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1.
A global weather analysis-forecast system is used to produce six hourly analysis of meteorological fields at roughly 150 km × 150 km resolution at the National Center for Medium Range Weather Forecast (NCMRWF). In this paper, we have studied the Total Precipitable Water Content (TPWC) and Cloud Liquid Water Path (CLWP) derived from the Indian Remote Sensing (IRS-P4) Satellite over the Indian Ocean region in relation to operational numerical weather prediction (NWP) model analysis and short-range forecasts. An objective analysis was carried out by introducing the observations of CLWP, TPWC and their values (six hour forecasts) from the T80 model as the first guess, for a 20 days period of August 1999 using the standard Cressman’s technique. The reanalysis could capture the signature of TPWC and CLWP data from IRS-P4 satellite. In general the observed values of TPWC and CLWP from IRS-P4 have a positive bias compared to NCMRWF analysis over the region where the satellite passed. The CLWP values have been compared with Special Sensor Microwave/Imager (SSM/I) products from the Defense Meteorological Satellite Program (DMSP) satellites. Results indicate that the model derived CLWP values were within acceptable limits, whereas the observations from the Multi-channel Scanning Microwave Radiometer (MSMR) showed slightly larger values. 相似文献
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The timing of spring initiates an important period for resource availability for large trophic webs within ecosystems, including forage for grazing animals, flowers for pollinators, and the higher trophic levels that depend on these resources. Spring timing is highly variable across space, being influenced strongly by the departure of snow cover (i.e. snowmelt timing, in locations with a seasonal snowpack), climate, weather, elevation, and latitude. When spring timing occurs along a gradient (e.g. spring arriving later in higher elevations of mountainous terrain), the organisms that rely on spring resources often migrate to maintain an optimal position for spring resources – a phenomenon known as ‘surfing the green wave.’ While this behavior has been observed by tracking animals, there have been no studies to quantify the green wave as a movement across space and time. Furthermore, considering that snowmelt timing has moderate power to explain green-up timing for a given location, we ask the question: does snowmelt velocity predict green wave velocity? Here, we introduce the first continental maps of snowmelt and green wave velocity for North America from 2001 to 2016 as derived from the MODIS MCD12Q2 phenology dataset. We show that both snowmelt and green wave velocities are influenced strongly by topography, including slope and aspect. Furthermore, we quantify the relationships between snowmelt and green wave velocities according to three variables: direction, speed, and distance traveled. We conclude that mountainous ecoregions, such as the western North American cordillera, have the highest correspondence between snowmelt and green wave velocities, compared to flatter regions such as the Great Plains and tundra. This work will be of interest to wildlife ecologists, biologists, and land managers who seek to conserve migratory animals and the ecosystems that support them. 相似文献
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由垂直重力梯度异常反演全球海底地形模型 总被引：2，自引：2，他引：0
本文给出了海底地形起伏与垂直重力梯度异常之间的响应函数关系。据此,联合船测海深和垂直重力梯度异常数据,构建了全球75°S~70°N范围内1′×1′海底地形模型。以船测海深为检核参考,考察了本文模型在印度洋南部和西北太平洋地区的精度。结果表明,在考察区域内,本文模型精度优于ETOPO1、GEBCO和DTU10模型,且在印度洋南部与SIO的最新海底地形模型V15.1精度相当,在西北太平洋地区略优于V15.1。探讨了高次项和地壳均衡现象的影响量级,发现两者对反演结果的影响很小,可以忽略。通过与重力异常反演结果的比较,发现垂直梯度异常反演在中短波长部分（100~200km）表现较优。在西北太平洋地区,联合重力异常和垂直梯度数据进行海底地形反演计算,反演结果的精度较V15.1模型提高了约29.5％,说明联合这两种数据可以计算精度更高的海底地形模型。 相似文献
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Aerosol and water vapour are very important element in the Earth’s climate system which has direct role in the Earth’s radiation budget. In this paper the seasonality, latitudinal distribution and the relationship of aerosol optical thickness (AOD) and water vapour (WV) using MODIS Level 3 monthly data from 2001 to 2008 are analysed. The analysis shows that AOD (0.55 μm) values reach maximum during southwest monsoon and remain minimum during northeast monsoon period. The Equatorial Indian Ocean shows minimum AOD (0.115 to 0.153) throughout the year compared to Arabian Sea (0.208 to 0.613) and Bay of Bengal (0.214 to 0.351). Arabian Sea shows high variation and maximum value of AOD compared to Bay of Bengal and Equatorial Indian Ocean. During southwest monsoon WV over Bay of Bengal was found higher in concentration compared to Arabian Sea and Equitorial Indian Ocean throughout the study period. Comparison between Arabian Sea (2.98 cm to 5.07 cm) and Bay of Bengal (3.49 cm to 5.94 cm) shows that WV concentration is less in Arabian Sea throughout the year. The analysis of correlation between WV and AOD was found to be inconsistent. However, AOD and WV shows a strong positive correlation for whole year (Mean R2 =0.90) in the Equitorial Indian Ocean region except in the months of January, February and March. In general, the correlation between WV and AOD is found to be strongly positive for oceanic aerosol (sea salt) in low water vapour condition. 相似文献
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基于GPS数据的地震前电离层TEC异常研究 总被引：2，自引：0，他引：2
选取印度洋区域7个IGS站,运用2004年12月26日印度洋地震前后共计25 d的GPS观测数据,计算出高时空分辨率的VTEC.综合考虑了太阳和地磁活动参数,运用统计分析的方法,详尽阐释了地震发生前TEC减小的电离层异常现象. 相似文献
7.
无人航道测量船由于具有低成本、高效率、便捷等优点,在航道测量领域受到越来越多的关注。在避碰过程中,为保证无人航道测量船测量数据的有效性,新规划的避碰路线应尽可能地与原规划测量航线一致。针对传统A*算法所规划的路径在避开障碍物之后无法快速回到预设航线上的问题,提出了一种改进的A*算法。该算法主要是在原始代价函数的基础上,新增了一个与当前点到预设航线的垂直距离相关的代价值,且该代价值的取值与无人航道测量船所处的位置相关。首先在MATLAB仿真环境下对改进A*算法进行仿真实验,然后利用无人航道测量船实船平台开展航行验证实验并进行围栏分析。实验结果表明,相比于传统A*算法,在保证安全的前提下,改进A*算法能够使无人航道测量船在避开障碍物之后更快地回到预设航线。 相似文献
8.
P. M. Muraleedharan P. G. Nisha P. V. Sathe K. U. Sivakumar 《Journal of the Indian Society of Remote Sensing》2012,40(1):75-83
Sea surface temperature (SST) and wind speed (WS) derived from Multichannel Scanning Microwave Radiometer (MSMR), onboard
IRS-P4 (Oceansat-1) satellite were used to generate spatially averaged (80° to 100° E & 0° to 10° S) daily data during June
to September from 1999 to 2001 along with collocated outgoing long wave radiation (OLR) data from NCEP/NCAR reanalysis product.
Daily rainfall data over the peninsular India during the above period was taken from the weekly weather report published by
the Indian Meteorological Department. The data were then subjected to power spectral analysis. Dominant 30 to 60 days oscillations
were observed over both ocean and land during all the 3 years investigated. It is quite interesting to note that the intra-seasonal
oscillation with 60 days periodicity dominates in both ocean and land during 1999 and then transforms to 30 and 40 days periodicities
in 2000 and 2001 respectively with a phase lag of about 25 to 30 days. It was also observed that the time-latitude section
of zonally averaged OLR and TMI derived cloud liquid water data clearly depict the propagation of convection and cloud from
the equator to the north at the rate of 0.75° to 1° latitude per day which corroborates well with the rate of propagation
derived from the phase lag obtained between the processes occurring at the equatorial Indian Ocean and rainfall recorded at
the designated land segments. The results are in good agreement with the observations made by earlier investigators. 相似文献
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We have used up to 12 years of data to assess DORIS performance for geodynamics applications. We first examine the noise characteristics of the DORIS time-series of weekly station coordinates to derive realistic estimates of velocity uncertainties. We find that a combination of white and flicker noise best explains the DORIS time-series noise characteristics. Second, weekly solutions produced by the Institut Géographique National/Jet Propulsion Laboratory (IGN/JPL) DORIS Analysis Centre are combined to derive a global velocity field. This solution is combined with two independent GPS solutions, including 11 sites on Nubia and 5 on the Somalia plate. The combination indicates that DORIS horizontal velocities have an average accuracy of 3 mm/year, with best-determined sites having velocity accuracy better than 1 mm/year (one-sigma levels). Using our combined velocity field, we derive an updated plate kinematics model with a focus on the Nubia–Somalia area. Including DORIS data improves the precision of the angular velocity vector for Nubia by 15%. Our proposed model provides robust bounds on the maximum opening rates along the East African Rift (4.7–6.7 mm/year). It indicates opening rates 15 and 7% slower than values predicted by NUVEL-1A for the southern Atlantic Ocean and Indian Ocean, respectively. These differences are likely to arise from the fact that NUVEL-1A considered Africa as a single non-deforming plate, while here we use a more refined approach. 相似文献
12.
Ching-Yuang Huang Ying-Hwa Kuo Shu-Ya Chen Chuen-Tsyr Terng Fang-Ching Chien Pay-Liam Lin Mien-Tze Kueh Shu-Hua Chen Ming-Jen Yang Chieh-Ju Wang Anisetty S. K. A. V. Prasad Rao 《GPS Solutions》2010,14(1):35-49
The impact of GPS radio occultation (RO) data assimilation on severe weather predictions in East Asia is introduced and reviewed. Both the local observation operator that assimilates the retrieved refractivity as local point measurement, and the nonlocal observation operator that assimilates the integrated retrieved refractivity along a straight raypath have been utilized in WRF 3DVAR to improve the initial analysis of the model. A general evaluation of the impact of these approaches on Asian regional analysis and daily prediction is provided in this paper. In general, the GPS RO data assimilation may improve prediction of severe weather such as typhoons and Mei-yu systems when COSMIC data were available, ranging from several points in 2006 to a maximum of about 60 in 2007 and 2008 in this region. Based on a number of experiments, regional model predictions at 5 km resolution were not significantly influenced by different observation operators, although the nonlocal observation operator sometimes results in slightly better track forecast. These positive impacts are seen not only in typhoon track prediction but also in prediction of local heavy rainfall associated with severe weather over Taiwan. The impact of 56 GPS RO soundings on track prediction of Cyclone Gonu (2007) over the Indian Ocean is also appealing when compared to other tracks assimilated with different observations. From a successive evaluation of skill scores for real-time forecasts on Mei-yu frontal systems operationally conducted over a longer period and predictions of six typhoons in 2008, assimilation of GPS RO data appears to have some positive impact on regional weather predictions, on top of existent assimilation with all other observations. 相似文献
13.
Maged Marghany 《Journal of the Indian Society of Remote Sensing》2004,32(2):185-198
This paper presents the application of the velocity bunching model to detect the wave spectra pattern. We have developed the
azimuth cut-off model which is estimated from the velocity bunching theory to model out the significant wave height. The velocity
bunching model utilized two ERS-1 images (First European Remote Sensing Satellite). These two ERS-1 images have been acquired
with the different monsoon periods. Several steps have been used to simulate the significant wave height from the velocity
bunching model, these were: the real ocean wave spectra simulated from the in situ wave data, and the SAR wave spectra, extracted
by applying two-dimensional Fourier transform (2-DFFT). Finally, the significant wave height was estimated based on the azimuth
cut-off arising from the velocity bunching model. Two hypotheses were established in modelling the wave spectra from the SAR
images: (i) azimuth cut-off was based on velocity bunching, which has been used to model the significant wave height with
high accuracy, and (ii) velocity bunching model has been used to map the SAR wave spectra into ocean wave spectra. In the
present study, a specific ERS-1 images of the South China Sea has been considered. No significant differences were found between
the velocity-bunching model and ocean wave spectra model where ERS-1 wave spectra has been found to be dominated by the azimuth
fall-off effects. Furthermore, the velocity bunching model produced wave spectra pattern approximately closed to the real
ocean wave compared to the SAR wave spectra. The highest rate of r2 (0.69) occurred when the significant wave height increased. It has been concluded that the velocity bunching model could
be used as the best fit model for estimating the significant wave height traveled along the azimuth direction. 相似文献
14.
Sukanta Kumar Das Sanjib Kumar Deb C. M. Kishtawal P. C. Joshi Pradip Kumar Pal 《Journal of the Indian Society of Remote Sensing》2011,39(3):323-336
Community Climate System Model (CCSM3), a coupled model developed by National Center for Atmospheric Research (NCAR) containing
atmosphere, ocean, sea-ice and land processes, simulation have been analysed for suitability in the Indian Monsoon region.
A long control run of CCSM3 with constant forcing at every year has been done and the model climatology has been generated
using 20 years of simulation. Atmospheric component of the model has been able to capture the large scale phenomena, however,
regional monsoon variability not fully captured by the model simulation. A suitable modification in the flux coupler and the
convective parameterization process in regional scale certainly improve the atmospheric part of the climate system. Another
major component of the climate model is the representation of Land Surface Processes (LSP). A successful inclusion of LSP
in climate model must address the issues related to the regional scale variation of the properties of LSP. A proper understanding
of land surface processes is very crucial for climate simulations using numerical models. To understand the LSP-monsoon coupling,
the offline Community Land Model (CLM), taken from CCSM3 land component, simulation forced with three hourly atmospheric boundary
conditions have also been analyzed and compared with the CLM version of coupled CCSM mode. The distribution of surface heat
flux in CCSM coupled mode shows some discrepancies compared to the offline CLM. Both the simulation results are compared with
existing climatological features and assessment to improve CCSM3 for the regional climate change studies is made. 相似文献
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针对目前对海上船舶采用传统手段进行监管存在盲区及资费昂贵的痛点,利用北斗卫星导航系统所具有的定位、测速、授时,及其北斗一代所特有的短报文双向通信及功能,设计了一套北斗船舶航线监管平台系统,并将它应用于武汉市港航局所辖的船舶航线的监管工作中。结果证明,该系统在不依赖其它通信技术手段前提下,能够实现船舶实时定位、测速、精密授时、船舶之间、以及船舶与监控中心和授权手机短报文双向通信。另外,还具有防撞报警、航迹偏差告警等功能,以及全天候、无盲区、低资费、高可靠的优势,有较大的实用价值。 相似文献
16.
M.V.R. Sesha Sai P.V. Narasimha Rao 《International Journal of Applied Earth Observation and Geoinformation》2008,10(2):206-1
Subsequent to the launch of the state-of-art third generation Indian Remote Sensing satellite, Resourcesat-1, studies have been conducted to understand the capabilities of the on-board sensors for crop discrimination. The paper discusses the unique capabilities of the AWiFS, LISS-III and LISS-IV sensors in terms of their dimensionality, radiometry and spatial resolutions for crop discrimination and monitoring. The studies have indicated better crop discriminability especially using the short wave infrared data in 1.55–1.70 μm data among the spectrally confusing land cover classes, attributed to the relative differences of water contents. 10-bit radiometry of AWiFS data in four bands has been observed to be a better discriminant. Intrafield variability was very well captured by the LISS-IV data revealing the potential of data for applications like precision farming. The studies have revealed that potential of Resourcesat-1 data becoming the workhorse for several agricultural applications. 相似文献
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Centimeter-Level Positioning of a U. S. Coast Guard Buoy Tender 总被引：1，自引：1，他引：0
David B. Zilkoski J. Don D'Onofrio Rudolf J. Fury Curtis L. Smith Lloyd C. Huff Barry J. Gallagher 《GPS Solutions》1999,3(2):53-65
With the availability of high-accuracy, differential global positioning system (GPS) results in real-time, there is a new
opportunity to use GPS to accurately measure a marine vessel's dynamic draft (settlement and squat) and 3D attitude (roll,
pitch, and heading). The National Geodetic Survey (NGS) and the Coast Survey (CS), offices of the National Ocean Service (NOS),
National Oceanic and Atmospheric Administration (NOAA), propose to transfer this technology to the shipping industry. The
overall goal of this project is to provide the position of a vessel's keel in real time to within 10 cm (about 4 inches) relative
to the bottom of the shipping channel.
In support of this phase of the project, there were three meetings hosted by the Port of Oakland, California and NOS to discuss
the real-time positioning of vessels project. On December 3 and 4, 1996, CS, NGS, Trimble Navigation Ltd., and the U. S. Coast
Guard (USCG) performed GPS tests on a USCG buoy-tender ship. GPS data were used to compute the vessel's dynamic draft and
3D attitude. During the test, five receivers continually collected data; one receiver was located at a base station on the
USCG pier on Yerba Buena Island, and four were on the ship: two on the stern and two on the bow. CS installed a TSS-335B vertical
reference unit (to measure heave, pitch, and roll) in the engine room of the ship.
NOS processed the GPS data and computed the vessel's dynamic draft and 3D attitude. The results indicate that the linear equivalent
to the vessel's dynamic draft and 3D attitude were accurate to the 10-cm level using GPS. It was also demonstrated how a ship
can be used to measure local water-level changes and actual water-level values everywhere it travels. ? 1999 John Wiley &
Sons, Inc. 相似文献
18.
基于X波段雷达的海洋动力学参数提取算法初步研究 总被引：1，自引：0，他引：1
从X波段船舶雷达记录的连续雷达图像中,可以获得海浪频谱和海流的信息。在不存在海洋表面流的情况下,雷达图像的三维频谱分布在由静水色散关系确定的平面轨迹上。海流的存在会使三维频谱的能量分布产生相应的多普勒频移,对此频移进行最小二乘拟合,可以确定海流的大小和方向,进而得到有向浪高谱。本文基于通用的海浪谱和方向函数,在考虑阴影调制的情况下仿真海面X波段雷达图像序列,分别对无海流和有海流作用下的三维频谱进行了数值模拟,通过海流产生的多普勒频移拟合出海流,并获得二维图像谱。最后分析了McMaster大学X波段雷达的实测定向海面回波数据,获取了海浪的一维图像频谱。 相似文献
19.
基于CMONOC提供的GNSS观测和气象资料,开展中国大陆地区不同气候类型的MODIS PWV校正研究。首先依据不同气候类型,开展GNSS PWV与MODIS PWV的相关性分析;然后基于GNSS PWV构建不同气候类型的MODIS PWV校正模型;最后根据MODIS PWV、模型校正的MODIS PWV分别与GNSS PWV比较,开展模型改进效果检验。研究表明:不同气候类型的MODIS PWV校正模型,均能有效改善MODIS PWV精度,提高MODIS PWV在短期天气预报和InSAR大气校正的应用。 相似文献
20.
M.C. Naeije K.F. Wakker R. Scharroo B.A.C. Ambrosius 《ISPRS Journal of Photogrammetry and Remote Sensing》1992,47(5-6)
This paper discusses an altimeter data processing technique designed to compute time series of the mesoscale dynamic sea surface and to produce mean sea surfaces and surface variability. The technique has been applied to Geosat data collected over the North and South Atlantic and the South Indian Ocean. The computed mean sea surfaces show a high correlation with ocean bottom topography, whereas the variability is found to be associated with mesoscale ocean currents. High variability levels are spotted near the Gulfstream Extension and the Agulhas Return Current.Detailed examination of the sea surface and related flow field time series made it possible to identify a large number of eddies and to keep track of them in both the nort-west and south-east Atlantic. Additionally, some of the eddy characteristics have been resolved such as translation and swirl velocity. It is found that the eddy motion is affected by ocean bottom slopes. 相似文献