Broad-band calibration of marine seismic sources used by R/V Polarstern for academic research in polar regions     

Monika Breitzke  Olaf Boebel  Saad El Naggar  Wilfried Jokat  Berthold Werner 《Geophysical Journal International》2008,174(2):505-524

Air guns and air-gun arrays of different volumes are used for scientific seismic surveys with R/V Polarstern in polar regions. To assess the potential risk of these research activities on marine mammal populations, knowledge of the sound pressure field of the seismic sources is essential. Therefore, a broad-band (0–80 kHz) calibration study was conducted at the Heggernes Acoustic Range, Norway. A GI (2.4 l), a G (8.5 l) and a Bolt gun (32.8 l) were deployed as single sources, 3 GI (7.4 l), 3 G (25.6 l) and 8 VLF™ Prakla-Seismos air guns (24.0 l) as arrays. Each configuration was fired along a line of 3–4 km length running between two hydrophone chains with receivers in 35, 100, 198 and 263 m depth. Peak-to-peak, zero-to-peak, rms and sound exposure levels (SEL) were analysed as functions of range. They show the typical dipole-like directivity of marine seismic sources with amplitude cancellation close to the sea surface, higher amplitudes in greater depths, and sound pressure levels which continuously decrease with range. Levels recorded during the approach are lower than during the departure indicating a shadowing effect of Polarsterns's hull. Backcalculated zero-to-peak source levels range from 224–240 dB re 1 μPa @ 1 m. Spectral source levels are highest below 100 Hz and amount to 182–194 dB re 1 μPa Hz^–1. They drop off continuously with range and frequency. At 1 kHz they are ∼30 dB, at 80 kHz ∼60 dB lower than the peak level. Above 1 kHz amplitude spectra are dominated by Polarstern's self-noise. From the rms and sound exposure levels of the deepest hydrophone radii for different thresholds are derived. For a 180 dB rms-level threshold radii maximally vary between 200 and 600 m, for a 186 dB SEL threshold between 50 and 300 m.  相似文献   

Some Limnological Studies on the Lower Reaches of Tigris and Euphrates,Iraq     

M. A. H. Saad 《洁净——土壤、空气、水》1978,6(6):529-539

Some physical and chemical investigations of the lower reaches of Tigris and Euphrates as well as the upper reaches of Shatt al-Arab in Iraq were studied. The transparency showed local and seasonal variations. The Secchi values were markedly low due to the relative turbidity of Tigris and the maximum Secchi-disc values observed coincide with more sedimentation in Euphrates. The lowest Secchi values registered in April are attributed to the considerable increase in the amounts of suspended matter carried by the floods of the rivers. The slight decrease of water temperature with depth is related to the mixing processes. Considerable seasonal variations of air and water temperatures were observed. The lowest temperatures were recorded in January (winter) and the highest in August (summer). The temperatures gave considerably high values in April and October, since the region studied lies within an arid climate. Seasonal variations of pH were recorded and attributed to physical and biological changes in the region studied. The relatively high average pH values found in August and October give a good evidence for the phytoplankton abundance under better environmental conditions. The increase of the chlorosity content at the stations A, B, II and IV is mainly due to the effect of the brackish water from Hor Hammar on these localities. The dissolved oxygen showed remarkable seasonal variations and gave the highest average values in January and the lowest in August. It was concluded that the source of dissolved oxygen in the region studied is more related to the atmosphere than the photosynthetic activity, and the mixing processes as well as the water temperatures are the main factors affecting its concentration and distribution. The results obtained show strongly that the water characteristics at the stations I, II and III were different. This is a clear evidence that Tigris joins Euphrates at Qurna forming Shatt al-Arab.  相似文献   

New chord formulae     

Saad Bolbol 《Journal of Geodynamics》1987,7(3-4)

This paper introduces a formula for computing the chood distance between two points on a reference ellipsoid. The coordinates of the terminals are in terms of latitude and longitude. The accuracy of the formula is tested against the geodesic and the normal section formulae.  相似文献   

Status of nutrients in Lake Mariut,a delta lake in Egypt suffering from intensive pollution     

Massoud A.H. Saad  O.A. El-Rayis  H.H. Ahdy 《Marine pollution bulletin》1984,15(11):408-411

Levels of dissolved ammonia, nitrite, nitrate, phosphate and silicate, as well as chlorosity, dissolved oxygen and hydrogen sulphide in the water of Lake Mariut have been investigated over a year. This shallow brackish-water lake, situated south of Alexandria, suffers from intense pollution. Two different water bodies can be distinguished in Lake Mariut. One, occupying the eastern side of the lake, is affected by sewage and industrial waste disposal, as well as discharge of highly polluted water from Qalaa Drain. The water in this region, which had lower regional average chlorosity values, contained abnormal higher concentrations of phosphate and nitrogenous salts in the presence of H₂S. The western side was always oxic and showed higher average values of chlorosity. This western region contained lower concentrations of phosphate and nitrogenous salts, due to the influence of the relatively clean water from Umum Drain. The principal source of silicon for Lake Mariut is agricultural drainage. The annual average concentrations of phosphate and nitrogenous salts in this lake were considerably higher than those in the neighbouring comparatively less polluted Nozha Hydrodrome.  相似文献   

Reply to the Discussion by Shahid Azam on “Aiban, SA (2006) Compressibility and swelling characteristics of Al-Khobar Palygorskite, eastern Saudi Arabia, Engineering Geology 87(3–4):205–219”     

Saad A. Aiban   《Engineering Geology》2007,92(3-4):173-180

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Particle transfer in decelerating regions     

E. A. Saad  A. Hendi 《Astrophysics and Space Science》1984,107(1):1-9

Equations connecting the transmission and reflection functions of a finite medium to the reflection function of a semi-infinite one are used to get the albedos in the slowing-down region. The transport equation is solved by the modified Eddington method using Fermi's backward-forward scattering model, modulated to allow for different orders of backward-forward and isotropic scattering. Numerical results for the energy albedos are obtained and compared.On leave of absence from Atomic Energy Center, Inchass, Egypt.  相似文献   

Linear regression models for estimating true subsurface resistivity from apparent resistivity data     

Sabiu Bala Muhammad  Rosli Saad 《Journal of Earth System Science》2018,127(5):64

Simple linear regression (SLR) models for rapid estimation of true subsurface resistivity from apparent resistivity measurements are developed and assessed in this study. The objective is to minimize the processing time and computer memory required to carry out inversion with conventional algorithms. The arrays considered are Wenner, Wenner–Schlumberger and dipole–dipole. The parameters investigated are apparent resistivity (\(\rho _a \)) and true resistivity (\(\rho _t\)) as independent and dependent variables, respectively. For the fact that subsurface resistivity is nonlinear, the datasets were first transformed into logarithmic scale to satisfy the basic regression assumptions. Three models, one each for the three array types, are thus developed based on simple linear relationships between the dependent and independent variables. The generated SLR coefficients were used to estimate \(\rho _t\) for different \(\rho _a\) datasets for validation. Accuracy of the models was assessed using coefficient of determination (\(R^{2})\), F-test, standard error (SE) and weighted mean absolute percentage error (wMAPE). The model calibration \(R^{2}\) and F-value are obtained as 0.75 and 2286, 0.63 and 1097, and 0.47 and 446 for the Wenner, Wenner–Schlumberger and dipole–dipole array models, respectively. The SE for calibration and validation are obtained as 0.12 and 0.13, 0.16 and 0.25, and 0.21 and 0.24 for the Wenner, Wenner–Schlumberger and dipole–dipole array models, respectively. Similarly, the wMAPE for calibration and validation are estimated as 3.27 and 3.49%, 3.88 and 5.72%, and 5.35 and 6.07% for the three array models, respectively. When compared with standard constraint least-squares (SCLS) inversion and Incomplete Gauss–Newton (IGN) algorithms, the SLR models were found to reduce about 80–96.5% of the processing time and memory space required to carry out the inversion with the SCLS algorithm. It is concluded that the SLR models can rapidly estimate \(\rho _t\) for the various arrays accurately.  相似文献   

Effect of Geological Structure on Flyrock Prediction in Construction Blasting     

Edy Tonnizam Mohamad  Chang Shiang Yi  Bhatawdekar Ramesh Murlidhar  Rosli Saad 《Geotechnical and Geological Engineering》2018,36(4):2217-2235

Blasting is sometimes inevitable in civil engineering work, to fragment the massive rock to enable excavation and leveling. In Minyak Beku, Batu Pahat also, blasting is implemented to fragment the rock mass, to reduce the in situ rock level to the required platform for a building construction. However, during blasting work, some rocks get an excessive amount of explosive energy and this energy may generate flyrock. An accident occurred on 15 July 2015 due to this phenomenon, in which one of the workers was killed and two other workers were seriously injured after being hit by the flyrock. The purpose of this study is to investigate the causes of the flyrock accidents through evaluation of rock mass geological structures. The discontinuities present on the rock face were analyzed, to study how they affected the projection and direction of the flyrock. Rock faces with lower mean joint spacing and larger apertures caused excessive flyrock. Based on the steoreonet analysis, it was found that slope failures also produced a significant effect on the direction, if the rock face failure lay in the critical zone area. Empirical models are often used to predict flyrock projection. In this study five empirical models are used to compare the incidents. It was found that none of the existing formulas could accurately predict flyrock distance. Analysis shows that the gap between predicted and actual flyrock can be reduced by including blast deign and geological conditions in forecasts. Analysis revealed only 69% of accuracy could be achieved if blast design is the only parameter to be considered in flyrock projection and the rest is influenced by the geological condition. Other causes of flyrock are discussed. Comparison of flyrock prediction with face bursting, cratering and rifling is carried out with recent prediction models.  相似文献   

<Emphasis Type="Italic">Integrated Remote Sensing and</Emphasis> Structural Analysis Studies of Tayyib Al-Ism Area,Northwestern Arabian Shield,Saudi Arabia     

Osama M. K. Kassem  Habes A. Ghrefat  Haider Zaman  Awni T. Batayneh  Saad Almogren  Yousef Nazzal  Eslam Elawadi 《Journal of the Indian Society of Remote Sensing》2016,44(1):91-99

Geological and structural mappings of Tayyib Al-Ism area were carried out using the rocks finite strain data, the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) data and the field based observations. To analyze the finite strain in the studied rocks, the R_f /? and Fry methods are applied to feldspar porphyroclasts and mafic grains from nine metavolcano-sedimentary samples (Hegaf Formation), four diorite-gabbros suite samples (Sawawin Complex), two meta-granite samples (Ifal suite) and five Zuhd alkali granite samples. The obtained data indicate traces of high to moderate level of deformation in the meta-granite and metavolcano-sedimentary rocks. The axial ratios along the XZ section range from 1.70 to 4.80 for the R_f/? method and from 1.50 to 4.50 for the Fry method. A sub-vertical trend of short axes in association with sub-horizontal foliation is also observed. These informations allow us to conclude that a finite strain in the deformed granitic rocks is of the same order of magnitude as in the metavolcano-sedimentary rocks. The contacts between the metavolcano-sedimentary and granitic rocks in Tayyib al Ism area were formed during the granitic intrusions along some of the faults under brittle to semi-ductile deformation conditions. These faults have significantly influenced the geometry and style of rifting in the Red Sea during the Neogene. The finite strain was accumulated in the area during the process of deformation, which superimpose the already existed nappe structure. It indicates that the nappe contacts formed during the accumulation of finite strain. In addition to finite strain analysis, band ratio images (3/1, 5/3, 7/5) and Principal Component Analysis (PCA) technique have been used, which proved effective in mapping geological and structural features of various rock bodies exposed in the study area.  相似文献   

An integrated geophysical study for inferring the subsurface setting of water-bearing aquifers: case study at Wadi al-Dawasir area,Saudi Arabia     

Abdulsalam Al Asmari  Saad Mogren  Aref Lashin  Mohamed Hussein  Fouzan Al Fouzan 《Environmental Earth Sciences》2016,75(12):1028

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