Directional errors in remanent magnetization of non-cubic soft sediment specimens measured with spinner magnetometers     

William K. Steele 《Geophysical Journal International》1989,96(2):333-341

Summary. This paper assesses theoretically and experimentally the errors in palaeomagnetic directions introduced by measuring rectangular but non-cubic blocks of soft sediments in slow speed spinner magnetometers. Plastic boxes commonly used for this purpose hold samples 21 × 21 × 15 mm. This study models the response of Schonstedt and Molspin spinners to such specimens and presents the results of experiments in which the remanent magnetization (RM) of obsidian blocks, both as cubes and after subsequent cutting to fit within the boxes, was measured to determine actual instrument behaviour. These experiments indicate that the error introduced by use of specimens of the above dimensions may be as much as 8.5° for the smallest specimen-sensor separation in the Schonstedt spinner. For the Molspin spinner and for the next smallest specimen-sensor separation in the Schonstedt instrument, the error is smaller but nevertheless non-negligible.  相似文献   

Contribution of ionospheric irregularities to the error of dual-frequency GNSS positioning     

B. C. Kim  M. V. Tinin 《Journal of Geodesy》2007,81(3):189-199

This paper investigates the third-order residual range error in the dual-frequency correction of ionospheric effects on satellite navigation. We solve the two-point trajectory problem using the perturbation method to derive second-approximation formulas for the phase path of the wave propagating through an inhomogeneous ionosphere. It is shown that these formulas are consistent with the results derived from applying perturbation theory directly to the eikonal equation. The resulting expression for the phase path is used in calculating the residual range error of dual-frequency global positioning system (GPS) observations, in view of second- and third-order terms. The third-order correction includes not only the quadratic correction of the refractive index but also the correction for ray bending in an inhomogeneous ionosphere. Our calculations took into consideration that the ionosphere has regular large-scale irregularities, as well as smaller-scale random irregularities. Numerical examples show that geomagnetic field effects, which constitute a second-order correction, typically exceed the effects of the quadratic correction and the regular ionospheric inhomogeneity. The contribution from random irregularities can compare with or exceed that made by the second-order correction. Therefore, random ionospheric irregularities can make a significant (sometimes dominant) contribution to the residual range error.  相似文献   

Temporal correlations of atmospheric mapping function errors in GPS estimation     

Borys Stoew  Tobias Nilsson  Gunnar Elgered  Per O. J. Jarlemark 《Journal of Geodesy》2007,81(5):311-323

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The impact of inhomogenous background errors on a global wave data assimilation system   总被引：1，自引：0，他引：1  

Diana J. M. Greenslade  Ian R. Young 《Journal of Atmospheric & Ocean Science》2005,10(2):61-93

One of the main limitations in current wave data assimilation systems is the lack of an accurate representation of the structure of the background errors. In this work, models for the observational error variance, background error variance and background error correlations are developed based on the results of previous studies. These are tested in a global wave data assimilation system and the resulting wave forecasts are verified against independent observations from buoys. Forecasts of significant wave height show substantial improvement over the Australian Bureau of Meteorology's current operational wave forecasting system. However, forecasts of peak period are not similarly improved. The regional impacts of the new assimilation scheme are found to vary on a seasonal basis. Overall, it is shown that the inclusion of a latitudinally dependent background error, and improved specification of the background and observational error variances can reduce the root-mean-square error of 24-hour forecast Significant Wave Height by almost 10%.  相似文献   

测距仪周期误差及加常数的同时测定     

师郡 《测绘与空间地理信息》2000,23(2):38-39

文章提出的方法近似于平台法,但又有不同,不需要设置专用平台、检测可在室内进行,因此一般的测绘单位都可自己定期对测距仪进行检定,并且由于消除了外界因素的影响,使得检定结果更为可靠。  相似文献   

一种新改进的DPIV方法   总被引：1，自引：0，他引：1  

田晓东  李玉梁  陈嘉范  余常昭 《水科学进展》2000,11(1):59-63

数字粒子图像测速技术DPIV(Digital Particle Image Velocimetry)是一种快速提取流场速度的方法,但测速精度较低。已有的改进方法虽然使精度得到了提高,却丧失了DPIV快速处理的优点。本文综合已有方法的优点,提出了一种兼有快速和精度较高的处理方法。该方法以Willert提出的DPIV方法为基础,吸收了Huang提出的改进方法中的迭代思想,既保留了DPIV快速处理的优点,又在一定程度上提高了测速的精度,非常适合于多工况和非恒定流的测量。  相似文献   

含有粗差的起始数据对水下地形测量的影响及修正     

魏炳乾  黄志文  孙小军 《海洋测绘》2005,25(5):49-51

针对含有粗差的起始数据导致的错误碎部点成果,对粗差产生的途径进行了分析,给出了进行改正计算的必备条件,最后结合实际例子进行了计算验证。结果表明改正计算方法在理论上是严密的,在实际工作中也具有可操作性。  相似文献   

Supporting USLE‐MM reliability by analyzing soil loss measurement errors          下载免费PDF全文

Vincenzo Bagarello  Vito Ferro 《水文研究》2017,31(4):847-853

Sampling the collected suspension in a storage tank is a common procedure to obtain soil loss data. A calibration curve of the tank has to be used to obtain actual concentration values from those measured by sampling. However, literature suggests that using a tank calibration curve was not a common procedure in the past. For the clay soil of the Sparacia (Italy) experimental station, this investigation aimed to establish a link between the relative performances of the USLE‐M and USLE‐MM models, usable to predict plot soil loss at the event temporal scale, and soil loss measurement errors. Using all available soil loss data, lower soil loss prediction errors were obtained with the USLE‐MM (exponent of the erosivity term, b₁ > 1) than the USLE‐M (b₁ = 1). A systematic error of the soil loss data is unexpected for the Sparacia soil because the calibration curve does not depend on the water level in the tank. In any case, this type of error does not have any effect on the b₁ exponent. Instead, this exponent decreases as the level of underestimation increases for increasing soil loss values. This type of error can occur at Sparacia if it is assumed that a soil loss measurement can be obtained by a bottle sampler dipped close to the bottom of the tank after mixing the suspension and assuming that the measured concentration coincides with the actual one. In this case, the risk is to obtain a lower b₁ value than the actual one. In conclusion, additional investigations on the factors determining errors in soil loss data collected by a sampling procedure are advisable because these errors can have a noticeable effect on the calibrated empirical models for soil loss prediction.  相似文献   

Integrated water resource management in a major canal command in eastern India     

S. K. Raul  Sudhindra N. Panda  H. Holländer  M. Billib 《水文研究》2011,25(16):2551-2562

The present rice‐dominated cropping system in the Hirakud canal command (eastern India) is under severe threat due to imbalance between irrigation water supply and demand. The canal water supply, which is the only source of irrigation, only meets 54% of the demand at 90% probability of exceedance (PE). In order to mitigate the irrigation water deficit from canal water, groundwater is considered as a supplemental source. Quasi‐three‐dimensional groundwater flow simulation modelling was, therefore, carried out by using Visual MODFLOW to detect the change in hydraulic head due to transient pumping stresses. The simulation model was calibrated and validated satisfactorily. Sensitivity analysis of the model parameters shows that groundwater recharge is most sensitive followed by aquifer hydraulic conductivity at almost all the sites of the command area, whereas the model is comparatively less sensitive to specific storage and specific yield. Enhanced pumping scenarios showed that groundwater extraction can be increased up to 50 times of the existing pumping without causing any adverse effect to the aquifer but the aquifer does not permit to exploit water in order to fulfill the irrigation water demand even at 10% PE. Hence, it is imperative to develop an optimal land and water resources management plan of the command area. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Seasonal and interannual variations of carbon exchange over a rice-wheat rotation system on the North China Plain   总被引：2，自引：0，他引：2  

Chen Chen  Dan Li  Zhiqiu Gao  Jianwu Tang  Xiaofeng Guo  Linlin Wang  Bingcheng Wan 《大气科学进展》2015,32(10):1365-1380

Rice-wheat (R-W) rotation systems are ubiquitous in South and East Asia, and play an important role in modulating the carbon cycle and climate. Long-term, continuous flux measurements help in better understanding the seasonal and interannual variation of the carbon budget over R-W rotation systems. In this study, measurements of CO2 fluxes and meteorological variables over an R-W rotation system on the North China Plain from 2007 to 2010 were analyzed. To analyze the abiotic factors regulating Net Ecosystem Exchange (NEE), NEE was partitioned into gross primary production (GPP) and ecosystem respiration. Nighttime NEE or ecosystem respiration was controlled primarily by soil temperature, while daytime NEE was mainly determined by photosythetically active radiation (PAR). The responses of nighttime NEE to soil temperature and daytime NEE to light were closely associated with crop development and photosynthetic activity, respectively. Moreover, the interannual variation in GPP and NEE mainly depended on precipitation and PAR. Overall, NEE was negative on the annual scale and the rotation system behaved as a carbon sink of 982 g C m-2 per year over the three years. The winter wheat field took up more CO2 than the rice paddy during the longer growing season, while the daily NEE for wheat and rice were -2.35 and -3.96 g C m-2, respectively. After the grain harvest was subtracted from the NEE, the winter wheat field became a moderately strong carbon sink of 251-334 g C m-2 per season, whereas the rice paddy switched to a weak carbon sink of 107-132 per season.  相似文献