The correction for polar motion in gravimetry and in 3-D positioning

2020 ◽  
Author(s):  
Jaakko Mäkinen
Keyword(s):  
Geographical Distribution ◽  
Polar Motion ◽  
Low Frequency ◽  
Gravity Change ◽  
Absolute Gravity ◽  
Polar Wander ◽  
Gravity Measurements ◽  
Fixed Quantity

<p>In the correction for polar motion, terrestrial gravimetry and 3-D positioning follow different conventions. The 3-D positions are corrected to refer to the "mean pole" (IERS Conventions 2010) or to the "secular pole" (IERS update working version since 2018). In any case, the pole reference evolves in time and describes the track of secular or low-frequency polar wander. However, in terrestrial gravimetry the gravity values are corrected to refer to the IERS Reference Pole, a fixed quantity. This may lead to discrepancies when for instance gravity change rates from absolute gravity measurements are compared with vertical velocities from GNSS. I discuss the size and geographical distribution of the possible discrepancies.</p>

On the correction for polar motion in gravimetry and in 3-D positioning

2021 ◽  
Author(s):  
Jaakko Mäkinen
Keyword(s):  
Polar Motion ◽  
Low Frequency ◽  
Absolute Gravity ◽  
A Posteriori ◽  
Satellite Gravity ◽  
Polar Wander ◽  
Terrestrial Gravity ◽  
Gravity Measurements ◽  
Fixed Reference ◽  
Fixed Quantity

<p>In the correction for polar motion, terrestrial gravimetry and 3-D positioning follow different conventions. The 3-D positions were first corrected to refer to the "mean pole" (IERS Conventions up to 2010) and now to the "secular pole" (IERS Conventions update since 2018). In any case, the pole reference evolves in time and describes the track of secular or low-frequency polar wander. However, since 1988 terrestrial gravimetry follows the IAGBN (International Gravity Basestation Network) Processing Standards where the gravity values are corrected to refer to the IERS Reference Pole, a fixed quantity. This may lead to discrepancies when for instance gravity change rates from absolute gravity measurements are interpreted together with vertical velocities from GNSS. I discuss the size and geographical distribution of the possible discrepancies and how to account for them in geodynamical problems. The fixed reference of the IAGBN Processing Standards has served the gravity community well, by providing a stable system for terrestrial gravity for the last 30 years during which time the pole reference in the IERS Conventions has been revised several times. In fact, the recently proposed conventions for the International Gravity Reference System (IGRS) and the International Gravity Reference Frame (IGRF) maintain the IAGBN principle. However, it appears that with the adoption of the “secular pole” the reference in 3-D positioning may have become predictable for the foreseeable future. Therefore, it could be suggested that now is the time to harmonize terrestrial gravity with 3-D, by adopting the time-dependent secular pole as a reference for it as well, especially as this is already happening with satellite gravity. I argue that at present the practical drawbacks from such a change of reference would outweigh any theoretical advantages, and the harmonization, where necessary, can be simply performed a-posteriori to published gravity trends/values.</p>

scholarly journals Forty-three years of absolute gravity observations of the Fennoscandian postglacial rebound in Finland

2021 ◽  
Vol 95 (2) ◽  
Author(s):  
Mirjam Bilker-Koivula ◽  
Jaakko Mäkinen ◽  
Hannu Ruotsalainen ◽  
Jyri Näränen ◽  
Timo Saari
Keyword(s):  
Gravity Data ◽  
Gravity Change ◽  
Global Navigation Satellite Systems ◽  
Absolute Gravity ◽  
Data Sets ◽  
Postglacial Rebound ◽  
Land Uplift ◽  
Satellite Systems ◽  
Gravity Measurements ◽  
Global Navigation Satellite

AbstractPostglacial rebound in Fennoscandia causes striking trends in gravity measurements of the area. We present time series of absolute gravity data collected between 1976 and 2019 on 12 stations in Finland with different types of instruments. First, we determine the trends at each station and analyse the effect of the instrument types. We estimate, for example, an offset of 6.8 μgal for the JILAg-5 instrument with respect to the FG5-type instruments. Applying the offsets in the trend analysis strengthens the trends being in good agreement with the NKG2016LU_gdot model of gravity change. Trends of seven stations were found robust and were used to analyse the stabilization of the trends in time and to determine the relationship between gravity change rates and land uplift rates as measured with global navigation satellite systems (GNSS) as well as from the NKG2016LU_abs land uplift model. Trends calculated from combined and offset-corrected measurements of JILAg-5- and FG5-type instruments stabilized in 15 to 20 years and at some stations even faster. The trends of FG5-type instrument data alone stabilized generally within 10 years. The ratio between gravity change rates and vertical rates from different data sets yields values between − 0.206 ± 0.017 and − 0.227 ± 0.024 µGal/mm and axis intercept values between 0.248 ± 0.089 and 0.335 ± 0.136 µGal/yr. These values are larger than previous estimates for Fennoscandia.

Gravity Change Detected by Repeated Absolute Gravity Measurements in Western Yunnan and Lhasa, China and Its Implication

2004 ◽  
Vol 47 (1) ◽  
pp. 110-116 ◽  
Author(s):  
Yong WANG ◽  
Wei-Min ZHANG ◽  
Jin-Gang ZHAN ◽  
Xing-Hua HAO ◽  
Hu-Biao WANG ◽  
...  
Keyword(s):  
Gravity Change ◽  
Absolute Gravity ◽  
Western Yunnan ◽  
Gravity Measurements

scholarly journals Gravity reference at the Argentinean–German Geodetic Observatory (AGGO) by co-location of superconducting and absolute gravity measurements

2020 ◽  
Vol 94 (9) ◽  
Author(s):  
Ezequiel D. Antokoletz ◽  
Hartmut Wziontek ◽  
Claudia N. Tocho ◽  
Reinhard Falk
Keyword(s):  
Gravity Data ◽  
Total Error ◽  
International Comparisons ◽  
Superconducting Gravimeter ◽  
Calibration Factor ◽  
Absolute Gravity ◽  
Absolute Level ◽  
Gravity Measurements ◽  
Instrumental Drift

AbstractThe Argentinean–German Geodetic Observatory (AGGO) is a fundamental geodetic observatory located close to the city of La Plata, Argentina. Two high-precision gravity meters are installed at AGGO: the superconducting gravimeter SG038, which is in operation since December 2015, and the absolute gravimeter FG5-227, which has provided absolute gravity measurements since January 2018. By co-location of gravity observations from both meters between January 2018 and March 2019, calibration factor and instrumental drift of the SG038 were determined. The calibration factor of the SG038 was estimated by different strategies: from tidal models, dedicated absolute gravity measurements over several days and a joint approach (including the determination of the instrumental drift) using all available absolute gravity data. The final calibration factor differs from the determination at the previous station, the transportable integrated geodetic observatory, in Concepcion, Chile, by only 0.7‰, which does not imply a significant change. From the combined approach also the mean absolute level of the SG was determined, allowing to predict absolute gravity values from the SG at any time based on a repeatability of $$12\,\hbox {nm}/\hbox {s}^{2}$$ 12 nm / s 2 for the FG5-227 at AGGO. Such a continuous gravity reference function provides the basis for a comparison site for absolute gravimeters in the frame of the international gravity reference frame for South America and the Caribbean. However, it requires the assessment of the total error budget of the FG5-227, including the link to the international comparisons, which will be subject of future efforts.

scholarly journals Gravity variation around Shinmoe-dake volcano from February 2011 through March 2012—Results of continuous absolute gravity observation and repeated hybrid gravity measurements

2013 ◽  
Vol 65 (6) ◽  
pp. 563-571 ◽  
Author(s):  
Shuhei Okubo ◽  
Yoshiyuki Tanaka ◽  
Sadato Ueki ◽  
Hiromitsu Oshima ◽  
Tokumitsu Maekawa ◽  
...  
Keyword(s):  
Absolute Gravity ◽  
Gravity Variation ◽  
Gravity Observation ◽  
Gravity Measurements

Absolute gravity measurements at three sites characterized by different environmental conditions using two portable ballistic gravimeters

2015 ◽  
Vol 130 (3) ◽  
Author(s):  
Filippo Greco ◽  
Emanuele Biolcati ◽  
Antonio Pistorio ◽  
Giancarlo D’Agostino ◽  
Alessandro Germak ◽  
...  
Keyword(s):  
Environmental Conditions ◽  
Absolute Gravity ◽  
Gravity Measurements
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