分类： 地球科学 >> 空间物理学 分类： 地球科学 >> 海洋科学 提交时间： 2017-03-23
摘要： 海洋沉积物中天然气水合物的存在与分布与地温条件紧密相关。南海北部陆坡大部分区域更、全新世沉积速率较高，同时局部地区(如神狐天然气水合物钻探区)发育有大量的海底冲蚀谷。这些快速沉积或侵蚀作用可以对地温场及天然气水合物的形成与赋存产生重要影响，然而目前注意到这些问题的研究相对较少。本文中我们结合南海北部陆坡的实际情况，建立了针对地温场发生动态变化时的水合物成藏数值模型。我们给出两个成藏模拟案例，其一是快速沉积的情形，其二是地形遭受侵蚀、产生冲蚀谷时的情形。结果表明，在这两种情形下地温场将发生不同的瞬态调整，并对天然气水合物在地层中聚集及分布产状产生重要影响。在快速沉积发生时，地温梯度将变小，天然气水合物稳定带（HSZ）将增厚；然而当其底界将随着热传递而上升，天然气水合物将不断在原稳定带底界分解，而后在新的稳定带底界处重新生成水合物。这样长时间的快速沉积作用可以造成水合物主要富集在稳定带底界处。而当快速侵蚀作用发生时，地温梯度将变大，天然气水合物稳定带的厚度将变薄，原来位于冲蚀谷处的水合物藏将被侵蚀作用破坏。而后，随着热平衡的发展，逐渐形成新的、类似于似海底反射层的稳定带底界。单纯考虑甲烷扩散作用下，高丰度水合物的形成需要较长的时间，相对而言脊下的水合物成藏较好，形成矿点的概率较大。 The occurrence and distribution of gas hydrate in marine sediments is closely related to the state of geothermal field. The sedimentation rate is relatively high during the Pleistocene and Holocene in the northern margin of the South China Sea. Moreover, there are many erosional canyons at the sea bottom in some local areas. Such fast sedimentation and erosion can greatly affect the geothermal regime and the formation and occurrence of gas hydrate deposits. However, there are few studies that consider such scenarios. In this study, considering the geological reality, we build a numerical reservoir model aimed to simulate the evaluation of the gas hydrate system upon two cases: the fast sedimentation and the development of erosional canyons. The results indicate the geothermal filed and the accumulation and distribution of gas hydrate can be adjusted dynamically when the fast sedimentation or erosion occurs. Under fast sedimentation, the geothermal gradient becomes smaller and the thickness of gas hydrate stability zone (HSZ) becomes larger. However, due to the role of heat transfer, the bottom of HSZ rises upward. This process leads to the hydrate near the previous bottom of HSZ being dissociated and depositing near the bottom of new HSZ. After a long duration, the fast sedimentation will result the formation of hydrate being mainly enriched near the bottom of HSZ. By contrast, when fast erosion occurs, the geothermal gradient increases and the HSZ turn thinner. The gas hydrate deposit system can be partially destroyed by the formation of canyons. A long time is necessary for the recovery of a gas hydrate deposit with significant abundance. Relatively, the deposits under the residual ridges are more possible to be potential “sweet spots”.
分类： 地球科学 >> 海洋科学 提交时间： 2017-03-22 合作期刊: 《中国科学院院刊》
摘要： 水圈包括海洋、湖沼、河流、冰川、地下水等，水圈中居住着地球上一半以上的微生物，包括细菌、古菌、真菌、藻类、病毒等，蕴含着地球上最大的微生物组。已有的研究表明，水圈微生物在重要元素生物地球化学循环中发挥关键驱动作用。但是，人们对水圈微生物组的核心科学问题，即微生物如何发挥驱动作用至今了解不多。最近，国家自然科学基金委员会“水圈微生物驱动地球元素循环的机制”重大研究计划（简称“水圈微生物计划”）正式立项。该计划拟选择典型水圈环境，解析微生物群落构建及与环境之间的相互作用、微生物物质与能量代谢机制以及微生物代谢活动的生态学意义与贡献，从而揭示水圈微生物驱动碳、氮、硫等元素生物地球化学循环的机制。文章简述了该计划提出的背景与依据，以及涉及的主要科学问题和研究设想。
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： Electromagnetic waves used for deep space communications are mainly affected by the charged particles ejected by the sun. These effects may result in degradation of communication quality or communication interruption. This paper discusses the effects of solar scintillation on electro-magnetic waves, including the scintillation index which is a measure of the intensity scintillation, the coherence bandwidth and the coherence time of deep space communication channel. The deep space communication channel under solar scintillation is modeled by using Rician fading channel according to the scintillation index. The coherence bandwidth will determine whether the channel is flat fading or frequency selective fading and the coherence time will determine whether the channel is slow fading or fast fading. The approach of choosing signal band width is determined by the coherence bandwidth and the coherence time with the change of the solar elongation angle. The simulation results show the bit error rate of the signal bandwidth chosen by the proposed approach is lower than a random choice.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： A novel single-layer microstrip reflectarray element with fractal structure is proposed. Ansoft HFSS is used to analyze the reflect phase for the fractal element in honeycomb lattice. A 469-element prime focus microstrip reflectarray antenna composed of the proposed fractal elements is designed, manufactured, and measured. The measured gain level of 29.8 dB is obtained at the center frequency of 13.58 GHz with 1-dB gain bandwidth of 15.3%.
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 pencil-beam rotating scatterometer which is designed for snow water equivalent (SWE) measurement, and Doppler beam sharpening (DBS) technique is proposed for DFPSCAT to achieve the azimuth resolution. However, the DBS technique is inapplicable for the forward-looking and afterward-looking regions. Based on an approximate aperiodic model of scatterometer echo signal, an improved adaptive regularization deconvolution algorithm with gradient histogram preservation (GHP) constraint is implemented to settle the problem. To investigate its performance of resolution enhancement and resulted accuracy, both a synthetic backscattering coefficient (σ0field reconstruction and SWE σ0reconstruction are carried out. The results show that the proposed method can recover the truth signal and achieve azimuth resolution of 2 km with the designed scatterometer system, which is required by the SWE retrieval. Moreover, the relative errors of reconstructed σ0are less than 0.5 dB that satisfy the accuracy requirement for SWE retrieval, and comparisons with observed results show that the error reduction is more than 0.03 dB. Meanwhile, a comparison between the proposed algorithm and some existing resolution enhancement methods is analyzed, which concludes that the proposed method can obtain a comparable resolution enhancement as L1method and has less noise. The technique is also verified with advanced scatterometer (ASCAT) scatterometer data.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： Target brightness temperature maps can be used in geostationary interferometric microwave sounder (GIMS) system simulation. System simulation with accurate target brightness temperature maps can evaluate system performance in near real case and thus help adjust design parameters for the sensor before it is finally put into use. In this paper, method of simulating target brightness temperature using Weather Research and Forecasting Model and Radiative Transfer for TOVS (RTTOV) has been discussed. Target brightness temperature simulation results at oxygen absorption band and water-vapor absorption band have been presented. Some preliminary analyses of simulated brightness temperature for GIMS' observation have also been given.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： With a standard deviation as large as 2 cm, the sea state bias (SSB) has become the dominant source of error in satellite altimetry. The operational SSB correction models are two-dimensional (2-D) empirical (parametric or nonparametric) models based on the altimeter-measured wind speed (U) and significant wave height (SWH). However, these 2-D SSB models cannot entirely parameterize the range bias variability. The SSB uncertainty may be lowered through improved SSB models including additional measurable or predictable correlatives. This paper presents a method to estimate the SSB from crossover differences by using a three-dimensional (3-D) nonparametric model. The model is based on U, SWH from Jason-2 altimeter ocean observations, and the mean wave period from the European Centre for Medium-Range Weather Forecasts reanalysis project ERA-Interim (The SSB model developed with the method presented in this paper is called “3-D SSB model” and the SSB estimated with the 3-D SSB model is called “3-D SSB estimate”). Simulations indicate that the wave period can greatly affect the SSB. Evaluated by the separate annual datasets from 2009 to 2011, the 3-D SSB estimates can increase the explained variance by 1.32 cm2, or 1.15-cm RMS relative to the traditional 2-D SSB estimates based on U and SWH. Spatial evaluation of improvement shows that the 3-D SSB estimates are better than the traditional 2-D SSB estimates at all latitudes. The enhancement from 2-D to 3-D SSB estimates is of great significance to improve the precision of the altimeter product.[COMP]: Please set math TYPE gin the sentence below (40) as per the authors PDF.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： In order to satisfy a relatively high resolution for the retrieval of snow water equivalent, an X/Ku-band dual-frequency full-polarized SCATterometer (DFPSCAT) onboard Water Cycle Observation Mission (WCOM) satellite is designed for high-resolution observations. However, given the following situations, the method called “rotating azimuth Doppler discrimination” is proposed, which can satisfy the resolution requirement and real-time processing: 1) the conically rotation rate of antenna is relatively fast; 2) the swath width is larger than 1000 km; and 3) day or night observation capabilities are required. Considering the complexity of the system's design and the improvement of azimuth resolution capability, a burst pulsing scheme is addressed to satisfy the numbers of azimuth sampling. The simulation model is used to analyze the feasibility of azimuth discrimination method based on geometry and system parameters. It is shown that the achievable azimuth resolution is about 2–5 km at far end of the swath and only 5km at near end of the swath. The results show that when the size of a slice is set as 2–5 km, the Kpcis about less than 0.4 as snow depth varies, and the Kpcof combined slices is smaller than a single slice.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： In this paper a three component model-based decomposition with adaptive selection of unitary transformations for polarimetric synthetic aperture radar (POLSAR) data processing is proposed. Singh et al implemented two unitary transformations on the coherency matrix to minimize the power of cross-polarization, and as a result the T23element of the coherency matrix becomes zero. Another two unitary transformations are proposed by us to carry out on the coherency matrix also to minimize the power of crosspolarization, and the T13element of the coherency matrix becomes zero. Here, we first implement Singh's two unitary transformations and the proposed two unitary transformations on the coherency matrix separately. Then we select the one which leads to the smaller T33. At last, we carry out the three component model-based decomposition proposed by Freeman and Durden based on the obtained coherency matrix. The smaller T33is obtained, the better the over-estimation of volume scattering in model-based decomposition can be suppressed. The RADARSAT-2 POLSAR data of San Francisco area is used to validate the improvement of the proposed method over the three component decomposition only with Singh's two unitary transformations.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： This paper present a design for X/Ku dual-band reflectarray antennas with single layer which has two independent radiation patterns for X and Ku bands. In the design, a novel dual resonance structure has been used as the unit cell for both X and Ku band to achieve dual-band performance with a new approach. A 10�0 center-fed reflectarray operating at 9 GHz and 13.5 GHz with scattering angles of 12�and -30�respectively, is designed and the simulated results are presented to validate the approach.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： A novel X-band unit cell structure with improved bandwidth performance for single-layer microstrip reflectarray antenna is proposed. The new element structure consists of two circular rings, each with a pair of gaps, and two phase-delay lines are attached to the outer ring to provide the required phase shift. A 9� center-fed reflectarray antenna operating at 10 GHz is designed to validate the broadband performance of the proposed unit cell. Simulated results show 20% 1-dB gain bandwidth and 38.5% 3-dB gain bandwidth. The maximum gain at 10 GHz is 20.1 dB, which is equivalent to 40 % efficiency.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： The W-band full-polarization radar detection system is in need of a new type of antenna feed with good performance. The waveguide slot array antenna, has the advantages of low profile, high radiation efficiency, easy access to high gain. It has been become the research emphasis in the field of millimeter wave detection. In order to satisfy the need of developing complete polarization radar detection system, a W-band four-channel dual-polarization waveguide slot antenna is designed. The results of the simulation and optimization tests show that, the antenna has outstanding technical characteristics in double polarization. The antenna gain is higher than 13dB, and the cross-polarization level lower than -34dB. The bandwidth below VSWR 1.5 is better than 2.8GHz. High isolation of over 50dB is achieved between different polarization input ports.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： Deorientation plays an important role in polarimetric synthetic aperture radar (PolSAR) target decomposition, terrain classification, and geophysical parameters retrieval. The existing deorientation method roughly rotates the target by an average/mixed orientation angle (OA) about the line of radar sight. However, regarding the complex high-entropy mixed scatterer, which usually comprises several comparable sub-scatterers with different OAs, the average/mixed OA is obviously insufficient to account for the diverse OAs’ reality. To address this, a novel PolSAR data deorientation method is proposed in this letter. The proposed method deorients a mixed scatterer by reconstructing the underlying sub-scatterers using the eigenvalue-based Cloude–Pottier decomposition first, and then compensates the OA of each reconstructed sub-scatterer using Huynen’s desying operation, respectively. One important feature of the proposed method is that it is consistent with Huynen’s desying operation that the real part of the (1, 3) element of the deoriented coherency matrix should be zero. The proposed method provides a fine deorientation for mixed targets, and is especially suitable for the extraction of oriented urban regions. Comparative experiments with the existing method on RADARSAT-2 PolSAR data demonstrate the excellent deorientation performance of the proposed method. © 2016 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
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： In PolSAR data processing, deorientation operation is often necessary. The existing deorientation method uniformly deorients all the sub-scatterers of a resolution cell with one orientation angle. For high entropy situation, the sub-scatterers have diverse OAs, and the effect of the existing method is unsatisfactory. A novel deorientation method is proposed to well treat the high entropy situation. Cloude's eigen-decomposition to the coherency matrix is first carried out. The three eigenvectors are then separately deoriented with their own orientation angles. Experiments demonstrate that the proposed method is suitable for extraction of urban regions, especially for extraction of oriented urban regions. �VDE VERLAG GMBH �Berlin �Offenbach.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： Brightness temperature change of observation target in one imaging period will introduce image blur to the retrieved image of geostationary interferometric microwave sounder (GIMS), which uses rotating circular array to realize time-sharing sampling other than snap-shot to reduce system complexity but meanwhile resulting in a relatively long imaging period. In this paper, an interpolation method utilizing time sequence of visibilities collected by time-sharing sampling is presented. The method is verified through a simulation system that simulates GIMS's observation process in viewing a series of near real case brightness temperature maps modeled by FNL/WRF/RTTOV method. Results show that the interpolation method can de-blur the image and reduce imaging error to the degree of snap-shot imaging. �2016 IEEE.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： Man-made buildings detection is important in land use supervision and land control applications. Generally, polarimetric synthetic aperture radar (PolSAR) data are processed to detect buildings well. But for some buildings which are not aligned with the radar track, these buildings are usually incorrectly recognized as forest, because the oriented buildings produce additional cross-polarization. Polarimetric interferometric SAR (PolINSAR) acquires two measurements with a spatial baseline or a temporal baseline. For the PolINSAR with a temporal baseline i.e., the repeat pass PolInSAR, the two polarimetric measurements are sensitive to targets' temporal variations during the time. The buildings, regardless of the orientations, have high coherence, while some natural targets have low coherence. A novel parameter is proposed here, which represents the mean PolINSAR coherence and can be utilized to distinguish between buildings and some natural targets. The parameter is based on the coherence optimization theory of Cloude and Papathanassiou, and is the mean of the three optimal coherences with three pseudo-probabilities. Based on this new parameter and the SPAN, a method to detect buildings is further proposed. The excellent performance of the proposed method on buildings extraction is demonstrated by processing German Aerospace Center (DLR) L-band E-SAR repeat pass PolINSAR data of Oberpfaffenhofen area.
分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： In this paper, a novel X-band broadband single-layer unit cell with attached phase-delay lines for reflectarray antennas is proposed to surmount the limitation of the reflectarray bandwidth. The unit cell is composed of three circular rings, each with a pair of gaps which are mutually placed orthogonally, and two identical circular phase-delay lines are attached to the outer ring to provide the required reflection phase. After the simulation for the unit cell carried out, a large reflecting phase range of about 600�and almost linear phase curve are achieved at the center frequency of 10 GHz. Parallel phase curves of different frequencies ranging from 9 GHz to 12 GHz are also obtained. To validate the broadband performance of the proposed unit cell, a 9 �9 center-fed reflectarray antenna operating at X band is designed and simulated. Simulation results show that the designed antenna has 34% 1-dB gain bandwidth, which demonstrates that an obvious improvement on the bandwidth has been achieved compared to the previous works. Besides, the cross-polarization level is decreased to -40 dB by a mirror symmetric element arrangement.
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： Dual-Frequency Polarized Scatterometer (DFPSCAT) is a pencil-beam rotating scatterometer which is used to measure snow water equivalence (SWE). Respecting the low azimuth resolution of its forward-looking region, an adaptive regularization deconvolution super-resolution method, based on the scatterometer echo signal model, is proposed. Compared with the classical SIR and MAP algorithms, the proposed method can better reconstruct the original signal, and has less noise amplification. The algorithm processing accuracy with different Kpcis also studied, and the results show that when the value of Kpcis less than 0.1, nearly the entire restored data can satisfy the requirement of 0.5dB accuracy.
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