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181.
For high-accuracy geodetic applications, time-variable tropospheric propagation delay errors limit global positioning system real-time kinematic positioning accuracy. Potential improvements in positioning accuracy are evaluated by using the National Oceanic and Atmospheric Administration (NOAA) real-time tropospheric corrections (herein called NOAA model) within a multiple reference station network approach. The results are compared with those for modified Hopfield tropospheric model corrections, for six scenarios in three geographical regions in the U.S. National Geodetic Survey network of Continuously Operating Reference Stations, for baseline lengths of 60~150 km. Analyses are conducted at rover locations for relatively humid days, and misclosures for various double difference observations are computed; these observations include each frequency (L1 and L2) and three linear combinations [wide lane, ionosphere free (IF), and geometry free]. The effectiveness of the network approach is demonstrated, with overall performance improvements of 15 and 19%, using the modified Hopfield and the NOAA model, respectively. The IF linear combination, a measure of tropospheric and orbital errors, shows a 3% improvement for the NOAA model compared with the modified Hopfield model. 相似文献
182.
Tae-woong Kim Hosung Ahn Gunhui Chung Chulsang Yoo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(6):705-717
This paper presents a stochastic model to generate daily rainfall occurrences at multiple gauging stations in south Florida.
The model developed in this study is a space–time model that takes into account the spatial as well as temporal dependences
of daily rainfall occurrence based on a chain-dependent process. In the model, a Markovian method was used to represent the
temporal dependence of daily rainfall occurrence and a direct acyclic graph (DAG) method was introduced to encode the spatial
dependence of daily rainfall occurrences among gauging stations. The DAG method provides an optimal sequence of generation
by maximizing the spatial dependence index of daily rainfall occurrences over the region. The proposed space–time model shows
more promising performance in generating rainfall occurrences in time and space than the conventional Markov type model. The
space–time model well represents the temporal as well as the spatial dependence of daily rainfall occurrences, which can reduce
the complexity in the generation of daily rainfall amounts. 相似文献
183.
Local Meteorological and Synoptic Characteristics of Fogs Formed over Incheon International Airport in the West Coast of Korea 总被引:2,自引:0,他引:2
Fogs observed over Incheon international airport (IIA) in the west
coast of Korea from January 2002 to August 2006 are classified into categories
of coastal fog, cold sea fog, and warm sea fog based on the areal extent of the
fogs and the difference between the air temperature (T) and the SST, i.e.,
cold sea fog if TSST = T-SST>0oC and warm sea fog if TSST
<0oC. The numbers of coastal, cold, and warm sea fog cases
are 64, 26, and 9. Coastal fogs form most frequently in winter, while cold sea
fogs occur mostly in summer and warm sea fogs are observed from January to May
but not in November and December. On average the air gets colder by
1.6oC during the three hours leading up to the coastal fog
formation, and an additional cooling of 1.1oC occurs during the
fog. The change in the dew point temperature (Td) is minimal except
during the fog (0.6oC). Decreases in T for the cold and warm
sea fogs are relatively smaller. The average Td is higher than SST
during the cold sea fog periods but this Td is more than
4oC higher than that for the corresponding non-fog days,
suggesting that cold sea fogs be formed by the cooling of already humid air
(i.e., Td>SST). Increases of Td are significant during the
warm sea fog periods (1.4oC), implying that efficient moisture
supply is essential to warm sea fog formation. Four major synoptic patterns are
identified in association with the observed fogs. The most frequent is a north
Pacific high that accounts for 38% of cases. Surface or upper inversions are
present in 77%, 69%, and 81% of the fog periods for coastal, cold, and
warm sea fogs, respectively. 相似文献
184.
Since coastal waters are one of the most vulnerable marine systems to environmental pollution, it is very important to operationally monitor coastal water quality. This study attempts to estimate two major water quality indicators, chlorophyll-a (chl-a) and suspended particulate matter (SPM) concentrations, in coastal environments on the west coast of South Korea using Geostationary Ocean Color Imager (GOCI) satellite data. Three machine learning approaches including random forest, Cubist, and support vector regression (SVR) were evaluated for coastal water quality estimation. In situ measurements (63 samples) collected during four days in 2011 and 2012 were used as reference data. Due to the limited number of samples, leave-one-out cross validation (CV) was used to assess the performance of the water quality estimation models. Results show that SVR outperformed the other two machine learning approaches, yielding calibration R2 of 0.91 and CV root-mean-squared-error (RMSE) of 1.74 mg/m3 (40.7%) for chl-a, and calibration R2 of 0.98 and CV RMSE of 11.42 g/m3 (63.1%) for SPM when using GOCI-derived radiance data. Relative importance of the predictor variables was examined. When GOCI-derived radiance data were used, the ratio of band 2 to band 4 and bands 6 and 5 were the most influential input variables in predicting chl-a and SPM concentrations, respectively. Hourly available GOCI images were useful to discuss spatiotemporal distributions of the water quality parameters with tidal phases in the west coast of Korea. 相似文献
185.
Gwang H. Lee Dae C. Kim Mi K. Park Soo C. Park Han J. Kim Hyeong T. Jou Boo K. Khim 《Island Arc》2010,19(1):71-85
The Korea Strait shelf mud (KSSM) (Nakdong River subaqueous delta) is the most conspicuous Holocene sedimentary feature in the inner shelf off southeast Korea. Analysis of multi-channel sparker profiles and 14 C ages of sediment cores reveals that the KSSM consists of three seismic units at the depocenter (>60 m thick): (i) the thin transgressive bottom (> ca 8000 cal bp ); (ii) thick (>40 m) obliquely progradational middle ( ca 8000– ca 2600 cal bp ); and (iii) thin transgressive top ( ca 2600 cal bp –present) units. The relative base level, predicted from the internal reflection pattern of the KSSM, remained significantly deeper (up to >70 m) than global sealevel during much of the Holocene. The apparent gradual drop (∼20 m) of the relative base level during the deposition of the middle unit, followed by a rise, further suggests that base level does not conform to sealevel and is more sensitive than the relative sealevel is to the local oceanographic regime and processes. 相似文献
186.
A non-intrusive “Micro-Chirp” acoustic system and a signal-processing protocol have been developed to estimate the bulk density
of consolidating cohesive sediment beds. Using high-frequency (300–700 kHz) Chirp acoustic waves, laboratory measurements
were conducted with clay–water mixtures. Because acoustic echo strength is proportional to variations in acoustic impedance,
and the speed of sound in the clay bed hardly changed during consolidation, the bulk density could be successfully estimated
without disturbing the sediment bed. Based on acoustic signal analysis, this study demonstrates that the reflection coefficient
and bulk density at the water–sediment interface increase with consolidation time, and that a single speed of sound value
can be used for practical bulk density estimation in muddy environments. 相似文献
187.
This study examines the effects of tides on surges, wave setups and waves, in terms of tidal amplitudes and phases, by using a coupled numerical model of Surge, WAve and Tide (called as SuWAT). The SuWAT model, composed of depth integrated nonlinear shallow water equations and Simulating WAves Nearshore (SWAN) model, is able to simultaneously run with an arbitrary number of nested domains by using the Message Passing Interface. The results for an idealized case indicate that surge and wave setup are increased in the phase of low water and decreased in the high water phase; on the other hand, waves change in a reverse manner. Such changes are enhanced by large tidal variations. The conventional method (e.g., surge plus tide independently) has the possibility of overestimation for the total water level. The hindcast results for Typhoon Ewiniar in 2006 show that the run with tides is more accurate 10% than that without tides in coastal areas of Korea. The nested scheme improves the accuracy up to 40% for the prediction of water levels in the simulations. It is shown that the present coupled model, SuWAT, is capable of predicting both water levels and waves under storm events with reasonable accuracy against the observations. 相似文献
188.
189.
It is possible and common to obtain equivalent natural frequency and damping for a soil-foundation system from results of experimental or numerical analysis assuming the system has a single degree of freedom. Three approaches to extract natural frequency and damping were applied to the vertically vibrated soil-foundation system. The sensitivity of the computed natural frequency and damping to the soil properties was evaluated through parametric studies. About 10–20% of discrepancy in values of natural frequency was observed due to different approaches. The results help to assess the reliability of equivalent soil properties determined from the reported natural frequency of the system. Finally the results obtained using theoretical predictions with linear soil properties measured in situ were compared to those calculated from experimental data. The prediction and experimental results showed good agreements if the embedment of the foundation is neglected with stepped sine test but considered with impulse test. 相似文献
190.
Jongchul Chae Hyung-Min Park Kwangsu Ahn Heesu Yang Young-Deuk Park Kyung-Suk Cho Wenda Cao 《Solar physics》2013,288(1):89-103
The characteristics of Doppler shifts in a quiet region of the Sun are compared between the Hα line and the Ca?ii infrared line at 854.2 nm. A small area of 16″×40″ was observed for about half an hour with the Fast Imaging Solar Spectrograph (FISS) of the 1.6 meter New Solar Telescope (NST) at Big Bear Solar Observatory. The observed area contains a network region and an internetwork region, and identified in the network region are fibrils and bright points. We infer Doppler velocity v m from each line profile at each individual point with the lambdameter method as a function of half wavelength separation Δλ. It is confirmed that the bisector of the spatially averaged Ca?ii line profile has an inverse C-shape with a significant peak redshift of +?1.8 km?s?1. In contrast, the bisector of the spatially averaged Hα line profile has a C-shape with a small peak blueshift of ??0.5 km?s?1. In both lines, the bisectors of bright network points are significantly redshifted not only at the line centers, but also at the wings. The Ca?ii Doppler shifts are found to be correlated with the Hα ones with the strongest correlation occurring in the internetwork region. Moreover, we find that here the Doppler shifts in the two lines are essentially in phase. We discuss the physical implications of our results in view of the formation of the Hα line and Ca?ii 854.2 nm line in the quiet region chromosphere. 相似文献