便携式高频地波雷达台湾海峡浪高观测

As an important equipment for sea state remote sensing, high frequency surface wave radar(HFSWR) has received more and more attention. The conventional method for wave height inversion is based on the ratio of the integration of the second-order spectral continuum to that of the first-order region, where the strong external noise and the incorrect delineation of the first- and second-order Doppler spectral regions due to spectral aliasing are two major sources of errors in the wave height. To account for these factors, two more indices are introduced to the wave height estimation, i.e., the ratio of the maximum power of the second-order continuum to that of the Bragg spectral region(RSCB) and the ratio of the power of the second harmonic peak to that of the Bragg peak(RSHB). Both indices also have a strong correlation with the underlying wave height. On the basis of all these indices an empirical model is proposed to estimate the wave height. This method has been used in a three-months long experiment of the ocean state measuring and analyzing radar, type S(OSMAR-S), which is a portable HFSWR with compact cross-loop/monopole receive antennas developed by Wuhan University since 2006. During the experiment in the Taiwan Strait, the significant wave height varied from 0 to 5 m. The significant wave heights estimated by the OSMAR-S correlate well with the data provided by the Oceanweather Inc. for comparison, with a correlation coefficient of 0.74 and a root mean square error(RMSE) of 0.77 m. The proposed method has made an effective improvement to the wave height estimation and thus a further step toward operational use of the OSMAR-S in the wave height extraction.     

一株产碳酸酐酶附生菌对铜绿微囊藻(Microcystis aeruginosa)生长的影响

为研究生长环境中微生物对铜绿微囊藻碳代谢的影响,本文分析太湖典型微囊藻水华样品附生菌中产碳酸酐酶(CA)细菌的比例,结果显示CA菌占11.6%;从微囊藻群体中分离获得了一株高胞外CA附生菌P201,通过ITS基因鉴定,该菌为一株荧光假单胞菌(Pseudomonas fluorescence).并研究了该菌在不同浓度HCO3-条件下对铜绿微囊藻生长的影响,结果表明无论是高HCO3-浓度还是低HCO3-浓度环境中,加入该菌对铜绿微囊藻的生长均有促进作用,说明产CA酶附生菌对铜绿微囊藻的生长有一定的促进作用.     

利用高频雷达海面回波中奇异峰估计浪高的方法

The popular methods to estimate wave height with high-frequency(HF) radar depend on the integration over the second-order spectral region and thus may come under from even not strong external interference. To improve the accuracy and increase the valid detection range of the wave height measurement, particularly by the smallaperture radar, it is turned to singular peaks which often exceed the power of other frequency components. The power of three kinds of singular peaks, i.e., those around ±1,±2~(1/2) and ±1(2~(1/2)) times the Bragg frequency, are retrieved from a one-month-long radar data set collected by an ocean state monitoring and analyzing radar,model S(OSMAR-S), and in situ buoy records are used to make some comparisons. The power response to a wave height is found to be described with a new model quite well, by which obvious improvement on the wave height estimation is achieved. With the buoy measurements as reference, a correlation coefficient is increased to 0.90 and a root mean square error(RMSE) is decreased to 0.35 m at the range of 7.5 km compared with the results by the second-order method. The further analysis of the fitting performance across range suggests that the peak has the best fit and maintains a good performance as far as 40 km. The correlation coefficient is 0.78 and the RMSE is 0.62 m at 40 km. These results show the effectiveness of the new empirical method, which opens a new way for the wave height estimation with the HF radar.     

Measuring surface wind direction by monostatic HF ground-wave radar at the eastern China Sea

The extraction of full wind vectors from data obtained by single-site (monostatic) high-frequency ground-wave radar (HFGWR) is an ongoing challenge because of the inherent directional ambiguities. Here, a new algorithm for resolving the ambiguity of wind direction from monostatic data is presented. The true wind direction is determined by minimizing the sum of the difference among three wind directions derived from three different radar look angles. The wind directions estimated by applying the algorithm to data obtained from the OSMAR2000 HFGWR situated at the Eastern China Sea are compared with values obtained from ship-borne instrumentation. The mean difference between the ground-truthed values and those obtained from the radar data is approximately 20/spl deg/. The distance limit for wind direction sensing using the OSMAR2000 is about 200 km, which is the range for which signal-to-noise ratios typically exceed about 23 dB in the relevant first-order portions of the backscatter spectra.     

Wave extraction with portable high-frequency surface wave radar OSMAR-S

High frequency surface wave radar (HFSWR) has now gained more and more attention in real-time monitoring of sea surface states such as current, waves and wind. Normally a small-aperture antenna array is preferred to a large-aperture one due to the easiness and low cost to set up. However, the large beam-width and the corresponding incorrect division of the first- and second-order Doppler spectral regions often lead to big errors in wave height and period estimations. Therefore, for the HFSWR with a compact cross-loop/monopole antenna (CMA), a new algorithm involving improved beam-forming (BF) and spectral division techniques is proposed. On one hand, the cross-spectrum of the output sequence by the conventional beam-forming (CBF) with all the three elements and the output with only the two loops is used in place of the CMA output self-spectrum to achieve a decreased beam-width; on the other hand, the better null seeking process is included to improve the division accuracy of the first- and second-order regions. The algorithm is used to reprocess the data collected by the portable HFSWR OSMAR-S during the Sailing Competition of the 16th Asian Games held in Shanwei in November 2010, and the improvements of both the correlation coefficients and root-mean-square (RMS) errors between the wave height and period estimations and in situ buoy measurements are obvious. The algorithm has greatly enhanced the capabilities of OSMAR-S in wave measurements.     

Failure Characteristics of Complicated Random Jointed Rock Mass Under Compressive-Shear Loading

Most natural rock masses contain a large number of random joints and fissures, and most of the rock masses at the rock engineering are commonly in both compression and shear stress environment. However, the research on the failure characteristics of complex random jointed rock mass under compressive-shear loading is still limited. To address this gap, this paper uses the particle flow code 2D to establish a discrete fractured rock mass model and carry out a series of numerical tests with different compressive-shear angles (α) and different joint geometric parameters. The effects of compressive-shear angle and joint geometric parameters on the strength and failure characteristics of fractured rock masses are studied. The results indicate that with the increase of α, the peak strength of the specimen decreases gradually, and the failure mode changes from the composite shear failure mode (Mode-I) to a plane shear failure mode (Mode-II) and then to intact shear failure mode (Mode-III). Specifically, the three failure modes occur in the specimens with α?=?15°, 30° or 45°, 60°, respectively. The existence of joints affects stress distribution on rock mass during the loading process. Furthermore, the stress at the joint tip is relatively concentrated, while on both sides of the joint is smaller. Three kinds of crack coalescence patterns are observed: tensile, shear, and tensile-shear mixed coalescence. The inclination angle of the rock bridge between adjacent joints affects the specific type of coalescence.

     

Mapping wind by the first-order Bragg scattering of broad-beam high-frequency radar

Mapping wind with high-frequency(HF) radar is still a challenge. The existing second-order spectrum based wind speed extraction method has the problems of short detection distances and low angular resolution for broad-beam HF radar. To solve these problems, we turn to the first-order Bragg spectrum power and propose a space recursion method to map surface wind. One month of radar and buoy data are processed to build a wind spreading function model and a first-order spectrum power model describing the relationship between the maximum of first-order spectrum power and wind speed in different sea states. Based on the theoretical propagation attenuation model, the propagation attenuation is calculated approximately by the wind speed in the previous range cell to compensate for the first-order spectrum in the current range-azimuth cell. By using the compensated first-order spectrum, the final wind speed is extracted in each cell. The first-order spectrum and wind spreading function models are tested using one month of buoy data, which illustrates the applicability of the two models. The final wind vector map demonstrates the potential of the method.     

基于人工神经网络的高频雷达风速反演

风速是重要的海洋状态参数之一，对海面风速的准确提取是实现海洋环境监测和沿海工程应用的重要保证。目前，作为新兴海洋环境监测设备，高频雷达在风速提取方面仍然存在挑战。本文提出了一种基于人工神经网络的风速提取方法，利用历史浮标测量海态数据训练风速提取网络，实现风速与有效波高、波周期、风向及时间因素之间的非线性映射。测试结果表明了这一网络在时间和空间上的稳定性；进而将已训练的网络应用到便携式高频地波雷达OSMAR-S的风速反演中，得到的风速与浮标测量风速间的相关系数达到0.849，均方根误差为2.11 m/s。这一结果明显优于常规由浪高反演风速的SMB方法，验证了该方法在高频雷达风速反演中的可行性。