On “New standards for reducing gravity data: The North American gravity database” ()

The North American gravity database as well as data-bases from Canada, Mexico, and the United States are being revised to improve their coverage, versatility, and accuracy. An important part of this effort is revising procedures for calculating gravity anomalies, taking into account our enhanced computational power, improved terrain databases and datums, and increased interest in more accurately defining long-wavelength anomaly components. Users of the databases may note minor differences between previous and revised database values as a result of these procedures. Generally, the differences do not impact the interpretation of local anomalies but do improve regional anomaly studies. The most striking revision is the use of the internationally accepted terrestrial ellipsoid for the height datum of gravity stations rather than the conventionally used geoid or sea level. Principal facts of gravity observations and anomalies based on both revised and previous procedures together with germane metadata will be available on an interactive Web-based data system as well as from national agencies and data centers. The use of the revised procedures is encouraged for gravity data reduction because of the widespread use of the global positioning system in gravity fieldwork and the need for increased accuracy and precision of anomalies and consistency with North American and national databases. Anomalies based on the revised standards should be preceded by the adjective “ellipsoidal” to differentiate anomalies calculated using heights with respect to the ellipsoid from those based on conventional elevations referenced to the geoid.

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The experimental geoid 2020 – the first joint geoid model for the North American and Pacific Geopotential Datum

10.5194/egusphere-egu21-6011 ◽

2021 ◽

Author(s):

Yan Ming Wang ◽

Xiaopeng Li ◽

Kevin Ahlgren ◽

Jordan Krcmaric ◽

Ryan Hardy ◽

...

Keyword(s):

North American ◽

Gravity Data ◽

The United States ◽

Geodetic Survey ◽

Airborne Gravity ◽

Data Sets ◽

National Geodetic Survey ◽

Geoid Model ◽

Satellite Gravity ◽

The North

<p>For the upcoming North American-Pacific Geopotential Datum of 2022, the National Geodetic Survey (NGS), the Canadian Geodetic Survey (CGS) and the&#160;National Institute of Statistics and Geography of Mexico (INEGI) computed the first joint experimental gravimetric geoid model (xGEOID) on 1&#8217;x1&#8217; grids that covers a region bordered by latitude 0 to 85 degree, longitude 180 to 350 degree east.&#160;xGEOID20 models are computed using terrestrial gravity data, the latest satellite gravity model GOCO06S, altimetric gravity data DTU15, and an additional nine airborne gravity blocks of the GRAV-D project, for a total of 63 blocks. In addition, a digital elevation model in a 3&#8221; grid was produced by combining MERIT, TanDEM-X, and USGS-NED and used for the topographic/gravimetric reductions. The geoid models computed from the height anomalies (NGS) and from the Helmert-Stokes scheme (CGS) were combined using two different weighting schemes, then evaluated against the independent GPS/leveling data sets. The models perform in a very similar way, and the geoid comparisons with the most accurate Geoid Slope Validation Surveys (GSVS) from 2011, 2014 and 2017 indicate that the&#160;relative geoid accuracy&#160;could be around 1-2 cm baseline lengths up to 300 km for these GSVS lines in the United States. The xGEOID20 A/B models were selected from the combined models based on the validation results. The geoid accuracies were also estimated using the forward modeling.</p>

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Ophiolitic basement to the Great Valley forearc basin, California, from seismic and gravity data: Implications for crustal growth at the North American continental margin

Geological Society of America Bulletin ◽

10.1130/0016-7606(1997)109<1536:obttgv>2.3.co;2 ◽

1997 ◽

Vol 109 (12) ◽

pp. 1536-1562 ◽

Cited By ~ 64

Author(s):

N. J. Godfrey ◽

B. C. Beaudoin ◽

S. L. Klemperer

Keyword(s):

Continental Margin ◽

North American ◽

Gravity Data ◽

Crustal Growth ◽

Forearc Basin ◽

The North ◽

Great Valley

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PRECISE LEVELLING DATA PROCESSING NEAR TERRACED LANDFORMS

Geodesy and Cartography ◽

10.3846/20296991.2014.930247 ◽

2014 ◽

Vol 40 (2) ◽

pp. 51-57

Author(s):

Silja Talvik

Keyword(s):

Data Processing ◽

Gravity Field ◽

Field Gradient ◽

Information Needs ◽

Gravity Data ◽

Precise Levelling ◽

The North ◽

Gravity Database ◽

The Given

Precise levelling results are affected by the Earth’s gravity field, especially in areas of abrupt changes of landscape, such as terraced landforms. To eliminate the effect of the gravity field gradient, corrections need to be used in precise levelling data processing. To estimate the expected range of the correction due to the gravity field gradient (here called the gravimetric correction) within a region of terraced landforms, an experiment was proceeded in Estonia. Gravity data together with GNSS coordinates were acquired in 2011 in an area where a levelling section crosses the North Estonian Klint (height difference of 30 m within the levelling section). The gravimetric correction for the given 300 m long section proved to be 1.2 mm. Practically the same correction value can be obtained using interpolation of existing gravity data. However, in the case study area the gravity database had an extremely good quality which may not be the case elsewhere in which case gravimetric information needs to be collected alongside levelling. In height network calculations it is important to note that in such challenging areas all points should obtain their height values from an adjustment or from a point on the same side of a terrace, otherwise errors in heights may be as large as the gravimetric correction across the terrace.

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