Parametric estimation of ocean surface currents with HF radar     

Hickey  K. Khan  R.H. Walsh  J. 《Oceanic Engineering, IEEE Journal of》1995,20(2):139-144

Ocean surface currents can be estimated, over a large coastal area, by utilizing the backscatter of high frequency (HF) radar waves from ocean gravity waves. Although the overall backscatter mechanism is complicated, the surface current information is contained within the spectral characteristics of two dominant Bragg components. The accuracy of the current estimate, following the usual FFT-based spectral estimate, is limited by the frequency resolution of the FFT and the time-varying characteristics of the Bragg components. This paper describes a high resolution parametric estimation of the ocean currents based on a recently proposed technique for analyzing time-varying signals. This technique, together with a time-domain ocean clutter model, allows all the Bragg signal information to be extracted from the two dominant eigenvalues and eigenvectors of a matrix constructed from the radar data. Using signals from an operational coastal surveillance radar, current estimates made using this technique are compared with those estimated by the conventional FFT-based method  相似文献   

A Detailed Opaque Petrological and Magnetic Investigation of a Single Tertiary Lava Flow from Skye, Scotland—I     

J. M. Ade-Hall  M. A. Khan  P. Dagley  R. L. Wilson 《Geophysical Journal International》1968,16(4):375-388

  相似文献   

A Detailed Opaque Petrological and Magnetic Investigation of a Single Tertiary Lava Flow from Skye, Scotland—II Spatial Variations of Magnetic Properties and Selected Relationships between Magnetic and Opaque Petrological Properties     

J. M. Ade-Hall  M. A. Khan  P. Dagley  R. L. Wilson 《Geophysical Journal International》1968,16(4):389-399

  相似文献   

Quantification of the urban heat island under a changing climate over Anatolian Peninsula     

Huseyin Ozdemir  Alper Unal  Tayfun Kindap  Ufuk Utku Turuncoglu  Zeynep Okay Durmusoglu  Maudood Khan  Mete Tayanc  Mehmet Karaca 《Theoretical and Applied Climatology》2012,108(1-2):31-38

The Anatolian Peninsula is located at the confluence of Europe, Asia, and Africa and houses 81 cities of which 79 of them have population over 100,000. We employed some criteria to select the cities from the 81 cities. After accomplishing all the criteria, eight cities were remaining for the study. Nonparametric Mann–Kendall test procedure was employed for the urban and rural stations of these cities to detect the long-term change in temperature trends. Statistical analysis of daily minimum temperatures for the period between 1965 and 2006 suggest that there is no statistically significant increase in rural areas. In contrast to the findings of the previous studies, however, all the urban sites and difference between urban and rural pairs show significant increase in temperatures, a strong indication for the existence of urban heat island (UHI) affect over the region. Regional Climate Model was also utilized to assess the changes in temperature by the end of century for the region. The findings suggest that an increase of up to 5°C is possible. Climate change effects enforced with UHI have the potential to cause serious problems for the entire region and hence needs to be studied thoroughly.  相似文献   

On rising temperature trends of Karachi in Pakistan     

S. H. Sajjad  Babar Hussain  M. Ahmed Khan  Asif Raza  B. Zaman  Ijaz Ahmed 《Climatic change》2009,96(4):539-547

Karachi is the largest city of Pakistan. The temperature change in Karachi is studied in this research by analyzing the time series data of mean maximum temperature (MMxT), mean minimum temperature (MMiT) and mean annual temperature (MAT) from 1947 to 2005 (59 years). Data is analyzed in three parts by running linear regression and by taking anomalies of all time periods: (a) whole period from 1947–2005; (b) phase one 1947–1975 and (c) phase two 1976–2005. During 1947 to 2005 MMxT has increased about 4.6°C, MMiT has no change and MAT has increased 2.25°C. During 1947–1975, MMxT increased 1.9°C, in this period there is − 1.3°C decrease in MMiT and MAT has raised upto 0.3°C. During 1976–2005, the MMxT, MMiT and MAT increased 2.7°C, 1.2°C and 1.95°C, respectively. The analysis shows significantly the role of extreme vulnerability of MMxT in rising the temperature of Karachi than the MMiT.  相似文献   

Vulnerability and adaptability of wheat production in different climatic zones of Pakistan under climate change scenarios     

Humaira Sultana  Nazim Ali  M. Mohsin Iqbal  Arshad M. Khan 《Climatic change》2009,94(1-2):123-142

Ten wheat production sites of Pakistan were categorized into four climatic zones i.e. arid, semi-arid, sub-humid and humid to explore the vulnerability of wheat production in these zones to climate change using CSM-Cropsim-CERES-Wheat model. The analysis was based on multi-year (1971–2000) crop model simulation runs using daily weather series under scenarios of increased temperature and atmospheric carbon dioxide concentration (CO₂) along with two scenarios of water management. Apart from this, sowing date as an adaptation option to offset the likely impacts of climate change was also considered. Increase in temperature resulted in yield declines in arid, semi-arid and sub-humid zone. But the humid zone followed a positive trend of gain in yield with rise in temperature up to 4°C. Within a water regime, increase in CO₂ concentration from 375 to 550 and 700 ppm will exert positive effect on gain in wheat yield but this positive effect is significantly variable in different climatic zones under rainfed conditions than the full irrigation. The highest response was shown by arid zone followed by semi-arid, sub-humid and humid zones. But if the current baseline water regimes (i.e. full irrigation in arid and semi-arid zones and rainfed in sub-humid and humid zones) persist in future, the sub-humid zone will be most benefited in terms of significantly higher percent gain in yield by increasing CO₂ level, mainly because of its rainfed water regime. Within a CO₂ level the changes in water supply from rainfed to full irrigation shows an intense degree of responsiveness in terms of yield gain at 375 ppm CO₂ level compared to 550 and 700 ppm. Arid and semi-arid zones were more responsive compared to sub-humid and humid zones. Rise in temperature reduced the length of crop life cycle in all areas, though at an accelerated rate in the humid zone. These results revealed that the climatic zones have shown a variable intensity of vulnerability to different scenarios of climate change and water management due to their inherent specific and spatial climatic features. In order to cope with the negative effects of climate change, alteration in sowing date towards cooler months will be an appropriate response by the farmers.  相似文献   

Seismic sources for southern Pakistan and seismic hazard assessment of Karachi     

Waseem  Muhammad  Khan  Muhammad Asif  Khan  Sarfraz 《Natural Hazards》2019,99(1):511-536

Natural Hazards - Karachi is Pakistan’s largest city with population exceeding 18 million and is amongst the top five most congested cities in the world. Karachi has experienced no earthquake...  相似文献   

Application of Artificial Intelligence to Estimate Oil Flow Rate in Gas-Lift Wells     

Khan  Mohammad Rasheed  Tariq  Zeeshan  Abdulraheem  Abdulazeez 《Natural Resources Research》2020,29(6):4017-4029

Natural Resources Research - Optimization and monitoring schemes for oil well and reservoir system require accurate estimation of production rate. Real-time monitoring is conducted typically using...  相似文献   

Socio-political and ecological stresses on traditional pastoral systems: A review     

Muhammad  Khurshid  Mohammad  Nafees  Abdullah  Khan  Mehmet  Somuncu  Ashfaq  Ahmad Khan  Wajid  Rashid 《地理学报(英文版)》2019,29(10):1758-1770

Journal of Geographical Sciences - Pastoralism is a viable socio-economic system-shaped by landless and agro-pastoral communities in many pastoral regions of the world. This system is mainly based...  相似文献   

Greenhouse gases abatement by catalytic dry reforming of methane to syngas over samarium oxide-supported cobalt catalyst     

B. V. Ayodele  M. R. Khan  C. K. Cheng 《International Journal of Environmental Science and Technology》2017,14(12):2769-2782

Anthropogenic activities often result in the emissions of methane (CH₄) and carbon dioxide (CO₂) which are the principal components of greenhouse gases. The mitigation of these gases to avert further occurrence of global warming has attracted a lot of research interest. In this study, the potential of greenhouse gases abatement via catalytic CO₂ (dry) reforming of methane to syngas over samarium oxide-supported cobalt (20 wt% Co/80 wt% Sm₂O₃) catalyst was investigated. The 20 wt% Co/80 wt% Sm₂O₃ material was synthesized via wet impregnation method and characterized using different instrument techniques. The methane dry reforming reaction, as well as its kinetics over the catalyst, was studied in a stainless steel fixed-bed continuous flow reactor at feed (CH₄:CO₂) ratios range of 0.1–1.0, temperature range of 923–1023 K and gas hourly space velocity (GHSV) of 30,000 h^?1. The 20 wt% Co/80 wt% Sm₂O₃ catalyst showed promising catalytic activity evident from the highest CH₄ and CO₂ conversion of ~71 and ~74% as well as the highest hydrogen (H₂) and carbon monoxide (CO) yield of ~62 and ~73%, respectively. Moreover, the methane dry reforming over the 20 wt% Co/80 wt% Sm₂O₃ catalyst produces H₂/CO ratio close to unity hence suitable for use as a chemical intermediate for synthesis of oxygenated fuels. The kinetic data obtained from the methane dry reforming were fitted to power law model. Apparent activation energies of 88.62, 80.12, 108.12 and 100.91 kJ mol^?1 were obtained for CH₄, CO₂, H₂ and CO, respectively. The characterization of the spent 20 wt% Co/80 wt% Sm₂O₃ catalyst after 4 h of time-on-stream has confirmed the presence of amorphous carbon which can easily be gasified.  相似文献