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21.
Mapping of the soil texture using geostatistical method (a case study of the Shahrekord plain, central Iran) 总被引：1，自引：0，他引：1
Yaser Safari Isa Esfandiarpour Boroujeni Ardavan Kamali Mohammad Hassan Salehi Mohsen Bagheri Bodaghabadi 《Arabian Journal of Geosciences》2013,6(9):3331-3339
Soil texture is a key variable that reflect a number of soil properties such as soil permeability, water holding capacity, nutrient storage and availability, and soil erosion. The main objective of this study was to produce the kriged maps of soils of the Shahrekord region, central Iran. One hundred four soil samples were collected on a 375-m2 sampling grid from the depths of 0–30, 30–60, and 60–100 centimeter, and their particle sizes were determined using hydrometer method. The results showed a moderately spatial correlation in the soil particles among sampling soil layers and across the study area. Moreover, increasing clay and therewith observation of heavier soil textures is evident from surface to subsurface layers of the soils in the studied area due to rainfall and/or irrigation agriculture. These findings indicated that study of the soil texture variation with depth can be used as a clue for site-specific management and precision agriculture. Moreover, we suggest further analysis by using other data layers like topographical parameters, land use, parent material, soil erosion, and any other information which might influence the spatial distribution of soil texture. 相似文献
22.
A systematic investigation of optimal carrier-phase combinations for modernized triple-frequency GPS 总被引：12，自引：6，他引：6
The upcoming modernization of the GPS signals will allow for measurements on an additional third frequency L5 located at 1176.45 MHz.
To take advantage of carrier-phase measurements on this new signal, the strategies for integer ambiguity resolution, required
for centimeter-level accuracy, may need to be revised. The Least-squares Ambiguity Decorrelation Adjustment method remains
perhaps the most powerful tool for finding the best combinations based on a complete decorrelation of the variance–covariance
matrix related to the ambiguities. However, the computational load of that method plus the opportunity to comprehensively
study the interaction of multiple frequencies suggest a reconsideration of approaches using predefined combinations between
frequencies is not out of place. In this paper a systematic investigation is made of all possible triple-frequency geometry-free
carrier-phase combinations which retain the integer nature of the ambiguities. The concept of the lane-number is presented
to unambiguously describe the wavelength of a particular combination. The propagation of the observation noise and of the
ionospheric bias on these combinations is presented. These noise and ionospheric amplification factors are analysed with respect
to the resulting wavelength, in an effort to highlight optimal combinations characterized by a long wavelength, low noise
and limited ionospheric impact. 相似文献
23.
Summary The aim of this study is the evaluation of models that estimate daily global solar radiation on tilted surfaces from that
measured on horizontal surfaces. Global solar radiation incident on a tilted plane consists of three components: beam radiation,
diffuse radiation and reflected radiation from the ground.
The Klein (1977) method, modified by Andersen (1980), was used for estimating direct solar radiation incident on tilted surfaces
and an isotropic model was used for estimating reflected solar radiation incident on a tilted plane. In contrast models for
the diffuse radiation component show major differences, which justifies a validation study which has been done.
Eight models for derivation of daily slope diffuse irradiance from daily horizontal diffuse irradiance were tested against
recorded slope irradiances at Karaj (35°55′ N; 50°56′ E), Iran. The following models were included: Badescu (2002), Tian et
al. (2001), Reindl et al. (1990), Skartveit and Olseth (1986), Koronakis (1986), Steven and Unsworth (1980), Hay (1979) and
Liu and Jordan (1962).
All the models use the same method for calculating beam radiation as well as ground reflected radiation. However, only diffuse
component of radiation was compared. Statistical indices showed that Reindl’s model gives the most accurate prediction for
the south-facing surface and Koronakis’s model performs best for the west-facing surface. The Relative Root Mean Square Errors
(%RMSE), except for Steven and Unsworth’s model that has unacceptable results, for whole data range from 1.02 to 10.42%. In
general, Reindl’s model produces the best agreement with the measured tilted data. 相似文献
24.
A reconnaissance study has been made of the distribution of 238U, 232Th, 40K and 137Cs and geochemical features in soils and sediments samples at various locations in the northwestern coast of Persian Gulf. Activity concentration levels due to radionuclides were measured in 30 soil and sediment samples collected from this region. From the measured spectra, activity concentrations were determined for 40K (range from 146 to 500 Bq kg(-1)), 137Cs (from 5 to 20 Bq kg(-1)), 238U (from 21 to 65 Bq kg(-1)) and 232Th (from 15 to 45 Bq kg(-1)) with lowest limit detection (LLD) of 68, 3.2, 4.3 and 4.3 Bq kg(-1), respectively. The dose rate from ambient air at the soil ranges was between 19 and 58 nGy h(-1) with an average of 37.41+/-9.66 nGy h(-1). 相似文献
25.
Zare MR Mostajaboddavati M Kamali M Abdi MR Mortazavi MS 《Marine pollution bulletin》2012,64(9):1956-1961
The natural radioactivity levels in sediment samples of the northern coast of Oman Sea, covering the coastal strip from Hormoz canyon to Goatr seaport, as the first time has been determined. The results of measurements will serve as background reference level for Oman Sea coastlines. Sediments from 36 coastal and near shore locations were collected for analysis. Analysis on the collected samples were carried out to determine (235)U, (238)U, (232)Th, (40)K and (137)Cs using two high purity germanium detectors with 38.5% and 55% relative efficiencies. The concentration of (235)U, (238)U, (232)Th, (40)K and (137)Cs in sediment samples ranged between 1.01 and 2.87Bq/kg, 11.83 and 22.68Bq/kg, 10.7 and 25.02Bq/kg, 222.89 and 535.07Bq/kg and 0.14 and 2.8Bq/kg, respectively. The radium equivalent activity was well below the defined limit of 370Bq/kg. The external hazard indices were found to be less than 1, indicating a low dose. 相似文献