scholarly journals Coded continuous wave meteor radar

2015 ◽  
Vol 8 (7) ◽  
pp. 7879-7907
Author(s):  
J. Vierinen ◽  
J. L. Chau ◽  
N. Pfeffer ◽  
M. Clahsen ◽  
G. Stober
Keyword(s):  
Temporal Resolution ◽  
Large Scale ◽  
Pulse Compression ◽  
Continuous Wave ◽  
Signal To Noise Ratio ◽  
Field Measurements ◽  
Meteor Radar ◽  
Spatio Temporal ◽  
To Receive ◽  
Pulse Spacing

Abstract. The concept of coded continuous wave meteor radar is introduced. The radar uses a continuously transmitted pseudo-random waveform, which has several advantages: coding avoids range aliased echoes, which are often seen with commonly used pulsed specular meteor radars (SMRs); continuous transmissions maximize pulse compression gain, allowing operation with significantly lower peak transmit power; the temporal resolution can be changed after performing a measurement, as it does not depend on pulse spacing; and the low signal to noise ratio allows multiple geographically separated transmitters to be used in the same frequency band without significantly interfering with each other. The latter allows the same receiver antennas to be used to receive multiple transmitters. The principles of the signal processing are discussed, in addition to discussion of several practical ways to increase computation speed, and how to optimally detect meteor echoes. Measurements from a campaign performed with a coded continuous wave SMR are shown and compared with two standard pulsed SMR measurements. The type of meteor radar described in this paper would be suited for use in a large scale multi-static network of meteor radar transmitters and receivers. This would, for example, provide higher spatio-temporal resolution for mesospheric wind field measurements.

scholarly journals Coded continuous wave meteor radar

2016 ◽  
Vol 9 (2) ◽  
pp. 829-839 ◽  
Author(s):  
Juha Vierinen ◽  
Jorge L. Chau ◽  
Nico Pfeffer ◽  
Matthias Clahsen ◽  
Gunter Stober
Keyword(s):  
Frequency Band ◽  
Peak Power ◽  
Large Scale ◽  
Pulse Compression ◽  
Continuous Wave ◽  
Signal To Noise Ratio ◽  
Radar Data ◽  
Meteor Radar ◽  
To Receive ◽  
Computation Speed

Abstract. The concept of a coded continuous wave specular meteor radar (SMR) is described. The radar uses a continuously transmitted pseudorandom phase-modulated waveform, which has several advantages compared to conventional pulsed SMRs. The coding avoids range and Doppler aliasing, which are in some cases problematic with pulsed radars. Continuous transmissions maximize pulse compression gain, allowing operation at lower peak power than a pulsed system. With continuous coding, the temporal and spectral resolution are not dependent on the transmit waveform and they can be fairly flexibly changed after performing a measurement. The low signal-to-noise ratio before pulse compression, combined with independent pseudorandom transmit waveforms, allows multiple geographically separated transmitters to be used in the same frequency band simultaneously without significantly interfering with each other. Because the same frequency band can be used by multiple transmitters, the same interferometric receiver antennas can be used to receive multiple transmitters at the same time. The principles of the signal processing are discussed, in addition to discussion of several practical ways to increase computation speed, and how to optimally detect meteor echoes. Measurements from a campaign performed with a coded continuous wave SMR are shown and compared with two standard pulsed SMR measurements. The type of meteor radar described in this paper would be suited for use in a large-scale multi-static network of meteor radar transmitters and receivers. Such a system would be useful for increasing the number of meteor detections to obtain improved meteor radar data products.

Active pixel sensor array for high spatio-temporal resolution electrophysiological recordings from single cell to large scale neuronal networks

Lab on a Chip ◽  
2009 ◽  
Vol 9 (18) ◽  
pp. 2644 ◽  
Author(s):  
Luca Berdondini ◽  
Kilian Imfeld ◽  
Alessandro Maccione ◽  
Mariateresa Tedesco ◽  
Simon Neukom ◽  
...  
Keyword(s):  
Single Cell ◽  
Temporal Resolution ◽  
Large Scale ◽  
Neuronal Networks ◽  
Sensor Array ◽  
Active Pixel Sensor ◽  
Electrophysiological Recordings ◽  
Active Pixel ◽  
Spatio Temporal

scholarly journals Spatio-temporal development of large scale auroral electrojet currents relative to substorm onsets

2021 ◽  
Author(s):  
Sebastian Käki ◽  
Ari Viljanen ◽  
Liisa Juusola ◽  
Kirsti Kauristie
Keyword(s):  
Large Scale ◽  
Current System ◽  
Field Measurements ◽  
Low Earth Orbit ◽  
Satellite Mission ◽  
Low Earth Orbit Satellites ◽  
Spatio Temporal ◽  
Substorm Onsets ◽  
Auroral Current ◽  
Swarm Satellite

Abstract. During auroral substorms the electric currents flowing in the ionosphere change rapidly and a large amount of energy is dissipated in the auroral ionosphere. An important part of the auroral current system are the auroral electrojets whose profiles can be estimated from magnetic field measurements from Low Earth Orbit satellites. In this paper we combine electrojet data derived from the Swarm satellite mission of ESA with the substorm database derived from the SuperMAG ground magnetometer network data. We organize the electrojet data in relation to the location and time of the onset and obtain statistics for the development of the integrated current and latitudinal location for the auroral electrojets relative to the onset. The major features of the behaviour of the westward electrojet are found to be in accordance with earlier studies of field aligned currents and ground magnetometer observations of substorm time statistics. In addition we show that after the onset the latitudinal location of the maximum of the westward electrojet determined from Swarm satellite data is mostly located close to the SuperMAG onset latitude in the local time sector of the onset regardless of where the onset happens. We also show that the SuperMAG onset corresponds to a strengthening of the order of 100 kA in the amplitude of the median of the westward integrated current in the Swarm data from 15 minutes before to 15 minutes after the onset.

Resolving spatial dynamics at polar latitudes using the GROMOS-C radiometer on Svalbard and the Nordic meteor radar cluster

2020 ◽  
Author(s):  
Gunter Stober ◽  
Franziska Schranz ◽  
Chris Hall ◽  
Alexander Kozlovsky ◽  
Mark Lester ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Temporal Resolution ◽  
Lower Thermosphere ◽  
Winter Season ◽  
Spatial Characteristic ◽  
Small Scale ◽  
Meteor Radar ◽  
Atmospheric Waves ◽  
Spatio Temporal ◽  
Remote Sensing Techniques

<p>The middle polar atmosphere dynamics is driven by atmospheric waves from the planetary scale to small scale perturbation due to gravity waves. The different atmospheric waves are characterized by their temporal and spatial variability posing challenges to ground-based remote sensing techniques to disentangle and resolve the spatio-temporal ambiguity. Here we present two ground-based remote sensing techniques to resolving spatio-temporal variability at the polar middle atmosphere.</p><p>Since 2017 the GROMOS-C radiometer measures ozone and winds at NyÅlesund (78.9°N, 11.9°E) on Svalbard. The radiometer employs four beams in the cardinal directions at 22.5° elevation angle to retrieve ozone profiles and winds at altitudes between 30-75 km. the temporal resolution of the ozone retrievals is 30 minutes. Further, we obtain daily mean winds. Due to the high polar latitude the spatial separation between the beams at stratospheric altitudes covers several degrees in longitude to infer spatial gradients in the ozone densities and their perturbation due to planetary waves.</p><p>Another recently established ground-based remote sensing approach to retrieve the spatial characteristic at the mesosphere and lower thermosphere (MLT) is provided by the Nordic meteor radar cluster consisting of the meteor radars at Tromsø, Alta, Esrange, Sodankylä and on Svalbard. Since October 2019 horizontally resolved winds are obtained using a 3DVAR approach with a temporal resolution of 30 minutes and a vertical resolution of 2 km. Here we present preliminary results to infer horizontal wavelength spectra, the tidal variability as well as gravity activity of the winter season 2019/20.</p><p>Both datasets are of high value for data assimilation into weather forecast and reanalysis models or for cross-comparisons and validation of meteorological analysis systems (e.g. NAVGEM-HA).</p>

scholarly journals Removing independent noise in systems neuroscience data using DeepInterpolation

2020 ◽  
Author(s):  
Jérôme Lecoq ◽  
Michael Oliver ◽  
Joshua H. Siegle ◽  
Natalia Orlova ◽  
Christof Koch
Keyword(s):  
Temporal Resolution ◽  
Signal To Noise Ratio ◽  
Scientific Discovery ◽  
Fold Increase ◽  
General Purpose ◽  
Scientific Discipline ◽  
Missed Opportunities ◽  
Standard Data ◽  
Spatio Temporal

Progress in nearly every scientific discipline is hindered by the presence of independent noise in spatiotemporally structured datasets. Three widespread technologies for measuring neural activity—calcium imaging, extracellular electrophysiology, and fMRI—all operate in domains in which shot noise and/or thermal noise deteriorate the quality of measured physiological signals. Current denoising approaches sacrifice spatial and/or temporal resolution to increase the Signal-to-Noise Ratio of weak neuronal events, leading to missed opportunities for scientific discovery.Here, we introduce DeepInterpolation, a general-purpose denoising algorithm that trains a spatio-temporal nonlinear interpolation model using only noisy samples from the original raw data. Applying DeepInterpolation to in vivo two-photon Ca2+ imaging yields up to 6 times more segmented neuronal segments with a 15 fold increase in single pixel SNR, uncovering network dynamics at the single-trial level. In extracellular electrophysiology recordings, DeepInterpolation recovered 25% more high-quality spiking units compared to a standard data analysis pipeline. On fMRI datasets, DeepInterpolation increased the SNR of individual voxels 1.6-fold. All these improvements were attained without sacrificing spatial or temporal resolution.DeepInterpolation could well have a similar impact in other domains for which independent noise is present in experimental data.

Wind-Blown Sand Streamers and Turbulent Flow Structures

2020 ◽  
Author(s):  
Andreas Baas
Keyword(s):  
Turbulent Flow ◽  
Large Scale ◽  
Sonic Anemometer ◽  
Field Measurements ◽  
High Energy ◽  
Beach Sand ◽  
Flow Structures ◽  
Sand Transport ◽  
Near Surface ◽  
Spatio Temporal

<p>This contribution presents results of field measurements of wind-blown sand streamers and turbulent flow structures in the boundary layer airflow during gale-force winds on a beach. Sand transport and streamers were measured using Large-Scale Particle Image Velocimetry (LSPIV) combined with laser particle sensors (Wenglors), and airflow turbulence was monitored with a co-located sonic anemometer. The data analysis yields insight into the precise spatio-temporal relationships between sand streamers and near-surface airflow turbulence, at a high resolution of 25 Hz and a centimetre scale, including how high-energy sweeps correlate with the passage of fast-moving saltation clusters, and how Turbulent Kinetic Energy (TKE) may be linked to sediment mass flux.</p><p> </p>

IFPICS: Combining the advantages of hyperspectral imaging and filter cameras for trace gas imaging

2021 ◽  
Author(s):  
Alexander Nies ◽  
Christopher Fuchs ◽  
Jonas Kuhn ◽  
Nicole Bobrowski ◽  
Ulrich Platt
Keyword(s):  
Detection Limit ◽  
Temporal Resolution ◽  
High Selectivity ◽  
Image Acquisition ◽  
Trace Gases ◽  
Field Measurements ◽  
Trace Gas ◽  
Optical Absorption Spectroscopy ◽  
Specific Information ◽  
Spatio Temporal

<p>Imaging of atmospheric trace gases in the UV and visible wavelength range provides insight into the spatial distribution of physical and chemical processes in the atmosphere. Instruments for this purpose ideally combine a high spatio-temporal resolution with a high trace gas selectivity. In addition, they have to be built robust and compact for field measurements.</p><p>Atmospheric trace gas remote sensing by Differential Optical Absorption Spectroscopy (DOAS) is common and allows to measure several trace gases simultaneously with high selectivity and sensitivity. On the downside, image acquisition requires spatial scanning as for instance implemented in so-called hyperspectral cameras (also known as Imaging DOAS, IDOAS). This, however, results in reduced spatio-temporal resolution. Another approach to trace gas imaging is to use band pass filters, as for example in SO<sub>2</sub> cameras, which has the benefit of fast image acquisition combined with a high spatial resolution, but this advantage comes at the expense of low spectral sensitivity. Hence, only very high trace gas abundances can be reliably quantified, and the measurement is vulnerable to broadband interferences e.g. by aerosol.</p><p>We report an imaging technique combining the IDOAS and filter-based cameras’ advantages by utilizing the periodic transmission features of a Fabry-Perot-Interferometer (FPI). The FPI is tuned to two positions, so that its transmission either correlates or anti-correlates with the approximately periodic absorption structures of the target trace gas. From the measured intensities the differential optical density and the column density of the trace gas can be obtained with a high selectivity. Compared to IDOAS (or hyperspectral cameras) we only measure two different wavelength channels, however with maximum trace gas specific information. This reduces the amount of recorded data by at least two orders of magnitude for the same measurement resolution. This can be crucial for the feasibility of field measurements.</p><p>We present a compact and field-ready Imaging-FPI-Correlation-Spectroscopy (IFPICS) prototype. The FPI settings (or different FPIs) can be adapted to detect several different trace gases, our set-ups have been optimized for sulphur dioxide (SO<sub>2</sub>), bromine monoxide (BrO) or formaldehyde (HCHO).</p><p>We anticipate from laboratory studies using scattered skylight and HCHO cuvettes a detection limit of 4.7x10<sup>16</sup> molec cm<sup>-2</sup> for an image of about 90x90 pixel and an integration time of 6s. Because of the similar absorption features of BrO we expect a detection limit of 1.6x10<sup>14 </sup>molec cm<sup>^-2</sup>. Additionally, an outlook on the application of BrO imaging in volcanic plumes is given.</p><p> </p>

Spatio-temporal development of large scale auroral electrojet currents relative to substorm onsets

2021 ◽  
Author(s):  
Sebastian Käki ◽  
Ari Viljanen ◽  
Liisa Juusola ◽  
Kirsti Kauristie
Keyword(s):  
Large Scale ◽  
Current System ◽  
Field Measurements ◽  
Low Earth Orbit ◽  
Satellite Mission ◽  
Low Earth Orbit Satellites ◽  
Spatio Temporal ◽  
Substorm Onsets ◽  
Auroral Current ◽  
Swarm Satellite

<p>The electric currents flowing in the ionosphere change rapidly and a large amount of energy is dissipated in the auroral ionosphere during auroral substorms. An important part of the auroral current system are the auroral electrojets whose profiles can be estimated from magnetic field measurements from low Earth orbit satellites. We have combined electrojet data derived from the Swarm satellite mission of ESA with the substorm database derived from the SuperMAG ground network data. We organize the electrojet data in relation to the location of the onset and obtain statistics for the development of the integrated current and latitudinal location for the auroral electrojets relative to the onset. Especially we show that just after the onset the latitudinal location of the maximum of the westward electrojet determined from Swarm satellite data is mostly located close to the onset latitude in the local time sector of the onset regardless of where the onset happens.</p>

scholarly journals Building long-term and high spatio-temporal resolution precipitation and air temperature reanalyses by mixing local observations and global atmospheric reanalyses: the ANATEM method

2015 ◽  
Vol 12 (1) ◽  
pp. 311-361 ◽  
Author(s):  
A. Kuentz ◽  
T. Mathevet ◽  
J. Gailhard ◽  
B. Hingray
Keyword(s):  
Time Series ◽  
Temporal Resolution ◽  
Air Temperature ◽  
Large Scale ◽  
Precipitation Time Series ◽  
Time Step ◽  
Spatial Homogeneity ◽  
Temperature And Precipitation ◽  
Spatio Temporal

Abstract. Improving the understanding of past climatic or hydrologic variability has received a large attention in different fields of geosciences, such as glaciology, dendrochronology, sedimentology or hydrology. Based on different proxies, each research community produces different kind of climatic or hydrologic reanalyses, at different spatio-temporal scales and resolution. When considering climate or hydrology, numerous studies aim at characterising variability, trends or breaks using observed time-series of different regions or climate of world. However, in hydrology, these studies are usually limited to reduced temporal scale (mainly few decades, seldomly a century) because they are limited to observed time-series, that suffers from a limited spatio-temporal density. This paper introduces a new model, ANATEM, based on a combination of local observations and large scale climatic informations (such as 20CR Reanalysis). This model allow to build long-term air temperature and precipitation time-series, with a high spatio-temporal resolution (daily time-step, few km2). ANATEM was tested on the air temperature and precipitation time-series of 22 watersheds situated on the Durance watershed, in the french Alps. Based on a multi-criteria and multi-scale diagnostic, the results show that ANATEM improves the performances of classical statistical models. ANATEM model have been validated on a regional level, improving spatial homogeneity of performances and on independent long-term time-series, being able to capture the regional low-frequency variabilities over more than a century (1883–2010).

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