分类： 地球科学 >> 地理学 提交时间： 2019-01-17 合作期刊: 《干旱区科学》
摘要： The countries of Central Asia are collectively known as the five ''-stans'': Uzbekistan, Kyrgyzstan, Turkmenistan, Tajikistan and Kazakhstan. In recent times, the Central Asian region has been affected by the shrinkage of the Aral Sea, widespread desertification, soil salinization, biodiversity loss, frequent sand storms, and many other ecological disasters. This paper is a review article based upon the collection, identification and collation of previous studies of environmental changes and regional developments in Central Asia in the past 30 years. Most recent studies have reached a consensus that the temperature rise in Central Asia is occurring faster than the global average. This warming trend will not only result in a higher evaporation in the basin oases, but also to a significant retreat of glaciers in the mountainous areas. Water is the key to sustainable development in the arid and semi-arid regions in Central Asia. The uneven distribution, over consumption, and pollution of water resources in Central Asia have caused severe water supply problems, which have been affecting regional harmony and development for the past 30 years. The widespread and significant land use changes in the 1990s could be used to improve our understanding of natural variability and human interaction in the region. There has been a positive trend of trans-border cooperation among the Central Asian countries in recent years. International attention has grown and research projects have been initiated to provide water and ecosystem protection in Central Asia. However, the agreements that have been reached might not be able to deliver practical action in time to prevent severe ecological disasters. Water management should be based on hydrographic borders and ministries should be able to make timely decisions without political intervention. Fully integrated management of water resources, land use and industrial development is essential in Central Asia. The ecological crisis should provide sufficient motivation to reach a consensus on unified water management throughout the region.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要：Two single-layer X/Ku dual-band dual-polarization reflectarray antennas of different sizes with double parallel dipole elements are presented. Elements of the two bands are set to two orthogonal linear polarizations and placed in interlaced grid. The proposed reflectarrays operate in two frequency-bands within X-band centered at 10 GHz and Ku-band centered at 13.58 GHz. The smaller size reflectarray with elements arranged in a 13 �13 grid for X-band and in a 12 �12 grid for Ku-band is designed and simulated first. Based on the excellent dual-band performance of the small size reflectarray, then a larger size prototype has been designed, manufactured and measured. Measured results demonstrate the maximum gain of 28.54 dB with 50.93% aperture efficiency at 10 GHz and 31.06 dB with 51.34% aperture efficiency at 13.58 GHz, which show desirable dual-band dual-polarization radiation performance.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要：A broadband center-fed reflectarray antenna is presented in this paper. Patch with slot ring on ground plane elements are used for bandwidth improvement. It is shown that quasi-linear phase responses with broad frequency band can be achieved by such a phasing element. An 11�1 elements reflectarray is designed and simulated. The results show that the simulated gain is 23.92 dB at the center frequency of 13.58 GHz with 3-dB bandwidth of 52%, which demonstrate significant broadband operation compared with that of conventional reflectarray.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要：A novel single-layer reflectarray element for broadband use is proposed. Ansoft HFSS is used to analyze the reflection phase for the element. By varying the element size, a slow slope of the reflection phase curve with the phase range over 600° is achieved. A center-fed 121-element reflectarray antenna is designed using the proposed elements and a linearly polarized pyramidal horn antenna is used as the feed of the reflectarray. The simulated results show that the gain of 24.42dB at the center frequency of 13.58GHz with 3-dB gain bandwidth of 36.8% (from 11.08∼16.08GHz), demonstrating a wideband performance compared to the conventional designs.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要：Cloude-Pottier incoherent target decomposition (ICTD) and Touzi ICTD has been widely applied as a popular approach to interpret the scattering characteristics of a target in polarimetric synthetic aperture radar (PolSAR) data processing. However, they have a common drawback, i.e. proliferation of parameters (PoP) is unavoidable. Paladini et al. solved this problem by developing an orientation-invariant ICTD based on the coherency matrix under circular polarization basis. As an alternative to Paladini decomposition, we proposed a novel ICTD based on the frequently used coherency matrix under linear polarization basis. The proposed method can also avoid the problem of PoP, and avoid the ambiguity of alpha angle of Paladini decomposition as well. Real PolSAR data is processed to validate the proposed decomposition.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要：Dual-Frequency Polarized Scatterometer (DFPSCAT) is a new system utilizing Doppler beam sharpening (DBS) technology for azimuthal resolution enhancement. Considering the DBS technology is inapplicable for the middle areas of the swath, a theoretical framework of deconvolution signal processing is proposed to improve resolution. A deconvolution method of the nonlocally centralized sparse representation (NCSR) is adopted to verify its feasibility, and simulation results show that the deconvolution method have obviously better resolution enhancement and higher recovery accuracy than these of the classical scatterometer image reconstruction (SIR) method. �2016 IEEE.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要：In this paper, an SMMW interferometric radiometer concept is demonstrated by a two-element interferometer with dedicated high accuracy SMMW devices. Point-source calibration method is introduced in order to reduce instrument errors. Interference fringes and point target images are presented by this SMMW interferometer. The linear phase error of the interference fringes is less than 2�and the angular resolution is better than 0.57� The measured performance characteristics of the two-element interferometer are consistent with the theoretical analysis. This interferometer demonstrates a new method for passive SMMW remote sensing. �2016, Science Press. All right reserved.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要：An one-dimensional variational retrieval system was developed to retrieve the clear sky atmospheric temperature and humidity profiles over land using the measurements of microwave humidity-temperature sounder (MWHTS) on Chinese FY-3C satellite. The system parameters are configured by analyzing the MWHTS channel properties and the climate condition over land. The retrieval results are evaluated by root mean square error (rmse) with respect to European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data. The validated results show that the maximum root mean square error of temperature and humidity are 2.59K and 11.87%, respectively. The retrieval results, compared with National Centers for Environmental Prediction (NCEP) 6 hour forecast profiles, show that the background profiles can affect the accuracy of retrieval profiles and FY-3C/MWHTS measurements can improve forecast precision of humidity. �2016 IEEE.
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