Local gravity network as a reference station for the IGRF Ilya - - PowerPoint PPT Presentation

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Local gravity network as a reference station for the IGRF Ilya - - PowerPoint PPT Presentation

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Local gravity network as a reference station for the IGRF Ilya Oshchepkov Roman Sermyagin Department of Gravimetry and Geodynamics Center of Geodesy, Cartography and Spatial Data Infrustructure (CGCSDI) Moscow, Russia EGU General Assembly

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SLIDE 1

Local gravity network as a reference station for the IGRF

Ilya Oshchepkov Roman Sermyagin

Department of Gravimetry and Geodynamics Center of Geodesy, Cartography and Spatial Data Infrustructure (CGCSDI) Moscow, Russia EGU General Assembly 2019

  • Apr. 8 – 12, 2019

Vienna, Austria

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SLIDE 2

Outline

1

International Gravity Reference Frame (IGRF)

2

Moscow gravity network Structure and collocation Reference, comparison and core station for the IGRF Network maintenance Vertical and horizontal gravity gradients

3

Ensuring traceability of measurements Traceability in time–variable gravity field Loading effects on gravity Measurement frequency requirements Calibration of relative gravimeters

4

Conclusions and future work

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SLIDE 3

International Gravity Reference Frame (IGRF)

The work is based on the IAG Resolution 2015 (No.2) within the working group: IAG JWG 2.1.1: Establishment of a global absolute gravity reference system. Basic infrustructure1

1

Reference station provide a continuous gravity reference function:

very precisely by superconducting (SG) and/or quantum gravimeter (QG), approximately with the periodical absolute gravity (AG) measurements.

2 Comparison station: reference station + facility to compare (≥ 2) AG. 3 Core station: reference station + space geodetic technique, link to the ITRF.

Frame definition, site requirements and maintenance1 The reference frame is based on absolute gravity measurements. Uncertainty for measurements: < 10 µGal. Levelling network connection + collocated GNSS. Vertical gravity gradients (VGG) are required. Should be documented in AGrav database.

1From IAG JWG2.1.1 Report to IAG 2015–2019 (draft) by Hartmut Wziontek

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SLIDE 4

Moscow gravity network

Structure and collocation

M O S C O W

4 6 −6 1 20 27 −52 −19 −7 − 1 9 −7

TSNI TSEL KPRE MEND ZVEN LEDO 3 pillars+GNSS+gPhone 2 pillars 1 pillar+GNSS 1 pillar+GNSS+SLR 2 pillars+GNSS 2 pillars+GNSS

Absolute sites Gravity ties (mGal)

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SLIDE 5

Moscow gravity network

Reference, comparison and core station for the IGRF Reference station Very stable: no crustal movements, no tectonics, no volcanos, no GIA, located far from the oceans and seas, etc. No superconducting (SG) or quantum gravimeter (QG) yet. Regular absolute gravity measurements, but not precisely scheduled. Unfortunately, very noisy at some stations (large city). 4 out of 6 stations are connected with the national levelling network. Comparison station Up to three simultaneously working AG at one station. Core station MEND (Mendeleevo) is IGS station (MDVJ) and ILRS station (MDVL) ZWEN (Zvenigorod) is IGS station (ZWE2).

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SLIDE 6

Moscow gravity network

Example: Comparison station TSNI (TsNIIGAiK) AGrav database integration

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SLIDE 7

Network maintenance

Connection with Key comparisons Indirectly by Russian–Finnish Comparisons in 2013 (RFCAG2013) and FG5–X # 221. Tidal parameters and environmental effects Tides analysis with gPhone (in progress). Collect information about local and global environmental variables. Precise transfer correction Non–linear vertical gravity changes are determined for all stations. Non–linear horizontal gravity changes are determined only at TSNI. Continuous gravity reference function Ensuring traceability in time–varibale gravity field. Regular absolute and relative gravity measurements.

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SLIDE 8

Precise transfer correction

Vertical gravity changes

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SLIDE 9

Precise transfer correction

Vertical gravity gradients (VGG) TSNI — 109a

30 20 10 10 20 30

X / cm

30 20 10 10 20 30

Y / cm 3240 3280 3280 3320 3320 3320 3360 3360 3360 3400 3400 3440 Z = 27 cm - 16 cm = 11 cm

30 20 10 10 20 30

X / cm 3225 3240 3240 3255 3255 3255 3255 3270 3285 3300 Z = 71 cm - 27 cm = 44 cm

30 20 10 10 20 30

X / cm 3150 3150 3156 3156 3162 3168 3174 3180 3186 Z = 126 cm - 71 cm = 54 cm

3200 3280 3360 3440

E

TSNI — 109b

30 20 10 10 20 30

X / cm

30 20 10 10 20 30

Y / cm 3350 3350 3375 3375 3375 3400 3425 3425 3450 3450 3475 3500 Z = 27 cm - 15 cm = 11 cm

30 20 10 10 20 30

X / cm 3210 3225 3225 3225 3240 3240 3240 3255 3255 3270 3285 3300 Z = 71 cm - 27 cm = 44 cm

30 20 10 10 20 30

X / cm 3170 3180 3190 3190 3200 3200 3210 3220 3230 Z = 126 cm - 71 cm = 54 cm

3200 3280 3360 3440

E

TSNI — 110a

30 20 10 10 20 30

X / cm

30 20 10 10 20 30

Y / cm 3300 3330 3330 3360 3360 3390 3420 3450 3480 Z = 27 cm - 15 cm = 11 cm

30 20 10 10 20 30

X / cm 3225 3225 3225 3225 3240 3240 3240 3255 3255 3270 3285 3300 Z = 71 cm - 27 cm = 44 cm

30 20 10 10 20 30

X / cm 3165 3170 3175 3180 3180 3185 3185 3190 3195 Z = 126 cm - 71 cm = 55 cm

3200 3280 3360 3440

E

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SLIDE 10

Precise transfer correction

Horizontal gravity changes TSNI — 109a

30 20 10 10 20 30

X / cm

30 20 10 10 20 30

Y / cm

  • 7
  • 7
  • 6
  • 6
  • 5
  • 5
  • 4
  • 4
  • 4
  • 3
  • 3
  • 3
  • 2
  • 2
  • 1

Level: 16 cm

30 20 10 10 20 30

X / cm

  • 5
  • 4
  • 4
  • 3
  • 2
  • 1

Level: 27 cm

30 20 10 10 20 30

X / cm

  • 2
  • 1

Level: 71 cm

30 20 10 10 20 30

X / cm

1 2 Level: 126 cm

7.5 5.0 2.5 0.0 2.5

Gal

TSNI — 109b

30 20 10 10 20 30

X / cm

30 20 10 10 20 30

Y / cm

  • 9
  • 8
  • 7
  • 7
  • 6
  • 6
  • 5
  • 5
  • 4
  • 3
  • 2
  • 1

Level: 15 cm

30 20 10 10 20 30

X / cm

  • 7
  • 6
  • 5
  • 5
  • 4
  • 3
  • 2
  • 1

Level: 27 cm

30 20 10 10 20 30

X / cm

  • 3
  • 3
  • 2
  • 2
  • 1

1 Level: 71 cm

30 20 10 10 20 30

X / cm

  • 5
  • 4
  • 3
  • 2
  • 1

1 2 Level: 126 cm

9 6 3 3

Gal

TSNI — 110a

30 20 10 0 10 20 30

X / cm

20 20

Y / cm

  • 9
  • 8
  • 7
  • 6
  • 5
  • 5
  • 4
  • 4
  • 3
  • 2
  • 1

Level: 15 cm

30 20 10 0 10 20 30

X / cm

  • 7
  • 6
  • 5
  • 4
  • 4
  • 3
  • 3
  • 3
  • 2
  • 2
  • 1

Level: 27 cm

30 20 10 0 10 20 30

X / cm

  • 4
  • 3
  • 2
  • 1
  • 1

Level: 71 cm

30 20 10 0 10 20 30

X / cm

  • 4
  • 3
  • 2
  • 1

Level: 126 cm

10.0 7.5 5.0 2.5 0.0

Gal

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SLIDE 11

Ensuring traceability in time–variable gravity field

National gravity network and other users/applications

1

Through absolute and relative gravimeters.

2 Through measurements at the reference station/network.

Absolute gravimeters

1

Directly through comparisons at several points.

2 Indirectly through the reference station/network.

Relative gravimeters Through calibration between the reference stations.

But gravity is changing. How to ensure traceability?

Current requirement: mesure gravity with AG every two months.

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SLIDE 12

Loading effects on gravity

Atmospheric, hydrological and ocean non–tidal loading Estimations are taken from EOST Loading Service. TSNI is included in EOST computations (code: MOSC). Ocean non–tidal loading is negligible. Atmospheric loading was averaged over months. Strong correlation between FG5 and hydrological data.

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SLIDE 13

Measurement frequency requirements

There are several data gaps. Continuous gravity reference function is just linear. RMS before substructing: 3.4 µGal, RMS after substructing: 1.3 µGal. Residuals are from −2.7 µGal to 2.5 µGal ≈ ±3 µGal. Measurements with AG performed every two months will reduce residuals to ±2 µGal.

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SLIDE 14

Calibration of relative gravimeters

Traceability to relative gravimeters Needed in precise gravity measurements in the national gravity network. Should be based on absolute gravity measurements. Precision requirements: dY1 Y1 = d(∆g) ∆g − d(∆z) ∆z For dY1 Y1 = 10−5 . . . 10−4, ∆z ≈ ∆g = 52 mGal, d(∆z) = 5 µGal we get for the reference difference d(∆g): d(∆g) = 5.5 . . . 10.2 µGal this leads to the uncertainty ≈ 3.9 . . . 7.2 µGal of the individual absolute

  • measurement. It is very difficult in a time–variable gravity field.

Very high standards of measurements, including relative gravimeters. Ties between all nearest stations: 10 ties between 6 stations. Ideally, twice a year. Absolute and relative measurements are carried out simultaneously for no more than one month (10 days for relative measurements only). Measurements performed in 2015—2018. Every year is adjusted with absolute measurements.

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SLIDE 15

Conclusions and future work

A local gravity netowrk can be accepted as a reference statioin for the IGRF. The network is better than one station, because relative gravimeters can be calibrated on it. But it is also a more time–consuming task to maintain it. Maintenance should include:

connection with key comparisons, vertical and horizontal gravity changes determintaion, regular absolute and relative gravity measurements, tides analysis with continuously operating gravimeter, analysis of the environmental non–tidal effects.

The Moscow gravity network is maintained and it is a possible cadidate for the International Gravity Reference Frame (IGRF). It is (finaly!) included in AGrav database. Future work Finish tidal analysis for gPhone data. Continue regular absolute gravity measurements, increase measurement frequency. Use local data for hydrology, snow, etc.

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SLIDE 16

Thank you!