scholarly journals On the Feasibility of Interhemispheric Patch Detection Using Ground-Based GNSS Measurements

2018 ◽  
Vol 10 (12) ◽  
pp. 2044 ◽  
Author(s):  
Rafal Sieradzki ◽  
Jacek Paziewski
Keyword(s):  
Continuous Monitoring ◽  
Dual Frequency ◽  
Degree Polynomial ◽  
Opposite Situation ◽  
Gnss Measurements ◽  
Gnss Data ◽  
Dusk Sector ◽  
Northern And Southern Hemispheres ◽  
Different Parts

Dual-frequency GNSS data processing is currently one of the most useful techniques for sounding the ionosphere. Hence, this work was aimed at the evaluation of ground-based GNSS data for the continuous monitoring of polar patches in both hemispheres. In this contribution, we proposed to use epoch-wise relative STEC values in order to detect these structures. The applied indicator is defined as a difference between an undifferenced geometry-free linear combination of GNSS signals and the background ionospheric variations, which were assessed with an iterative algorithm of four-degree polynomial fitting. The occurrence of patches during the St. Patrick geomagnetic storm was performed for validation purposes. The first part of the work confirmed the applicability of the relative STEC values for such investigations. On the other hand, it also revealed the limitations related to the inhomogeneous distribution of stations, which may affect the results in both hemispheres. This was confirmed with a preliminary cross-evaluation of GNSS and in situ SWARM datasets. Apart from the periods with a well-established coincidence, the opposite situation, when both methods indicated different parts of the polar ionosphere, was also observed. The second part of this contribution depicted the feasibility of continuous patch detection for both regions, and thus the interhemispheric comparison of the analyzed structures. It has demonstrated the strong disproportion between patches in the northern and southern hemispheres. This discrepancy seems to be related to the different amount of plasma propagating from the dusk sector, which is justified by the values of relative STEC at mid-latitudes. The observed structures are also strongly dependent on the orientation of the interplanetary magnetic field.

scholarly journals Impact of UAS Image Orientation on Accuracy of Forest Inventory Attributes

2020 ◽  
Vol 12 (3) ◽  
pp. 404 ◽  
Author(s):  
Luka Jurjević ◽  
Mateo Gašparović ◽  
Anita Simic Milas ◽  
Ivan Balenović
Keyword(s):  
Carrier Phase ◽  
Single Frequency ◽  
Pedunculate Oak ◽  
Dual Frequency ◽  
3D Point Clouds ◽  
Sensor Orientation ◽  
Forested Areas ◽  
Gnss Measurements ◽  
Image Orientation ◽  
Gnss Data

The quality and accuracy of Unmanned Aerial System (UAS) products greatly depend on the methods used to define image orientations before they are used to create 3D point clouds. While most studies were conducted in non- or partially-forested areas, a limited number of studies have evaluated the spatial accuracy of UAS products derived by using different image block orientation methods in forested areas. In this study, three image orientation methods were used and compared: (a) the Indirect Sensor Orientation (InSO) method with five irregularly distributed Ground Control Points (GCPs); (b) the Global Navigation Satellite System supported Sensor Orientation (GNSS-SO) method using non-Post-Processed Kinematic (PPK) single-frequency carrier-phase GNSS data (GNSS-SO1); and (c) using PPK dual-frequency carrier-phase GNSS data (GNSS-SO2). The effect of the three methods on the accuracy of plot-level estimates of Lorey’s mean height (HL) was tested over the mixed, even-aged pedunculate oak forests of Pokupsko basin located in Central Croatia, and validated using field validation across independent sample plots (HV), and leave-one-out cross-validation (LOOCV). The GNSS-SO2 method produced the HL estimates of the highest accuracy (RMSE%: HV = 5.18%, LOOCV = 4.06%), followed by the GNSS-SO1 method (RMSE%: HV = 5.34%, LOOCV = 4.37%), while the lowest accuracy was achieved by the InSO method (RMSE%: HV = 5.55%, LOOCV = 4.84%). The negligible differences in the performances of the regression models suggested that the selected image orientation methods had no considerable effect on the estimation of HL. The GCPs, as well as the high image overlaps, contributed considerably to the block stability and accuracy of image orientation in the InSO method. Additional slight improvements were achieved by replacing single-frequency GNSS measurements with dual-frequency GNSS measurements and by incorporating PPK into the GNSS-SO2 method.

scholarly journals GNSS Profile from the Greenland Korth Expeditions in the Context of Satellite Data

2021 ◽  
Vol 11 (3) ◽  
pp. 1115
Author(s):  
Aleš Bezděk ◽  
Jakub Kostelecký ◽  
Josef Sebera ◽  
Thomas Hitziger
Keyword(s):  
Ice Sheet ◽  
Satellite Observations ◽  
Elevation Change ◽  
Gradual Decline ◽  
Satellite Gravimetry ◽  
Surface Elevation Change ◽  
Satellite Radar ◽  
Gnss Measurements ◽  
Gnss Data ◽  
Satellite Radar Altimetry

Over the last two decades, a small group of researchers repeatedly crossed the Greenland interior skiing along a 700-km long route from east to west, acquiring precise GNSS measurements at exactly the same locations. Four such elevation profiles of the ice sheet measured in 2002, 2006, 2010 and 2015 were differenced and used to analyze the surface elevation change. Our goal is to compare such locally measured GNSS data with independent satellite observations. First, we show an agreement in the rate of elevation change between the GNSS data and satellite radar altimetry (ERS, Envisat, CryoSat-2). Both datasets agree well (2002–2015), and both correctly display local features such as an elevation increase in the central part of the ice sheet and a sharp gradual decline in the surface heights above Jakobshavn Glacier. Second, we processed satellite gravimetry data (GRACE) in order for them to be comparable with local GNSS measurements. The agreement is demonstrated by a time series at one of the measurement sites. Finally, we provide our own satellite gravimetry (GRACE, GRACE-FO, Swarm) estimate of the Greenland mass balance: first a mild decrease (2002–2007: −210 ± 29 Gt/yr), then an accelerated mass loss (2007–2012: −335 ± 29 Gt/yr), which was noticeably reduced afterwards (2012–2017: −178 ± 72 Gt/yr), and nowadays it seems to increase again (2018–2019: −278 ± 67 Gt/yr).

Expression of the SMP antigen by oligodendrocytes in the developing avian central nervous system

Development ◽  
1989 ◽  
Vol 107 (4) ◽  
pp. 825-833
Author(s):  
P. Cameron-Curry ◽  
C. Dulac ◽  
N.M. Le Douarin
Keyword(s):  
Monoclonal Antibody ◽  
Schwann Cell ◽  
Basic Protein ◽  
Culture Conditions ◽  
Cell Marker ◽  
Cellular Expression ◽  
Early Expression ◽  
Different Parts

Expression of the avian antigen SMP (Schwann cell Myelin Protein, Mr 75-80000), first characterized in the PNS with a monoclonal antibody as an early and strictly specific Schwann cell marker, was further studied in the CNS. Comparing SMP immunoreactive areas in the different parts of the CNS with those expressing the Myelin Basic Protein (MBP), we showed a strict colocalisation of both phenotypes. In vitro, MBP+ oligodendrocytes express the surface antigen SMP as well. SMP cellular expression was followed in situ and in culture using nervous tissues from embryos at different stages. We were thus able to detect an early expression of this marker by oligodendroblasts before the first appearance of MBP immunoreactivity. We have also identified a subpopulation of SMP+/MBP- and SMP+/GC- cells, which persists under our culture conditions as precursors remaining in an immature state.

scholarly journals UAV-LiCAM SYSTEM DEVELOPMENT: CALIBRATION AND GEO-REFERENCING

2018 ◽  
Vol XLII-1 ◽  
pp. 107-114 ◽  
Author(s):  
C. Cortes ◽  
M. Shahbazi ◽  
P. Ménard
Keyword(s):  
Particle Filtering ◽  
System Development ◽  
Low Cost ◽  
Base Station ◽  
Dual Frequency ◽  
Body Frame ◽  
Integrated Sensor ◽  
Sensor Orientation ◽  
Wide Range ◽  
Gnss Measurements

<p><strong>Abstract.</strong> In the last decade, applications of unmanned aerial vehicles (UAVs), as remote-sensing platforms, have extensively been investigated for fine-scale mapping, modeling and monitoring of the environment. In few recent years, integration of 3D laser scanners and cameras onboard UAVs has also received considerable attention as these two sensors provide complementary spatial/spectral information of the environment. Since lidar performs range and bearing measurements in its body-frame, precise GNSS/INS data are required to directly geo-reference the lidar measurements in an object-fixed coordinate system. However, such data comes at the price of tactical-grade inertial navigation sensors enabled with dual-frequency RTK-GNSS receivers, which also necessitates having access to a base station and proper post-processing software. Therefore, such UAV systems equipped with lidar and camera (UAV-LiCam Systems) are too expensive to be accessible to a wide range of users. Hence, new solutions must be developed to eliminate the need for costly navigation sensors. In this paper, a two-fold solution is proposed based on an in-house developed, low-cost system: 1) a multi-sensor self-calibration approach for calibrating the Li-Cam system based on planar and cylindrical multi-directional features; 2) an integrated sensor orientation method for georeferencing based on unscented particle filtering which compensates for time-variant IMU errors and eliminates the need for GNSS measurements.</p>

Dual-frequency impedance assays for intracellular components in microalgal cells

Lab on a Chip ◽  
2021 ◽  
Author(s):  
Tao Tang ◽  
Xun Liu ◽  
yapeng Yuan ◽  
Ryota Kiya ◽  
Yigang Shen ◽  
...  
Keyword(s):  
Cost Effective ◽  
Label Free ◽  
Dual Frequency ◽  
Cost Effective Approach

Intracellular components (including organelles and biomolecules) at the submicron level are typically analyzed in situ by special preparation or expensive setups. Here, a label-free and cost-effective approach of screening microalgal...

Importance of Continuous Monitoring: Case Study of Shallow CO2 Injection at the CSIRO in-situ Laboratory Site

2020 ◽  
Author(s):  
K. Tertyshnikov ◽  
L. Ricard ◽  
K. Michael ◽  
A. Avijegon ◽  
R. Pevzner
Keyword(s):  
Continuous Monitoring ◽  
Co2 Injection

Static Pressure-Volume Curves for the Lung of the Frog (Rana Pipiens)

1978 ◽  
Vol 76 (1) ◽  
pp. 149-165 ◽  
Author(s):  
G. M. HUGHES ◽  
G. A. VERGARA
Keyword(s):  
Volume Change ◽  
Rana Pipiens ◽  
Static Pressure ◽  
Large Diameter ◽  
The Difference ◽  
Isolated Lungs ◽  
Precise Role ◽  
Different Parts

1. Static pressure/volume curves have been determined for isolated frog lungs inflated with either air or saline. In both cases a hysteresis was present: the pressure required to produce unit change of volume being greater during inflation than deflation. 2. The pressure necessary for a given volume change was less for the saline-filled than the air-filled lungs. The difference between these curves is due to the surface tension at the air/lung interface. 3. Pressure/volume curves for air-filled lungs in situ were similar to curves for isolated lungs. However, a greater pressure was required for the same volume change during both inflation and deflation. 4. Compliance was calculated from different parts of air pressure/volume curves and gave values greater than those obtained using similar calculations for higher vertebrates. 5. These observations support other evidence for the presence of a surfactant in the lung lining of frogs in spite of the relatively large diameter of their ‘alveoli.’ The precise role of such a lining is uncertain and it is concluded that similar forces may be involved during the inflation and deflation of lungs of frogs and higher vertebrates in spite of differences in gross morphology.

Intercomparison and Validation of GNSS-IWV Derived with G-Nut and Bernese Software

2017 ◽  
Author(s):  
Pawel Golaszewski ◽  
Pawel Wielgosz ◽  
Katarzyna Stepniak
Keyword(s):  
Water Vapor ◽  
Meteorological Data ◽  
Microwave Radiometer ◽  
Severe Weather ◽  
Final Solution ◽  
Weather Forecasts ◽  
Software Packages ◽  
Gnss Measurements ◽  
Gnss Data ◽  
Permanent Station

GNSS is an important source of meteorological data. GNSS measurements can provide tropospheric Zenith Wet Delays (ZWD) over wide area covered with permanent stations. In addition, when using surface synoptical data, GNSS can provide Integrated Water Vapor (IWV) which is very valuable information utilized in weather forecasts and severe weather monitoring. Hence, there is a need to test and validate various algorithms and software used for ZWD estimation. In this research, the accuracy of the ZWD estimates was tested using two different software packages: Bernese GNSS Software v.5.2 and G-Nut/Tefnut. In addition, their computational load was evaluated. The GNSS data were obtained from POTS permanent station, which is located in Potsdam, Germany. To validate the estimation results, the derived ZWD was transformed into the IWV, and afterwards compared to the reference IWV measured by the collocated Microwave Radiometer. In addition, the ZWD estimates were also compared to the EUREF final solution.

scholarly journals Terrain changes from images acquired on opportunistic flights by SfM photogrammetry

2017 ◽  
Vol 11 (2) ◽  
pp. 827-840 ◽  
Author(s):  
Luc Girod ◽  
Christopher Nuth ◽  
Andreas Kääb ◽  
Bernd Etzelmüller ◽  
Jack Kohler
Keyword(s):  
Low Cost ◽  
Rapid Change ◽  
Satellite System ◽  
Light Transport ◽  
Area Of Interest ◽  
Accuracy And Precision ◽  
Global Navigation Satellite ◽  
The Cost ◽  
Gnss Data

Abstract. Acquiring data to analyse change in topography is often a costly endeavour requiring either extensive, potentially risky, fieldwork and/or expensive equipment or commercial data. Bringing the cost down while keeping the precision and accuracy has been a focus in geoscience in recent years. Structure from motion (SfM) photogrammetric techniques are emerging as powerful tools for surveying, with modern algorithm and large computing power allowing for the production of accurate and detailed data from low-cost, informal surveys. The high spatial and temporal resolution permits the monitoring of geomorphological features undergoing relatively rapid change, such as glaciers, moraines, or landslides. We present a method that takes advantage of light-transport flights conducting other missions to opportunistically collect imagery for geomorphological analysis. We test and validate an approach in which we attach a consumer-grade camera and a simple code-based Global Navigation Satellite System (GNSS) receiver to a helicopter to collect data when the flight path covers an area of interest. Our method is based and builds upon Welty et al. (2013), showing the ability to link GNSS data to images without a complex physical or electronic link, even with imprecise camera clocks and irregular time lapses. As a proof of concept, we conducted two test surveys, in September 2014 and 2015, over the glacier Midtre Lovénbreen and its forefield, in northwestern Svalbard. We were able to derive elevation change estimates comparable to in situ mass balance stake measurements. The accuracy and precision of our DEMs allow detection and analysis of a number of processes in the proglacial area, including the presence of thermokarst and the evolution of water channels.

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