基于DDS技术的Loran—C信号源的杂散信号抑制的分析与实现     

皇甫江  华宇  李实锋 《时间频率学报》2014,(1):41-48

采用直接数字频率合成（DDS）技术设计的Loran—C信号源,具有输出杂散多且难以预测的缺点。基于对DDS基本原理的研究分析,针对DDS输出信号存在的相位舍位杂散问题,对其关键部位的相位累加模块进行优化设计,并基于FPGA技术,在QuartusII环境下完成了对Loran．C信号源的实现与仿真验证。结果表明,通过优化的设计算法能够产生失真小,稳定度好的输出波形,从而验证了该方法抑制杂散的有效性与可行性。  相似文献   

基于多普勒频移的单频载波相位周跳探测   总被引：1，自引：0，他引：1  

任永超  汪顺喜  方荣新 《测绘信息与工程》2010,35(1):8-10

阐述了多普勒探测周跳的原理，利用了静态和车载动态高频数据的L1上的载波和多普勒观测值，试验探测了其周跳。  相似文献   

Palaeoflood activity and climate change over the last 1400 years recorded by lake sediments in the north‐west European Alps     

B. Wilhelm  F. Arnaud  P. Sabatier  O. Magand  E. Chapron  T. Courp  K. Tachikawa  B. Fanget  E. Malet  C. Pignol  E. Bard  J. J. Delannoy 《第四纪科学杂志》2013,28(2):189-199

A high‐resolution sedimentological and geochemical study of a high‐altitude proglacial lake (Lake Blanc, Aiguilles Rouges, 2352 m a.s.l.) revealed 195 turbidites, 190 of which are related to flood events over the last 1400 years. We used the coarsest sediment fraction of each turbidite as a proxy for the intensity of each flood event. Because most flood events at this locality are triggered by localized summer convective precipitation events, the reconstructed sedimentary record reveals changes in the frequency and intensity of such events over the last millennium. Comparisons with other temperature, palaeohydrological and glacier reconstructions in the region suggest that the most intense events occurred during the warmest periods, i.e. during the Medieval Climate Anomaly (AD 800–1300) and the current period of global warming. On a multi‐decadal time scale, almost all the flood frequency peaks seem to correspond to warmer periods, whereas multi‐centennial variations in flood frequency appear to follow the regional precipitation pattern. Consequently, this new Alpine flood record provides further evidence of a link between climate warming and an increase in the frequency and intensity of flooding on a multi‐decadal time scale, whereas the centennial variability in flood frequencies is related to regional precipitation patterns. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Stable ⁸⁵Rb micro vapour cells: fabrication based on anodic bonding and application in chip-scale atomic clocks     

苏娟  邓科  郭等柱  汪中  陈兢  张耿民  陈徐宗 《海洋学报(英文版)》2010,29(11)

We describe the microfabrication of ⁸⁵Rb vapour cells using a glass-silicon anodic bonding technique and in situ chemical reaction between rubidium chloride and barium azide to produce Rb. Under controlled conditions, the pure metallic Rb drops and buffer gases were obtained in the cells with a few mm³ internal volumes during the cell sealing process. At an ambient temperature of 90 ℃ the optical absorption resonance of ⁸⁵Rb D1 transition with proper broadening and the corresponding coherent population trapping (CPT) resonance, with a signal contrast of 1.5% and linewidth of about 1.7 kHz, have been detected. The sealing quality and the stability of the cells have also been demonstrated experimentally by using the helium leaking detection and the after-9-month optoelectronics measurement which shows a similar CPT signal as its original status. In addition, the physics package of chip-scale atomic clock (CSAC) based on the cell was realized. The measured frequency stability of the physics package can reach to 2.1×10^-10 at one second when the cell was heated to 100 ℃ which proved that the cell has the quality to be used in portable and battery-operated devices.  相似文献   

Compact and tunable mid-infrared source based on a 2 μm dual-wavelength KTiOPO₄ intracavity optical parametric oscillator     

耿优福  谭晓玲  李学金  姚建铨 《海洋学报(英文版)》2010,29(11)

Using a double resonant KTiOPO₄ (KTP) intracavity optical parametric oscillator operating at degenerated point of 2 μm, we demonstrate a unique mid-infrared source based on difference frequency generation in GaSe crystal. The output tuning range is 8.42-19.52 μm, and a peak power of 834 W for type-I phase matching scheme and 730 W for type-II phase matching scheme are achieved. Experimental results show that this oscillator is a good alternative to the generator of a compact and tabletop mid-infrared radiation with a widely tunable range.  相似文献   

Analyse fréquentielle régionale des précipitations journalières maximales annuelles au Québec,Canada / Regional frequency analysis of annual maximum daily precipitation in Quebec,Canada     

《水文科学杂志》2013,58(4)

Abstract

Abstract A complete regional analysis of daily precipitations is carried out in the southern half of the province of Quebec, Canada. The first step of the regional estimation procedure consists of delineating the homogeneous regions within the area of study and testing for homogeneity within each region. The delineation of homogeneous regions is based on using L-moment ratios. A simulation-based testing of statistical homogeneity allows one to verify the inter-site variability. The second step of the procedure deals with the identification of the regional distribution and the estimation of its parameters. The General Extreme Value (GEV) distribution was identified as an appropriate parent distribution. This distribution has already been recommended by several previous research studies for regional frequency analysis of precipitation extremes. The parameters of the GEV distribution are estimated based on the computation of the regional L-CV, L-C_S and the mean of annual maximal daily precipitations. The third step consists of the estimation of precipitation quantiles corresponding to various return periods. The final procedure allows for the estimation of these quantiles at sites where no precipitation information is available. The use of a jack-knife resampling procedure with data from the province of Quebec allows one to demonstrate the robustness and efficiency of the regional estimation procedure. Values of the root mean square error were below 10% for a return period of 20 years, and 20% for a return period of 100 years.  相似文献   

Extreme value modelling of daily areal rainfall over Mediterranean catchments in a changing climate     

Yves Tramblay  Luc Neppel  Julie Carreau  Emilia Sanchez‐Gomez 《水文研究》2012,26(25):3934-3944

Heavy rainfall events during the fall season are causing extended damages in Mediterranean catchments. A peaks‐over‐threshold model is developed for the extreme daily areal rainfall occurrence and magnitude in fall over six catchments in Southern France. The main driver of the heavy rainfall events observed in this region is the humidity flux (FHUM) from the Mediterranean Sea. Reanalysis data are used to compute the daily FHUM during the period 1958–2008, to be included as a covariate in the model parameters. Results indicate that the introduction of FHUM as a covariate can improve the modelling of extreme areal precipitation. The seasonal average of FHUM can improve the modelling of the seasonal occurrences of heavy rainfall events, whereas daily FHUM values can improve the modelling of the events magnitudes. In addition, an ensemble of simulations produced by five different general circulation models are considered to compute FHUM in future climate with the emission scenario A1B and hence to evaluate the effect of climate change on the heavy rainfall distribution in the selected catchments. This ensemble of climate models allows the evaluation of the uncertainties in climate projections. By comparison to the reference period 1960–1990, all models project an amplification of the mean seasonal FHUM from the Mediterranean Sea for the projection period 2070–2099, on average by +22%. This increase in FHUM leads to an increase in the number of heavy rainfall events, from an average of 2.55 events during the fall season in present climate to 3.57 events projected for the period 2070–2099. However, the projected changes have limited effects on the magnitude of extreme events, with only a 5% increase in the median of the 100‐year quantiles. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Design hydrograph estimation in small and ungauged watersheds: continuous simulation method versus event‐based approach     

S. Grimaldi  A. Petroselli  F. Serinaldi 《水文研究》2012,26(20):3124-3134

The proper assessment of design hydrographs and their main properties (peak, volume and duration) in small and ungauged basins is a key point of many hydrological applications. In general, two types of methods can be used to evaluate the design hydrograph: one approach is based on the statistics of storm events, while the other relies on continuously simulating rainfall‐runoff time series. In the first class of methods, the design hydrograph is obtained by applying a rainfall‐runoff model to a design hyetograph that synthesises the storm event. In the second approach, the design hydrograph is quantified by analysing long synthetic runoff time series that are obtained by transforming synthetic rainfall sequences through a rainfall‐runoff model. These simulation‐based procedures overcome some of the unrealistic hypotheses which characterize the event‐based approaches. In this paper, a simulation experiment is carried out to examine the differences between the two types of methods in terms of the design hydrograph's peak, volume and duration. The results conclude that the continuous simulation methods are preferable because the event‐based approaches tend to underestimate the hydrograph's volume and duration. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

A-10绝对重力仪残差谱分析     

赵珞成  罗志才  王东晓  王德征 《测绘科学》2010,35(1):47-49

自由落体式绝对重力仪A-10的测量数据拟合残差呈现出明显的周期信号,对4个测站的残差进行FFT处理,并进行频谱分析,结果表明残差组平均的频谱更加稳定,主峰频率与测站无关,主峰幅值与测站明显相关,加周期项改正的绝对重力值偏小。  相似文献   

An analysis of change in alpine annual maximum discharges: implications for the selection of design discharges     

Attilio Castellarin  Alberto Pistocchi 《水文研究》2012,26(10):1517-1526

The paper presents an analysis of 17 long annual maximum series (AMS) of flood flows for Swiss Alpine basins, aimed at checking the presence of changes in the frequency regime of annual maxima. We apply Pettitt's change point test, the nonparametric sign test and Sen's test on trends. We also apply a parametric goodness‐of‐fit test for assessing the suitability of distributions estimated on the basis of annual maxima collected up to a certain year for describing the frequency regime of later observations. For a number of series the tests yield consistent indications for significant changes in the frequency regime of annual maxima and increasing trends in the intensity of annual maximum discharges. In most cases, these changes cannot be explained by anthropogenic causes only (e.g. streamflow regulation, construction of dams). Instead, we observe a statistically significant relationship between the year of change and the elevation of the catchment outlet. This evidence is consistent with the findings of recent studies that explain increasing discharges in alpine catchments with an increase in the temperature controlling the portion of mountain catchments above the freezing point. Finally, we analyse the differences in return periods (RPs) estimated for a given flood flow on the basis of recent and past observations. For a large number of the study AMS, we observe that, on average, the 100‐year flood for past observations corresponds to a RP of approximately 10 to 30 years on the basis of more recent observation. From a complementary perspective, we also notice that estimated RP‐year flood (i.e. flood quantile (FQ) associated with RP) increases on average by approximately 20% for the study area, irrespectively of the RP. Practical implications of the observed changes are illustrated and discussed in the paper. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献