共查询到20条相似文献,搜索用时 15 毫秒
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《国土资源遥感》2016,(2)
遥感特征指数法是一种简单、高效的信息提取方法。根据气溶胶散射或吸收引起的卫星不同波段间表观反射率变化,构建了基于MODIS的城市大气颗粒物污染指数,结合石家庄市各环境空气质量站实测颗粒物浓度数据,分析差值植被指数(difference vegetation index,DVI)、归一化灰霾指数(normalized difference haze index,NDHI)、归一化建筑指数(normalized difference built-up index,NDBI)和差值建筑指数(difference built-up index,DBI)与PM10之间的相关关系。结果表明,除NDHI外,DVI,NDBI和DBI与大气颗粒物质量浓度均呈现负相关关系,DBI与PM10之间线性相关关系较为明显,综合多种大气颗粒物污染指数构建的大气颗粒物质量浓度估算模型,可以用来简便、快速地指示城市大气颗粒物污染状况。 相似文献
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小波分析技术在GPS动态测量数据处理中的应用 总被引:1,自引:0,他引:1
目前,小波分析技术已经广泛应用于数据处理、图象处理、语音识别与合成、天体识别,机器视觉、故障诊断与监控等诸多科技领域。在GPS动态测量中,由于在数据的采集和处理过程中存在一些偶然性的误差,这些误差会在一定程度影响测量结果的精度。因此,怎样有效地剔除这些误差以提高测量的精度和可靠性就成为一个不可回避的问题。针对这个问题,本文基于动态测量平台用两台NovAtel DL-4 plus GPS接收机设计了双动态测量实验。利用GrafMov数据处理软件对采集的GPS数据进行了解算,对解算的结果利用小波分析技术进行了降噪处理,求得了其噪声信号分布和特性,并对该噪声对测量结果的影响进行了评估分析。 相似文献
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采用小波技术对GPS观测数据进行处理。应用小波变换技术对GPS相位观测值进行周跳的探测和修复。GPS相位观测值可以作为时间序列来进行分析,作为时间函数,它所表现出来的是一条光滑度很好的曲线,一旦出现周跳,这种光滑性就被破坏,从发生周跳的历元开始,后继相位观测值序列发生等量阶跃,通过小波变换的信号特性检测原理,能够有效地探测出周跳的发生,这种方法对于缩小模糊度搜索空间及提高模糊度解的有效性有明显的作用,从而提高基线解算的精度。 相似文献
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The accuracy and feasibility of computing the zenith tropospheric delays (ZTDs) from data of the European Center for Medium-Range
Weather Forecasts (ECMWF) and the United States National Centers for Environmental Prediction (NCEP) are studied. The ZTDs
are calculated from ECMWF/NCEP pressure-level data by integration and from the surface data with the Saastamoinen model method
and then compared with the solutions measured from 28 global positioning system (GPS) stations of the Crustal Movement Observation
Network of China (CMONOC) for 1 year. The results are as follows: (1) the error of the integration method is 1–3 cm less than
that of the Saastamoinen model method. The agreement between the ECMWF ZTD and GPS ZTD is better than that between NCEP ZTD
and GPS ZTD; (2) the bias and root mean square difference (RMSD), especially the latter, have a seasonal variation, and the
RMSD decreases with increasing altitude while the variation with latitude is not obvious; and (3) when using the full horizontal
resolution of 0.5° × 0.5° of the ECMWF meteorological data in place of a reduced 2.5° × 2.5° grid, the mean RMSD between GPS
and ECMWF ZTD decreases by 4.5 mm. These results illuminated the accuracy and feasibility of computing the tropospheric delays
and establishing the ZTD prediction model over China for navigation and positioning with ECMWF and NCEP data. 相似文献
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小波变换在处理GPS噪声的应用中有较好的效果.本文研究利用GPS连续观测资料的小波变换去噪结果进行质量评价,通过对分析资料采用不同的小波基函数、对同一小波基函数下的小波变换各尺度结果进行比较,并结合实例分析得出了初步的结论:对GPS连续观测资料进行小波变换去噪,采用sym6、sym8和coif4小波,分解尺度在4~6之... 相似文献
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This study evaluates the quality of GPS radio occultation (RO) atmospheric excess phase data derived with single- and double-difference
processing algorithms. A spectral analysis of 1 s GPS clock estimates indicates that a sampling interval of 1 s is necessary
to adequately remove the GPS clock error with single-difference processing. One week (May 2–8, 2009) of COSMIC/FORMOSAT-3
data are analyzed in a post-processed mode with four different processing strategies: (1) double-differencing with 1 s GPS
ground data, (2) single-differencing with 30 s GPS clock estimates (standard COSMIC Data Analysis and Archival Center product),
(3) single-differencing with 5 s GPS clocks, and (4) single-differencing with 1 s GPS clocks. Analyses of a common set of
5,596 RO profiles show that the neutral atmospheric bending angles and refractivities derived from single-difference processing
with 1 s GPS clocks are the highest quality. The random noise of neutral atmospheric bending angles between 60 and 80 km heights
is about 1.50e−6 rad for the single-difference cases and 1.74e−6 rad for double-differencing. An analysis of pairs of collocated
soundings also shows that bending angles derived from single-differencing with 1 s GPS clocks are more consistent than with
the other processing strategies. Additionally, the standard deviation of the differences between RO and high-resolution European
Center for Medium range Weather Forecasting (ECMWF) refractivity profiles at 30 km height is 0.60% for single-differencing
with 1 and 5 s GPS clocks, 0.68% for single-differencing with 30 s clocks, and 0.66% for double-differencing. A GPS clock-sampling
interval of 1 s or less is required for single- and zero-difference processing to achieve the highest quality excess atmospheric
phase data for RO applications. 相似文献
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Zhigui Kang Byron Tapley Jianli Chen John Ries Srinivas Bettadpur 《Journal of Geodesy》2009,83(10):895-901
Two 4.5-year sets of daily geocenter variations have been derived from GPS-LEO (Low-Earth Orbiter) tracking of the GRACE (Gravity
Recovery And Climate Experiment) satellites. The twin GRACE satellites, launched in March 2002, are each equipped with a BlackJack
global positioning system (GPS) receiver for precise orbit determination and gravity recovery. Since launch, there have been
significant improvements in the background force models used for satellite orbit determination, most notably the model for
the geopotential, which has resulted in significant improvements to the orbit determination accuracy. The purpose of this
paper is to investigate the potential for determining seasonal (annual and semiannual) geocenter variations using GPS-LEO
tracking data from the GRACE twin satellites. Internal comparison between the GRACE-A and GRACE-B derived geocenter variations
shows good agreement. In addition, the annual and semiannual variations of geocenter motions determined from this study have
been compared with other space geodetic solutions and predictions from geophysical models. The comparisons show good agreement
except for the phase of the z-translation component. 相似文献
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Vertical velocities of 30 European permanent Global Positioning System (GPS) stations at or close to tide gauge sites are estimated from more than 3 years of continuous observations. The results of two different solution strategies are presented and compared. The first approach accumulates the daily free network normal equations, the second introduces all sets of daily ellipsoidal height estimates and their covariance matrix into a subsequent common least squares adjustment. In both solutions, mean station heights at a reference epoch, linear vertical velocities, height discontinuities and short period height offsets are estimated. The second approach solves in addition for periodic annual signals and for site-specific pressure loading coefficients. The vertical velocities range from +8 mm/year in the center of the Fennoscandian uplift area to –4 mm/year at a few subsiding locations. Apart from these extrema, most of the sites experience only very small vertical motions. The standard deviations from the second approach providing more realistic error estimates are well below 0.15 mm/year. Some specific data problems are discussed. 相似文献
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GPS Solutions - The rate of change of total electron content (TEC) index (ROTI), an important parameter to characterize ionospheric irregularities and associated scintillation activities, can be... 相似文献
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Detection of crop water stress is crucial for efficient irrigation water management. Potential of Satellite data to provide spatial and temporal dynamics of crop growth conditions makes it possible to monitor crop water stress at regional level. This study was conducted in parts of western Uttar Pradesh and Haryana. Multi-temporal Landsat data were used for detecting wheat crop water stress using vegetation indices (VIs), viz. vegetation water stress index (VWSI) and land surface wetness index water stress factor (Ws_LSWI). The estimated water stress from satellite data-based VIs was validated by water stress factor (Ws) derived from flux-tower data. The study observed Ws_LSWI to be better index for water stress detection. The results indicated that Ws_LSWI was superior over other index showing RMSE = 0.12, R2 = 0.65, whereas VWSI showed overestimated values with mean RD 4%. 相似文献
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GNSS observations provided by the global tracking network of the International GNSS Service (IGS, Dow et al. in J Geod 83(3):191–198, 2009) play an important role in the realization of a unique terrestrial reference frame that is accurate enough to allow a detailed monitoring of the Earth’s system. Combining these ground-based data with GPS observations tracked by high-quality dual-frequency receivers on-board low earth orbiters (LEOs) is a promising way to further improve the realization of the terrestrial reference frame and the estimation of geocenter coordinates, GPS satellite orbits and Earth rotation parameters. To assess the scope of the improvement on the geocenter coordinates, we processed a network of 53 globally distributed and stable IGS stations together with four LEOs (GRACE-A, GRACE-B, OSTM/Jason-2 and GOCE) over a time interval of 3 years (2010–2012). To ensure fully consistent solutions, the zero-difference phase observations of the ground stations and LEOs were processed in a common least-squares adjustment, estimating all the relevant parameters such as GPS and LEO orbits, station coordinates, Earth rotation parameters and geocenter motion. We present the significant impact of the individual LEO and a combination of all four LEOs on the geocenter coordinates. The formal errors are reduced by around 20% due to the inclusion of one LEO into the ground-only solution, while in a solution with four LEOs LEO-specific characteristics are significantly reduced. We compare the derived geocenter coordinates w.r.t. LAGEOS results and external solutions based on GPS and SLR data. We found good agreement in the amplitudes of all components; however, the phases in x- and z-direction do not agree well. 相似文献
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V. N. Sridhar R. P. Singh Anjum Mahtab Ranendu Ghosh 《Journal of the Indian Society of Remote Sensing》2005,33(2):339-344
This paper reports a study on multi-temporal polarized response of wheat crop from spaceborne ADEOS-POLDER sensor over a homogeneous
wheat region of Punjab, India. Both the polarized as well as total reflectance of wheat were observed at different scattering
angles for two spectral bands i.e. 670 nm and 865 nm during crop growth from November to April in rabi 1996-97 season. Results
show that sun-target-viewing geometry plays an important role in polarization property. The top of atmosphere (TOA) polarized
reflectance is found to decrease exponentially with increasing scattering angle. Polarized reflectance of crop was found to
be an order of magnitude smaller in comparison to the total reflectance. An attempt was also made to model the observed polarized
behavior over an agricultural area using a theoretical simplified crop reflectance model and accounting for atmospheric molecular
(Rayleigh) contribution in the single scattering approximation. It was found that there was a decrease in the polarized reflectance
at the grain filling (heading) stage of wheat crop. This is in accordance with ground- based observations and can be due to
the reduction in the specular component of the reflected light during post-heading stage of the crop. 相似文献
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The ionospheric effect is one of the major errors in GPS data processing over long baselines. As a dispersive medium, it is
possible to compute its influence on the GPS signal with the ionosphere-free linear combination of L1 and L2 observables,
requiring dual-frequency receivers. In the case of single-frequency receivers, ionospheric effects are either neglected or
reduced by using a model. In this paper, an alternative for single-frequency users is proposed. It involves multiresolution
analysis (MRA) using a wavelet analysis of the double-difference observations to remove the short- and medium-scale ionosphere
variations and disturbances, as well as some minor tropospheric effects. Experiments were carried out over three baseline
lengths from 50 to 450 km, and the results provided by the proposed method were better than those from dual-frequency receivers.
The horizontal root mean square was of about 0.28 m (1σ). 相似文献
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利用小波工具剔除噪声的思想对全球部分GPS测站坐标残差序列进行应用试验。通过选取特定的阈值和小波基函数,成功提取出GPS测站坐标残差序列的一些非线性周期规律,对于进一步深入研究GPS测站坐标非线性变化规律有重要意义。 相似文献
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针对研究中国西部长期重力变化的问题,该文利用GRACE月重力场模型,基于Slepian变换构建中国西部区域局部重力场,并采用GIA和GLDAS等模型扣除相应误差,通过时间序列分析方法得到该区域2003—2013年卫星重力变化。结果表明,东天山呈现负重力变化,可能由区域冰川消融引起的;西天山的正重力变化,应与冰川小幅增加和构造运动引起的壳幔物质积累有关;青藏高原内陆正重力变化可能由区域地壳抬升、粘弹性地壳的构造应变以及壳幔物质的质量迁移与积累引起;青藏高原边界区域的负重力变化,应与冰川加速消融以及地下水抽取有关。Slepian方法较好地克服了滤波平滑处理带来的重力变化信号压制及细节平滑,可为中国西部的地壳运动、地震活动和气候变化等研究提供数据支撑。 相似文献
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Ionospheric calibration of single frequency VLBI and GPS observations using dual GPS data 总被引:3,自引:1,他引:3
Summary The ionospheric effect is one of the main sources of error in Very Long Baseline Interferometry (VLBI) and Global Positioning System (GPS) high precision geodesy. Although the use of two frequencies allows the estimation of this effect, in some cases dual observations are not possible due to the available equipment or the type of observation. This paper presents the ionospheric calibration of single frequency VLBI and GPS observations based on the ionospheric electron content estimated from dual frequency GPS data. The ionospheric delays obtained with this procedure and the VLBI baseline length results have been compared with those obtained with dual frequency data. For the European geodetic VLBI baselines, both solutions agree at the 3–5 parts in 10–9 level. The noise introduced by the GPS-based calibration is in the order of 3 cm for the VLBI observables and of 10 cm for the GPS observables. 相似文献