scholarly journals Pre and post Mount Merapi eruption of free air anomaly in 2010

2018 ◽  
Author(s):  
Rina Dwi Indriana
Keyword(s):  
Free Air ◽  
Free Air Anomaly

Airborne gravity measurements over mountainous areas by using a LaCoste & Romberg air‐sea gravity meter

Geophysics ◽  
2002 ◽  
Vol 67 (3) ◽  
pp. 807-816 ◽  
Author(s):  
Jérôme Verdun ◽  
Roger Bayer ◽  
Emile E. Klingelé ◽  
Marc Cocard ◽  
Alain Geiger ◽  
...  
Keyword(s):  
Data Reduction ◽  
Classical Method ◽  
Gravity Data ◽  
Airborne Gravity ◽  
Mountainous Area ◽  
Vertical Acceleration ◽  
Mountainous Areas ◽  
Free Air ◽  
Gravity Measurements ◽  
Free Air Anomaly

This paper introduces a new approach to airborne gravity data reduction well‐suited for surveys flown at high altitude with respect to gravity sources (mountainous areas). Classical technique is reviewed and illustrated in taking advantage of airborne gravity measurements performed over the western French Alps by using a LaCoste & Romberg air‐sea gravity meter. The part of nongravitational vertical accelerations correlated with gravity meter measurements are investigated with the help of coherence spectra. Beam velocity has proved to be strikingly correlated with vertical acceleration of the aircraft. This finding is theoretically argued by solving the equation of the gravimetric system (gravity meter and stabilized platform). The transfer function of the system is derived, and a new formulation of airborne gravity data reduction, which takes care of the sensitive response of spring tension to observable gravity field wavelengths, is given. The resulting gravity signal exhibits a residual noise caused by electronic devices and short‐wavelength Eötvös effects. The use of dedicated exponential filters gives us a way to eliminate these high‐frequency effects. Examples of the resulting free‐air anomaly at 5100‐m altitude along one particular profile are given and compared with free‐air anomaly deduced from the classical method for processing airborne gravity data, and with upward‐continued ground gravity data. The well‐known trade‐off between accuracy and resolution is discussed in the context of a mountainous area.

Free Air Anomaly Map of Canada from Piece-Wise Surface Fittings Over Half-Degree Blocks

1973 ◽  
Vol 27 (4) ◽  
pp. 293-300 ◽  
Author(s):  
Dezsö Nagy
Keyword(s):  
Gravity Anomaly ◽  
Extreme Values ◽  
Free Air ◽  
Equivalent Length ◽  
Order Polynomial ◽  
Standard Deviations ◽  
Anomaly Map ◽  
Half Degree ◽  
Free Air Anomaly ◽  
Polynomial Surface

The region of Canada, which has been covered by gravity surveys (including 1970 data), has been subdivided into 2,923 surface elements of sides of a half-degree along the meridian and approximately equivalent length along the parallels. The gravity anomaly at the center of each element was estimated by fitting a low-order polynomial surface to the free air anomalies within each element. The extreme values are —160 and 96 milligals, with over 85 per cent of the anomalies being in the range of —40 and 20 milligals. About two thirds of all computed anomalies are estimated to have standard deviations less than ±10 milligals.

scholarly journals GRAVIMETRIC GEOID MODELLING OVER PENINSULAR MALAYSIA USING TWO DIFFERENT GRIDDING APPROACHES FOR COMBINING FREE AIR ANOMALY

2019 ◽  
Vol XLII-4/W16 ◽  
pp. 515-522
Author(s):  
M. F. Pa’suya ◽  
A. H. M. Din ◽  
J. C. McCubbine ◽  
A. H. Omar ◽  
Z. M. Amin ◽  
...  
Keyword(s):  
Gravity Data ◽  
Reference Signal ◽  
Digital Terrain Model ◽  
Peninsular Malaysia ◽  
Airborne Gravity ◽  
Geopotential Model ◽  
Gravimetric Geoid ◽  
Geoid Model ◽  
Free Air ◽  
Free Air Anomaly

Abstract. We investigate the use of the KTH Method to compute gravimetric geoid models of Malaysian Peninsular and the effect of two differing strategies to combine and interpolate terrestrial, marine DTU17 free air gravity anomaly data at regular grid nodes. Gravimetric geoid models were produced for both free air anomaly grids using the GOCE-only geopotential model GGM GO_CONS_GCF_2_SPW_R4 as the long wavelength reference signal and high-resolution TanDEM-X global digital terrain model. The geoid models were analyzed to assess how the different gridding strategies impact the gravimetric geoid over Malaysian Peninsular by comparing themto 172 GNSS-levelling derived geoid undulations. The RMSE of the two sets of gravimetric geoid model / GNSS-levelling residuals differed by approx. 26.2 mm. When a 4-parameter fit is used, the difference between the RMSE of the residuals reduced to 8 mm. The geoid models shown here do not include the latest airborne gravity data used in the computation of the official gravimetric geoid for the Malaysian Peninsular, for this reason they are not as precise.

scholarly journals Subsurface geological model of Malay basin using free air anomaly

2021 ◽  
Vol 880 (1) ◽  
pp. 012007
Author(s):  
Chia Jing Hwee ◽  
Farouq Jamil ◽  
Akhmal Sidek ◽  
Zaidi Jaafar ◽  
Radzuan Junin ◽  
...  
Keyword(s):  
Positive Anomaly ◽  
Intelligence Agency ◽  
Salt Domes ◽  
Free Air ◽  
Geological Features ◽  
3D Euler Deconvolution ◽  
Elevation Correction ◽  
Basement Depth ◽  
Free Air Anomaly ◽  
Modelling Process

Abstract The aim of gravity survey is to assist in the detection and delineation of subsurface geological features such as salt domes and faults. In this study, free air anomaly (FAA) data was adopted for mapping and modelling process to delineate subsurface geological features and basement depth in Malay Basin. FAA is the measured gravity anomaly after a free air correction is applied, and it is used for elevation correction. The data of FAA in this study is obtained from Earth Gravitational Model (EGM) 2008 released by the National Geospatial-Intelligence Agency (NGA)-EGM Development Team. Oasis Montaj software was used in the mapping and modelling process whereby the base map which constructed by the Oasis Montaj is used to form the FAA map of Malay Basin. Typically, the positive anomaly is associated with the high-density intrusion at the base of the crust, while in contrast (negative anomaly), it is related to the sedimentary basin in the upper crust. On top of that, the regional-residual anomaly, total horizontal derivative (THD) and 3D Euler Deconvolution enhanced maps were produced and interpreted to acquire comprehensive insight of subsurface geological features. To conclude, this study showed 5% deviation as compared to previous reported works and the deepest basement depth encountered is 14.5 km.

INTERPRETASI BAWAH PERMUKAAN GUNUNG ANAK RANAKAH DENGAN PEMODELAN DUA DIMENSI (2D) BERDASARKAN DATA ANOMALI GRAVITASI LOKAL

2018 ◽  
Vol 3 (1) ◽  
pp. 54-58
Author(s):  
Godensius Tematur ◽  
Jehunias L. Tanesib ◽  
Redi K. Pingak
Keyword(s):  
Continuation Method ◽  
Atmospheric Correction ◽  
Bouguer Anomaly ◽  
Geophysical Research ◽  
Subsurface Geology ◽  
Dimensional Modeling ◽  
Free Air ◽  
Geological Conditions ◽  
Free Air Anomaly ◽  
Surrounding Areas

ABSTRAK Penelitian geofisika dengan menggunakan metode gravitasi telah dilakukan di Gunung Anak Ranakah dan sekitarnya di kabupaten Manggarai Nusa Tenggara Timur pada bulan Juni sampai dengan bulan Juli 2016. Penelitian ini bertujuan untuk mengetahui kondisi geologi bawah permukaan daerah penelitian dengan menggunakan data anomali udara bebas dari Sandwell dan Smith 2016. Data tersebut direduksi dengan koreksi atmosfer, koreksi Bouguer Sederhana, dan koreksi kurvatur hingga memperoleh anomali Bouguer Lengkap. Data anomali Bouguer dibawa ke bawah bidang topografi dengan metode kontinuasi ke bawah sedalam 300 m menggunakan program Magpic. Selanjutnya dilakukan pemodelan 2 dimensi menggunakan program Grav2DC. Hasil yang diperoleh menunjukkan bahwa kondisi geologi bawah permukaan gunung Anak Ranakah dan Sekitarnya didominasi oleh batuan basalt (densitas 2,70 -3.30 ), andesit (densitas 2.4 -2.8 ), dan soil (densitas 1.2 -2.40 ). Kata kunci: Anomali Gravitasi, Pemodelan 2D, Gunung Anak Ranakah ABSTRACT Geophysical research by using the gravity method has been carried out on the Ranakah child mountain and surrounding areas in Manggarai Regency of East Nusa Tenggara in June until July 2016. This research aims to know the condition of the subsurface geology of the area of research using the free air anomaly data from Sandwell and Smith 2016. The data are reduced by atmospheric correction, Simple Bouguer correction, and the correction of curvature to obtain complete Bouguer anomalies. Bouguer anomaly data brought down the field topography with continuation method down as deep as 300 m using the Magpic. Then, 2 dimensional modeling is done using the Grav2DC. The results obtained show that the geological conditions under the surface of the Ranakah Child mountaoin and its surrounding area was dominated by basalt rocks (density of ), andesite (density of ), and soil rocks (density of ). Keywords: Gravity Anomaly, 2D Modelling, Ranakah child Mountain.

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