Journal of the Earth and Space Physics
Year:2001 | Volume:27 | Issue:2|Papers Count:10

The study of variations of different ionospheric layers at the day of solar eclipse and the calculation of the recombination factor of electrons (α), were our aim. In this regard, the measurements were made with an ionospheric vertical sounding instrument at the interval 15 to I minutes at the control day and the day of solar eclipse. The ionospheric data extracted from the ionospheric records (ionograms) and electron density variations with height of the different layers were obtained based on the relation between electron density and frequency of the layers. Finally the recombination factor for F1 layer was calculated. The behaviors of the electron density variations indicate a rapid decrease of ionization of different ionospheric layers.

A great deal of attention has been paid to quantitative interpretation in recent years Two methods, namely the analytic signal an4 the Euler deconvolution (EULDPH) were discussed in this paper. After a short review on the mathematical bases of the methods. two field examples were used to examine the efficiency and limits of the methods when they are applied on a complex geology structure. These methods have already been applied to synthetic models and high - resolution data such as gradiometeric or microgravity data. Noisy gravity data especially in areas of complex geology has rarely been used by these methods and the field examples are exceptions. The low- resolution gravity data was used to provide with residual anomalies. Gravity gradients were generated ftom the residual anomaly values. Then applying the gravity gradients to the analytic signal and EULDPH methods. we determine the coordinates of a perturbing body in the field of data. Two field examples, one in the west of Tehran (Mardabad) and another in the southwest of Iran are considered. In the first field we were to determine the location of a hydrocarbon density anomaly. In the second field, we were to determine a Choromit anomaly.

In the present study seismic data was carried out at Bibi -Shahr Banoo mountainous area located in Shar-e-Ray south-east of Tehran to estimate amplification of seismic waves. For this purpose microtremors and explosion generated waves were acquired. The layout of three recording stations was arranged along a profile. Microtremors were recorded after midnight with time interval of 30 minutes; record length for each interval was 2 minutes. Explosion charges were about 120 kg of dynamite, and 850 kg of amfo. Three Protable Data Acquisition System (PDAS 100) recording stations along a profile with interval of 50 to 150 meters were deployed to record the seismic waves. Data was processed using Digital Signal Processing (DSP) software. Then the classical Spectrum ratio and Nakamura"s ratio methods have been evaluated. It should be noted that, all obtained results are reliable in frequency range of 0 to 10 Hertz. The obtained results were classified in four stages as follows: Microtremors: obtained amplification factor, in average, from two recording stations using Nakamura's ratio method shows greater values than that of obtained from classic reference station method. The obtained results for the used methods are summerised as the following; Explosion: The above result was obtained the same, while explosion was used as a source. Nakamura's method: In comparison between microtremors and explosion generated waves, the Nakamura's method, in average resulted greater amplification factor while explosion was used as a source. Classic reference station method: In comparison between microtremors and explosion, classic reference station method, in average resulted greater amplification factor while explosion was used as a source.

Snowmelt-runoff simulation is a significant and common module in hydrological models. During the last decade, a number of hydrological distributed models, have been developed, using different snowmelt algorithms and many of the previous models have been updated with more improved snowmelt approaches. Also, an especial consideration has been developed to distributed modeling. In the present paper, snowmelt modules of hydrological models have been reviewed. Data problems to some extent have been resolved compared with the previous decade, but it is still the main obstacle. Application of Geographical Information System (GIS) has been one of the great successes and some of the models have been facilitated by GIS interface. In spite of these improvements, because of the rareness of snowmelt measurements in a few studies snowmelt components of hydrological models have been independently evaluated. It has been suggested that under the coordination of International Association of Hydrological Science (IAHS), in an international attempt, snowmelt data set of different research works that have been done so far to be collected and made available to snow hydrologist and modelers.

In this study, cloud formation and its seeding efficiency at room temperature have been envestigated by different particles such as ambient aerosols, salt, and smoke induced by burning match. In the first step, the effect of ambient aerosol concentration on the time of clearing cloud was considered. Since the aerosols concentration is almost constant during the day, there for it is accepted as base point for comparison of not-seeded and seeded condition for cloud formation and precipitation. The effect of aerosols concentration variation in different days also was considered. In the second step, the effect of salt and smoke injected as seeding nuclei to the chamber on the cloud clearing time was studied. The salt solution density was used with 20, 30 and 40 g/lit. The time of cloud clearing by the salt nuclei is less than ambient aerosols. The results showed, the more salt solution density, the less cloud clearing time. In most experiments with increasing smoke concentration the precipitation increased too and extraordinary amounts of smoke concentration rarely caused cloud to be overseed. The experimental results on nucleation efficiency showed that hygroscopic and giant salt particles are more efficient than smaller smoke particles but with respect to higher concentrations of smoke it is observed that the cloud has precipitated in shorter time by smoke nuclei. In fact, if it would be possible to make the experiments under the quantity control coditions, the cloud could be cleaned with salt nuclei in the shorter time.

In this research the porosity of Shurijeh formation in northeast of Iran is measured from neutron and density logs in the well GL2. Then we measured compressional wave velocity from acoustic log, and the clay content from geology log. With the data of clay content, porosity and compressional wave velocity we found a linear relationship between these parameters as follows: Vp =5.55- 9.62Æ-1.37C    R2 = 0.86 where Vp, Æ and C are respectively the velocity of saturated sandstone (in km/s), porosity and clay content (both in fractional volume). Based on the above relationship, if Vp calculated from sonic log and with the knowledge of the clay content, them the porosity of the formation could be estimated.

Vibroseis is the cheapest and the most convenient source of energy for seismic data acquisition. Unfortunately, in certain areas continuous seismic date acquisition with Vibroseis is not possible (due to the varying terrain conditions, jungles woods and swamp or others environmental problems). Impulsive sources, alternatively, can be used to maintain continuous subsurface coverage and to keep the fold at the desired level. Different seismic sources usually generate different seismic wavelets. Vibroseis source produces a two-sided signal after correlation, whereas an impulsive source results in a onesided (causal) signal. During interpretation, if the above mentioned differences, the would mat be taken into account resulting seismic sections could possibly reveal false facies changes. In this study we showed that how one could solve this problem by applying two-sided recursive (TSR) shaping filters. We employed a deterministic, non-trace adaptive procedure considering the known parts of the seismic signal. The proposed strategy contains a minimum-phase conversion of both the Vibroseis and impulsive seismic data. It followed by a deconvolution and subsequent bandwidth limitation in the frequency range of data using a zero-phase band pass filter.