- Email: [email protected]
Mapping 137Cs at Maralinga nuclear test site, South Australia, using conventional 4-channel airborne gammaray spectrometry
72A
SITE INVESTIGATIONS:GEOPHYSICS
western haft of the Thor Lake Syenite, and the other forms a crescent-shaped feature within the Grace Lake Granite. These two anomalies are related to magnetite produced by alteration of ferromaguesian minerals. The electromagnetic patterns relate primarily to conductive lake bottom material and faults. (from Authors)
952200 Mapping l~nCs at Maralinga nuclear test site, South Australia, using conventional 4-channel airborne gammaray spectrometry B. R. S. Minty & R. C. Brodie, AGSO Journal of Australian Geology & Geophysics, 15(2), 1994, pp 217-222. A simple method has been developed for separating the gamma radiation due to 137Cs from that due to natural sources using conventional 4-channel airborne gamma-ray spectrometry. The method uses the fact that whilst the 137Cs photopeak falls within the conventional total-count window, it occurs well below the three windows used to monitor naturally present K, U and Th. The method maps the distribution of 13~Cs contamination in the vicinity of the Marafinga nuclear test site very effectively. (from Authors)
952201 Correlation filtering: a terrain correction method for aeromagnetic maps with application P. S. Naidu & M. P. Mathew, Journal of Applied Geophysics, 32(2-3), 1994, pp 269-277. Correlation filtering attempts to remove that component of the aeromaguetic field which is closely related to the topography. The magnetization vector is assumed to be spatially variable, but it can be successively estimated under the additional assumption that the magnetic component due to topography is uncorrelated with the magnetic signal of deeper origin. The filtered field compares very well with the known signal of deeper origin. This method was applied to real data from the south Indian shield. (Authors)
952202 A foidradar modszerfejlesztes mnsfei ELGI-ben
eves
tapnsztalatal az
(One and a half year experiences of ground penetrating radar applications in ELGI, Hungary) M. Pattantyus-A, B. Neducza, Z. S. Pronay & E. Toros, Magyar Geofizika, 35(1), 1994, pp 32-41. This paper gives a short view on the activity of ELGI in introducing GPR to domestic geophysical prospection and reviews the result of several field applications and of the development in data processing. (from English summary)
952204 Density in Bougner anomalies and its consequences M. Bernabini, P. Favaro & L. Orlando, Journal of Applied Geophysics, 32(2-3), 1994, pp 187-197. This paper e x a ~ n e s the density-induced errors which can result when calculating the Bonguer anomaly in areas of complex geology and morphology. In order to minimize the errors in such areas the authors suggest a procedure consisting of: 1) considering Bouguer anomalies at constant density; 2) interpreting them with 3-D models taking into account all geological bodies starting from ground surface. As an example the comparison between the usual procedures and the method proposed has been applied to a 50 x 50 km area in central Italy. (Authors)
952205 Terrain correction progrm for regional gravity surveys X. Q. Ma & D. R. Watts, Computers & Geosciences, 20(6), 1994, pp 961-972. An algorithm is presented for the computation of gravity terrain corrections from a digitized grid representing topography. Different approximations for topography at various distances from the gravity station are used to make the computation more efficient. A new method is used to compute the correction for the inner zone which is the digitized square where the gravity station is located. The gravity effect of topography in the inner zone is calculated from four triangular prisms with vertices made of the station location and the corners of the square. The computer program has been tested comprehensively with a regional gravity database from the Southern Uplands of Scotland. (from Authors)
952206 Analyses of wavefields by the common excitation array (CEA) method M. Bliznetsov & C. Juhlin, Journal of Applied Geophysics, 32(2-3), 1994, pp 245-256. There are a number of problems associated with the processing of seismic data acquired over crystalline rocks where velocities vary as much in the horizontal direction as in the vertical direction and near-surface low-velocity layers may distort the signals recorded on the surface. In addition, waves arriving at the same time but at different dips will interfere with one another thereby masking reflections of interest. By employing a series of closely spaced shotpoints in an array, quasi-planar waves emanating at different angles may be simulated through slant stacking. After slant stacking to illuminate interfaces of various dips, the major reflecting events may be picked automatically and the data quantity reduced to the time, slowness and amplitude of the picked events. These picked events can then be migrated onto a depth section image. The method is applied to seismic data from the Urals. (from Authors)
952203 Felhagyott melysegi banyamuveletek hatnsvizsgalata geo-
952207 Factor analysis of ambiquity in geophysics
flzikal modszerekkci (Prospecting for old mine workings by GPR and seismics) E. Gogh, M. Pattantyus-A, B. Neducza, E. Toros & L. Hermann, Magyar Geofizika, 35(1), 1994, pp 19-23.
S. G. C. Fraiha & J. B. C. Silva, Geophysics, 59(7), 1994, pp 1083-1091.
An integrated geophysical survey was carried out over an old mine. The site is to be built up but problems arose due to the unconsolidated zones and improperly bacidilled shafts of the mine. The method used were GPR, EM conductivity and resistivity profiling for detecting near surface features and seismics for detecting fractured or unconsolidated zones caused by old mine workings. (English summary)
The paper presents an empirical ambiguity analysis method based on a finite number of acceptable solutions that are representative of the ambiguity region. These solutions are submitted to a Q-mode factor analysis that indicates which parameters are ambiguous and their ambiguity range. A synthetic nonlinear example illustrates that the method is more effective than singular value decomposition analysis in producing an average trend of the ambiguity region. It requires less restrictive hypotheses and is more robust than
SITE INVESTIGATIONS:GEOPHYSICS
western haft of the Thor Lake Syenite, and the other forms a crescent-shaped feature within the Grace Lake Granite. These two anomalies are related to magnetite produced by alteration of ferromaguesian minerals. The electromagnetic patterns relate primarily to conductive lake bottom material and faults. (from Authors)
952200 Mapping l~nCs at Maralinga nuclear test site, South Australia, using conventional 4-channel airborne gammaray spectrometry B. R. S. Minty & R. C. Brodie, AGSO Journal of Australian Geology & Geophysics, 15(2), 1994, pp 217-222. A simple method has been developed for separating the gamma radiation due to 137Cs from that due to natural sources using conventional 4-channel airborne gamma-ray spectrometry. The method uses the fact that whilst the 137Cs photopeak falls within the conventional total-count window, it occurs well below the three windows used to monitor naturally present K, U and Th. The method maps the distribution of 13~Cs contamination in the vicinity of the Marafinga nuclear test site very effectively. (from Authors)
952201 Correlation filtering: a terrain correction method for aeromagnetic maps with application P. S. Naidu & M. P. Mathew, Journal of Applied Geophysics, 32(2-3), 1994, pp 269-277. Correlation filtering attempts to remove that component of the aeromaguetic field which is closely related to the topography. The magnetization vector is assumed to be spatially variable, but it can be successively estimated under the additional assumption that the magnetic component due to topography is uncorrelated with the magnetic signal of deeper origin. The filtered field compares very well with the known signal of deeper origin. This method was applied to real data from the south Indian shield. (Authors)
952202 A foidradar modszerfejlesztes mnsfei ELGI-ben
eves
tapnsztalatal az
(One and a half year experiences of ground penetrating radar applications in ELGI, Hungary) M. Pattantyus-A, B. Neducza, Z. S. Pronay & E. Toros, Magyar Geofizika, 35(1), 1994, pp 32-41. This paper gives a short view on the activity of ELGI in introducing GPR to domestic geophysical prospection and reviews the result of several field applications and of the development in data processing. (from English summary)
952204 Density in Bougner anomalies and its consequences M. Bernabini, P. Favaro & L. Orlando, Journal of Applied Geophysics, 32(2-3), 1994, pp 187-197. This paper e x a ~ n e s the density-induced errors which can result when calculating the Bonguer anomaly in areas of complex geology and morphology. In order to minimize the errors in such areas the authors suggest a procedure consisting of: 1) considering Bouguer anomalies at constant density; 2) interpreting them with 3-D models taking into account all geological bodies starting from ground surface. As an example the comparison between the usual procedures and the method proposed has been applied to a 50 x 50 km area in central Italy. (Authors)
952205 Terrain correction progrm for regional gravity surveys X. Q. Ma & D. R. Watts, Computers & Geosciences, 20(6), 1994, pp 961-972. An algorithm is presented for the computation of gravity terrain corrections from a digitized grid representing topography. Different approximations for topography at various distances from the gravity station are used to make the computation more efficient. A new method is used to compute the correction for the inner zone which is the digitized square where the gravity station is located. The gravity effect of topography in the inner zone is calculated from four triangular prisms with vertices made of the station location and the corners of the square. The computer program has been tested comprehensively with a regional gravity database from the Southern Uplands of Scotland. (from Authors)
952206 Analyses of wavefields by the common excitation array (CEA) method M. Bliznetsov & C. Juhlin, Journal of Applied Geophysics, 32(2-3), 1994, pp 245-256. There are a number of problems associated with the processing of seismic data acquired over crystalline rocks where velocities vary as much in the horizontal direction as in the vertical direction and near-surface low-velocity layers may distort the signals recorded on the surface. In addition, waves arriving at the same time but at different dips will interfere with one another thereby masking reflections of interest. By employing a series of closely spaced shotpoints in an array, quasi-planar waves emanating at different angles may be simulated through slant stacking. After slant stacking to illuminate interfaces of various dips, the major reflecting events may be picked automatically and the data quantity reduced to the time, slowness and amplitude of the picked events. These picked events can then be migrated onto a depth section image. The method is applied to seismic data from the Urals. (from Authors)
952203 Felhagyott melysegi banyamuveletek hatnsvizsgalata geo-
952207 Factor analysis of ambiquity in geophysics
flzikal modszerekkci (Prospecting for old mine workings by GPR and seismics) E. Gogh, M. Pattantyus-A, B. Neducza, E. Toros & L. Hermann, Magyar Geofizika, 35(1), 1994, pp 19-23.
S. G. C. Fraiha & J. B. C. Silva, Geophysics, 59(7), 1994, pp 1083-1091.
An integrated geophysical survey was carried out over an old mine. The site is to be built up but problems arose due to the unconsolidated zones and improperly bacidilled shafts of the mine. The method used were GPR, EM conductivity and resistivity profiling for detecting near surface features and seismics for detecting fractured or unconsolidated zones caused by old mine workings. (English summary)
The paper presents an empirical ambiguity analysis method based on a finite number of acceptable solutions that are representative of the ambiguity region. These solutions are submitted to a Q-mode factor analysis that indicates which parameters are ambiguous and their ambiguity range. A synthetic nonlinear example illustrates that the method is more effective than singular value decomposition analysis in producing an average trend of the ambiguity region. It requires less restrictive hypotheses and is more robust than