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1.
GPS数据用于改正InSAR中大气延迟误差的方法受GPS站点密度的限制,只利用有限的几个站点所观测到的大气数据来生成干涉图的大气改正图,往往达不到很好的效果.本文研究利用GPS与MODIS数据的联合使用来生成大气改正图,首先用GPS数据对MODIS水汽产品进行分块校准,并且对MODIS水汽数据进行了空间结构函数分析,得到研究区域内水汽场的空间分布规律.然后把这种区域水汽场的空间分布信息结合到Kriging内插法中生成更为合理的水汽图.通过上海地区ENVISAT ASAR数据的实验发现,这种加以改正的GPS和MODIS数据联合改正法不仅可以对长波大气信号有明显的消弱,还能消弱一些短波的大气信号,特别是一些幅度较强的短波信号;经过GPS+MODIS算法改正后,短波信号占优和长波信号占优的两幅差分大气延迟图的整体RMS分别降低了32.74%和38.82%,去除幅度较大.与GPS+ATM(大气传输模型)算法比较,我们发现,在上海地区有限的数据条件下（即研究区域内只有6个GPS点）,GPS+MODIS法在大气去除效果或者说大气信号重现能力方面优于GPS+ATM算法.GPS+MODIS算法在捕获短波大气信号方面要比GPS+ATM更有优势,因此也可以改正短波大气误差.  相似文献   

2.
Water vapor plays a crucial role in atmospheric processes that act over a wide range of temporal and spatial scales, from global climate to micrometeorology. The determination of water vapor distribution in the atmosphere and its changing pattern is very important. Although atmospheric scientists have developed a variety of means to measure precipitable water vapor(PWV) using remote sensing data that have been widely used, there are some limitations in using one kind satellite measurements for PWV retrieval over land. In this paper, a new algorithm is proposed for retrieving PWV over land by combining different kinds of remote sensing data and it would work well under the cloud weather conditions. The PWV retrieval algorithm based on near infrared data is more suitable to clear sky conditions with high precision. The 23.5 GHz microwave remote sensing data is sensitive to water vapor and powerful in cloud-covered areas because of its longer wavelengths that permit viewing into and through the atmosphere. Therefore, the PWV retrieval results from near infrared data and the indices combined by microwave bands remote sensing data which are sensitive to water vapor will be regressed to generate the equation for PWV retrieval under cloud covered areas. The algorithm developed in this paper has the potential to detect PWV under all weather conditions and makes an excellent complement to PWV retrieved by near infrared data. Different types of surface exert different depolarization effects on surface emissions, which would increase the complexity of the algorithm. In this paper, MODIS surface classification data was used to consider this influence. Compared with the GPS results, the root mean square error of our algorithm is 8 mm for cloud covered area. Regional consistency was found between the results from MODIS and our algorithm. Our algorithm can yield reasonable results on the surfaces covered by cloud where MODIS cannot be used to retrieve PWV.  相似文献   

3.
应用地基GPS遥感倾斜路径方向大气水汽总量   总被引：26，自引：2，他引：24       下载免费PDF全文
应用地基GPS沿倾斜路径方向遥测大气水汽总量,是获得测站周围水汽三维空间分布信息(水汽层析)的基础.本文介绍了地基GPS沿倾斜路径方向遥感大气水汽总量的原理和方法;首先用湿梯度、后处理残差联合计算接收机上空不同方位上大气水汽各向异性成分,在此基础上重构倾斜路径水汽总量.为验证GPS观测结果精度,用微波辐射计（WVR）与GPS一起进行了联合观测,不同观测地点和时间的对比结果表明,二者root mean square (RMS)误差小于4mm,证明应用此种方法地基GPS可较精确地反演出倾斜路径方向大气水汽总量,而且这种反演方法适合于近实时大气遥感探测.地基GPS测量具有全天候可连续观测等优点,可以弥补常规观测的不足,为气候研究提供高精度且连续的水汽数据资料;组网观测可以为数值天气预报提供好的初始场,提高模式预报精度.  相似文献   

4.
A global numerical weather prediction system is extended to the mesosphere and lower thermosphere (MLT) and used to assimilate high-altitude satellite measurements of temperature, water vapor and ozone from MLS and SABER during May–July 2007. Assimilated temperature and humidity from 100 to 0.001 hPa show minimal biases compared to satellite data and existing analysis fields. Saturation ratios derived diagnostically from these assimilated temperature and water vapor fields at PMC altitudes and latitudes compare well with seasonal variations in PMC frequency measured from the aeronomy of ice in the mesosphere (AIM) satellite. Synoptic maps of these diagnostic saturation ratios correlate geographically with three independent transient mesospheric cloud events observed at midlatitudes by SHIMMER on STPSat-1 and by ground observers during June 2007. Assimilated temperatures and winds reveal broadly realistic amplitudes of the quasi 5-day wave and migrating tides as a function of latitude and height. For example, analyzed winds capture the dominant semidiurnal MLT wind patterns at 55°N in June 2007 measured independently by a meteor radar. The 5-day wave and migrating diurnal tide also modulate water vapor mixing ratios in the polar summer MLT. Possible origins of this variability are discussed.  相似文献   

5.
The present study reports the analysis of GPS TEC prior to 3 earthquakes (M > 6.0). The earthquakes are: (1) Loyalty Island (22°36′S, 170°54′E) on 19 January 2009 (M = 6.6), (2) Samoa Island (15°29′S, 172°5′W) on 30 August 2009 (M = 6.6), and (3) Tohoku (38°19′N, 142°22′E) on 11 March 2011 (M = 9.0). In an effort to search for a precursory signature we analysed the land and ocean parameters prior to the earthquakes, namely SLHF (Land) and SST (Ocean). The GPS TEC data indicate an anomalous behaviour from 1–13 days prior to earthquakes. The main purpose of this study was to explore and demonstrate the possibility of any changes in TEC, SST, and SLHF before, during and after the earthquakes which occurred near or beneath an ocean. This study may lead to better understanding of response of land, ocean, and ionosphere parameters prior to seismic activities.  相似文献   

6.
Space geodetic techniques (e.g., Global Positioning System, GPS and very long baseline interference, VLBI) have been widely used to determine the precipitable water vapor (PWV) for meteorology and climatology, which was verified by comparing with co-located independent technique observations. However, most of these comparisons have been conducted using only short-time spanning observations at several stations. The goal of this study is to identify and quantify the systematic errors between VLBI and GPS PWV estimates using a 5-year (2002–2007), PWV data set constructed from co-located measurements and radiosonde data as well. It has found systematic errors between VLBI and GPS PWV estimations from comparisons with long-term co-located GPS measurements. The total mean VLBI PWVs are systematically smaller than GPS estimates with 0.8–2.2 mm for all sites, but can be as much as 15–30%. The subdiurnal PWV variation magnitudes and long-term trends between VLBI and GPS are nearly similar, but the VLBI-derived PWV trends are systematically smaller than GPS estimates with about 0.1±0.02 mm/year. These systematic errors in PWV estimates between VLBI and GPS are probably due to technique own problems, different used elevation angles and co-location separation.  相似文献   

7.
This paper presents the results from a study designed to investigate the ability of a newly developed neural network (NN) based model to follow total electron content (TEC) dynamics over the Southern African region. The investigation is carried out by comparing results from the NN model with actual TEC data derived from Global Positioning System (GPS) observations and TEC values predicted by the International Reference Ionosphere (IRI-2007) model during magnetic storm periods over Southern Africa. The magnetic storm conditions chosen for the study presented in this paper occurred during the periods 16–21 April 2002, 1–6 October 2002, and 28 October–01 November 2003. A total of six South African GPS stations were used for the validation of the two models during these periods. A statistical analysis of the comparison between the actual TEC behaviour and that predicted by the two models is shown. In addition, ionosonde measurements from the South African Louisvale (28.5°S, 21.2°E) station, located close to one of the validation GPS stations used, are also considered during the Halloween storm period of 28–31 October 2003. The generalisation of TEC behaviour by the NN model is demonstrated by producing predicted TEC maps during magnetic storm periods over South Africa. Presented results demonstrate the ability of NNs in predicting TEC variability over South Africa during magnetically disturbed conditions, and highlight areas for improvement.  相似文献   

8.
With a view to difficulties with explaining the physical mechanism of solar forcing on the Earth’s climate, we applied a new approach of determining and quantifying an influence of solar-related events on water vapor variability by correlating the total electron content (TEC) and precipitable water vapor (PWV), both derived from ground-based GPS observations. In this study, ionospheric TEC and atmospheric PWV values are employed as solar activity and terrestrial climate parameters, respectively. Three-year GPS data at five stations in Antarctica are analyzed on a daily mean basis. Results show significant correlation between TEC and PWV differences during storms-affected days. The high correlation between the daily mean values of TEC and PWV, both of which follow the seasonal signals and subsisting downward trend, suggests an influence of solar activity on climate variability in Antarctica. These quantities are determined by changes of the upper-atmosphere level, which varies in conformity with the zenith angle of the Sun.  相似文献   

9.
Analysis of wind, air temperature, humidity and rainfall data from Land Surface Processes Experiment (LASPEX) in the surface layer at Anand (22°35′N, 72°55′E) and Khandha (22°02′N, 73°11′E) during January to December 1997 is presented. Wind and temperature at various levels showed prominent diurnal variation. Progression of daily wind and temperature revealed the intra-seasonal, quasi-biweekly and 6–9 day oscillations indicated large-scale convection, transport of heat and water vapor from Arabian Sea towards these stations.Power spectrum of wind and humidity corroborated the planetary scale Madden–Julian oscillation in the surface layer. Periodic oscillations of 21, 6–9, 1 day and 12 h were prominent in the spectrum of all variables. Low-frequency spectral peaks showed the energy in wind is 2–3 times higher over Khandha than at Anand whereas temperature is 3 times higher at Anand than Khandha.  相似文献   

10.
In this study, data from MODIS land surface temperature product level 3 (MOD11A2) were used to investigate the spatiotemporal variation of Eurasian lakes water surface temperature (LSWT) from 2001 to 2015, and to examine the most influencing factors of that variation. The temperature of most lakes in the dry climate zone and in the equatorial climatic zone varied from 17 to 31°C and from 23 to 27°C, respectively. LSWTs in the warm temperate and cold climatic zones were in the range of 20 to 27°C and −0.6 and 17°C, respectively. The average day time LSWT in the polar climate zone was −0.71°C in the summer. Lakes in high latitude and in the Tibetan Plateau displayed low LSWT, ranging from −11 to 26°C during the night time. Large spatial variations of diurnal temperature difference (DTD) were observed in lakes across Eurasia. However, variations in DTDs were small in lakes located in high latitude and in tropical rainforest regions. The shallow lakes showed a rapid response of LSWT to solar and atmospheric forcing, while in the large and deep lakes, that response was sluggish. Results of this study demonstrated the applicability of remote sensing and MODIS LST products to capture the spatial–temporal variability of LSWT across continental scales, in particular for the vast wilderness areas and protected environment in high latitude regions of the world. The approach can be used in future studies examining processes and factors controlling large scale variability of LSWT.  相似文献   

11.
The Los Alamos Raman lidar has been used to make high resolution (25 m) estimates of the evapotranspiration rate over adjacent corn and soybean canopies. The lidar makes three-dimensional measurements of the water vapor content of the atmosphere directly above the canopy that are inverted using Monin–Obukhov similarity theory. This may be used to examine the relationship between evapotranspiration and surface moisture/soil type. Lidar estimates of evapotranspiration reveal a high degree of spatial variability over corn and soybean fields that may be associated with small elevation changes in the area. The spatial structure of the variability is characterized using a structure function and correlation function approach. The power law relationship found by other investigators for soil moisture is not clear in the data for evapotranspiration, nor is the data a straight line over the measured lags. The magnitude of the structure function and the slope changes with time of day, with a probable connection to the amount of evapotranspiration and the spatial variability of the water vapor source. The data used was taken during the soil moisture–atmosphere coupling experiment (SMACEX) conducted in the Walnut Creek Watershed near Ames, Iowa in June and July 2002.  相似文献   

12.
《水文科学杂志》2013,58(6):1079-1093
Abstract

A time series analysis of 152 VV-polarized Advanced Synthetic Aperture Radar (ASAR) Wide Swath Mode (WSM) images collected over the central part of the Tibetan Plateau is presented for the period from April 2005 to September 2007. The signatures of a grassland and a wetland are studied to identify the impact of three land-surface states on the backscatter (σ°). The considered land-surface states are soil moisture, soil temperature and vegetation biomass represented by Système Pour l'Observation de la Terre (SPOT) Normalized Difference Vegetation Index (NDVI). Comparison of the σ° time series with these land-surface states via a multivariate regression shows that the grassland σ° are well represented by the soil moisture dynamics, while the wetland σ° also has a strong correlation with soil temperature. Further, we found that the contribution of the NDVI to the explanation of the temporal σ° variability is limited for both the grassland and wetland.  相似文献   

13.
This paper reports differences in the occurrence statistics of global positioning system (GPS) L-band scintillations at observational sites located in the inner regions of the northern and southern crests of the equatorial ionization anomaly. Ground-based GPS data acquired at the closed magnetically aligned stations of Manaus (3.1°S; 59.9°W; dip lat. 6.2°N) and Cuiabá (15.5°S; 56.1°W; dip. lat. 6.2°S), Brazil, from December 2001 to February 2007 are used in the analysis. The drift dynamics of Fresnel-scale ionospheric irregularities at the southern station of Cuiabá are also investigated. Only geomagnetically quiet days with the sum of daily Kp < 24 were used in the analysis statistics and in the irregularity drift studies. The results reveal a clear dependence of the scintillation occurrence with the solar activity, but there exists an asymmetry in the percentage of scintillation occurrence between the two stations throughout the period analyzed. The nocturnal occurrence of the scintillations over Cuiabá is predominantly larger than over Manaus, but this scenario seems to change with the decline in the solar activity (mainly during local post-midnight hours). A broad minimum and maximum in the scintillation occurrence appears to occur over both the stations, respectively, during the June solstice (winter) and December solstice (summer) months. The dynamics of the Fresnel-scale irregularities, as investigated from the estimations of the mean zonal drift velocities, reveals that the amplitude of the eastward drifts tends to reduce with the decline in the solar activity. The magnitude of the zonal drift velocities during the December solstice months is larger than during the equinoxes, with the differences being more pronounced at solar maximum years. Other relevant aspects of the observations, with complementary data from a low-latitude ionospheric model, are highlighted and discussed.  相似文献   

14.
The tropospheric atmosphere is neither absolutely dry nor completely saturated. It is, in general, moist. The purpose of the present study is to reveal the role of generalized potential temperature (GPT) in describing the humid state of the real moist atmosphere pertaining to understanding the prevalence of high impact weather systems over an urban station, Kolkata (22°32′N; 88°20′E), of India. A comparative study among GPT, equivalent potential temperature (EPT), potential temperature and relative humidity to reveal the significance of GPT in a precise understanding of the high impact weather of Kolkata is carried out. To attain the objectives, 50 cases of thunderstorms, 15 cases of tropical cyclones and 15 heavy rainfall days are selected during the pre-monsoon season (April–May) over Kolkata (22°32′N; 88°20′E), India. The condition—decision support system of rough set theory is adopted as the methodology. The result of the study reveals that GPT is the most pertinent convective parameter in estimating the prevalence of the high impact weather of Kolkata during the pre-monsoon season and is observed to be better than RH. The results, thus, show that the moist air is capable of describing the distribution of water vapour and thermodynamic properties of the real atmosphere more precisely than an absolutely dry and completely saturated state of the atmosphere.  相似文献   

15.
Two lower tropospheric inversion layers (named as LTI1 and LTI2) over Yichang (111°18′E, 30°42′N) were studied by using the data from intensive radiosonde observations in January 2007 on an eight-times-daily basis. Our observations reveal that both the inversion layers are closely related to the intensive inertial gravity waves propagating in winter tropospheric jets. However, their formation mechanisms are likely to be different. Gravity-wave-induced intensive turbulence via convective instability may yield a downward energy transport and finally form the LTI1, while we speculate that the reflection of gravity waves by the strong tropospheric jet is responsible for the LTI2.  相似文献   

16.
AMSR-E and MODIS are two EOS (Earth Observing System) instruments on board the Aqua satellite. A regression analysis between the brightness of all AMSR-E bands and the MODIS land surface tem-perature product indicated that the 89 GHz vertical polarization is the best single band to retrieve land surface temperature. According to simulation analysis with AIEM,the difference of different frequen-cies can eliminate the influence of water in soil and atmosphere,and also the surface roughness partly. The analysis results indicate that the radiation mechanism of surface covered snow is different from others. In order to retrieve land surface temperature more accurately,the land surface should be at least classified into three types:water covered surface,snow covered surface,and non-water and non-snow covered land surface. In order to improve the practicality and accuracy of the algorithm,we built different equations for different ranges of temperature. The average land surface temperature er-ror is about 2―3℃ relative to the MODIS LST product.  相似文献   

17.
Performance of a feed‐forward back‐propagation artificial neural network on forecasting the daily occurrence and annual depth of rainfall at a single meteorological station is presented. Both short‐term and long‐term forecasting was attempted, with ground level data collected by the meteorological station in Colombo, Sri Lanka (79° 52′E, 6° 54′N) during two time periods, 1994–2003 and 1869–2003. Two neural network models were developed; a one‐day‐ahead model for predicting the rainfall occurrence of the next day, which was able to make predictions with a 74·3% accuracy, and one‐year‐ahead model for yearly rainfall depth predictions with an 80·0% accuracy within a ± 5% error bound. Each of these models was extended to make predictions several time steps into the future, where accuracies were found to decrease rapidly with the number of time steps. The success rates and rainfall variability within the north‐east and south‐west monsoon seasons are also discussed. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

18.
The Global Positioning System (GPS) finds important application in satellite-based navigation. This application requires priori modeling of tropospheric refraction of GPS signal, which is in the microwave domain. The tropospheric delay for microwaves estimated by ray tracing through the Earth's atmosphere is modeled in terms of measurable surface meteorological parameters such as atmospheric pressure, temperature, water vapor partial pressure as well as columnar water vapor for different locations over the Indian subcontinent using the upper air data for three years (1995–1997). Different forms of the empirical relation were examined to develop these models. Site-specific models are first generated for different locations selected for this study (eight Range and Integrity Monitoring Station). Taking all these models into account a unified model is developed, which is applicable for the entire subcontinent. Though the unified model is slightly inferior to site-specific models, the deviations are within the allowable limits for this specific application. The merit of unified model, however, lies in the fact that a single model can be used for any location over the subcontinent. The model predictions are compared with the tropospheric delay derived from ground-based GPS measurements to establish the model accuracy.  相似文献   

19.
The occurrence of strong ionospheric scintillations with S4≥0.2 was studied using global positioning system (GPS) measurements at Guilin (25.29°N, 110.33°E; geomagnetic: 15.04°N, 181.98°E), a station located near the northern crest of equatorial anomaly in China. The results are presented for data collected from January 2007 to December 2008. The results show that amplitude scintillations occurred only during the first five months of the considered years. Nighttime amplitude scintillations, observed mainly in the south of Guilin, always occurred with phase scintillations, total electron content (TEC) depletions, and Rate Of change of TEC (ROT) fluctuations. However, TEC depletions and ROT fluctuations were weak during daytime amplitude scintillations, and daytime amplitude scintillations usually occurred in most of the azimuth directions. GPS scintillation/TEC observations recorded at Guilin and signal-to-noise-ratio measurements obtained from GPS-COSMIC radio occultation indicate that nighttime and daytime scintillations are very likely caused by ionospheric F region irregularities and sporadic E, respectively.  相似文献   

20.
Daily swath MODIS Terra Collection 6 fractional snow cover (MOD10_L2) estimates were validated with two‐day Landsat TM/ETM + snow‐covered area estimates across central Idaho and southwestern Montana, USA. Snow cover maps during spring snowmelt for 2000, 2001, 2002, 2003, 2005, 2007, and 2009 were compared between MODIS Terra and Landsat TM/ETM + using least‐squared regression. Strong spatial and temporal map agreement was found between MODIS Terra fractional snow cover and Landsat TM/ETM + snow‐covered area, although map disagreement was observed for two validation dates. High‐altitude cirrus cloud contamination during low snow conditions as well as late season transient snowfall resulted in map disagreement. MODIS Terra's spatial resolution limits retrieval of thin‐patchy snow cover, especially during partially cloudy conditions. Landsat's image acquisition frequency can introduce difficulty when discriminating between transient and resident mountain snow cover. Furthermore, transient snowfall later in the snowmelt season, which is a stochastic accumulation event that does not usually persist beyond the daily timescale, will skew decadal snow‐covered area variability if bi‐monthly climate data record development is the objective. As a quality control step, ground‐based daily snow telemetry snow‐water‐equivalent measurements can be used to verify transient snowfall events. Users of daily MODIS Terra fractional snow products should be aware that local solar illumination and sensor viewing geometry might influence fractional snow cover estimation in mountainous terrain. Cross‐sensor interoperability has been confirmed between MODIS Terra and Landsat TM/ETM + when mapping snow from the visible/infrared spectrum. This relationship is strong and supports operational multi‐sensor snow cover mapping, specifically climate data record development to expand cryosphere, climate, and hydrological science applications. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

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