Long-Term Orbit Determination and Prediction for Geodynamic Investigations

1976 ◽  
pp. 321-326
Author(s):  
Bruce E. Douglas
Keyword(s):  
Orbit Determination

Copernicus Sentinel Orbit Validation – Investigations on systematic geographical differences

2020 ◽  
Author(s):  
Javier Berzosa ◽  
Marc Fernández Usón ◽  
Jaime Fernández Sánchez ◽  
Heike Peter ◽  
Pierre Féménias
Keyword(s):  
Time Series ◽  
Orbit Determination ◽  
Precise Orbit Determination ◽  
Geographical Differences ◽  
Laser Tracking ◽  
Term Stability ◽  
Long Term Stability ◽  
Precise Orbit ◽  
Geocenter Motion

<p>The Copernicus POD (Precise Orbit Determination) Service delivers, as part of the PDGS of the Copernicus Sentinel-1, -2, and -3 missions, orbital products and auxiliary data files for their use in the corresponding PDGS processing chains. The precise orbit results from the three missions are validated based on orbit comparisons to independent orbit solutions from member of the Copernicus POD Quality Working Group (QWG). In the case of Sentinel-3 a validation based on satellite laser tracking (SLR) measurements is also possible. The orbit comparisons are done based on orbit time series. Typically, only daily RMS metrics are derived, and its time-series mean and standard deviation are provided. Another possibility is to analyse the dependence of orbit differences with geographical differences; this is already done for the altimeter satellites to guarantee long-term stability of the orbit solutions.</p><p>Geographical orbit differences may reveal systematics due to, e.g., different background models or different geocenter motion models used in the orbit determination process. The geographical orbit differences of all six satellites and from all POD QWG contributions are analysed and checked for model- or satellite-specific systematics to improve the orbit quality and long-term stability.   </p><p>Additionally, it is proposed to analyse the orbit differences (with respect to other orbital solutions, either reduced-dynamic or kinematic) with Fourier transformation, in order to derive amplitude vs. frequency plots. This could provide light into the sub-daily differences. The Fourier analysis of the sub-daily differences will be assessed for all the six satellites.</p>

scholarly journals Analysis of Parameter Correlations of the ECOM Solar Radiation Pressure Model for GPS Orbit

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Tae-Suk Bae ◽  
Chang-Ki Hong
Keyword(s):  
Solar Radiation ◽  
Radiation Pressure ◽  
Orbit Determination ◽  
Annual Variation ◽  
Orbital Plane ◽  
Solar Radiation Pressure ◽  
Significant Difference ◽  
Orbit Model ◽  
Over Time

The modeling of solar radiation pressure is the most important issue in precision GNSS orbit determination and is usually represented by constant and periodic terms in three orthogonal axes. Unfortunately, these parameters are generally correlated with each other due to overparameterization, and furthermore, the correlation does not remain constant throughout a long-term period. A total of 500 weeks of GPS daily solutions were estimated with the empirical CODE orbit model (ECOM) to cover various block types of satellites. The statistics of the postfit residuals were analyzed in this study, which shows the dominant annual variation of the correlations over time. There is no significant difference between eclipsing and noneclipsing satellites, and the frequency of the correlation exactly corresponds to the GPS draconitic year. Based on the residual analysis, the ECOM is the most appropriate for the Block IIR/IIR-M satellites but does not properly account for the behavior of either older Block IIA or newer IIF satellites. In addition, the daily mean residuals show a different pattern for satellite orbital planes. Therefore, the orbit model should be customized for the block types and orbital plane for better representation of multi-GNSS orbits.

Long-term evaluation of estimated solar radiation pressure coefficients from Copernicus Sentinel-1, -2, -3 satellites

2020 ◽  
Author(s):  
Heike Peter ◽  
Javier Berzosa ◽  
Jaime Fernández ◽  
Pierre Féménias
Keyword(s):  
Solar Radiation ◽  
Radiation Pressure ◽  
Orbit Determination ◽  
Pressure Coefficient ◽  
Precise Orbit Determination ◽  
Solar Radiation Pressure ◽  
Mean Values ◽  
Pressure Coefficients ◽  
Set Up

<p>The Copernicus POD (Precise Orbit Determination) Service is responsible for the generation of precise orbital products of the Copernicus Sentinel-1, -2, and -3 missions. In the near future, the processing setup of the Copernicus POD Service will be updated to state-of-the-art background models (geopotential, ocean tides and atmospheric gravity) and the use of single-receiver ambiguity fixing using CODE (Center for Orbit Determination in Europe) products.</p><p>In the current orbit parametrization of the six satellites, a solar radiation pressure coefficient is estimated for each daily arc. To provide long-term stability, in particular for the time series of the altimeter Sentinel-3 satellites, it would be preferable to use a constant solar radiation pressure coefficient in the processing. A reprocessing based on the updated models and set-up will be used to compute daily estimates of the solar radiation pressure coefficient for all satellites. The analysis may reveal satellite model deficiencies and might help to improve the satellite macro-models.</p><p>Mean values of the solar radiation pressure coefficients from the long-term series can be used on future operational processing. At the same time a refinement of the selection of the estimated orbit parameters might also be done if necessary, in particular the empirical accelerations. Impact on the orbit determination results and on the quality of the orbits is presented for all six satellites.</p>

Impact of re-scaled macro models for GNSS orbit determination

2020 ◽  
Author(s):  
Arturo Villiger ◽  
Rolf Dach ◽  
Adrian Jäggi
Keyword(s):  
Radiation Pressure ◽  
Orbit Determination ◽  
Solar Radiation Pressure ◽  
Key Factors ◽  
One Year ◽  
Analytical Approaches ◽  
Incomplete Models ◽  
Earth Radiation

<p>Radiation pressure from the sun and the Earth are not negligible forces for orbit determination. Most analysis centers use empirical approaches (i.e., the classical Empirical CODE Orbit Model ECOM or the adapted version ECOM2), analytical approaches (simplified box wing models or detailed macro models), or a combination of both to account for the solar radiation pressure (SRP) and Earth radiation (albedo).</p><p>The European GNSS Agency and the Cabinet Office, Government of Japan, disclosed meta data for Galileo resp. QZSS satellites. For the other GNSS constellations either no or incomplete models are available. This is in particular problematic for SRP modeling. In case of albedo the issue is less critical as the corresponding force acting on GNSS satellites is much smaller compared to the SRP. Our approach to overcome this issue is to re-scale the existing box-wing models based on long term analysis (one year) and introduce the re-scaled macro models for the final orbit determination. The main goal is to achieve better orbit quality with fewer empirical parameters compared to our traditional solution based on pure empirical SRP models.  The key factors to determine the quality of the re-scaled macro models are, among others, the evaluation of the resulting orbits and the behavior of the long term time series of the corresponding geodynamic parameters.</p>

Therapy and prevention for mental health: What if mental diseases are mostly not brain disorders?

2019 ◽  
Vol 42 ◽  
Author(s):  
John P. A. Ioannidis
Keyword(s):  
Mental Health ◽  
Mental Disease ◽  
Brain Disorders ◽  
Social Stressors ◽  
Labor Education ◽  
Mental Diseases ◽  
Long Term Follow Up ◽  
Political Decisions

AbstractNeurobiology-based interventions for mental diseases and searches for useful biomarkers of treatment response have largely failed. Clinical trials should assess interventions related to environmental and social stressors, with long-term follow-up; social rather than biological endpoints; personalized outcomes; and suitable cluster, adaptive, and n-of-1 designs. Labor, education, financial, and other social/political decisions should be evaluated for their impacts on mental disease.

Conceptual short-term memory (CSTM) supports core claims of Christiansen and Chater

2016 ◽  
Vol 39 ◽  
Author(s):  
Mary C. Potter
Keyword(s):  
Working Memory ◽  
Rapid Serial Visual Presentation ◽  
Language Comprehension ◽  
Short Term Memory ◽  
Visual Presentation ◽  
Long Term Memory ◽  
Short Term ◽  
Term Memory ◽  
Use Of Knowledge

AbstractRapid serial visual presentation (RSVP) of words or pictured scenes provides evidence for a large-capacity conceptual short-term memory (CSTM) that momentarily provides rich associated material from long-term memory, permitting rapid chunking (Potter 1993; 2009; 2012). In perception of scenes as well as language comprehension, we make use of knowledge that briefly exceeds the supposed limits of working memory.

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