单频BDS定位的可靠性分析     

杨威  张秋昭  鲍国  王坚 《测绘科学》2016,41(12):254-260

针对BDS系统中存在的模型误差对模糊度解算造成估计偏差的问题,该文提出了以最小可探测偏差(MDB)为模型误差计算有偏估计成功率对模糊度解算的正确性进行评价,并分别以码观测和相位观测进行了仿真实验,得出了存在码观测MDB和相位观测MDB等情形时的有偏估计成功率大小的规律,并与不存在模型误差时的成功率进行对比分析。鉴于GNSS定位粗差包括伪距码观测粗差和相位周跳,推导了码观测和相位观测情况下的BDS系统单频定位可靠性指标MDB和最小可探测效应(MDE),并进行了中国大陆内某地点的BDS单频定位性能的仿真模拟,着重分析了载波相位MDB与周跳之间的关系。  相似文献   

Reproductive success of Calanus pacificus during diatom blooms in Dabob Bay, Washington   总被引：1，自引：4，他引：1  

James J. Pierson  Claudia Halsband-Lenk  Andrew W. Leising 《Progress in Oceanography》2005,67(3-4):314

While numerous laboratory studies in the last decade have shown that diatoms can induce reproductive failure in copepods, field evidence for a negative diatom effect is equivocal. To unambiguously elucidate the effects diatoms have on copepod reproduction in situ, we undertook a study of the abundance, distribution, grazing rates, and reproductive success of Calanus pacificus in Dabob Bay, Washington, USA, during two spring bloom periods. We simultaneously measured the phytoplankton composition, abundance, and distribution. Here we present results for the reproductive success of C. pacificus using four measurements: egg production rate, clutch size, egg hatching success, and naupliar survival (to the first feeding stage). Egg production rate was positively correlated with chlorophyll a concentration, and egg hatching success and naupliar survival were usually greater than 80%. However, in February 2002 and 2003 – during blooms of diatoms of the genus Thalassiosira – either egg hatching success, naupliar survival, or both were significantly depressed compared to other times in spring and summer. These effects, combined with evidence that C. pacificus was grazing aldehyde-producing Thalassiosira at the time of their blooms, indicate that diatoms can negatively affect copepod reproduction in the field, albeit only under specific circumstances and for brief periods.  相似文献   

All washed up: spatial and temporal variation in the wash-up and fate of chondrichthyan egg cases along a section of the Garden Route,South Africa     

S Schmöle  M Brown 《African Journal of Marine Science》2020,42(2):141-149

Washed-up chondrichthyan egg cases were collected along three different sandy beaches around Plettenberg Bay, South Africa, between April 2016 and March 2017. GPS location was recorded upon collection, and, after being soaked in fresh water for 12 hours, egg cases were identified to species level. Additionally, boreholes, damage, biofouling and state of the hatchling slit were recorded. The hatching success of each egg case was inferred from these factors. Over the year, 6 996 egg cases of nine species were collected. Egg cases of the tiger catshark Halaelurus natalensis had the highest hatching rate at 70%. Egg cases of the leopard catshark Poroderma pantherinum had the highest predation rate at 57%. Season had no significant effect either on overall egg-case counts or on per-species counts. Location, however, significantly affected the overall egg-case counts, as well as per-species counts, with the exceptions of H. natalensis and the St Joseph Callorhinchus capensis. The results of this study provide insight into chondrichthyan species occurrence and spatial variation along a section of the Garden Route in the Western Cape Province and can act as a baseline for future research.  相似文献   

基于部分整周模糊度固定的非差GPS精密单点定位方法   总被引：2，自引：2，他引：0  

潘宗鹏  柴洪洲  刘军  董冰全  刘鸣  王华润 《测绘学报》2015,44(11):1210-1218

近年来,精密单点定位(PPP)模糊度固定技术不断发展,模糊度正确固定后可以提高短时间的定位精度。然而固定错误的模糊度,将引起严重的定位偏差,因此对PPP模糊度固定的成功率和可靠性进行研究很有必要。本文探讨了采用非差小数偏差(FCBs)改正的PPP模糊度固定方法;同时提出了一种分步质量控制的PPP部分模糊度固定(PAR)策略。通过欧洲CORS数据对该方法进行验证,结果表明:PPP模糊度固定可以提高小时解静态PPP定位精度。同时,采用部分模糊度固定策略,能够有效控制未收敛模糊度影响,提高用户端PPP模糊度固定成功率。  相似文献   

不分散低固相钻井液体系在张掖平山湖矿区中的应用          下载免费PDF全文

蔡晓文  纪卫军  阮海龙  李艳宁 《探矿工程》2010,37(8):27-28,31

平山湖矿区第四系、第三系地层属于遇水不稳定地层,钻探施工时,地层造浆严重、孔径扩大率高,造成钻探事故频发、施工效率低。采用以聚合物为主要添加剂的不分散低固相钻井液体系在该矿区进行了应用试验,有效地抑制了粘土造浆及泥页岩水化膨胀,取得了很好的效果。  相似文献   

受控石油定向井技术初步实践     

王国政  张奎秀等 《中国煤田地质》2001,13(3):71-72

通过石油定向井技术初步实践，为今后的定向井施工奠定了基础，并取得了显著的经济效益。  相似文献   

草原农垦区土地沙质荒漠化过程的生物学机制   总被引：11，自引：1，他引：10  

赵文智  何志斌  李志刚 《地球科学进展》2003,18(2):257-262

以沙质荒漠化正处在发展过程的河北坝上地区和沙质荒漠化严重的科尔沁沙地流沙治理区为例,结合国内外已有的研究成果,探讨草原沙质荒漠化的主要生物学机制。指出在草原农垦区开垦和过度放牧引起的土壤细颗粒物质、养分损失,促进了灌木侵入。灌木侵入又加剧了土壤养分、水分空间格局的改变,在灌丛周围形成一个包括微生物在内的土壤肥力富集区,即灌丛"土壤肥岛",而在丛间发生土壤风蚀和水蚀,导致斑块状流沙甚至大面积流沙的出现。诱发荒漠化的不合理耕作、灌溉、盐渍化、过度放牧等过程同样影响菌根菌的密度和接种成功率,从而降低草地生产力。在草原地区的流沙上建立各种固沙植被不仅使流沙地土壤养分、水分异质性加强,而且使沙地景观异质性增加。还提出用土壤颗粒分形维数来表征土地沙质荒漠化的程度,以空间上不同样点土壤属性变异系数（方差与平均值之比）作为沙质荒漠化土壤属性异质性的测度。  相似文献   

评价GPS相位模糊度整数解正确性的严密方法     

周扬眉  刘经南  李信 《武汉大学学报(信息科学版)》2004,29(11):1004-1007

针对如何评价模糊度整数解的正确性，指出了基于传统的假设检验理论的三步法存在的理论缺陷，介绍了模糊度归整域的概念和可容许整数估计的定义，并在Teunissen关于可容许整数估计原定义的基础上给出了更为严密的新定义。基于这个新定义，讨论了模糊度成功率的概念及其计算公式。  相似文献   

On container versus time based inspection policies in invasive species management     

Amitrajeet A. Batabyal  Peter Nijkamp 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(5):340-347

We study the problem of precluding biological invasions caused by ships transporting internationally traded goods in containers between different regions of the world. Using the long run expected net cost (LRENC) of inspections as the apposite managerial objective, we address the following important question: given that inspection is a cyclical activity, is the LRENC lower when a port manager’s inspector inspects cargo upon the arrival of a specified number of containers (container policy) or is this LRENC lower when this inspector inspects cargo at fixed points in time (temporal policy)? We construct a queuing theoretic model and show that in an inspection cycle, irrespective of whether the inspection policy choice is made on the basis of an explicit optimization exercise or on the basis of rules of thumb, the container policy is superior to the temporal policy because the container policy results in lower LRENC from inspection activities.  相似文献   

Estimating contributions of sources of soil CO2 at the shallower layer in a Japanese larch forest area     

Wei LIU Jun MORIIZUMI Hiromi YAMAZAWA Takao IIDA 《中国地球化学学报》2006,25(B08):198-198

Soils contain about twice the amount of carbon presented in the atmosphere, so a small change in the soil carbon will influence atmospheric chemistry and heat balance. The soil carbon ultimately exchanged with the atmospheric CO2 as soil CO2, which mainly exists at the depth of 0-20 cm. The transport of soil CO2 is affected by the sources of soil CO2. Thus, separation of the contributions of sources of soil CO2 is a fundamental need to understand and predict implications of environmental change on soil carbon cycling and sequestration. It is a complicated task, so that a number of different methodological approaches such as component integration, root removal, and gap analyses have been developed. However, these methods could not avoid changing soil characteristics such as air-filled porosity, soil temperature and soil water contents. Consequently, fractional contributions of respiration of living root and decomposition of soil organic matter to the total soil CO2 cannot be estimated correctly. In this study, based on mass balance theory of both concentrations and δ^13C of soil CO2, a trenching method with a stable-isotope technique was used to determine both soil CO2 sources at the depth of 3-13 cm in a Japanese larch forest area during 30 May to 7 October 2005 and fractional contributions of these sources. Experimental results showed that the amount of atmospheric CO2 invaded the soil air was not significantly variable while its percent rate in the total soil CO2 had significantly temporal variations with the lower values between 5 August and 1 September. The litter-layer decomposition was very small. The soil CO2 derived from the respiration of living root and the decomposition of soil organic matter showed significantly temporal variations with increase from 30 May to 5 Aug. and decrease from 1 September to 7 October, 2005; and it accounted for 82%-98% of the total soil CO2 in which the respiration of living root was in the range from 32% to 62%.  相似文献