scholarly journals Enhancing the spatio-temporal features of polar mesosphere summer echoes using coherent MIMO and radar imaging at MAARSY

2018 ◽  
Author(s):  
Juan Miguel Urco ◽  
Jorge Luis Chau ◽  
Tobias Weber ◽  
Ralph Latteck
Keyword(s):  
Angular Resolution ◽  
Imaging Techniques ◽  
Three Dimensional ◽  
Radar Imaging ◽  
Horizontal Resolution ◽  
Atmospheric Dynamics ◽  
Polar Regions ◽  
Background Wind ◽  
Summer Echoes ◽  
Spatio Temporal

Abstract. Polar mesospheric summer echoes (PMSEs) are very strong radar echoes caused by the presence of ice particles, turbulence, and free electrons in the mesosphere over polar regions. For more than three decades, PMSEs have been used as natural tracers of the complicated atmospheric dynamics of this region. Neutral winds and turbulence parameters have been obtained assuming PMSE horizontal homogeneity in scales of tens of kilometers. Recent radar imaging studies have shown that PMSEs are not homogeneous in these scales and instead they are composed of kilometer-scale structures. In this paper, we present a technique that allows PMSE observations with unprecedented angular resolution (~ 0.6°). The technique combines the concept of coherent MIMO (Multi-input multiple-output) and two high-resolution imaging techniques, i.e., Capon and Maximum Entropy (MaxEnt). The resulting resolution is evaluated by imaging specular meteor echoes. The gain in angular resolution compared to previous approaches using SIMO (single input and multiple-output) and Capon is at least a factor of 2, i.e., at 85 km, we obtain a horizontal resolution of ~ 900 meters. The goodness of the new technique is evaluated with two events of three-dimensional PMSEs structures showing: (1) horizontal wavelengths of 8–10 km and periods of 4–7 minutes, drifting with the background wind, and (2) horizontal wavelengths of 12–16 km and periods of 15–20 minutes not drifting with the background wind. Besides the advantages of the implemented technique, we discuss its current challenges, like the use of reduced power-aperture and processing time, as well as the future opportunities for improving the understanding of the complex atmospheric dynamics behind PMSEs.

scholarly journals Enhancing the spatiotemporal features of polar mesosphere summer echoes using coherent MIMO and radar imaging at MAARSY

2019 ◽  
Vol 12 (2) ◽  
pp. 955-969 ◽  
Author(s):  
Juan Miguel Urco ◽  
Jorge Luis Chau ◽  
Tobias Weber ◽  
Ralph Latteck
Keyword(s):  
Angular Resolution ◽  
Imaging Techniques ◽  
Radar Imaging ◽  
Horizontal Resolution ◽  
Atmospheric Dynamics ◽  
Small Scale ◽  
Polar Regions ◽  
Background Wind ◽  
Input Multiple Output ◽  
Summer Echoes

Abstract. Polar mesospheric summer echoes (PMSEs) are very strong radar echoes caused by the presence of ice particles, turbulence, and free electrons in the mesosphere over polar regions. For more than three decades, PMSEs have been used as natural tracers of the complicated atmospheric dynamics of this region. Neutral winds and turbulence parameters have been obtained assuming PMSE horizontal homogeneity on scales of tens of kilometers. Recent radar imaging studies have shown that PMSEs are not homogeneous on these scales and instead they are composed of kilometer-scale structures. In this paper, we present a technique that allows PMSE observations with unprecedented angular resolution (∼0.6∘). The technique combines the concept of coherent MIMO (Multiple Input Multiple Output) and two high-resolution imaging techniques, i.e., Capon and maximum entropy (MaxEnt). The resulting resolution is evaluated by imaging specular meteor echoes. The gain in angular resolution compared to previous approaches using SIMO (Single Input Multiple Output) and Capon is at least a factor of 2; i.e., at 85 km, we obtain a horizontal resolution of ∼900 m. The advantage of the new technique is evaluated with two events of 3-D PMSE structures showing: (1) horizontal wavelengths of 8–10 km and periods of 4–7 min, drifting with the background wind, and (2) horizontal wavelengths of 12–16 km and periods of 15–20 min, not drifting with the background wind. Besides the advantages of the implemented technique, we discuss its current challenges, like the use of reduced power aperture and processing time, as well as the future opportunities for improving the understanding of the complex small-scale atmospheric dynamics behind PMSEs.

scholarly journals Marine sources of bromoform in the global open ocean – global patterns and emissions

2014 ◽  
Vol 11 (11) ◽  
pp. 15693-15732
Author(s):  
I. Stemmler ◽  
I. Hense ◽  
B. Quack
Keyword(s):  
Three Dimensional ◽  
Open Ocean ◽  
Published Data ◽  
Polar Regions ◽  
Model Studies ◽  
Temporal Features ◽  
Simulated Surface ◽  
Spatio Temporal ◽  
The Tropics ◽  
Atmospheric Concentrations

Abstract. Bromoform (CHBr3) is one important precursor of atmospheric reactive bromine species that are involved in ozone depletion in the troposphere and stratosphere. In the open ocean bromoform production is linked to phytoplankton that contains the enzyme bromoperoxidase. Coastal sources of bromoform are higher than open ocean sources. However, open ocean emissions are important, because the transfer of tracers into higher altitude in the air, i.e. into the ozone layer, strongly depends on the location of emissions. For example, emissions in the tropics are more rapidly transported into the upper atmosphere than emissions from higher latitudes. Global spatio-temporal features of bromoform emissions are poorly constrained. Here, a global three-dimensional ocean biogeochemistry model (MPIOM-HAMOCC) is used to simulate bromoform cycling in the ocean and emissions into the atmosphere using recently published data of global atmospheric concentrations (Ziska et al., 2013) as upper boundary conditions. In general, simulated surface concentrations of CHBr3 match the observations well. Simulated global annual emissions based on monthly mean model output are lower than previous estimates, including the estimate by Ziska et al. (2013), because the gas-exchange reverses when less bromoform is produced in non-blooming seasons. This is the case for higher latitudes, i.e. the polar regions and northern North Atlantic. Further model experiments show that future model studies may need to distinguish different bromoform producing phytoplankton species and reveal that the transport of CHBr3 from the coast considerably alters open ocean bromoform concentrations, in particular in the northern sub-polar and polar regions.

scholarly journals Marine sources of bromoform in the global open ocean – global patterns and emissions

2015 ◽  
Vol 12 (6) ◽  
pp. 1967-1981 ◽  
Author(s):  
I. Stemmler ◽  
I. Hense ◽  
B. Quack
Keyword(s):  
Three Dimensional ◽  
Open Ocean ◽  
Published Data ◽  
Polar Regions ◽  
Model Studies ◽  
Temporal Features ◽  
Simulated Surface ◽  
Spatio Temporal ◽  
The Tropics ◽  
Atmospheric Concentrations

Abstract. Bromoform (CHBr3) is one important precursor of atmospheric reactive bromine species that are involved in ozone depletion in the troposphere and stratosphere. In the open ocean bromoform production is linked to phytoplankton that contains the enzyme bromoperoxidase. Coastal sources of bromoform are higher than open ocean sources. However, open ocean emissions are important because the transfer of tracers into higher altitude in the air, i.e. into the ozone layer, strongly depends on the location of emissions. For example, emissions in the tropics are more rapidly transported into the upper atmosphere than emissions from higher latitudes. Global spatio-temporal features of bromoform emissions are poorly constrained. Here, a global three-dimensional ocean biogeochemistry model (MPIOM-HAMOCC) is used to simulate bromoform cycling in the ocean and emissions into the atmosphere using recently published data of global atmospheric concentrations (Ziska et al., 2013) as upper boundary conditions. Our simulated surface concentrations of CHBr3 match the observations well. Simulated global annual emissions based on monthly mean model output are lower than previous estimates, including the estimate by Ziska et al. (2013), because the gas exchange reverses when less bromoform is produced in non-blooming seasons. This is the case for higher latitudes, i.e. the polar regions and northern North Atlantic. Further model experiments show that future model studies may need to distinguish different bromoform-producing phytoplankton species and reveal that the transport of CHBr3 from the coast considerably alters open ocean bromoform concentrations, in particular in the northern sub-polar and polar regions.

MODELLING THREE-DIMENSIONAL GROWTH OF BRAIN TUMOURS FROM TIME SERIES OF SCANS

1999 ◽  
Vol 09 (04) ◽  
pp. 581-598 ◽  
Author(s):  
PHILIPPE TRACQUI ◽  
MAHIDINE MENDJELI
Keyword(s):  
Brain Tumour ◽  
Brain Tumours ◽  
Tumour Growth ◽  
Imaging Techniques ◽  
Three Dimensional ◽  
Growth Patterns ◽  
Nonlinear Growth ◽  
Mri Scans ◽  
Dimensional Growth ◽  
Spatio Temporal

The development of brain tumours, after diagnosis, is routinely recorded by different medical imaging techniques like computerised tomography (CT) or magnetic resonance imaging (MRI). However, it is only through the formulation of mathematical models that an analysis of the spatio-temporal tumour growth revealed on each patient serial scans can lead to a quantification of parameters characterising the proliferative and expensive dynamic of the brain tumour. This paper reviews some of the results and limitations encountered in modelling the different stages of a brain tumour growth, namely before and after diagnosis and therapy. It extends an original two-dimensional approach by considering three-dimensional growth of brain tumours submitted to the spatial constraints exerted by the skull and ventricles boundaries. Considering the dynamic of both the pre- and post-diagnosis stages, the tumour growth patterns obtained with various combinations of nonlinear growth rates and cellular diffusion laws are considered and compared to real MRI scans taken in a patient with a glioblastoma and having undergone radiotherapy. From these simulations, we characterise the effects of different therapies on survival durations, with special attention to the effect of cell diffusion inside the resected brain region when surgical resection of the tumour is carried out.

Near-field three-dimensional radar imaging techniques and applications

2010 ◽  
Vol 49 (19) ◽  
pp. E83 ◽  
Author(s):  
David Sheen ◽  
Douglas McMakin ◽  
Thomas Hall
Keyword(s):  
Imaging Techniques ◽  
Near Field ◽  
Three Dimensional ◽  
Radar Imaging

Three-dimensional radar imaging techniques and systems for near-field applications

2016 ◽  
Author(s):  
David M. Sheen ◽  
Thomas E. Hall ◽  
Douglas L. McMakin ◽  
A. Mark Jones ◽  
Jonathan R. Tedeschi
Keyword(s):  
Imaging Techniques ◽  
Near Field ◽  
Three Dimensional ◽  
Radar Imaging

scholarly journals Three-dimensional radar imaging of atmospheric layer and turbulence structures using multiple receivers and multiple frequencies

2014 ◽  
Vol 32 (8) ◽  
pp. 899-909 ◽  
Author(s):  
J.-S. Chen ◽  
J. Furumoto ◽  
M. Yamamoto
Keyword(s):  
Layer Structure ◽  
Imaging Techniques ◽  
Three Dimensional ◽  
Radar Imaging ◽  
Horizontal Wind ◽  
Small Scale ◽  
Turbulent Structures ◽  
Turbulence Structures ◽  
Air Turbulence ◽  
Finite Resolution

Abstract. The pulsed, beamwidth-limited atmospheric radar suffers from a finite resolution volume, making it difficult to resolve the small-scale irregularity structure of refractive index (or clear-air turbulence) in the scattering region. Multi-receiver and multi-frequency imaging techniques were thus proposed to improve the spatial resolution of the measurements in the finite resolution volume. The middle and upper atmosphere radar (MUR; 34.85° N, 136.10° N) possesses the capabilities of 5 frequencies, ranging from 46 MHz to 47 MHz, and up to 25 receivers to carry out the imaging techniques. In this paper, we exhibit the three-dimensional (3-D) radar imaging utilizing five frequencies and 19 receivers of the MUR. The Capon method was employed for the process of imaging, and examinations of a wavy layer and turbulent structures were made, in which the spatial weighting effect on the imaging were mitigated beforehand. Information such as echo center and structure morphology in the resolution volume was then extracted. For example, the location distribution of echo centers could imply the traveling orientation of the wavy layer, which was correspondent with horizontal wind direction. Such information of wavy layer structure was more difficult to disclose without removal of the spatial weighting effect. This paper demonstrates an advanced application of 3-D radar imaging to some practical atmospheric phenomena.

Mitochondrial Reconstructions Based on Serial Thick Sections and HVEM

1975 ◽  
Vol 33 ◽  
pp. 286-287
Author(s):  
Jerome J. Paulin
Keyword(s):  
Imaging Techniques ◽  
Three Dimensional ◽  
Posterior Pole ◽  
Dimensional Structure ◽  
Stereo Imaging ◽  
Thin Sections ◽  
Anatomical Features ◽  
The Past ◽  
Cellular Components ◽  
Mitochondrial Reticulum

Within the past decade it has become apparent that HVEM offers the biologist a means to explore the three-dimensional structure of cells and/or organelles. Stereo-imaging of thick sections (e.g. 0.25-10 μm) not only reveals anatomical features of cellular components, but also reduces errors of interpretation associated with overlap of structures seen in thick sections. Concomitant with stereo-imaging techniques conventional serial Sectioning methods developed with thin sections have been adopted to serial thick sections (≥ 0.25 μm). Three-dimensional reconstructions of the chondriome of several species of trypanosomatid flagellates have been made from tracings of mitochondrial profiles on cellulose acetate sheets. The sheets are flooded with acetone, gluing them together, and the model sawed from the composite and redrawn.The extensive mitochondrial reticulum can be seen in consecutive thick sections of (0.25 μm thick) Crithidia fasciculata (Figs. 1-2). Profiles of the mitochondrion are distinguishable from the anterior apex of the cell (small arrow, Fig. 1) to the posterior pole (small arrow, Fig. 2).

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