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1.
This study is devoted to oceanographic features of the semi-enclosed Gulf of Aqaba, Red Sea. The data were recorded in winter—spring
1999 on the R/V Meteor cruise leg 44/2. Temperature and salinity profiles were measured at six positions (I—VI). The shipboard
NarrowBand Acoustic Doppler Current Profiler (NB ADCP) 150 kHz continuously recorded current profiles down to 350 m en route.
The research revealed that the current near the Strait of Tiran front (position VI) represents a semidiurnal signal of an
internal tide wave (∼12 h period; 0.2 ms−1 amplitude) that might be generated by the barotropic tide at the sill of the Strait. A sequence of cyclonic and anticyclonic
eddy pairs is found along the axis of the Gulf of Aqaba during winter-spring seasons. These sub-mesoscale signals are dominant
above the main thermocline and might be caused by wind forcing and the narrowness of the Gulf; it might remain in other seasons
with different dimensions in relation to the depth of thermocline. The total diameter of each pair was twice the baroclinic
Rossby radius (R ≈ 10 km). A single anti-cyclonic eddy was observed in the upper 300 m in the northern tip of the Gulf with a diameter of
about 5–8 km. 相似文献
2.
Modelling forest canopy gaps using LiDAR-derived variables 总被引：1，自引：0，他引：1
Remote sensing has revolutionized forest management and has been widely employed to model canopy gaps. In this study, a canopy height model (CHM) and an intensity raster (IR) derived from light detection and ranging (LiDAR) data were used to model canopy gaps within a four-year-old Eucalyptus grandis forest using an object-based image analysis (OBIA) approach. Model thematic accuracies using the CHM, intensity raster and combined data set (CHM and IR) were all above 90%, with KHAT values ranging from 0.88 to 0.96. Independent test thematic accuracies were also above 90%, with KHAT values ranging from 0.82 to 0.91. A comparative area-based assessment yielded accuracies ranging from 70 to 90%, with the highest accuracies achieved using the combined data set. The results of this study show that using a CHM and intensity raster, and an OBIA approach, provides a viable framework to accurately detect and delineate canopy gaps within a commercial forest environment. 相似文献
3.
Saber Al-Rousan Mohammed Rasheed Fuad Al-Horani Riyad Manasrah 《Journal of Oceanography》2006,62(6):839-849
The physicochemical properties of 21 marine sediment samples were investigated, collected from five different localities along
the Jordanian coast of the Gulf of Aqaba. According to the chemical parameters, sediments were categorized into three groups:
carbonate (80% CaCO3), composed mainly of materials of calcareous skeletal structures; terrigenous (<10% CaCO3) depositional areas for land-derived materials from surrounding rocks and alluviums; and a admixture of the first two (19–37%
CaCO3). High significant linear correlations were found between organic carbon (OC) and total nitrogen (TN), indicating the occurrence
of these components in a common phase (organic matter). Despite the co-occurrence of TP in organic matter, these two elements
were negatively correlated, indicating anthropogenic sources of pollution such as phosphate exportation (hotel areas and clinker
port sites) and industrial activities (industrial complex site). The study found that variations in texture properties and
mud contents were due to differences in sediment sources, topography and their response during currents and waves. The finer,
well-sorted sediments contain lower elemental concentrations of OC, calcium carbonate and TN (excluding TP) than coarser,
poorly-sorted sediments. 相似文献
4.
Al-Zibdah Mohammad Oqaily Firas Al-Najjar Tariq Manasrah Riyad 《Ocean Science Journal》2008,43(1):9-16
Environmental qualities of coastal water and bottom sediment were assessed at Jordan's northernmost tip of Gulf of Aqaba to
evaluate possible impacts of the bordering fish pen cages in Eilat. Results showed significant differences between surface
and bottom water in the chemical and physical variables in the different months of the year (2004-2005). Chlorophyll a was
also significantly higher in bottom water when compared to that of the offshore water. Nitrate and ammonia were significantly
higher in bottom water than the surface water at each individual station. The upper 2 cm of sediment sample recorded higher
values of total phosphorus and organic matter. Seasonality affected the content of total phosphorus, organic matter, redox
potential and color especially at the sediment layer below 3 cm of the sediment core. The present investigation showed slight
modification of water and sediment qualities but no clear sign of eutrophication was observed. However, to maintain sustainability
of healthy environmental conditions at the northern tip of Gulf of Aqaba potentials of any possible environmental risks arising
from the fish farms or any other coastal investment should be carefully considered. 相似文献
5.
High-data dimensionality is a common problem in hyperspectral data processing. Consequently, remote sensing techniques that reduce the number of bands are considered essential tools for most hyperspectral applications. The aim of this study was to examine the utility of the random forest ensemble to select the optimal subset of hyperspectral bands to predict the age of Pinus patula stands. Airborne AISA Eagle hyperspectral image data were collected over the study area. The random forest ensemble was used to test whether the forward or backward variable selection methods could identify the optimal subset of bands. Results indicate that both the selection methods produced high-predictive accuracies (root mean square error = 3.097 years). However, the backward variable selection method utilized 206 bands for the final model, while the forward variable selection utilized only a small subset of non-redundant bands (n = 9) while preserving the highest model accuracy (R 2 = 0.6). 相似文献
6.
Riyad Manasrah Mohammad Zibdah Firas Al-Ougaily Najim Yusuf Tariq Al-Najjar 《Ocean Science Journal》2007,42(2):103-116
Seasonal changes of tide signal(s), temperature, salinity and current were studied during the years 2004-2005 in the northernmost
Gulf of Aqaba, which is under developmental activities, to obtain scientific bases for best management and sustainability.
Spectrum analysis revealed permanent signals of tide measurements during all seasons, which represented semidiurnal and diurnal
barotropic tides. The other signal periods of 8.13, 6.10-6.32, 4.16 and 1.02-1.05 h were not detected in all seasons, which
were related to shallow water compound and overtides of principle solar and lunar constituent and to seiches generated in
the Red Sea and the Gulf of Aqaba. Spatial and temporal distribution of temperature, salinity and density showed significant
differences between months in the coastal and offshore region and no significant differences among the coastal sites, between
the surface and bottom waters and between coastal and offshore waters. Therefore, the temporal and spatial variation of water
properties in the northernmost Gulf of Aqaba behave similarly compared to other parts. The coastal current below 12 m depth
was weak (3-6 cms-1) and fluctuated from east-northeastward to west-southwestward (parallel to the shoreline), which may be related to the effect
of bottom topography and/or current density due to differential cooling between eastern and western parts in the study area,
and windinduced upwelling and downwelling in the eastern and western side, respectively. The prevailing northerly winds and
stratification conditions during summer were the main causes of the southward current at 6 and 12 m depths with average speed
of 28 and 12 cms-1, respectively. 相似文献
7.
Riyad S. Manasrah Fuad A. Al-Horani Mohammad Y. Rasheed Saber A. Al-Rousan Marouf A. Khalaf 《Estuarine, Coastal and Shelf Science》2006,69(3-4):567
This study was focused on analysis of the horizontal and vertical current components with correspondence to tide variation, heat flux, seiches and relative backscatter intensity in coastal waters of the northern Gulf of Aqaba during the summers of 2001–2004. Spectrum analysis has shown eight distinguishable peaks of the tide measurements. In addition to semidiurnal and diurnal barotropic tides, signal periods of 8.13, 5.89–6.32 and 4.06 h were related to shallow water compound and overtides of the principal solar and lunar constituent and to seiches (second and third mode) generated in the Red Sea, whereas seiches of the first mode might enhance the semidiurnal tide signal. The shortest periods of 1.02–1.05, 0.50 and 0.36 h were related to seiches (first, second and third mode, respectively) generated in the Gulf of Aqaba. The spectrum analysis and cross-correlation tests of the horizontal and vertical current components and relative backscatter intensity suggested that the vertical motion at the diurnal period was either due to migration of zooplankton or to water convection. Both of which were of the same order as vertical motion induced by horizontal motions of water particles projected parallel on the bottom gradient line. On the other hand, semidiurnal and diurnal periods detected in the vertical currents were caused by the strong signal in the cross-shore current component, first mode seiches generated from the Red Sea and tide. This could be considered as an indicator of the dominant force influencing the currents, such as winds, thermocline depth, seiches and tidal forcing. A permanent convection during summer is likely to occur in the shallow coastal waters due to relatively high inclined bottom, high evaporation and blowing of dry air, as well as the observed dominance of the downward vertical currents in coastal waters. 相似文献
8.
Elhadi Adam Onisimo Mutanga Riyad Ismail 《International journal of geographical information science》2013,27(10):1924-1938
The cossid moth, Coryphodema tristis was first noted on Eucalyptus nitens trees in Mpumalanga province, South Africa during July 2004. Currently, the moth poses a major threat to commercial forestry in the country. In this study, selected climatic and topographical variables were used to model the susceptibility of E. nitens forests to cossid moth occurrence, thereby providing insight into the variables that may influence the occurrence and spread of the moth. A zigzag sampling technique was used to survey 5316 ha of E. nitens forests for the presence or absence of the moth. The random forest classification algorithm was then used to model the relationship between the climatic and topographical variables and the occurrence of the cossid moth. Results indicate that four variables that included elevation, maximum temperature for September, maximum temperature for April and the median rainfall for April best explained the presence or absence of C. tristis with an overall accuracy of 82% and a kappa value of 0.63. Partial dependence plots indicated that the areas that have a maximum temperature greater than 23°C in September and 22°C in April are likely to be infested by the cossid moth. The results from this study provide a robust and accurate spatial framework to assist forest managers in focussing their existing monitoring and control efforts to specific E. nitens forested areas that are highly susceptible to C. tristis infestations. 相似文献
9.
The present study investigated the variability of monthly mean sea level data and discussed its relation with climatic events in the Red Sea during 1958–2001. The data were obtained from Simple Ocean Data Assimilation (SODA), for three different locations (north, central and south) in the Red Sea. Spatial and temporal variability as well as trends and periodicity of sea level time series records in the three locations was investigated using One-way ANOVA test, weighted running mean filter and autocorrelation spectral analysis. Results revealed that mean sea level in the northern Red Sea was permanently lower than its central and southern parts. Moreover, the mean sea level during winter and spring in the three locations was significantly higher than summer and autumn seasons. Increasing and decreasing of sea level trends with respect to time were also observed. Inter-decadal variations in sea level including a fairly regular quasi 2.5–2.7 year oscillation in all seasons were detected, although its amplitude varied among different cycles. Studying the cyclicity in the hydroclimatic record can resolve some of the complexities of the hydroclimate system. The sign of Quasi Biennial Oscillation, El Niño Southern Oscillation and sunspots events may have an important influence in sea level variations of the Red Sea. 相似文献
10.
Reducing the impact of the siricid wasp, Sirex noctilio is crucial for the future productivity and sustainability of commercial pine resources in South Africa. In this study we present a machine learning model that serves as a spatial guide and allows forest managers to focus their existing detection and monitoring efforts on key areas and proactively adopt the most appropriate course of intervention. We implemented the random forest model within a spatial framework to determine which pine forests in Mpumalanga are highly susceptible to S. noctilio infestations. Results indicate that a majority (63%) of pine forest plantations located in Mpumalanga have a high susceptibility (>70%) to S. noctilio infestation. A KHAT value of 0.84 and F measures above 0.87 indicate that the random forest model is a robust classifier that produces accurate results. Additionally, the use of the backward variable selection method enabled us to simplify the random forest modeling process and identify the minimum number of explanatory variables that offer the best discriminatory power and help in the empirical interpretation of the final random forest model. Overall, the results show that pine forests that experience stress caused by evapotranspiration and evaporation followed by rainfalls, especially during the summer months are more susceptible to S. noctilio infestations. 相似文献