فصلنامه فیزیک زمین و فضا
سال سی و پنجم شماره 2 (تابستان 1388)

Wavelet transform is one of the useful and suitable tools for time series and signal analysis. Nowadays wavelet transform is frequently used in geophysical data processing and interpretation, especially seismic data. However, the use of this method isn’t widespread in gravity and geomagnetic. Fedi and Quarta (1998), Martelet et al. (2001) and de Oliveira Lyrio (2004) used the wavelet transform for processing and interpretation of the potential field data. In this paper, a new method based on continuous wavelet transform for determination of depth and location of gravity anomalies is introduced. Continuous Wavelet Transform and Gravity Source Identification: All of the time-frequency or time-scale transforms intend to show how the energy of a signal is distributed in time-frequency or time-scale plan. The Continuous Wavelet Transform (CWT) maps the time (space) domain signal into the time (space)-scale plan. The CWT of a signal is defined as the convolution of signal with a translated and scaled wavelet (Equation (1)).

method for deformation computation based on strain tensor elements, as an alternative to the usual way of application of gradient of displacement vector, is proposed. The method computes directly the strain tensor elements from the computed/observed changes in distances and angles between the stations of a geodetic network in two epochs of observations. Displacement vector which is determined from the coordinate differences with respect to “reference” and “current” states depends on the definition of coordinate system and as such can not be considered as suitable measure of deformation. On the contrary from strain tensor invariant parameters like “dilatation” and “maximum shear” can be computed which allow correct interpretation of deformation. The strain tensor can be derived from the difference between line elements of a massive body in the reference and current states as follows:

Gravity Recovery and Climate Experiment (GRACE) satellite gravimetry mission launched in March 2002 based on its twin gravimetric satellites makes application of both High-Low (HL) and Law-Low (LL) gravimetric techniques possible. The LL is based on Satellite-to-Satellite Tracking (SST) via the one way two frequencies K-Band-Ranging between the two GRACE satellites. As a result of combination of LL and HL structures via geodesy community following gravity observables are developed: (1) Potential Difference between the two GRACE satellites based on Line of Sight (LOS) velocity using energy integral method. (2) Projection of the gravitational acceleration difference of the two GRACE satellites along the LOS, using LOS acceleration. The latter observable which can provide finer details is one of the important observation quantities of the GRACE mission. Application of this observable as a boundary data for local and regional modeling of the Earth’s gravity field provides valuable information about short and medium wavelength spectrums of the field.

Geospatial Information System (GIS) has emerged as a very powerful tool for capturing, storing, analyzing, managing, and presenting data that is linked to location. The location information, which is usually obtained from existing maps or the Global Positioning Systems (GPS), refers to different coordinate and map projection systems. Therefore, unification of the coordinate and mapping systems of the spatial information is absolutely necessary before any data processing in a GIS system. In the classical approach, coordinate transformation among different map projection systems is performed via the reference geodetic ellipsoids. The transformation is possible if the reference ellipsoids and their corresponding datum definition parameters are known. In many cases, implementation of the classical approach is impossible due to lack of information. Herein, we introduce an innovative approach for coordinate transformation which is completely datum-independent. It is based on the mathematical relationship between the coordinate systems. From mathematical point of view, two functions mathematically define the relationship between the horizontal coordinates in two systems. For simplicity, two polynomial functions are employed. The optimal degree of the polynomials and the unknown coefficients can be determined using the common points in two systems

Sea Surface Topography (SST) by definition is the separation between the geoid and the Mean Sea Level (MSL). The separation between the geoid and MSL is caused by various non-gravitational physical effects. If determination of the geoid as the zero point of the height systems from the tide gauge observation be the goal, it is necessary that the affect of the physical effect be precisely computed and removed from MSL. One of the methods used for the study of physical response of a system to environmental effects in time domain is the “local response with weight function” or “impact response function” technique. The aforementioned function reveals the point-wise relation between the input and output of the physical system of interest, and in this way makes the point-wise modeling of the local variations of the system possible. In this study the weighted local response technique is used for SST computations in four tide gauge stations along the Persian Gulf, namely Shahid-Rajai Port, Kangan Port, Bushehr Port, Imam-Hasan Harbor, as well as the related meteorological stations. According to the numerical results, SST within the winter time in the studied stations varies between -82cm (in Bushehr Port) to +2cm (in Shahid-Rajai Port). The maximum SST value in Bushehr Port shows the reduction of the mean Persian Gulf level, while the minimum value of SST in Shahid-Rajai Port shows the rise of sea level due to SST in that area. This result is also in agreement with the geographical location of the two stations. Shahid-Rajai port being closer to the Oman Sea is dominantly affected by the topography of the Oman Sea and sea incoming currents to the Persian Gulf from the Oman Sea. Bushehr Port is farther away from the Oman Sea and as such is less affected by the Oman Sea currents. This finding is also reported in the previous studies over the region. Therefore, it can be concluded that SST computation using weighted local response technique is sufficienty accurate for the computation of SST and specially SST difference between the tide gauge stations.

Mixed layer is a part of the atmospheric boundary layer in which pollutants are uniformly distributed. It is sensitive to the Earth’s surface, controls the flow of heat and momentum between the surface and the free atmosphere, thus playing a key role in atmospheric circulation. Most of atmospheric pollution models require the height of the mixed layer as an input to determine the depth of atmosphere through which surface emitted pollutants are well mixed. Thus, the study of the depth variation of this layer is important in the spatial and temporal distribution of air pollution. This can be estimated from direct measurement and also from numerical forecasting models (such as MM5) with a proper boundary layer scheme

In this paper, seasonal and diurnal variation of pollutants and the relation between meteorological parameters and the amount of pollutant concentrations is investigated. The data used were obtained from the Air Quality Department of the Municipality and from the synoptic station of the Institute of Geophysics. In this survey, the data used are from 2004 to 2007. The result of survey for seasonal variation of pollutants showed that for CO, NO2 and PM-10, two maxima exist one of which occurs in summer and the other in winter, the maximum of SO2 is in winter and the maximum of O3 occurs in spring. The existence of maximum in winter may be from increasing consumption of fuels in thermal sources, besides meteorological conditions like increased air pressure, stability and temperature inversion. Maximum in summer may be from various factors like surface temperature inversion and decreased precipitation. In October, often because of the reopening of schools and universities, and the consequent increased traffic, a temporary rise in the quantity of pollutants. The increased ozone production of photochemical reactions in spring and summer can be one of the effective factors for the existence of an ozone maximum in these seasons. Increased dry air in summer can help to raise PM-10 concentration in this season.

Determination of waves and the pattern of coastal currents is the first step in finding the effective physical factors on marine environments and coastal regions. Moreover, wave induced currents play important roles in the determination of geometry and shape of coasts. In this research, patterns of longshore currents are simulated for situations before and after construction of jetties on the mouth of the Kiashahr lagoon. Construction of jetties may lead to change in the pattern of coastal currents not only near the entrance of the lagoon, but also in the adjacent areas. Therefore, a precise study is necessary to understand and prevent the possible impact of the jetties on the study area. For this purpose, MIKE 21 software package was used to simulate patterns of longshore currents before and after construction of the jetties. The field measurements in the Kiashahr coastal area are also used for calibration of the model parameters. Besides, the results of this study can be used for other related research works on sediment transport, water quality, etc. in the study area.

A microgravity survey was conducted for detecting the sink-holes at site of a power plant. Pits, man-made tunnels and canals were considered as topographical effects and were corrected. To show the capability of the method two sites in a power plant have been surveyed for existing areas which can be affected by sink-holes overnight. Ground shakes due to the running facilities were also preventing us from taking a calm measurement. Despite all unwanted factors at site, we could delineate the sink holes quite accurately. The depth of and the shape of these anomalies have been modeled by 3-D inversion of micro-gravity data.

A new method derived by Salem et al. (2004) for interpretation of gravity and magnetic anomalies is used to determine the depth and shape factor of the gravity anomalies. The depth and shape factor of some rectangular prisms as synthetic models are estimated using the method. The gravity effects of the models are contaminated with some random noise and then the parameters of the models are extracted through the erroneous data. A field example is interpreted and the depth and shape factor of the main anomaly has also been estimated through the method.