The impact of accelerometer calibration approach on estimation of thermospheric density variations 

2021 ◽  
Author(s):  
Akbar Shabanloui ◽  
Jakob Flury ◽  
Sergiy Svitlov
Keyword(s):  
Gravity Field ◽  
Scale Factor ◽  
Satellite Orbits ◽  
Gravitational Forces ◽  
Main Challenge ◽  
The Impact ◽  
Calibration Approach

<p>The environmental non-gravitational accelerations observed by ultra-precise electro-static accelerometers onboard Low Earth Orbiters (LEOs) such as GRACE (FO) and Swarm missions provide a unique opportunity to estimate and monitor the neutral thermospheric density variations. One of main challenge in using such ultra-precise accelerometer observations for thermospheric density application is the calibration approach which delivers the realistic non-gravitational forces acting on satellite surface. The realistic scale factor and bias of accelerometers are estimated during retrieval of Earth’s monthly gravity field solutions.</p><p>In this contribution, a realistic accelerometer calibration approach based on Earth’s gravity solutions and precise satellite orbits is introduced and its impacts on neutral thermoshperic density variations for some special periods are investigated. This approach demonstrates the potential of using realistic calibrated ultra-prcise accelerometers for neutral thermospheric density studies.</p>

Helmert transformation strategies in analysis of GPS position time-series

2020 ◽  
Vol 223 (2) ◽  
pp. 973-992
Author(s):  
Shiwei Guo ◽  
Chuang Shi ◽  
Na Wei ◽  
Min Li ◽  
Lei Fan ◽  
...  
Keyword(s):  
Time Series ◽  
Reference Frame ◽  
Scale Factor ◽  
Network Effect ◽  
Satellite Orbits ◽  
Surface Mass ◽  
Helmert Transformation ◽  
Position Time Series ◽  
Transformation Parameters ◽  
The Impact

SUMMARY Global positioning system (GPS) position time-series generated using inconsistent satellite products should be aligned to a secular Terrestrial Reference Frame by Helmert transformation. However, unmodelled non-linear variations in station positions can alias into transformation parameters. Based on 17 yr of position time-series of 112 stations produced by precise point positioning (PPP), we investigated the impact of network configuration and scale factor on long-term time-series processing. Relative to the uniform network, the uneven network can introduce a discrepancy of 0.7–1.1 mm, 21.3–27.5 μas and 1.3 mm in terms of root mean square (RMS) for the translation, rotation and scale factor (if estimated), respectively, no matter whether the scale factor is estimated. The RMS of vertical annual amplitude differences caused by such network effect reaches 0.5–0.6 mm. Whether estimating the scale factor mostly affects the Z-translation and vertical annual amplitude, leading to a difference of 1.3 mm when the uneven network is used. Meanwhile, the annual amplitude differences caused by the scale factor present different geographic location dependences over the north, east and up components. The seasonal signals derived from the transformation using the uniform network and without estimating scale factor have better consistency with surface mass loadings with more than 41 per cent of the vertical annual variations explained. Simulation studies show that 40–50 per cent of the annual signals in the scale factor can be explained by the aliasing of surface mass loadings. Another finding is that GPS draconitic errors in station positions can also alias into transformation parameters, while different transformation strategies have limited influence on identifying the draconitic errors. We suggest that the uniform network should be used and the scale factor should not be estimated in Helmert transformation. It is also suggested to perform frame alignment on PPP time-series, even though the used satellite products belong to a consistent reference frame, as the origin of PPP positions inherited from satellite orbits and clocks is not so stable during a long period. With Helmert transformation, the seasonal variations would better agree with surface mass loadings, and noise level of time-series is reduced.

scholarly journals Sensitivity of Lageos Orbits to Global Gravity Field Models

2012 ◽  
Vol 47 (2) ◽  
pp. 47-65 ◽  
Author(s):  
K. Sośnica ◽  
D. Thaller ◽  
A. Jäggi ◽  
R. Dach ◽  
G. Beutler
Keyword(s):  
Gravity Field ◽  
Orbit Determination ◽  
Measurement Techniques ◽  
Precise Orbit Determination ◽  
Satellite Orbits ◽  
Gravity Field Model ◽  
Global Gravity ◽  
The Impact ◽  
Gravity Field Models

Sensitivity of Lageos Orbits to Global Gravity Field ModelsPrecise orbit determination is an essential task when analyzing SLR data. The quality of the satellite orbits strongly depends on the models used for dynamic orbit determination. The global gravity field model used is one of the crucial elements, which has a significant influence on the satellite orbit and its accuracy. We study the impact of different gravity field models on the determination of the LAGEOS-1 and -2 orbits for data of the year 2008. Eleven gravity field models are compared, namely JGM3 and EGM96 based mainly on SLR, terrestrial and altimetry data, AIUB-CHAMP03S based uniquely on GPS-measurements made by CHAMP, AIUB-GRACE03S, ITG-GRACE2010 based on GRACE data, and the combined gravity field models based on different measurement techniques, such as EGM2008, EIGEN-GL04C, EIGEN51C, GOCO02S, GO-CONS-2-DIR-R2, AIUB-SST. The gravity field models are validated using the RMS of the observation residuals of 7-day LAGEOS solutions. The study reveals that GRACE-based models have the smallest RMS values (i.e., about 7.15 mm), despite the fact that no SLR data were used to determine them. The coefficient C20is not always well estimated in GRACE-only models. There is a significant improvement of the gravity field models based on CHAMP, GRACE and GOCE w.r.t. models of the pre-CHAMP era. The LAGEOS orbits are particularly sensitive to the long wavelength part of the gravity fields. Differences of the estimated orbits due to different gravity field models are noticeable up to degree and order of about 30. The RMS of residuals improves from about 40 mm for degree 8, to about 7 mm for the solutions up to degrees 14 and higher. The quality of the predicted orbits is studied, as well.

Two-step LRI1B data calibration approach

2020 ◽  
Author(s):  
Saniya Behzadpour ◽  
Andreas Kvas ◽  
Torsten Mayer-Gürr
Keyword(s):  
Gravity Field ◽  
Scale Factor ◽  
Laser Ranging ◽  
Measurement Technology ◽  
Additional Measurement ◽  
Time Offset ◽  
Range Rate ◽  
Calibration Parameters ◽  
Calibration Approach ◽  
Data Calibration

<p class="western" align="justify">GRACE-FO carries a Laser Ranging Interferometer (LRI) as a technology demonstration to provide measurements of inter-satellite range changes. This additional measurement technology provides supplementary observations, which improve the reliability of the range rate measurements and allow for a cross-instrument diagnostics and calibration with the K-band ranging (KBR) system.</p> <p class="western" align="justify">We present a two-step approach used for LRI1B data calibration within the ITSG-Grace2018 scheme, which is compatible with the entire v04 release timespan. The aim of this study is to mitigate the remaining systematics due to the LRI datation time offset and LRI scale factor. We discuss the implementation of calibration parameters and the contribution of the calibration approach to the overall accuracy of gravity field solutions.</p>

A multiscale homogenization procedure to predict the elasto-viscoplastic behavior of polymer-based nanocomposites

2021 ◽  
pp. 096739112110233
Author(s):  
Mohammad Hassan Shojaeefard ◽  
Abolfazl Khalkhali ◽  
Sharif Khakshournia
Keyword(s):  
Design Procedure ◽  
Polymeric Matrix ◽  
Elastic Behavior ◽  
Algorithm Optimization ◽  
Multiphase Materials ◽  
Rate Dependent ◽  
Main Challenge ◽  
Compressive Loads ◽  
Structural Parts ◽  
The Impact

It has been demonstrated that adding a few percent of nanoscale reinforcements, leads to remarkable improvement in mechanical properties of the polymers such as stiffness, damping, and energy absorption. These lightweight materials are attractive substitutes for the heavy metallic structural parts in the automotive, military, aerospace and many other industries. However, due to complexity of these multiphase materials, accurate modeling of their behavior in real loading cases is still ambiguous. The impact simulation is a vital step in design procedure of a vehicle, where a strain rate-dependent model of its components is required. In this paper, an elasto-viscoplastic modeling procedure of the polymer-based nanocomposites, assuming the elastic behavior of the nano-phase is presented; whereas the polymeric matrix deformation is dependent to the loading rate and is characterized by the method of Genetic algorithm optimization-based fitting to the experimental observations. By introducing a modified Halpin-Tsai method, the nanocomposite is then modeled as a homogenized material where the modification algorithm is the main challenge. A combination of approaches including parametric analysis, central composite design of experiments and response surface method is proposed to modify the tangent modulus of the polymeric matrix to be passed as the input to the Halpin-Tsai equations. Finally, the procedure is implemented to a set of epoxy-GNP nanocomposites under unidirectional compressive loads with different rates and the stress-strain curves are predicted with a decent precision.

scholarly journals Geoinformation Technologies in Support of Environmental Hazards Monitoring under Climate Change: An Extensive Review

2021 ◽  
Vol 10 (2) ◽  
pp. 94
Author(s):  
Andreas Tsatsaris ◽  
Kleomenis Kalogeropoulos ◽  
Nikolaos Stathopoulos ◽  
Panagiota Louka ◽  
Konstantinos Tsanakas ◽  
...  
Keyword(s):  
Climate Change ◽  
Environmental Monitoring ◽  
Environmental Hazards ◽  
Geographic Information ◽  
Added Value ◽  
Spatial Data Analysis ◽  
Anthropogenic Factors ◽  
Geospatial Technologies ◽  
Main Challenge ◽  
The Impact

Human activities and climate change constitute the contemporary catalyst for natural processes and their impacts, i.e., geo-environmental hazards. Globally, natural catastrophic phenomena and hazards, such as drought, soil erosion, quantitative and qualitative degradation of groundwater, frost, flooding, sea level rise, etc., are intensified by anthropogenic factors. Thus, they present rapid increase in intensity, frequency of occurrence, spatial density, and significant spread of the areas of occurrence. The impact of these phenomena is devastating to human life and to global economies, private holdings, infrastructure, etc., while in a wider context it has a very negative effect on the social, environmental, and economic status of the affected region. Geospatial technologies including Geographic Information Systems, Remote Sensing—Earth Observation as well as related spatial data analysis tools, models, databases, contribute nowadays significantly in predicting, preventing, researching, addressing, rehabilitating, and managing these phenomena and their effects. This review attempts to mark the most devastating geo-hazards from the view of environmental monitoring, covering the state of the art in the use of geospatial technologies in that respect. It also defines the main challenge of this new era which is nothing more than the fictitious exploitation of the information produced by the environmental monitoring so that the necessary policies are taken in the direction of a sustainable future. The review highlights the potential and increasing added value of geographic information as a means to support environmental monitoring in the face of climate change. The growth in geographic information seems to be rapidly accelerated due to the technological and scientific developments that will continue with exponential progress in the years to come. Nonetheless, as it is also highlighted in this review continuous monitoring of the environment is subject to an interdisciplinary approach and contains an amount of actions that cover both the development of natural phenomena and their catastrophic effects mostly due to climate change.

The Impact of Temporal Gravity Variations on GOCE Gravity Field Recovery

2006 ◽  
pp. 255-269 ◽  
Author(s):  
Oleg Abrikosov ◽  
Focke Jarecki ◽  
Jürgen Müller ◽  
Svetozar Petrovic ◽  
Peter Schwintzer
Keyword(s):  
Gravity Field ◽  
Gravity Field Recovery ◽  
Gravity Variations ◽  
The Impact ◽  
Temporal Gravity

scholarly journals The Impact of Error Accounting in a Bayesian Approach to Calibrating Modeled Turbulent Fluxes in an Open-Canopy Forest

2017 ◽  
Vol 18 (7) ◽  
pp. 2029-2042
Author(s):  
Tony E. Wong ◽  
William Kleiber ◽  
David C. Noone
Keyword(s):  
Markov Chain ◽  
Land Surface ◽  
Hydrological Modeling ◽  
Soil Layer ◽  
Turbulent Fluxes ◽  
Surface Model ◽  
Model Parameters ◽  
Top Soil ◽  
The Impact ◽  
Calibration Approach

Abstract Land surface models are notorious for containing many parameters that control the exchange of heat and moisture between land and atmosphere. Properly modeling the partitioning of total evapotranspiration (ET) between transpiration and evaporation is critical for accurate hydrological modeling, but depends heavily on the treatment of turbulence within and above canopies. Previous work has constrained estimates of evapotranspiration and its partitioning using statistical approaches that calibrate land surface model parameters by assimilating in situ measurements. These studies, however, are silent on the impacts of the accounting of uncertainty within the statistical calibration framework. The present study calibrates the aerodynamic, leaf boundary layer, and stomatal resistance parameters, which partially control canopy turbulent exchange and thus the evapotranspiration flux partitioning. Using an adaptive Metropolis–Hastings algorithm to construct a Markov chain of draws from the joint posterior distribution of these resistance parameters, an ensemble of model realizations is generated, in which latent and sensible heat fluxes and top soil layer temperature are optimized. A set of five calibration experiments demonstrate that model performance is sensitive to the accounting of various sources of uncertainty in the field observations and model output and that it is critical to account for model structural uncertainty. After calibration, the modeled fluxes and top soil layer temperature are largely free from bias, and this calibration approach successfully informs and characterizes uncertainty in these parameters, which is essential for model improvement and development. The key points of this paper are 1) a Markov chain Monte Carlo calibration approach successfully improves modeled turbulent fluxes; 2) ET partitioning estimates hinge on the representation of uncertainties in the model and data; and 3) despite these inherent uncertainties, constrained posterior estimates of ET partitioning emerge.

Green Infrastructure Development in Sustainable Water Resources Management System

2015 ◽  
Vol 747 ◽  
pp. 127-131
Author(s):  
Quintarina Uniaty
Keyword(s):  
Water Management ◽  
Green Infrastructure ◽  
Management System ◽  
Urban Systems ◽  
Difficult Situation ◽  
Sustainable Water Resources Management ◽  
Main Challenge ◽  
The Impact ◽  
Green City

The main challenge in the twenty-first century is to work towards a more resilient urban world and sustainable. In the context of a global urban strategy, endurance is the attention to the capacity of urban systems, including the natural environment, the built environment, social and economic elements; to be able to manage change, to learn from a difficult situation and be in a position to rise from urban problems. Globally, the townsfolk face a water crisis within the next ten years, as the impact of climate change in exhaust emissions will affect the quality of air, land and water; which will ultimately reduce the quality of the environment. Sustainability questioned whether certain aspects of the day-to-day activities, and the systems of community life, can be ongoing into the futureonce again from the standpoint of social, economic and environmental. Eco city is a phrase that is often used in ecological issues raised in the concept of sustainable urban planning and green city embodiment of the challenges ahead in sustainable economic development, and the future development of smart green city. The convergence of technology and environmental issues has changed the world economy that offers a green city promising future - a city that appreciates natural heritage and offer all parties involved. This paper will discuss green infrastructure as water management control system in urban development concepts that contribute to build a sustainable green city management.Key words : green infrastructure, water management system.

Impact of low-degree gravity field estimation in the SLR data processing of spherical satellites at AIUB

2021 ◽  
Author(s):  
Linda Geisser ◽  
Ulrich Meyer ◽  
Daniel Arnold ◽  
Adrian Jäggi ◽  
Daniela Thaller
Keyword(s):  
Gravity Field ◽  
Lower Altitude ◽  
Earth’S Gravity Field ◽  
Low Degree ◽  
Station Coordinates ◽  
Earth Rotation Parameters ◽  
Field Estimation ◽  
University Of Bern ◽  
The University ◽  
The Impact

<p>The Astronomical Institute of the University of Bern (AIUB) collaborates with the Federal Agency for Cartography and Geodesy (BKG) in Germany to develop new procedures to generate products for the International Laser Ranging Service (ILRS). In this framework the SLR processing of the standard ILRS weekly solutions of spherical geodetic satellites at AIUB, where the orbits are determined in 7-day arcs together with station coordinates and other geodetic parameters, is extended from LAGEOS-1/2 and the Etalon-1/2 satellites to also include the LARES satellite orbiting the Earth at much lower altitude. Since a lower orbit experiences a more variable enviroment, e.g. it is more sensitive to time-variable Earth's gravity field, the orbit parametrization has to be adapted and also the low degree spherical harmonic coefficients of Earth's gravity field have to be co-estimated. The impact of the gravity field estimation is studied by validating the quality of other geodetic parameters such as geocenter coordinates, Earth Rotation Parameters (ERPs) and station coordinates. The analysis of the influence of LARES on the SLR solution shows that a good datum definition is important.</p>

scholarly journals Analysis of a risk prevention document using depend ability techniques: a first step towards an effectiveness model

2017 ◽  
Author(s):  
Laetitia Ferrer ◽  
Corinne Curt ◽  
Jean-Marc Tacnet
Keyword(s):  
Failure Modes ◽  
Communication Effectiveness ◽  
Decision Support Model ◽  
Analytical Methodology ◽  
Regulatory Constraints ◽  
Effectiveness Model ◽  
Main Challenge ◽  
Technical Functions ◽  
The Impact ◽  
The Way

Abstract. Major hazard prevention is a main challenge given than it's particularly based on information communicated to the general public. In France, preventive information is provided by the way of a regulatory document named DICRIM (In French Document d'Information Communal sur les Risques Majeurs that means in English Municipal Information Document on Major Risks). It is made by mayors and addressed to the public in order to provide information on major hazards affecting their municipalities. Unfortunately, the law imposes only few specifications concerning its content therefore one can question the impact on the general population relative to the way it is concretely realized. Ergo, the purpose of our work is to propose an analytical methodology to evaluate preventive risk communication effectiveness and apply it to the DICRIM. The methodology is based on dependability approaches. EFA (External Functional Analysis) permits the identification of (i) the service and technical functions involved, and (ii) the form, content and regulatory constraints of a DICRIM. FMEA (Failure Modes and Effects Analysis) is used to define the dysfunctions and detection elements are then listed to evaluate conformity with the 3 types of constraint. The outputs are validated by experts from the different fields investigated. Those results are obtained in order to build in future works a decision support model for the municipality (or specialized consulting firms) in charge of drawing up documents. The method is applied to a database of 30 DICRIMs. This analysis leads to a discussion on points such as usefulness of the elements missing.

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