cloud reconstruction above an area of 10 × 10 km2 using two hemispheric sky imagers with fisheye lenses in a stereo setup. We examine an epipolar rectification model designed for fisheye cameras, which allows the use of efficient out-of-the-box dense matching algorithms designed for classical pinhole-type cameras to search for correspondence information at every pixel. The resulting dense point cloud allows to recover a detailed and more complete cloud morphology compared to previous approaches that employed sparse feature-based stereo or assumed geometric constraints on the cloud field. Our approach is very efficient and can be fully automated. From the obtained 3-D shapes, cloud dynamics, size, motion, type and spacing can be derived, and used for radiation closure under cloudy conditions, for example. Fisheye lenses follow a different projection function than classical pinhole-type cameras and provide a large field of view with a single image. However, the computation of dense 3-D information is more complicated and standard implementations for dense 3-D stereo reconstruction cannot be easily applied. Together with an appropriate camera calibration, which includes internal camera geometry, global position and orientation of the stereo camera pair, we use the correspondence information from the stereo matching for dense 3-D stereo reconstruction of clouds located around the cameras. We implement and evaluate the proposed approach using real world data and present two case studies. In the first case, we validate the quality and accuracy of the method by comparing the stereo reconstruction of a stratocumulus layer with reflectivity observations measured by a cloud radar and the cloud-base height estimated from a Lidar-ceilometer. The second case analyzes a rapid cumulus evolution in the presence of strong wind shear.

scholarly journals Retrieval of 3D information in X-ray dark-field imaging with a large field of view

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jana Andrejewski ◽  
Fabio De Marco ◽  
Konstantin Willer ◽  
Wolfgang Noichl ◽  
Theresa Urban ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Dark Field ◽  
Large Field ◽  
X Ray ◽  
Dark Field Imaging ◽  
Beam Geometry ◽  
Different Dimensions ◽  
3D Information ◽  
Human Thorax ◽  
Field Imaging

AbstractX-ray dark-field imaging is a widely researched imaging technique, with many studies on samples of very different dimensions and at very different resolutions. However, retrieval of three-dimensional (3D) information for human thorax sized objects has not yet been demonstrated. We present a method, similar to classic tomography and tomosynthesis, to obtain 3D information in X-ray dark-field imaging. Here, the sample is moved through the divergent beam of a Talbot–Lau interferometer. Projections of features at different distances from the source seemingly move with different velocities over the detector, due to the cone beam geometry. The reconstruction of different focal planes exploits this effect. We imaged a chest phantom and were able to locate different features in the sample (e.g. the ribs, and two sample vials filled with water and air and placed in the phantom) to corresponding focal planes. Furthermore, we found that image quality and detectability of features is sufficient for image reconstruction with a dose of 68 μSv at an effective pixel size of $$0.357 \times {0.357}\,\mathrm{mm}^{2}$$ 0.357 × 0.357 mm 2 . Therefore, we successfully demonstrated that the presented method is able to retrieve 3D information in X-ray dark-field imaging.

Stereophotogrammetry of Oceanic Clouds

2014 ◽  
Vol 31 (7) ◽  
pp. 1482-1501 ◽  
Author(s):  
Rusen Öktem ◽  
Prabhat ◽  
James Lee ◽  
Aaron Thomas ◽  
Paquita Zuidema ◽  
...  
Keyword(s):  
Camera Calibration ◽  
Cloud Base ◽  
Biscayne Bay ◽  
Digital Cameras ◽  
Image Pair ◽  
Single Image ◽  
Calibration Technique ◽  
Launch Site ◽  
Stereo Cameras ◽  
Stereo Reconstruction

This study extends ground-based stereophotogrammetry of clouds to oceanic settings, where there are often none of the landmarks used in traditional camera calibration. This paper introduces a zero-landmark calibration technique and tests it with two off-the-shelf digital cameras situated about 1 km apart facing Biscayne Bay in Miami, Florida. The precision of the stereo reconstruction is studied theoretically, and the accuracy of the reconstructions is validated against lidar and radiosondes. The stereo cameras are able to accurately reconstruct a histogram of cloud-base heights from a single-image pair, a task that requires tens of minutes of observation from a cloud lidar. The stereo cameras are also able to accurately reconstruct horizontal winds in cloud layers with a temporal resolution in the range of 30 s to 5 min, compared to once every 12 h for a typical radiosonde launch site.

scholarly journals Microscopic Three-Dimensional Measurement Based on Telecentric Stereo and Speckle Projection Methods

Sensors ◽  
2018 ◽  
Vol 18 (11) ◽  
pp. 3882 ◽  
Author(s):  
Kepeng Chen ◽  
Tielin Shi ◽  
Qiang Liu ◽  
Zirong Tang ◽  
Guanglan Liao
Keyword(s):  
Measurement Accuracy ◽  
Three Dimensional ◽  
Projection Methods ◽  
Reconstruction Procedure ◽  
Cylinder Arrays ◽  
Stereo Reconstruction ◽  
Three Dimensional Measurement ◽  
Binocular Stereo ◽  
3D Information ◽  
Microscopic Measurement

Three-dimensional (3D) measurement of microstructures has become increasingly important, and many microscopic measurement methods have been developed. For the dimension in several millimeters together with the accuracy at sub-pixel or sub-micron level, there is almost no effective measurement method now. Here we present a method combining the microscopic stereo measurement with the digital speckle projection. A microscopy experimental setup mainly composed of two telecentric cameras and an industrial projection module is established and a telecentric binocular stereo reconstruction procedure is carried out. The measurement accuracy has firstly been verified by performing 3D measurements of grid arrays at different locations and cylinder arrays with different height differences. Then two Mitutoyo step masters have been used for further verification. The experimental results show that the proposed method can obtain 3D information of the microstructure with a sub-pixel and even sub-micron measuring accuracy in millimeter scale.

scholarly journals Microphysical Structure of the Marine Boundary Layer under Strong Wind and Spray Formation as Seen from Simulations Using a 2D Explicit Microphysical Model. Part I: The Impact of Large Eddies

2011 ◽  
Vol 68 (10) ◽  
pp. 2366-2384 ◽  
Author(s):  
J. Shpund ◽  
M. Pinsky ◽  
A. Khain
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Surface Fluxes ◽  
Cloud Base ◽  
Small Scale ◽  
Sea Spray ◽  
Strong Wind ◽  
Spray Droplets ◽  
The Impact ◽  
Large Eddies

Abstract The effects of large eddies (LE) on the marine boundary layer (MBL) microphysics and thermodynamics is investigated using a 2D Lagrangian model with spectral bin microphysics including effects of sea spray. The 600 m × 400 m MBL computational area is covered by 3750 adjacent interacting Lagrangian parcels moving in a turbulent-like flow. A turbulent-like velocity field is designed as a sum of a high number of harmonics with random time-dependent amplitudes and different wavelengths including large eddies with scales of several hundred meters. The model explicitly calculates diffusion growth/evaporation, collisions, and sedimentation of droplets forming both as sea spray droplets and background aerosols, as well as aerosol masses within droplets. The turbulent mixing between parcels is explicitly taken into account. Sea spray generation is determined by a source function depending on the background wind speed assumed in the simulations to be equal to 20 m s−1. The results of simulations obtained by taking into account the effects of LE are compared to those obtained under the assumption that the vertical transport of droplets and passive scalars is caused by small-scale turbulent diffusion. Small-scale turbulence diffusion taken alone leads to an unrealistic MBL structure. Nonlocal mixing of the MBL caused by LE leads to the formation of a well-mixed MBL with a vertical structure close to the observed one. LE lead to an increase in the sensible and latent heat surface fluxes by 50%–100% and transport a significant amount of large spray droplets upward. Microphysical processes lead to formation of spray-induced drizzling clouds with cloud base near the 200-m level.

scholarly journals Aerosol properties and meteorological conditions in the city of Buenos Aires, Argentina, during the resuspension of volcanic ash from the Puyehue-Cordón Caulle eruption

2016 ◽  
Vol 16 (9) ◽  
pp. 2159-2175 ◽  
Author(s):  
Ana Graciela Ulke ◽  
Marcela M. Torres Brizuela ◽  
Graciela B. Raga ◽  
Darrel Baumgardner
Keyword(s):  
Boundary Layer ◽  
Volcanic Ash ◽  
Buenos Aires ◽  
Volcanic Eruptions ◽  
Meteorological Conditions ◽  
Cloud Base ◽  
Volcanic Complex ◽  
Strong Wind ◽  
The City ◽  
Aerosol Properties

Abstract. The eruption in June 2011 of the Puyehue-Cordón Caulle Volcanic Complex in Chile impacted air traffic around the Southern Hemisphere for several months after the initial ash emissions. The ash deposited in vast areas of the Patagonian Steppe was subjected to the strong wind conditions prevalent during the austral winter and spring experiencing resuspension over various regions of Argentina. In this study we analyze the meteorological conditions that led to the episode of volcanic ash resuspension which impacted the city of Buenos Aires and resulted in the closure of the two main airports in Buenos Aires area (Ezeiza and Aeroparque) on 16 October 2011. A relevant result is that resuspended material (volcanic ash plus dust) imprints a distinguishable feature within the atmospheric thermodynamic vertical profiles. The thermodynamic soundings show the signature of "pulses of drying" in layers associated with the presence of hygroscopic ash in the atmosphere that has already been reported in similar episodes after volcanic eruptions in other parts of the world. This particular footprint can be used to detect the probable existence of volcanic ash layers. This study also illustrates the utility of ceilometers to detect not only cloud base at airports but also volcanic ash plumes at the boundary layer and up to 7 km altitude. Aerosol properties measured in the city during the resuspension episode indicate the presence of enhanced concentrations of aerosol particles in the boundary layer along with spectral signatures in the measurements at the Buenos Aires AERONET site typical of ash plus dust advected towards the city. The mandatory aviation reports from the National Weather Service about airborne and deposited volcanic ash at the airport near the measurement site (Aeroparque) correlate in time with the enhanced concentrations. The presence of the resuspended material was detected by the CALIOP lidar overpassing the region. Since the dynamics of ash resuspension and recirculation are similar to the dynamics of dust storms, we use the HYSPLIT model with the dust storm module to simulate the episode that affected Buenos Aires. The results of the modeling agree qualitatively with satellite lidar measurements.

scholarly journals Analysis and modeling of ducted and evanescent gravity waves observed in the Hawaiian airglow

2009 ◽  
Vol 27 (8) ◽  
pp. 3213-3224 ◽  
Author(s):  
D. B. Simkhada ◽  
J. B. Snively ◽  
M. J. Taylor ◽  
S. J. Franke
Keyword(s):  
Gravity Waves ◽  
Wave Structure ◽  
Small Scale ◽  
Wind Flow ◽  
Strong Wind ◽  
Mesopause Region ◽  
Opposite Case ◽  
Local Propagation ◽  
First Case ◽  
Short Period

Abstract. Short-period gravity waves of especially-small horizontal scale have been observed in the Maui, Hawaii airglow. Typical small-scale gravity wave events have been investigated, and intrinsic wave propagation characteristics have been calculated from simultaneous meteor radar wind measurements. Here we report specific cases where wave structure is significantly determined by the local wind structure, and where wave characteristics are consistent with ducted or evanescent waves throughout the mesopause region. Two of the documented events, exhibiting similar airglow signatures but dramatically different propagation conditions, are selected for simple numerical modeling case studies. First, a Doppler-ducted wave trapped within relatively weak wind flow is examined. Model results confirm that the wave is propagating in the 85–95 km region, trapped weakly by evanescence above and below. Second, an evanescent wave in strong wind flow is examined. Model results suggest an opposite case from the first case study, where the wave is instead trapped above or below the mesopause region, with strong evanescence arising in the 85–95 km airglow region. Distinct differences between the characteristics of these visibly-similar wave events demonstrate the need for simultaneous observations of mesopause winds to properly assess local propagation conditions.

scholarly journals Modeling Condensation in Shallow Nonprecipitating Convection

2015 ◽  
Vol 72 (12) ◽  
pp. 4661-4679 ◽  
Author(s):  
Wojciech W. Grabowski ◽  
Dorota Jarecka
Keyword(s):  
Cloud Droplet ◽  
Cloud Microphysics ◽  
Cloud Water ◽  
Cloud Base ◽  
Shallow Convection ◽  
Cloud Dynamics ◽  
Wide Range ◽  
High Vertical Resolution ◽  
The Impact ◽  
Theoretical Considerations

Abstract Two schemes for modeling condensation in warm nonprecipitating clouds are compared. The first one is the efficient bulk condensation scheme where cloudy volumes are always at saturation and cloud water evaporates instantaneously to maintain saturation. The second one is the comprehensive bin condensation scheme that predicts the evolution of the cloud droplet spectrum and allows sub- and supersaturations in cloudy volumes. The emphasis is on the impact of the two schemes on cloud dynamics. Theoretical considerations show that the bulk condensation scheme provides more buoyancy than the bin scheme, but the effect is small, with the potential density temperature difference around 0.1 K for 1% supersaturation. The 1D advection–condensation tests document the high-vertical-resolution requirement for the bin scheme to resolve the cloud-base supersaturation maximum and CCN activation, which is difficult to employ in 3D cloud simulations. Simulations of shallow convection cloud fields are executed applying bulk and bin schemes, with the mean droplet concentrations in the bin scheme covering a wide range, from about 5 to over 4000 cm−3. Simulations employ the microphysical piggybacking methodology to extract impacts with high confidence. They show that the differences in cloud fields simulated with bulk and bin schemes come not from small differences in the condensation but from more significant differences in the evaporation of cloud water near cloud edges as a result of entrainment and mixing with the environment. The latter makes the impact of cloud microphysics on simulated macroscopic cloud field properties even more difficult to assess because of highly uncertain subgrid-scale parameterizations.

scholarly journals Microphysical Structure of the Marine Boundary Layer under Strong Wind and Sea Spray Formation as Seen from a 2D Explicit Microphysical Model. Part III: Parameterization of Height-Dependent Droplet Size Distribution

2014 ◽  
Vol 71 (6) ◽  
pp. 1914-1934 ◽  
Author(s):  
J. Shpund ◽  
J. A. Zhang ◽  
M. Pinsky ◽  
A. Khain
Keyword(s):  
Wind Speed ◽  
Mixed Layer ◽  
Marine Boundary Layer ◽  
Droplet Size Distribution ◽  
Cloud Base ◽  
Sea Spray ◽  
Observation Data ◽  
Strong Wind ◽  
Size Distributions ◽  
Spray Formation

Abstract This paper completes a series of studies using a 2D hybrid Lagrangian–Eulerian model to investigate the effect of sea spray on the thermodynamics and microphysics of the hurricane mixed layer. The evolution of the mixed layer was simulated by mimicking the motion of an air volume (in a Lagrangian sense) toward a tropical cyclone eyewall along a background airflow. During the radial motion, sea surface temperature, pressure, background wind speed, sea spray production rate, and turbulence intensity were altered according to the available observations. Analysis of the interaction between the hurricane mixed layer and the upper layers in terms of entrainment heat and moisture fluxes gives a new insight into the role of sea spray in the thermodynamics and microphysics of the mixed layer. The evaporation of sea spray leads to an increase in the relative humidity by 10%–15% and to a decrease in temperature by about 1–1.5 K, as compared to cases where sea spray is excluded. Sea spray leads to formation of drizzling clouds with the cloud base at the height of about 250 m. Taking the sea spray effect into account provides a good agreement between the thermodynamics of a simulated mixed layer and the observation data. A parameterization of droplet mass and size distributions as functions of height and wind speed is proposed. The horizontally averaged size distributions are approximated by a sum of lognormal distributions. The moments of size distributions and other integral properties are parameterized as functions of 10-m wind speed by means of simple polynomial expressions.

scholarly journals Evaluation of cloud base height measurements from ceilometer CL31 and MODIS satellite over Ahmedabad, India

2015 ◽  
Vol 8 (11) ◽  
pp. 11729-11752 ◽  
Author(s):  
S. Sharma ◽  
R. Vaishnav ◽  
M. V. Shukla ◽  
P. Kumar ◽  
P. Kumar ◽  
...  
Keyword(s):  
Cloud Base ◽  
Monsoon Period ◽  
Post Monsoon ◽  
Cloud Dynamics ◽  
Cloud Characteristics ◽  
Moderate Resolution ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
High Level ◽  
Terra Satellite ◽  
Cloud Base Height

Abstract. Clouds play a tangible role in the Earth's atmosphere and in particular, the cloud base height (CBH) which is linked to cloud type is one of the important characteristic to describe the influence of clouds on the environment. In present study, CBH observations from ceilometer CL31 have been extensively studied during May 2013 to January 2015 over Ahmedabad (23.03° N, 72.54° E), India. A detail comparison has been performed with the use of ground-based CBH measurements from ceilometer CL31 and CBH retrieved from MODIS (Moderate Resolution Imaging Spectroradiometer) onboard Aqua and Terra satellite. Some interesting features of cloud dynamics viz. strong downdraft and updraft have been observed over Ahmedabad which revealed different cloud characteristics during monsoon and post-monsoon periods. CBH shows seasonal variation during Indian summer monsoon and post-monsoon period. Results indicate that ceilometer is one of the excellent instruments to precisely detect low and mid-level clouds and MODIS satellite provides accurate retrieval of high-level clouds over this region. The CBH algorithm used for MODIS satellite is also able to capture the low-level clouds.

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