GPS/BDS接收机端系统偏差实时估计方法     

隋心  邹鑫慈  徐爱功  陈玮娴 《测绘科学》2016,41(12):106-109,115

针对GPS-BDS系统偏差会导致GPS和BDS系统间的混合双差模糊度不具有整数特性,且其不完全稳定的问题,该文提出一种GPS/BDS系统偏差实时在线估计方法。通过将双差模糊度以单差模糊度之差的形式进行求解,然后再将以周为单位的单差模糊度投影为双差模糊度,以此消除GPS和BDS不同波长的影响;在此基础上,采用Kalman滤波对系统偏差进行实时动态估计。实验结果表明,该方法采用较少历元的观测数据便可使系统偏差收敛,并且收敛后十分稳定,可以将其作为校正参数;加入系统偏差改正的GPS/BDS紧组合定位在恶劣环境下表现良好,可将模糊度固定平均所需时间缩短29%,模糊度固定成功率提高45%。  相似文献   

Contrasting the Skills and Biases of Deterministic Predictions for the Two Types of El Nio     

Fei ZHENG  Jin-Yi YU 《大气科学进展》2017,34(12):1395-1403

The tropical Pacific has begun to experience a new type of El Nio, which has occurred particularly frequently during the last decade, referred to as the central Pacific(CP) El Nio. Various coupled models with different degrees of complexity have been used to make real-time El Nio predictions, but high uncertainty still exists in their forecasts. It remains unknown as to how much of this uncertainty is specifically related to the new CP-type El Nio and how much is common to both this type and the conventional Eastern Pacific(EP)-type El Nio. In this study, the deterministic performance of an El Nio–Southern Oscillation(ENSO) ensemble prediction system is examined for the two types of El Nio. Ensemble hindcasts are run for the nine EP El Nio events and twelve CP El Nio events that have occurred since 1950. The results show that(1) the skill scores for the EP events are significantly better than those for the CP events, at all lead times;(2) the systematic forecast biases come mostly from the prediction of the CP events; and(3) the systematic error is characterized by an overly warm eastern Pacific during the spring season, indicating a stronger spring prediction barrier for the CP El Nio. Further improvements to coupled atmosphere–ocean models in terms of CP El Nio prediction should be recognized as a key and high-priority task for the climate prediction community.  相似文献   

FY-2G卫星冬夏云量产品偏差分析   总被引：1，自引：0，他引：1       下载免费PDF全文

刘健  崔鹏  肖萌 《应用气象学报》2017,28(2):177-188

开展卫星反演云量的精度评估是业务应用的基础,也是充分发挥卫星观测效益的前提。利用同类卫星产品EOS Aqua/MODIS云产品,选取2015年6月和12月共80个个例,包括43个白天个例,37个夜间个例。采用交叉比对方法对FY-2G云量产品进行相对偏差分析。结果表明:FY-2G与Aqua/MODIS计算云量总体趋势相当,无论从时间分布（白天和夜间）还是季节分布（6月和12月）上看,FY-2G与Aqua云量相对偏差较为稳定,FY-2G反演云量小于Aqua/MODIS反演云量。匹配个例中FY-2G平均云量为72.81%,Aqua/MODIS平均云量是76.19%,两者相关系数为0.74。两者绝对偏差小于5%的像元比例为72.34%;云量偏差绝对值小于15%的像元比例为79.51%。FY-2G与Aqua/MODIS云量偏差主要来自各自卫星的观测能力与所采用的云检测算法。与具有36个探测通道、星下点最低空间分辨率为0.01°×0.01°的Aqua/MODIS观测数据相比,FY-2G所具有的5通道、星下点最高空间分辨率为0.05°×0.05°的观测数据会出现对云,尤其是破碎云和薄卷云的漏检。两种具有不同时空属性的数据在匹配处理时采用的不同算法也会在比对分析中引入偏差。  相似文献   

北斗广播星历偏差分析及改正     

张益泽  陈俊平  周建华  杨赛男  王彬  陈倩  巩秀强 《测绘学报》2016,45(Z2):64-71

以后处理精密轨道钟差为参考,分析了2014年2月至2016年10月北斗广播星历误差及空间信号精度,分析结果表明,北斗广播星历存在偏差,最大超过2m。在此基础上,基于广域差分改正数,采用18个MGEX站不同频点及频点组合连续97d的数据对以上广播星历偏差进行了进一步验证。验证结果表明,不同卫星的伪距观测残差存在与广播星历偏差一致的系统性偏差。比较后处理给出的TGD和广播星历给出的TGD参数的偏差(dTGD),发现dTGD与基于广域差分参数的BEB的相关系数达到0.89,这表明经广域差分参数改正后的星历偏差可能是由广播电文中的TGD偏差造成。将北斗广播星历偏差改正到TGD参数上,分析对用户定位的影响。结果表明,经改正后,双频用户在N、E、U 3个方向单点定位精度分别提高14.9%、28.4%、15.5%,其定位残差也明显得到改善。  相似文献   

Precisely wrong or vaguely right: simulations of noisy discard data and trends in fishing effort being included in the stock assessment of North Sea plaice     

Dickey-Collas  Mark; Pastoors  Martin A.; van Keeken  Olvin A. 《ICES Journal of Marine Science》2007,64(9):1641-1649

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Assessment of wind-forcing impact on a global wind-wave model using the TOPEX altimeter     

Hui Feng  Doug Vandemark  Yves Quilfen  Bertrand Chapron  Brian Beckley 《Ocean Engineering》2006,33(11-12):1431-1461

The study presents assessment of an operational wave model (Wavewatch III), focusing upon the model sensitivity to wind-forcing products. Four wind fields are used to drive the model, including the NCEP/NCAR reanalysis and three other products that assimilate various satellite wind measurements having high spatial resolution, including the QuikSCAT scatterometer. Three wave field statistics: significant wave height, mean zero-crossing wave period, and mean square slope are compared with collocated TOPEX altimeter derivatives to gauge the relative skill of differing wind-forced model runs, as well as to demonstrate an extended use of the altimeter beyond simply supplying wave height for wave model validation and assimilation. Results suggest that model output is critically sensitive to choice of the wind field product. Higher spatial resolution in the wind fields does lead to improved agreement for the higher-order wave statistics.  相似文献   

Bedload yields for sand‐bed streams in the Ngarradj Creek catchment,Northern Territory,Australia          下载免费PDF全文

Wayne D. Erskine  Mike J. Saynor 《水文研究》2015,29(17):3767-3778

Bedload yields were calculated by 39 methods at the East Tributary gauge, nine methods at Upper Swift Creek gauge and 11 methods at Swift Creek gauge in the Ngarradj Creek catchment in northern Australia. These methods involved combining various significant bedload rating curves determined for a measured bedload data set for a 4‐year period with either the hourly or daily hydrographs or flow duration curves for the same period, 1 September 1998 to 31 August 2002. Bedload ratings were both statistically significant (ρ ≤ 0.05) and explained at least 60% of the variance in bedload flux. Bias corrections were used with all methods based on log₁₀‐transformed ratings. Estimated mean annual bedload yields varied by three orders of magnitude at the East Tributary gauge and by two orders of magnitude at Upper Swift Creek and Swift Creek gauges. Hourly discharges usually produced higher estimated yields than daily discharges. The bedload rating‐flow duration curve technique overestimates yields and bias correction methods always produce even higher yields. Ratings using both immersed bedload weight and adjusted immersed bedload weight always under‐predicted yields because they contain an implicit threshold of motion condition that is at least four times greater than that predicted by Bagnold's threshold equation. Such a result questions the applicability of Bagnold's threshold equation to the Ngarradj Creek catchment. The best estimates of mean annual bedload yield at East Tributary, Upper Swift Creek and Swift Creek gauges are 600 ± 170 (SE), 1065 ± 150 and 1795 ± 270 t/year, respectively. © 2015 Commonwealth of Australia. Hydrological Processes © 2015 John Wiley & Sons Ltd.  相似文献   

Evaluation of dynamically downscaled reanalysis precipitation data for hydrological application          下载免费PDF全文

Satish Bastola  Vasubandhu Misra 《水文研究》2014,28(4):1989-2002

Skilful and reliable precipitation data are essential for seasonal hydrologic forecasting and generation of hydrological data. Although output from dynamic downscaling methods is used for hydrological application, the existence of systematic errors in dynamically downscaled data adversely affects the skill of hydrologic forecasting. This study evaluates the precipitation data derived by dynamically downscaling the global atmospheric reanalysis data by propagating them through three hydrological models. Hydrological models are calibrated for 28 watersheds located across the southeastern United States that is minimally affected by human intervention. Calibrated hydrological models are forced with five different types of datasets: global atmospheric reanalysis (National Centers for Environmental Prediction/Department of Energy Global Reanalysis and European Centre for Medium‐Range Weather Forecasts 40‐year Reanalysis) at their native resolution; dynamically downscaled global atmospheric reanalysis at 10‐km grid resolution; stochastically generated data from weather generator; bias‐corrected dynamically downscaled; and bias‐corrected global reanalysis. The reanalysis products are considered as surrogates for large‐scale observations. Our study indicates that over the 28 watersheds in the southeastern United States, the simulated hydrological response to the bias‐corrected dynamically downscaled data is superior to the other four meteorological datasets. In comparison with synthetically generated meteorological forcing (from weather generator), the dynamically downscaled data from global atmospheric reanalysis result in more realistic hydrological simulations. Therefore, we conclude that dynamical downscaling of global reanalysis, which offers data for sufficient number of years (in this case 22 years), although resource intensive, is relatively more useful than other sources of meteorological data with comparable period in simulating realistic hydrological response at watershed scales. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Three‐dimensional simulations of tensile cracks in geomaterials by coupling meshless and finite element method          下载免费PDF全文

Chong Peng  Wei Wu  Bingyin Zhang 《国际地质力学数值与分析法杂志》2015,39(2):135-154

Failure in geotechnical engineering is often related to tension‐induced cracking in geomaterials. In this paper, a coupled meshless method and FEM is developed to analyze the problem of three‐dimensional cracking. The radial point interpolation method (RPIM) is used to model cracks in the smeared crack framework with an isotropic damage model. The identification of the meshless region is based on the stress state computed by FEM, and the adaptive coupling of RPIM and FEM is achieved by a direct algorithm. Mesh‐bias dependency, which poses difficulties in FEM‐based cracking simulations, is circumvented by a crack tracking algorithm. The performance of our scheme is demonstrated by two numerical examples, that is, the four‐point bending test on concrete beam and the surface cracks caused by tunnel excavation. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

长波区间太阳辐射对气候模拟的影响   总被引：1，自引：0，他引：1       下载免费PDF全文

卢鹏  张华  荆现文  王志立 《大气科学学报》2015,38(2):175-183

长波区间的太阳辐射在气候模式中往往被忽略。利用国家气候中心BCC_AGCM2.0.1大气环流模式,采用矩阵算子辐射传输算法,研究了长波区间太阳辐射对气候模式辐射通量和温度模拟结果的影响。结果表明,以ISCCP和CERES辐射资料为标准,考虑长波区间太阳辐射后,长波区间晴空大气地表向下辐射通量平均误差减小2.05 W/m2,均方根误差减少1.29 W/m2;长波区间晴空大气模式顶向上辐射通量平均误差减小0.70 W/m2,均方根误差减小0.21 W/m2;长波区间有云大气地表向下辐射通量平均误差减小1.38 W/m2,均方根误差减小1.03 W/m2;长波区间有云大气模式顶向上辐射通量平均误差减小0.99 W/m2,均方根误差减小0.30 W/m2。以ECMWF再分析资料为标准,考虑长波区间太阳辐射后,赤道地区上对流层—下平流层区域温度的冷偏差得到改善,对流层顶温度平均误差减小0.27 K,均方根误差减小0.25 K。  相似文献