Comparison of daily and sub-daily SWAT models for daily streamflow simulation in the Upper Huai River Basin of China

Despite the significant role of precipitation in the hydrological cycle, few studies have been conducted to evaluate the impacts of the temporal resolution of rainfall inputs on the performance of SWAT (soil and water assessment tool) models in large-sized river basins. In this study, both daily and hourly rainfall observations at 28 rainfall stations were used as inputs to SWAT for daily streamflow simulation in the Upper Huai River Basin. Study results have demonstrated that the SWAT model with hourly rainfall inputs performed better than the model with daily rainfall inputs in daily streamflow simulation, primarily due to its better capability of simulating peak flows during the flood season. The sub-daily SWAT model estimated that 58 % of streamflow was contributed by baseflow compared to 34 % estimated by the daily model. Using the future daily and 3-h precipitation projections under the RCP (Representative Concentration Pathways) 4.5 scenario as inputs, the sub-daily SWAT model predicted a larger amount of monthly maximum daily flow during the wet years than the daily model. The differences between the daily and sub-daily SWAT model simulation results indicated that temporal rainfall resolution could have much impact on the simulation of hydrological process, streamflow, and consequently pollutant transport by SWAT models. There is an imperative need for more studies to examine the effects of temporal rainfall resolution on the simulation of hydrological and water pollutant transport processes by SWAT in river basins of different environmental conditions.     

Weak GPS signal tracking using FFT discriminator in open loop receiver

An open loop tracking architecture, which tracks GPS signals under weak and challenging conditions, is analyzed. The in-phase and quadrature-phase integration pair is regarded as a single tone complex signal. An FFT-based method is used as a frequency discriminator to estimate the Doppler frequency residual of the single tone signal. Another FFT-based method applies complex squaring to eliminate the effect of the navigation data bits polarities. The performance of the FFT-based discriminators is assessed in three criteria. Those criteria are the signal strength and dynamic range that can be tracked and the accuracy of the estimated Doppler frequency. In addition, the performance of the discriminators is analyzed to provide the theoretical and simulated peak detection probability. The results indicate that the FFT discriminator can track signals about 5 dB weaker than the signals that can be tracked by the complex squared FFT discriminator. In a quasi-static environment, the Doppler frequency residual can be assumed to be around zero, which can enable the FFT-based discriminators to track signals with approximately 2 dB less power. Moreover, the performance of the FFT-based discriminators is compared with the performance of two other frequency discriminators, namely the fast–slow and power-based. The comparison results indicate that these two frequency discriminators give higher frequency estimation accuracy, but they have a narrower dynamic range.     

A model for retrieval of dual linear polarization radar fields from model simulation outputs

An algorithm for retrieving polarimetric variables from numerical model fields is developed. By using this technique, radar reflectivity at horizontal polarization~ differential reflectivity, specific differential phase shift and correlation coefficients between the horizontal and vertical polarization signals at zero lag can be derived from rain, snow and hail contents of numerical model outputs. Effects of environmental temperature and the melting process on polarimetric variables are considered in the algorithm. The algorithm is applied to the Advanced Regional Prediction System （ARPS） model simulation results for a hail storm. The spatial distributions of the derived parameters are reasonable when compared with observational knowledge. This work provides a forward model for assimilation of dual linear polarization radar data into a mesoscale model.     

Underice Operation of SJT-5 ROV

- The authors have used a low-cost ROV of observation type for underice surveying of the Nen-Jiang Cross-river oil pipe line in the Da Qing oil field. The operation method, process and the safety measures for severe cold areas are presented. The fruitful tries and experience may be useful to ROV operators in severe cold areas.     

鞍山附近“樱桃园组”的构造样式及其时代讨论

本文区分了“樱桃园组”岩石在元古主构造旋回的三幕变形,详细描述了各幕SFL组合和按区段进行了投影。主变形幕D₁的构造最发育,F₁控制着本区的岩性分布。构造序列及样式变化显示由高塑性向脆性的变形格式。本组与下伏的太古鞍山群变粒岩在构造序列、样式和变质相上都有显著差异,过去许多地质学家把二者混划为一个单位,统名“鞍山群”,属太古宙。但本组与上覆的辽河群(上元古)的构造样式和变质相却相似,故其时代相当于早元古Ferrian期。     

浅谈可控震源在煤田地震勘探中应用的几点认识

使用可控震源应注意三方面的问题:一是与大地的耦合,二是参数的最佳选取,三是在保证野外采集工作量近似不变情况下,提高地震剖面质量。解决方法是:配备可控震源力控装置、改变表层介质波阻抗可消除震源脱耦现象;选取参数应考虑清晰度、分辨率、信噪比,避免虚像出现在有效记录范围内;在野外数据采集时应减少振动次数、增加覆盖次数并注意压制不规则干扰和噪声,以提高地震剖面质量。     

Prevention of water and quicksand inrush during extracting contiguous coal seams under the lowermost aquifer in the unconsolidated Cenozoic alluvium—a case study

Extracting the contiguous coal seams under the lowermost aquifer in the unconsolidated Cenozoic alluvium is apt to water and quicksand inrush. By using a series of investigation methods including empirical formulas, numerical simulation, theoretical analysis, etc., the study focused on the fracture and the excess pore water pressure in the overlying strata in the process of extracting no. 8 coal seam firstly and no. 9 coal seam (under no. 8 coal seam) subsequently in no. 8102 working face of Luling coal mine in the north of Anhui Province of China. When no. 8 coal seam was extracted, the water-conducting fractured zone penetrated into the lowermost aquifer and rapid dissipation of excess pore water pressure above the gob occurred, accompanied by relatively high seepage hydraulic gradient over the headgate and the tailgate. When no. 9 coal seam was extracted, failure did not obviously extend upwards and the excess pore water pressure decreased slowly and a relatively high seepage hydraulic gradient transferred downwards from the headgate to the tailgate in the inclined profile. The safe water head (H _s) in the lowermost aquifer was confirmed to 15.6 m. Therefore, water and quicksand inrush was avoided effectively in the process of extracting the contiguous coal seams by dewatering, controlling mining height, and laying double resistance nets in the working face.     

超高压变质作用研究现状及问题

本文从超高压变质作用的矿物学、Ｐ－Ｔ－ｔ轨迹和超高压地体抬升、保存机制三个方面总结了近年来超高压变质作用研究所取得的重要进展和存在的问题。超高压变质作用的矿物学研究正在向深入发展，其Ｐ－Ｔ－ｔ轨迹具有三种成因类型。而其超高压地体的抬升、保存机制则是争论的焦点，其中增生楔模式（Ｐｌａｔｔ，１９８７）和连续俯冲─仰冲机制较好地解释了抬升过程，但也存在一些问题需进一步研究。     

云南地区地震的重新定位及b值研究

通过联合使用固定台站和流动台站资料,对2010年5月~2011年7月发生在云南地区的7127个地震进行重新定位。考虑到速度模型对定位结果的影响,用VELEST方法获得云南地区走时残差均方根最小的一维P波速度模型,基于反演模型用双差法对地震进行重新定位,得到5836个地震的定位结果。结果表明,云南地区发震层主要位于中上地壳,且滇西地区震源深度相对较深。用精定位后的地震目录计算云南地区b值,从b值空间分布特征可以看出,b值随深度逐渐减少,且在9~10km深度时,b值变化最为明显,可能表明云南地区中强震孕震层主要位于9km以下;同时,盈江5.8级地震序列b值的三维空间分布显示,主震发生在高低b值的过渡带。