Optimal linear combinations of triple frequency carrier phase data from future global navigation satellite systems   总被引：5，自引：2，他引：5  

Todd Richert  Naser El-Sheimy 《GPS Solutions》2007,11(1):11-19

With the introduction of a third frequency on GPS Block IIF satellites and the implementation of Galileo, there will be three freely available carrier phase measurements transmitted from each system. This change in satellite navigation infrastructure will enable the use of linear combinations of the original measurements that are not currently available. As a result, it is conceivable that there may be an optimal choice of combination coefficients for a given positioning campaign. This article outlines some of the motivations of using linear combinations of Global Navigation Satellite System (GNSS) data. For example, linear combinations can be used to eliminate or mitigate individual sources of error, they can be used to alleviate excessive computational burdens, and they can be used to reduce the necessary bandwidth in communication systems. Upon establishing the motivations for using linear combinations of data, the mathematical theory involved in creating linear combinations is given. The variance of the combined signal is shown to be a weighted sum of the variances of the error sources in the untransformed signals. The weights depend on the choice of combination coefficients and the nominal frequencies of the carrier signals. As a result, there are certain choices of combination coefficients that eliminate or mitigate individual sources of error. Three categories of combinations are developed: those that eliminate the ionospheric effect, those that mitigate the effects of thermal noise and multipath, and those that mitigate the tropospheric effects. The relationships between these various categories of linear combinations are shown geometrically and the concept of optimal linear combinations of data is discussed. Finally, experimental results using optimal linear combinations of data are shown. The results are obtained using a commercially available software simulator and a GNSS processing engine from the Mobile Multi-Sensor Research Group in the Geomatics Engineering Department of the University of Calgary. It is shown that there indeed exist combinations that produce approximately the same ambiguity estimation accuracy as the pure L1 (or E1) signals, but that deliver far better baseline precision results. However, like the pure L1 (or E1) signals, instantaneously resolving integer ambiguities with these combinations will be impossible for baselines longer than about 15 km depending on the existing ionospheric conditions.  相似文献   

Fractures Effect in Reservoir Quality of Ilam and Sarvak Formations in Hengam Oilfield Using Imaging Logs     

Naser Ebadati 《Journal of the Geological Society of India》2018,92(4):491-497

In this study, an attempt has been made through the data of one of exploratory wells as well as using petrophysical and FMI visual logs, the lithology, structures and failures of the field is investigated. For petro physical analysis of the area, after initial field investigation and controlling the drilled units, final approximation of the lithology of the area was made. Afterwards the raw data of well was used for the evaluation of petrophysical parameters by Geolog software. In the next step the effect of fractures on the oil production and their comparison with the initial porosity was analyzed. The results showed that the points with highest production and exploitation of the oil exists, have the greatest expansion of fractures. Comparison of the obtained results with the lithology specifications of other wells of the field shows that in zones with secondary fractures relative to the porosity the reservoir quality has been more appropriate and outputs the highest production and in comparison, the wells No.3, 4 and 5 in spite of having zones of higher porosity than the well number 2 of the lower reservoir quality.  相似文献   

Comparison of SRM and WetSpa models efficiency for snowmelt runoff simulation     

Hamid Karimi  Hossein Zeinivand  Naser Tahmasebipour  Ali Haghizadeh  Mirhassan Miryaghoubzadeh 《Environmental Earth Sciences》2016,75(8):664

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Pasture degradation effects on soil quality indicators at different hillslope positions in a semiarid region of western Iran   总被引：1，自引：0，他引：1  

Shamsollah Ayoubi  Nazanin Emami  Nasrin Ghaffari  Naser Honarjoo  Kanwar L. Sahrawat 《Environmental Earth Sciences》2014,71(1):375-381

A study was made to determine the influence of pasture degradation on soil quality indicators that included physical, chemical, biological and micromorphological attributes, along the hillslope positions in Chaharmahal and Bakhtiari province, western Iran. Soil samples from different slope positions were collected from 0 to 30 cm depth for physical and chemical properties and from 0 to 15 cm depth for biological properties at two adjacent sites in the two ecosystems: natural pasture and cultivated land. Soil quality indicators including bulk density, mean weight diameter, soil organic carbon (SOC), particulate organic material (POM) in aggregate fractions, total nitrogen, available potassium, available phosphorus, cation exchange capacity, soil microbial respiration (SMR) and microbial biomass C and N were determined. The results showed that SOC decreased cultivation from 1.09 to 0.77 % following pasture degradation. The POM decreased by about 19.35 % in cultivated soils when compared to natural pasture; also, SMR and microbial biomass C and N decreased significantly following pasture degradation. Furthermore, aggregate stability and pore spaces decreased, and bulk density increased in the cultivated soils. Overall, our results showed that long-term cultivation following pasture degradation led to a decline in soil quality in all selected slope positions at the site studied in the semiarid region.  相似文献   

Variability of Airborne Dust Fallout and Associated Trace Metals around Industrial Sites in Esfahan,Iran     

Anahita Moradi  Naser Honarjoo  Ali Asghar Besalatpour 《洁净——土壤、空气、水》2023,51(1):2200327

The seasonal and spatial variability of airborne dust deposits and associated trace metals such as Pb, Co, Ni, Cd, Mn in 15 sites surrounding a heavily industrialized region in south Esfahan (central Iran) are investigated. Total deposit rates (TDR) of dusts and trace metals are analyzed, contamination factor (CF) and pollution load index (PLI) are also calculated. Furthermore, correlation and cluster analysis are performed to identify the source of the pollution. The highest dust-TDR (15.97 g m⁻² per season), the highest concentration of trace metals, CF and PLI are recorded in summer because of the lack of precipitation, high temperature, and drought conditions in this season. Pb and Cd show the highest CF values. In the towns near the two major steel mills in the region (i.e., Esfahan Steel Company and Mobarekeh Steel Complex), the CF values for Pb and Cd are about 13 and 12, respectively (i.e., 13 and 12 times higher than the pre-industrial values, respectively). The spatial distribution maps of the dust deposit rate, dust-borne trace metals, and the obtained PLI of the trace metals in the study area reveal that the two major industries in the region are the main sources of dust and trace metal distribution.  相似文献