精密水准折光改正模型研究

大气折光差是精密水准测量系统误差的主要来源之一,必须设法予以削减。本文在分析现有水准折光改正方法的基础上,导出了一种基于水准视线折光角的改正模型。该模型具有跟经典的库卡梅基模型大致相同的改正精度,但适用性更强。     

大气竖直折光改正的新方法

本文分析了几种常用的大气折光改正方法,提出了在EDM三角高程测量中,不需要测定气象参数,利用观测双棱镜的垂直角和距离,从大气垂直偏角入手直接推算出大气折光系数公式的新方法。最后并对公式做了精度分析,计算的折光系数中误差能达到±0.05。此方法适用于测区气象条件复杂、不便于精确测定测线全程气象参数的情况。     

测区垂直大气折光系数的变化及因地选择大气折光系数的意义

根据几年的测量数据统计出岔路河测区夏季垂直大气折光系数的变化,并得到其平均值、同期变化幅度、年变化幅度、同一地区不同测线的变化幅度,从而为该地区的测量工作和气象地质等研究提供了参考数据.由此,也得出垂直大气折光系数差值对正反高差较差的影响,随边长的增大而增大,边长较长时必须选用接近实际的垂直大气折光系数.     

大气折光与视准线观测

视准线观测是目前我国土石坝水平位移观测中最常见的方法。通过对大气水平折光的理论探讨,本文对大气水平折光影响进行了定量分析,给出了利用气象元素计算大气折光对视准线观测结果影响的实用公式,并对视准线观测中的有关问题进行了讨论。     

基于大气湍流理论的折光模型

基于大气湍流理论,严密推导出折射系数、折光角、折光曲率等折光公式。这些折光公式综合考虑了普热通量、云量、地面潮湿度等多种气象参数,更能贴切地反映大气折光的影响。最后,通过采集数据对公式进行了验证,所得结果符合湍流理论。     

近地层大气折光系数变化特征分析

本文从大气垂直折光基本定义出发,分析了导致近地层折光系数变化的根本原因和直接原因,指出折光系数的变化具有５个特征,即时间、气候、高度、土壤及均值特征,并据此提出了应用中的一些看法。     

对榆林北部地区大气垂直折光系数的几点认识

大气折光差在垂直面的投影，即垂直折光差。产生垂直折光差的主要原因是大气在垂直方向上的密度分布不均匀，它受地理，地貌、时间、气候等因素影响。三角高程测量作业过程中，正确选用大气折光系数，可以有效地提高测量精度，减少不必要的返工浪费。     

在大气折射延迟模型中避免采用大气分布模型的论证

天文大气折射是经典天体测量学和大地测量的一项误差源,大气折射延迟是空间大地测量技术中的一项重要误差源,它们的改正模型都直接与大气折射率和大气分布模型有关。文章简述了大气的垂直分布状况,以及大气折射率(或折射率差)因地和因方位而异的情况,分析了目前只能采用球对称大气分布模型的原因。论证了随测站和随方位而异的天文大气折射和电磁波大气折射延迟实测模型建立的必要性和可能性。实测模型已经包含了测站上空大气实际分布及其非球对称的特性,不必再去寻找或建立随地势而异和随季节而变的大气分布模型,避免了大气分布模型选择不当的影响,从而排除了空间大地测量技术中的一项主要误差源。     

珠峰高程测量大气垂直折光系数的研究

大气垂直折光是影响珠峰高程测量成果和精度的重要因素之一。本文根据2005年珠峰高程测量实际数据详细分析研究了大气温度垂直梯度与大气垂直折光系数的计算原则、方法及其变化特征与变化趋势,结合同以往(1975、1992年)珠峰高程测量中大气温度垂直梯度与大气垂直折光系数变化趋势的比较,得出气温垂直梯度与大气垂直折光系数均存在周日变化并给出了它们的变化趋势,提高了珠峰高程的计算精度。     

Effects of water and heat on growth of winter wheat in the North China Plain

The North China Plain (NCP) was selected as the study area and the effects of water and heat were analysed to determine the dominant factor affecting winter wheat growth. The mean, minimum and maximum temperatures, precipitation and soil moisture data were selected to analyse the correlations between the leaf area index (the growth indicator) and these factors using long time series half-monthly data (2–5 months) (from 1982 to 2010). The results showed that temperature was the main factor affecting the growth of winter wheat in the NCP. The growth of winter wheat had weak correlations with precipitation and soil moisture and the influence of water on winter wheat growth was smaller than the influence of heat. In the northern part of the NCP, mainly including the north-west region of Shandong Province and the southern region of Hebei Province, irrigation was necessary in late February and early March.     

Impact of aerosols on terrestrial gross primary productivity in North China using an improved boreal ecosystem productivity simulator with satellite-based aerosol optical depth

ABSTRACT

Atmospheric aerosols can alter the direct and diffuse components of global solar radiation, which further influences terrestrial gross primary productivity (GPP) via photosynthesis. To investigate the impact of aerosols on GPP, GPP is modeled using the Boreal Ecosystem Productivity Simulator (BEPS) under two aerosol scenarios (S1& S2) over cropland and grassland ecosystems in the highly polluted North China. In S1, the aerosol-effect is not considered and an original empirical method is used when estimating direct and diffuse solar radiation in BEPS. In S2, BEPS is improved by a new empirical method which incorporates the impact of aerosols using the remote sensing-based aerosol optical depth (AOD). Results suggest that aerosols can reduce GPP of the sunlit leaves by decreasing direct solar radiation, but increase GPP of the shaded leaves by increasing diffuse solar radiation. The impact of aerosols on GPP is more significant over the cropland ecosystem (p < 0.05) with a more complex canopy structure during the peak period of the growing season. Furthermore, an AOD value of 0.3–0.6 with a diffuse fraction (the fraction of diffuse solar radiation in global solar radiation) around 30-40% can largely increase total GPP over the cropland ecosystem. The study improves the accuracy of GPP modeling using BEPS by highlighting the aerosol-effect on GPP via solar radiation over highly polluted regions.

Abbreviations: gross primary productivity (GPP); aerosol optical depth (AOD); boreal ecosystem productivity simulator (BEPS)     

Influence of atmospheric refraction on horizontal angle surveying

IntroductionCurrently , the ultrahigh-precision terrestrialtriangulateration network (concluding construc-tion control network and deformation monitoringnetwork) is widely usedinthe branch of survey-ing and mappingfor hydropower .The character-istics of t…     

Monitoring winter wheat growth in North China by combining a crop model and remote sensing data

Both of crop growth simulation models and remote sensing method have a high potential in crop growth monitoring and yield prediction. However, crop models have limitations in regional application and remote sensing in describing the growth process. Therefore, many researchers try to combine those two approaches for estimating the regional crop yields. In this paper, the WOFOST model was adjusted and regionalized for winter wheat in North China and coupled through the LAI to the SAIL–PROSPECT model in order to simulate soil adjusted vegetation index (SAVI). Using the optimization software (FSEOPT), the crop model was then re-initialized by minimizing the differences between simulated and synthesized SAVI from remote sensing data to monitor winter wheat growth at the potential production level. Initial conditions, which strongly impact phenological development and growth, and which are hardly known at the regional scale (such as emergence date or biomass at turn-green stage), were chosen to be re-initialized. It was shown that re-initializing emergence date by using remote sensing data brought simulated anthesis and maturity date closer to measured values than without remote sensing data. Also the re-initialization of regional biomass weight at turn-green stage led that the spatial distribution of simulated weight of storage organ was more consistent to official yields. This approach has some potential to aid in scaling local simulation of crop phenological development and growth to the regional scale but requires further validation.     

基于球面的电子全站仪测高大气竖直折射角严密计算方法研究

大气竖直折射是影响竖直角观测精度的关键因素之一.大气竖直折射的计算一直是困扰测绘界的难题.为了更加合理地计算大气竖直折射,提出了基于球面的电子全站仪测高大气竖直折射计算方法,给出了基于球面的电子全站仪测高严格计算公式.     

VLBI中性大气折射延迟的研究进展——天顶延迟的改正模型

大气传播延迟是空间大地测量技术的主要误差源,特别是在低高度角的观测情况下尤其如此。因此,大气折射改正的研究仍然是当代新空间技术研究的重要课题之一,完善大气折射理论不仅可以改善新技术的归算精度,而且有希望降低仪器的观测截止角,提高仪器的使用效应。详细地综述了对流层大气折射延迟研究的基本概念和理论方法,探讨了对不同精度要求和不同高度截至角的VLBI观测可以采用的大气折射延迟模型的计算方法。     

20世纪末华北地区冬小麦物候期监测及时空格局分析

基于1983—1999年7 d时间分辨率5 km空间分辨率的AVHRR传感器数据,利用曲线特征点的物候监测方法,反演获得华北地区冬小麦关键物候期并分析其时空演变规律.结果表明:1)冬小麦的拔节期、抽穗期和成熟期主要集中在60—100、105—125和120—155 d.冬小麦物候期空间格局特征和纬度相关,纬度每升高一度...     

多波束测深表层声速误差的动态影响及改正方法

表层声速不准确会对多波束测深波束的归位产生影响,对于平面换能器阵,使波束角产生偏差,从而影响波束最终位置,但Snell常数保持不变;对于曲面换能器阵,虽然波束未束控不产生波束角偏差,但Snell常数发生改变,会使波束在传播过程中出现折射误差,对深水环境测量不利。对于表层声速误差带来的水深误差,外部波束比内部波束受到的影响更严重。当表层声速无法实时准确获取时,根据内外部波束对水深的影响大小识别表层声速误差的存在,通过逐步调整表层声速值,计算波束指向角差值,再重新进行声线跟踪,计算改正后的波束位置,消除其带来的水深的影响,完成表层声速误差的改正。文中用实测数据进行了验证,对多波束测深数据质量的改善有一定的参考意义。