Geoid Determination and Gravity Works in Nepal

2018 ◽  
Vol 17 (1) ◽  
pp. 7-15
Author(s):  
Niraj Manandhar ◽  
Shanker K.C.
Keyword(s):  
Gravity Anomalies ◽  
Satellite Orbit ◽  
Surface Gravity ◽  
Gravity Measurement ◽  
Airborne Gravity ◽  
Geopotential Model ◽  
Geoidal Undulation ◽  
Factors Affecting ◽  
Gravity Observation ◽  
Best Fit

Gravimetric geoid plays the important role in the process of local/regional geoidal undulation determination. This approach uses the residual gravity anomalies determined by the surface gravity measurement using the gravimeter together with best fit geopotential model, with the geoid undulations over the oceans determined from the method of satellite altimetry. Mass distribution, position and elevation are prominent factors affecting the surface gravity. These information in combination with geopotential model helps in satellite orbit determination, oil, mineral and gas exploration supporting in the national economy. The preliminary geoid thus computed using airborne gravity and other surface gravity observation and the accuracy of computed geoid was likely at the 10-20cm in the interior of Nepal but higher near the border due to lack of data in China and India. The geoid thus defined is significantly improved relative to EGM –08 geoid.

Reply by the author to N. C. Steenland

Geophysics ◽  
1984 ◽  
Vol 49 (3) ◽  
pp. 311-311
Author(s):  
Sigmund Hammer
Keyword(s):  
Standard Deviation ◽  
Data Processing ◽  
Gravity Anomalies ◽  
Probable Error ◽  
Resolving Power ◽  
Gravity Measurement ◽  
Airborne Gravity ◽  
Implicit Assumption ◽  
Grid System ◽  
Gravity Method

Dr. Steenland’s principal criticism arises from an unfortunate overstatement, in my paper, of the precision and anomaly resolving power of the Carson Airborne Gravity method. This criticism is well deserved. My calculation of the probable error of an airborne gravity measurement was based on many thousands of Δg gravity differences at grid‐line intersections, but it made the implicit assumption that the two reported gravity values at each grid intersection were independent. This is incorrect because the grid system of intersection differences is used for controls in the data processing. A realistic value for the probable error of an airborne gravity measurement is of the order of 1 mgal (standard deviation of 1.5 mgal). The associated resolving power for gravity anomalies, above this magnitude, is of the order of 2 to 3 miles (3 to 5 km) at flight speed of 50 knots. Smaller anomalies may be resolved at lower speeds.

scholarly journals Accuracy assessment of test flights using the Turnkey Airborne Gravity System over Alabama in 2008

2013 ◽  
Vol 3 (2) ◽  
pp. 136-142 ◽  
Author(s):  
Y.M. Wang ◽  
S. Preaux ◽  
T. Diehl ◽  
V. Childers ◽  
D. Roman ◽  
...  
Keyword(s):  
Gravity Data ◽  
Gravity Anomalies ◽  
Gravity Models ◽  
Surface Gravity ◽  
Airborne Gravity ◽  
National Geodetic Survey ◽  
The Mean ◽  
The Impact ◽  
Gravity System ◽  
Better Than

AbstractThe National Geodetic Survey (NGS) performed a few test flights using Micro-g’s Turnkey Airborne Gravity System (TAGS) at altitude of 1700, 6300 and 11000 meters over Alabama in 2008. The cross-track spacing was 10 km for the two lower flights and 5 km for the highest flight. The test flights not only provided important information regarding the precision and accuracy of the TAGS but also revealed the impact of flight altitudes and track spacing on the collected gravity data. The gravity anomalies at three altitudes were modeled using 3-dimensional Fourier series, then compared at the three altitudes. The agreement was excellent - the gravity anomalies agree with each other from 1.4 to 3.3 mGal RMS at the three altitudes. When the bias was removed, the agreement was improved to better than 1.1 mGal. On the ground (h =0), the three gravity models agree from 1.9 to 3.8 mGal RMS. After removing the mean, the agreement improved to better than 1.7 mGal. Similar results were obtained in comparison with recent surface gravity which was of sub-mGal accuracy. The overall agreement between the downward continued airborne gravity and the surface gravity was better than 1.7 mGal after removing the mean values.As expected, the flight altitude had a direct impact on accuracy of the values of gravity downward continued to the Earth’s surface. The comparisons with terrestrial gravity show that gravity collected at 11000 m is having an accuracy of ±3 mGal on the ground. This accuracy is slightly worse than the other two altitudes most probably due to smaller signal/noise ratios and larger downward continuation effects. The RMS values of differences between the downward continued airborne gravity at altitude 1700 and 6300 meters and the surface gravity are 2.0 and 1.6 mGals, respectively. Based on these comparisons, airborne gravity data collected at altitudes below 6300 meters should result in accuracy better than ±2 mGals on the ground. Note, however, that the test area is flat and the accuracy of airborne gravity would likely be worse in more rugged mountainous regions.

scholarly journals Comparison of Gravity Anomalies from Recent Global Geopotential Models with Terrestrial Gravity and Airborne Gravity over Johor Region

2021 ◽  
Vol 13 (3) ◽  
Author(s):  
Shuib Rambat ◽  
◽  
Nazirah Mohamad Abdullah ◽  
Norehan Yaacob ◽  
Nor’ Azizi Othman ◽  
...  
Keyword(s):  
Rapid Development ◽  
Gravity Anomalies ◽  
Airborne Gravity ◽  
Geopotential Model ◽  
Class Model ◽  
Rock Composition ◽  
Earth’S Gravity Field ◽  
Global Geopotential Model ◽  
Satellite Technology ◽  
Geopotential Models

Gravity anomalies can yield an indirect but extremely useful picture of lateral changes in rock composition and structural patterns especially for rapid development area such as Johor region. The gravity anomalies can be derived from Global Geopotential Model (GGM) which is one of special product from the satellite technology that able to determine high accuracy of the earth’s gravity field. In this study, the gravity anomalies derived from recent GGM published by International Global Geopotential Model were compared with five other GGMs model that compromised either terrestrial or airborne or both to derive the gravity anomalies. In order to identify the best gravity model over the Johor region, two types of GGM class model has been selected for the comparisons which known as satellite only and combined class model. The result shows that the gravity anomalies de-rived from satellite only class model with up 300 spherical harmonic coefficients is the best fit model and can be used as a reference for the Johor region. The RSME for the recent GGM via satellite only were +/- 5.865 and +/- 3.347 mGal for terrestrial and airborne gravity anomalies respectively compared to other GGM.

Some factors affecting the growth of lotononis (Lotononis bainesii)

1971 ◽  
Vol 11 (48) ◽  
pp. 29 ◽  
Author(s):  
WW Bryan ◽  
JP Sharpe ◽  
KP Haydock
Keyword(s):  
Dry Matter ◽  
Detrimental Effect ◽  
Meteorological Parameters ◽  
Dry Matter Yield ◽  
Seasonal Fluctuations ◽  
Factors Affecting ◽  
Production Growth ◽  
Measurable Growth ◽  
Best Fit ◽  
Coastal Lowlands

On the coastal lowlands of South Queensland, Lotononis bainesii responded in dry matter yield and potassium content to increasing applications of potassium. It did not respond to additions of sulphur. Higher annual yields were obtained from cutting at 8 or 12 weeks than at 4 weeks. Continued frequent cutting had no permanent adverse effect as measured by a 12-week regrowth after treatments were discontinued. Yield was closely associated with radiation received, with a minimum of about 11,200 Langleys in a 4-week period being required for measurable growth, and radiation provided the best fit of meteorological parameters with seasonal fluctuations in production. Growth did not occur in winter and was not resumed in spring until the weekly mean minimum temperature reached 9�C. The detrimental effect of dense shade on lotononis is discussed.

scholarly journals Analysis of Factors Affecting Asynchronous RTK Positioning with GNSS Signals

2019 ◽  
Vol 11 (10) ◽  
pp. 1256
Author(s):  
Shu ◽  
Liu ◽  
Feng ◽  
Xu ◽  
Qian ◽  
...  
Keyword(s):  
Satellite Orbit ◽  
Latency Time ◽  
Short Baseline ◽  
Factors Affecting ◽  
Broadcast Ephemeris ◽  
Geo Satellites ◽  
Short Baselines ◽  
Broadcast Orbit ◽  
Different Characteristics ◽  
Clock Offset

For short baseline real-time kinematic (RTK) positioning, the atmosphere and broadcast ephemeris errors can be usually eliminated in double-differenced (DD) processing for synchronous observations. However, in the case of possible communication latency time, these errors may not be eliminated in DD treatments due to their variations during latency time. In addition, the time variation of these errors may present different characteristics among GPS, GLONASS, BDS, and GALILEO due to different satellite orbit and clock types. In this contribution, the formulas for studying the broadcast orbit and clock offset errors and atmosphere error in asynchronous RTK (ARTK) model is proposed, and comprehensive experimental analysis is performed to numerically show time variations of these errors and their impacts on RTK results from short-baselines among four systems. Compared with synchronous RTK, the degradation of position precision for ARTK can reach a few centimeters, but the accuracy degradation to a different degree by different systems. BDS and Galileo usually outperform GPS and GLONASS in ARTK due to the smaller variation of broadcast ephemeris error. The variation of broadcast orbit error is generally negligible compared with the variation of broadcast clock offset error for GPS, BDS, and Galileo. Specifically, for a month of data, the root mean square (RMS) values for the variation of broadcast ephemeris error over 15 seconds are 11.2, 16.9, 7.3, and 3.0 mm for GPS, GLONASS, BDS, and Galileo, respectively. The variation of ionosphere error for some satellites over 15 seconds can reach a few centimeters during active sessions under a normal ionosphere day. In addition, compared with other systems, BDS ARTK shows an advantage under high ionosphere activity, and such advantage may be attributed to five GEO satellites in the BDS constellation.

Coastal Gravity Anomalies from Retracked Geosat/GM Altimetry: Improvement, Limitation and the Role of Airborne Gravity Data

2006 ◽  
Vol 80 (4) ◽  
pp. 204-216 ◽  
Author(s):  
Cheinway Hwang ◽  
Jinyun Guo ◽  
Xiaoli Deng ◽  
Hsin-Ying Hsu ◽  
Yuting Liu
Keyword(s):  
Gravity Data ◽  
Gravity Anomalies ◽  
Airborne Gravity
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