智能手机多频多系统实时动态的定位性能分析

随着位置服务的发展,人们对定位精度的需求不断提升. 目前智能手机定位主要依赖于全球卫星导航系统(GNSS)芯片所提供的芯片解,其精度仅为米级. 2016年,谷歌宣布允许开发者获取手机GNSS原始观测数据,为研究手机GNSS高精度定位算法提供了支持. 为探索智能手机多频多系统实时动态(RTK)的定位精度和可靠性,文中基于华为P40智能手机开展了静态和动态环境下的多频多系统RTK的定位性能分析. 结果表明:在静态环境下,智能手机多频多系统的RTK定位精度要优于芯片解,在东(E)、北(N)、天(U)三个方向的定位误差均方根(RMS)分别为0.20 m、0.39 m和0.31 m,比芯片解提高了57%、71%和75%;在动态环境下的定位精度依然能够达到分米级,相比于芯片解在E、N、U三个方向上的定位精度提高了37.84%、47.22%、53.68%.      

Remote Sensing of suspended sediments along the Tamil Nadu coastal waters

Indian Remote Sensing satellite (IRS) 1A & 1B digital data in combination with field measurement were used to map distribution and concentration of suspended sediments along the Tamil Nadu coastal waters for monsoon and non-monsoon periods. Qualitative suspended sediment mapping was done for entire Tamil Nadu coast while quantitative studies were taken at two selected sites (eg. Tuticorin and Ennore). For qualitative mapping both monsoon (17-12-90) and non-monsoon (18-4-90) season data were analysed by level slicing technique and a qualitative scale was assigned to different sediment classes based on tonal variations. The suspended sediment concentration (SSC) samples were collected on April 15, 1992 and March 10, 1992 around Ennore and Tuticorin coastal waters respectively, synchronous to IRS-1A satellite overpass. This data was used for quantitative estimation of SSC using digital chromaticity technique. The study shows that the plumes of high suspended sediment concentration are contributed from the nearshore wetlands and river mouths and were finally dispersing towards Jaffna coast. Different classes of high to low SSC values ranging from less than 5 mg/L in offshore areas to 21 mg/L in nearshore of Tuticorin were also delineated. The dispersal pattern of the sediments on different is discussed.     

基于卡尔曼滤波方法的BDS动态伪距差分定位算法研究

针对北斗卫星导航系统(BDS)最小二乘伪距差分方法定位精度及稳定性不足的问题,提出了一种基于卡尔曼滤波方法的伪距差分算法,并进行了静态以及人行慢动态两种条件下的实验.对实测数据结果的处理分析表明,卡尔曼滤波方法在静态条件下,东、北、高三个方向精度分别提升55％、23％、48％．在动态条件下,东、北、高三个方向精度分别提升71％、49％、33％．      

基于Landsat影像的杭州湾最大浑浊带年际变化研究

杭州湾最大浑浊带（turbidity maximum zone，TMZ）受自然和人类活动的双重影响，年际变化显著。为探究杭州湾水域TMZ和表层悬浮泥沙浓度的年际变化特征，优选1984-2015年间30幅Landsat卫星影像，建立杭州湾水域表层悬沙浓度反演模型，模型经实测数据验证，平均相对误差为23.3%。对每张卫星影像进行悬沙浓度反演，进而提取TMZ面积数据。结果表明，杭州湾悬沙浓度面积分布类型均为正偏分布，且偏态系数由0.63增长至2.03，高悬沙浓度区域占比不断缩小。杭州湾各区域悬沙浓度均呈下降趋势，北岸芦潮港站下降趋势最为显著，减幅达73%。杭州湾TMZ面积年化下降率为4.57%，大于长江和钱塘江年输沙量的年化下降率3.74%。河流来沙减少和潮滩围垦导致的当地泥沙来源减少及水流携沙能力降低是影响TMZ面积降低的重要因素。     

Mapping of Marine Chl-a and Suspended Solid Concentration Using OCM-2 Sensor

Chlorophyll-a (Chl-a) and Suspended Solid Concentration (SSC) shows the productivity of water and their surrounding environment. These parameters can be effectively estimated through several remote sensing techniques. From the recent reports on the Gulf of Thailand, it is found that Chl-a and SSC are increasing in coastal areas due to changing environment caused by variations in the global carbon cycle, climate change and water pollution linking to anthropogenic conditions such as high population density and rapid urbanization in neighbouring coastal areas deteriorating the coastal and marine environment. Various models are evaluated in this study for estimation of marine Chl-a and SSC by employing Ocean Colour Monitor-2 sensor of Oceansat-2 satellite for Northern Gulf of Thailand. The retrieval of Chl-a and SSC by the atmospheric correction of visible bands from 400 to 700 nm to attain normalized water-leaving radiances and then a suitable algorithm is applied. The In-situ reflectance values of sea waters are measured using the ASD spectroradiometer. The reflectance values of the spectroradiometer are correlated for the same day atmospherically corrected satellite reflectance and the analysis offers high correlation R² 0.73. Satellite derived, Chl-a and SSC are correlated with observed in situ Chl-a and SSC. This analysis offered better correlation of R² 0.86 and 0.85 respectively with the algorithms of Chl-a and SSC.     

融合对流层模型及其在精密单点定位中的应用

受实测气象参数的限制，使用标准大气参数的传统对流层模型的精度并不高；使用参数估计法的精密对流层模型增加了观测方程的待估参数，影响收敛速度. 针对实测气象参数缺失的情况，提出一种融合对流层模型，使用两种非实测气象参数模型分别计算出平均海平面处和测站处的气象参数，再利用Saastamoinen模型经验公式求解天顶对流层延迟（ZTD）. 利用RTKLIB软件进行精密单点定位（PPP）实验. 提出的融合对流层模型摆脱了实测气象参数的限制，解算结果表明:使用该模型时，在东、北、天方向的定位精度分别比Saastamoinen模型提高16 mm、1 mm、2.2 mm，比MOPS模型提高13.8 mm、0.7 mm、1.6 mm，比GPT/UNB3m+Sa模型提高2.9 mm、0.4 mm、0.7 mm，在天、北方向的定位精度接近参数估计模型，实现了PPP定位精度的提高.      

中国大陆主要块体现今变形状态的反演研究

本文利用中国大陆的GPS运动速度场,研究了其中的7个亚板块和14个构造块体的变形状态,并做了动力学解释。研究中,构造了一种运动-变形模型来提取观测数据中的变形信息。结果表明:南北构造带东西两侧应变状态表现出显著的差异,西部各亚板块或块体的主应变量值从约4.5×10-8.a-1到约1.3×10-8.a-1,东部则从约3.0×10-.8a-1到约0.4×10-.8a-1,表明东西两部应变量值有较大的落差,并且主压应变方向从西部的北北东向逐步转到东部北东东向。南北构造带表现为其不同段落的各块体的变形趋势和量级都有显著不同。川滇块体是东部与西部的结合部位,变形量较大,主压应变为3.4×10-8.a-1,反映了印度板块向北的推挤在川滇块体造成了较大变形。中国北部地区向东西两个方向运动,塔里木块体、准噶尔块体、天山块体向西,柴达木-祁连山块体、阿拉善块体向东。这种推挤力和太平洋板块阻碍、遏制作用,造成了华北块体、鄂尔多斯块体以拉张为主的应变和逆时针旋转。     

Ground validation of an algorithm for estimating surface suspended sediment concentrations from multi-spectral reflectance data

Pollution of water resources by sediments eroded from degraded watersheds is a critical concern around the world. Current methods for locating these eroding areas and off-site damage to water resources through visual observations and field sampling with subsequent laboratory analysis are time consuming and expensive. There is thus, a justified interest in developing algorithms for quick estimation of suspended sediment concentrations in large water-bodies from remotely sensed data. This paper presents the results of a ground validation study on characterization and quantification of surface suspended sediment concentrations (SSC) in sediment laden water bodies through an n-waveband specific numerical index, total information content. A comparison of SSC-predictive potential of the proposed new index, derived from four broad (100–300 nm) Landsat MSS, five broad (40–300 nm) Landsat TM and eight narrow (20–40 nm) IRS-P4 OCM spectral bands, with that of the conventional (NIR-Red and NIR+Red) indices, computed from the same spectral band data, is also presented. The study reveaied that at SSCs 250 mg/1, the proposed index (derived from either broad / narrow landsat MSS/TM or IRS-P4 OCM spectral data) could lead to SSC predictions (with mean errors within 20%) comparable with those obtained with the conventional indices (derived from the same spectral band data). It could further be observed that, in general, lower sediment concentrations (i.e. SSCs 150 mg/1) were associated with higher prediction inaccuracies. A comparison of the mean errors of predictions associated with the proposed and the conventional (NIR-Red and NIR+Red) indices computed from broad and narrow band data for SSCs 150 mg/I, revealed that an increase in number of wavebands (from 4 MSS to 5 TM or 8 OCM bands) and a decrease in the bandwidth of these wavebands (from broad MSS/ TM bands to narrow OCM bands) led to a significant increase in the prediction accuracy of the proposed new index. These prediction accuracies were observed to be the highest with the proposed index calculated from narrow OCM-P4 spectral data. However this could not be observed with the conventional indices at any of the SSC ranges and with the proposed index at SSCs 250 mg/l. This shows that the lower SSC-predictive potential of proposed index was a significant function of both the number and the bandwidth of spectral bands used for its computation. In fact in one of the cases, lower SSC (150 mg/l) -predictive accuracy of the proposed index was found to be significantly higher than that of the conventional (NIR+R) index. The proposed algorithm could thus compress the information contained in the entire reflectance spectrum of the sediment laden water bodies to their sediment type and concentration specific characteristic values. This characteristic of the proposed index was not shared by any of the conventional indices, based on only two waveband data. In fact the proposed index appears to be the only mean of completely compressing and quantifying the information contained in all the information channels of a narrow band spectrometer (consisting of 200 wavebands) to be shortly launched by ISRO for satellite based inventory of natural resources.     

Real-time clock offset prediction with an improved model

The GPS orbit precision of the IGS ultra-rapid predicted (IGU-P) products has been remarkably improved since 2007. However, the satellite clock offsets of the IGU-P products have not shown sufficient high-quality prediction to achieve sub-decimeter precision in real-time precise point positioning (RTPPP), being at the level of 1–3 ns (30–90 cm) RMS in recent years. An improved prediction model for satellite clocks is proposed in order to enhance the precision of predicted clock offsets. First, the proposed prediction model adds a few cyclic terms to absorb the periodic effects, and a time adaptive function is used to adjust the weight of the observation in the prediction model. Second, initial deviations of the predictions are reduced by using a recomputed constant term. The simulation results have shown that the proposed prediction model can give a better performance than the IGU-P clock products and can achieve precision better than 0.55 ns (16.5 cm) in real-time predictions. In addition, the RTPPP method was chosen to test the efficiency of the new model for real-time static and kinematic positioning. The numerical examples using the data set of 140 IGS stations show that the static RTPPP precision based on the proposed clock model has been improved about 22.8 and 41.5 % in the east and height components compared to the IGU-P clock products, while the precisions in the north components are the equal. The kinematic example using three IGS stations shows that the kinematic RTPPP precision based on the proposed clock model has improved about 30, 72 and 44 % in the east, north and height components.     

中国陆地生态系统脆弱带遥感模型

本研究通过对我国陆地生态系统8个典型样地的植被指数取样实验和图像计算结果发现，这8个样地植被指数随着水、热因子的季节变化，在时间和空间上具有一定的“绿波推移”和“景观更替”规律。在中国东部湿润的季风区（样地1－3），随着纬度的增高，其月平均植被指数与月平均气温有较大的相关。发现降水相对丰沛的地带，热量和光照条件的变化成为植被生长和变化的自然限制因子；而在中国北方森林－森林草原－典型昌原－荒漠草原－荒漠地带上，随着从东部（湿润地区）到西部（干旱地区）干湿条件的更替，月平均植被指数与降水多寡有较大的正相关关系。在8个样地上都呈现出共同的规律，即定向风的分布与植被指数的分布在时间和空间上具有逆相分布的“套合关系”。尤其在时间上有相逆套合关系，这正是中国北方沙尘暴和沙漠化加剧的自然原因。本研究定量地给出了我国陆地不同经纬度带生态系统脆弱季节和累积时间的分布。     

中国西部地壳现今变形特征及其机制探讨

以中国大陆及周边10年来近400个GPS测站的复测资料为基础，获取并绘制了现今地壳水平运动与变形图像，结果表明：青藏块体内西半部南北向只存在微弱的缩短变化（5mm/a左右），东半部南北向则没有缩短的迹象，南北缩短的区域主要位于青藏块体南缘的喜马拉雅条带（约15mm/a），北缘中部的柴达木西区（约15mm/a）和青藏块体北面的天山块体及周围地区（约15mm/a）；青藏块体大约有10mm/a的东西拉张，但不均匀，自西向东经历了由弱到强再有所减弱的过程，整个西部地区东边缘的东向运动表现为南强北弱的左旋特征；川滇菱形块体不是逃逸块体而是变形块体；青藏块体东缘及附近地区是东向运动的消减区带，面应变结果显示，青藏块体周边以面收缩为主，内部则以面膨胀为主；其以北的地区以面收缩为主（但压中有张），面应变的量级为10^-8/a。这样的变形结果，若只靠来处于印度板块的北向挤压是无法解释的。由此并结合最新的地球物理研究成果可推断或证实，地壳下部来自南向的物质涌入是控制青藏块体乃至中国大陆形变的另一大动力源，甚至可能是主导动力源；或者具有深、浅立体活动的某种协同性。     

Spatiotemporal filtering for regional GPS network in China using independent component analysis

Removal of the common mode error (CME) is a routine procedure in postprocessing regional GPS network observations, which is commonly performed using principal component analysis (PCA). PCA decomposes a network time series into a group of modes, where each mode comprises a common temporal function and corresponding spatial response based on second-order statistics (variance and covariance). However, the probability distribution function of a GPS time series is non-Gaussian; therefore, the largest variances do not correspond to the meaningful axes, and the PCA-derived components may not have an obvious physical meaning. In this study, the CME was assumed statistically independent of other errors, and it was extracted using independent component analysis (ICA), which involves higher-order statistics. First, the ICA performance was tested using a simulated example and compared with PCA and stacking methods. The existence of strong local effects on some stations causes significant large spatial responses and, therefore, a strategy based on median and interquartile range statistics was proposed to identify abnormal sites. After discarding abnormal sites, two indices based on the analysis of the spatial responses of all sites in each independent component (east, north, and vertical) were used to define the CME quantitatively. Continuous GPS coordinate time series spanning \(\sim \)4.5 years obtained from 259 stations of the Tectonic and Environmental Observation Network of Mainland China (CMONOC II) were analyzed using both PCA and ICA methods and their results compared. The results suggest that PCA is susceptible to deriving an artificial spatial structure, whereas ICA separates the CME from other errors reliably. Our results demonstrate that the spatial characteristics of the CME for CMONOC II are not uniform for the east, north, and vertical components, but have an obvious north–south or east–west distribution. After discarding 84 abnormal sites and performing spatiotemporal filtering using ICA, an average reduction in scatter of 6.3% was achieved for all three components.     

中国大陆GPS速度场的球面小波模型及多尺度特征分析

利用1999—2009年间中国大陆共1068个GPS站点在东方向、北方向的速度值,采用DOG球面小波多尺度分析方法,建立了中国大陆东方向、北方向多尺度速度场。球面小波模型的尺度主要根据观测站点的密度来确定,利用检核点上的已知速度与模型速度之间的均方差来评定模型的精度。利用球面小波模型可以更加清晰地表示速度场的大尺度特征和复杂的局部变化特征。站点稠密区域,模型在东方向、北方向上的精度分别为±0.95mm/a、±0.97mm/a,稀疏区域对应的精度分别为±1.32mm/a和±1.30mm/a。     

利用AVHRR植被指数数据集分析中国东部季风区的物候季节特征

利用ＮＯＡＡ／ＮＡＳＡＰａｔｈｆｉｎｄｅｒＡＶＨＲＲ陆地数据集,建立了中国东部季风区（１０８°－１２３°Ｅ,２１°－４５°Ｎ）的１９８６年归一化植被指数（ＮＤＶＩ）距平图像序列。对此数据集进行主成分分析（ＰＣＡ）,前２个主成分的时间序列和空间场展示了中国东部季风区植被物候季节性特征和地域差异。南岭一五夷山以南的华南地区,植被生长季的物候季节性变化不明显。在南岭－五夷山以北地区,植被生长季的物候季节性特征明显,可以比较清晰地确定生长季的变化过程。以淮河流域为界,植被生长季的物候季节性特征又存在明显差异。华北平原表现出强烈的双峰植被物候过程。淮河以南地区,虽然也存在这种双峰物候过程,但比较华北平原的植被,还具有持续性的植被生长特征。淮河流域构成一条区分南北物候季节特征差异的过渡带。     

Integrated GIS and Remote Sensing Approach to Map Pollution in Upper Lake,Bhopal, India

Abstract

Upper Lake is the lifeline of Bhopal City, India for drinking and other water needs. In recent years, environmentalists have expressed their serious concern on deteriorating water quality of this lake. Conventional field sampling methods for monitoring lake water quality lack spatial information about the pollution in the lake. It is desirable to have spatial information about the lake for better management and control. In the present paper the remote sensing data from IRS-1C LISS III have been integrated into a GIS environment to analyse and create a pollution zone map of the Upper Lake.

Spectral reflectance analysis was carried out to find the suitability of wavelengths for determining chlorophyll‐a concentration (chl‐a), suspended solid concentration (SSC) and secchi depth (SD). Empirical models relating spectral reflectance and chl‐a, SSC and SD were developed using least square regression analysis. These models were found valid on unused samples. Chl‐a, SSC and SD distribution maps were generated using proposed models and were incorporated as datalayers in the GIS for further analysis of pollution zones. The spatial information of pollution offered by the pollution zone map could delineate regions of lake having high pollution load. The methodology employed in this work can be used for regular monitoring of the pollution in surface water bodies and serve the data needs for better management of the water quality.     

Can suspended sediment concentrations be estimated from multispectral imagery using only image-derived information?

Sampling for suspended sediment concentrations (SSC) in inland waters is traditionally based on collecting samples at sparse locations and in limited intervals. A number of investigators explored the utility of earth-observing satellites and air-borne sensors for monitoring of SSC over vast areas. Two approaches are commonly deployed: (1) empirical relationships between a chosen remotely sensed quantity and the actual in-situ SSC; and (2) bio-optical models founded on radiative transfer modeling. Unfortunately, in-situ measurements are often unavailable for direct image calibration, and inherent optical properties of optically active constituents (specific scattering and absorption coefficients) are usually unknown. This paper examines the possibility to retrieve SSC from multispectral satellite imagery without any in-situ data, i.e. using only image-derived information. The fundamental principle of image selfcalibration relies on the fact that in the visual domain of wavelengths (∼400–700 nm) the at-sensor reflectance becomes “saturated“ at high SSC, whereas the near-infrared domain (∼700–900 nm) remains almost perfectly linearly related to sediment concentrations. The core idea of the self-calibrating procedure is rather simple and is based on fitting an exponential function between reflectance and SSC, with SSC replaced by a linear relationship between SSC and reflectance in the near-infrared domain. As a first approximation of the non-linearity between reflectance and SSC levels in the 400–700 nm range, we used the equation proposed by Schiebe et al. (1992), although other equations, especially those arising from optical theory could be used as well. The technique is illustrated on a moderately sediment-laden reservoir and two scenes acquired from Landsat ETM+. The standard error of the estimated SSC was below 15 mg/L (i.e. ∼25 % relative error for the observed range of SSC). Although the proposed algorithm does not yield better results than other models mentioned in the literature, the primary advantage of the outlined methodology is that no in-situ measurements (water sampling nor spectral profiling) are needed — i.e. only image-derived information is used.     

Evaluation of Air Pollution Trend Using GIS and RS Applications in South West of Iran

In this paper, remote sensing and GIS have been used to assess the status of NO₂ at the south west of Iran. 221 data about concentration of NO₂ was extracted from Ozone Monitoring Instrument. Ordinary kriging and inverse distance weighting interpolation methods was used to interpolate data. Results showed that ordinary kriging method using cross-validation have had less error. North east of the study area has the highest concentration of NO₂ (329 molecule/cm²) and the concentration of NO₂ decreases from north east to South west of the study area. On the other hand, data trend results showed that the data seems to exhibit a fairly strong trend in the east west direction and a weaker one in the north–south direction.     

Studies on the morphological changes in the mahanadi estuary and hukitola barrier island with the aid of photo interpretation techniques

Hukitola Bay, situated north of Mahanadi River Delta system in Orissa State is ptotected by a barrier island. This island also provides protection to the coastline in this region from the onslogunt of high waves during southwest monsoon. As such, the changes in the Mahanadi estuary governs the stability of this island to a considerable extent. From the examination of hydrographic charts as well as the toposheets prior to the year 1952 it is observed that the Mahanadi river had a long northerly course along a sandspit six km long prior to its confluence with the sea. With the breach in the sandspit at its southern extrem ty during October 1 51, the mouth of the river shifted southwards by about six km. Photographs taken during 1973 have indicated that the mouth of this river has again migrated northwards by about four Km between 1952 and 1973. The development of a new barrier isiand towards east of the existing Hukitola island is also in evidence. As a sequel to these studies it is inferred that despite the changes in the morphology of the barrier island over the past three decades, the barrier island at this region would be a permanent feature and continue to provide protection to the main coastline in this reach.     

Forecasting of onset of southwest monsoon over Kerala coast using satellite data

The Global Precipitation Climatology Project and in situ gauge data have been used in the present study of the Indian monsoon for the region bounded by 8/spl deg/ to 13/spl deg/N; 70/spl deg/ to 95/spl deg/E, from March 1 to May 31 for the years 1979 to 2001. The monsoon onset dates over Kerala, as declared by India Meteorological Department has been used in the present study as an indicator of the onset of this event. For each year, the midday of the pentad with the rainfall peak was located in the period from 1st April to 10th May and identified as the pre-monsoon rainfall peak (PMRP). The analysis showed that the PMRP exists about six pentads prior to the onset of the monsoon over the Kerala coast. A regression equation developed using the first 20 years of data (1979-1998) with a standard error estimate of four days was used for predicting the onset dates for the years 1999, 2000 and 2001, with encouraging results. Thus, we feel that the pre-monsoon rainfall estimate from the satellite data can be used for predicting the monsoon onset over Kerala coast.     

Real-Time Precise Point Positioning (RTPPP) with raw observations and its application in real-time regional ionospheric VTEC modeling

Precise Point Positioning (PPP) is an absolute positioning technology mainly used in post data processing. With the continuously increasing demand for real-time high-precision applications in positioning, timing, retrieval of atmospheric parameters, etc., Real-Time PPP (RTPPP) and its applications have drawn more and more research attention in recent years. This study focuses on the models, algorithms and ionospheric applications of RTPPP on the basis of raw observations, in which high-precision slant ionospheric delays are estimated among others in real time. For this purpose, a robust processing strategy for multi-station RTPPP with raw observations has been proposed and realized, in which real-time data streams and State-Space-Representative (SSR) satellite orbit and clock corrections are used. With the RTPPP-derived slant ionospheric delays from a regional network, a real-time regional ionospheric Vertical Total Electron Content (VTEC) modeling method is proposed based on Adjusted Spherical Harmonic Functions and a Moving-Window Filter. SSR satellite orbit and clock corrections from different IGS analysis centers are evaluated. Ten globally distributed real-time stations are used to evaluate the positioning performances of the proposed RTPPP algorithms in both static and kinematic modes. RMS values of positioning errors in static/kinematic mode are 5.2/15.5, 4.7/17.4 and 12.8/46.6 mm, for north, east and up components, respectively. Real-time slant ionospheric delays from RTPPP are compared with those from the traditional Carrier-to-Code Leveling (CCL) method, in terms of function model, formal precision and between-receiver differences of short baseline. Results show that slant ionospheric delays from RTPPP are more precise and have a much better convergence performance than those from the CCL method in real-time processing. 30 real-time stations from the Asia-Pacific Reference Frame network are used to model the ionospheric VTECs over Australia in real time, with slant ionospheric delays from both RTPPP and CCL methods for comparison. RMS of the VTEC differences between RTPPP/CCL method and CODE final products is 0.91/1.09 TECU, and RMS of the VTEC differences between RTPPP and CCL methods is 0.67 TECU. Slant Total Electron Contents retrieved from different VTEC models are also validated with epoch-differenced Geometry-Free combinations of dual-frequency phase observations, and mean RMS values are 2.14, 2.33 and 2.07 TECU for RTPPP method, CCL method and CODE final products, respectively. This shows the superiority of RTPPP-derived slant ionospheric delays in real-time ionospheric VTEC modeling.