排序方式： 共有6条查询结果，搜索用时 15 毫秒
1
1.
Dudy D. Wijaya Haris Haralambous Christina Oikonomou Wedyanto Kuntjoro 《Journal of Geodesy》2017,91(9):1117-1133
The critical frequency of ionospheric F2 layer (foF2) is a measure of the highest frequency of radio signal that may be reflected back by the F2 layer, and it is associated with ionospheric peak electron density in the F2 layer. Accurate long-term foF2 variations are usually derived from ionosonde observations. In this paper, we propose a new method to observe foF2 using a stand-alone global positioning system (GPS) receiver. The proposed method relies on the mathematical equation that relates foF2 to GPS observations. The equation is then implemented in the Kalman filter algorithm to estimate foF2 at every epoch of the observation (30-s rate). Unlike existing methods, the proposed method does not require any additional information from ionosonde observations and does not require any network of GPS receivers. It only requires as inputs the ionospheric scale height and the modeled plasmaspheric electron content, which practically can be derived from any existing ionospheric/plasmaspheric model. We applied the proposed method to estimate long-term variations of foF2 at three GPS stations located at the northern hemisphere (NICO, Cyprus), the southern hemisphere (STR1, Australia) and the south pole (SYOG, Antarctic). To assess the performance of the proposed method, we then compared the results against those derived by ionosonde observations and the International Reference Ionosphere (IRI) 2012 model. We found that, during the period of high solar activity (2011–2012), the values of absolute mean bias between foF2 derived by the proposed method and ionosonde observations are in the range of 0.2–0.5 MHz, while those during the period of low solar activity (2009–2010) are in the range of 0.05–0.15 MHz. Furthermore, the root-mean-square-error (RMSE) values during high and low solar activities are in the range of 0.8–0.9 MHz and of 0.6–0.7 MHz, respectively. We also noticed that the values of absolute mean bias and RMSE between foF2 derived by the proposed method and the IRI-2012 model are slightly larger than those between the proposed method and ionosonde observations. These results demonstrate that the proposed method can estimate foF2 with a comparable accuracy. Since the proposed method can estimate foF2 at every epoch of the observation, it therefore has promising applications for investigating various scales (from small to large) of foF2 irregularities. 相似文献
2.
Land subsidence characteristics of Jakarta between 1997 and 2005, as estimated using GPS surveys 总被引：4，自引：0，他引：4
Hasanuddin Z. Abidin H. Andreas Rochman Djaja Dudy Darmawan M. Gamal 《GPS Solutions》2008,12(1):23-32
Jakarta is the capital city of Indonesia with a population of about 12 million people, inhabiting an area of about 625 km2. It is well known that several areas in Jakarta are subsiding rapidly. There are four different types of land subsidence
that can be expected to occur in the Jakarta basin, namely: subsidence due to groundwater extraction, subsidence induced by
the load of constructions (i.e., settlement of high compressibility soil), subsidence caused by natural consolidation of alluvial
soil and tectonic subsidence. In addition to the leveling method, Global Positioning System (GPS) survey methods have been
used to study land subsidence in Jakarta. In this paper, we characterize subsidence in the Jakarta basin using eight episodic/campaign
GPS surveys between 1997 and 2005. The estimated subsidence rates are 1–10 cm/year. The observed subsidence rates in several
locations show a positive correlation with known abstraction volumes of groundwater extraction. These basin-wide series of
GPS measurements show how this type of measurement can play an important role in multiple public policy decision making in
this rapidly growing area. 相似文献
3.
Abidin Hasanuddin Z. Djaja Rochman Darmawan Dudy Hadi Samsul Akbar Arifin Rajiyowiryono H. Sudibyo Y. Meilano I. Kasuma M. A. Kahar J. Subarya Cecep 《Natural Hazards》2001,23(2-3):365-387
Jakarta is the capital city of Indonesia with a population of about 10 million people, inhabiting an area of about 25 × 25 km. It has been reported for sometime that locations in Jakarta are subsiding at different rates. Up to the present, there has been no comprehensive information about the characteristics and pattern of land subsidence in the Jakarta area. Usually land subsidence in Jakarta is measured using extensometers and ground water level observations, or estimated using geological and hydrological parameters. To give a better picture about land subsidence, geodetic-based monitoring systems utilizing leveling and GPS surveys have also been implemented.The land subsidence characteristics of Jakarta and its surrounding area areinvestigated using data from three repeated leveling surveys performed in1982, 1991, and 1997, and two repeated GPS surveys conducted in 1997and 1999. Leveling surveys detected subsidence up to about 80 cm duringthe period of 1982–1991, and up to about 160 cm during the 1991–1997period; while GPS surveys observed subsidence up to about 20 cm duringthe period of 1997–1999. Comparison with the hydrological data shows thatland subsidence in Jakarta is strongly related to excessive groundwater extraction. 相似文献
4.
5.
Arifudin Idrus Jochen Kolb F.Michael Meyer Johan Arif Dudy Setyandhaka Syamsul Kepli 《Resource Geology》2009,59(3):295-306
Batu Hijau is a world-class gold-rich porphyry copper deposit, situated in Sumbawa Island, Indonesia. Deep drilling indicates that several intervals of calc-silicate rock were intersected, where they are apparently interbedded with volcaniclastic rocks. The calc-silicate rocks occur at the contact with copper-gold-bearing tonalite porphyries. The rocks are fine-grained and granular with green, reddish-brown and white layers. The green layers consist mostly of fine-grained clinopyroxene (diopside and hedenbergite) and the reddish-brown layers consist mostly of garnet (andradite), whereas the white layers are commonly composed of calcite and zeolite (chabazite). The calc-silicate rocks were formed by contact metasomatism of andesitic volcaniclastic rocks, as it is calcic in composition. Paragenesis study reveals at least two stages of calc-silicate mineralization. Stage 1 (prograde) is characterized by the presence of garnet (andradite), clinopyroxene (diopside and hedenbergite), anorthite and quartz at 340–360 C (high salinity 35–45 NaCl wt percentage eqn.). Stage 2 (retrograde) is characterized by chlorite and rare epidote at 280–300 C (low salinity 1–10 NaCl wt% eqn.). Late calcite ± quartz veinlets and calcite + chabazite veins/veinlets may also be related to this stage and cross cut the oldest mineral assemblages. Mineralization (magnetite, chalcopyrite and pyrite) may occur during the retrograde stage. Clinopyroxene and garnet were modified by Fe-rich hydrothermal fluid (oxidizing condition) indicated by increase of Fe from core to rim of both the cogenetic minerals. The presence of the calc-silicate rocks associated with massive magnetite-chalcopyrite-pyrite assemblage indicates the occurrence of calcic-exoskarn surrounding the Batu Hijau porphyry copper-gold deposit. 相似文献
6.
It has been widely known that the use of two-frequency Satellite Laser Ranging (SLR) system is limited by stringent precision
requirements of the range measurements and the proper atmospheric model. Owing to the stringent requirements, this SLR system
is impractical for the current requirement of SLR measurements within the framework of global geodetic observing system (GGOS).
If in the future this stringent requirement could be met, this SLR system would be an attractive tool to reduce atmospheric
propagation effects of SLR and would be of great benefit for the next generation of GGOS design. To anticipate possible future
developments of the two-frequency SLR systems, we have developed a new atmospheric correction formula for the two-frequency
SLR measurements. The new formula eliminates the total atmospheric density effect including its gradient and provides two
terms to calculate the curvature effect and the water vapor distribution effect. While the curvature effect can be calculated
by an accurate model, the required information about the water vapor distribution along the propagation path can be calculated
using previous developments of optical delay modeling or alternatively using results from microwave measurements. Theoretical
simulations using the two-frequency systems of the Graz and TIGO-Concepción stations shows that the new formula completely
reduces all propagation effects at any elevation angle above 3° with an accuracy better than 1 mm. However, the required precision
for the difference of the two-frequency SLR measurements, i.e. better than 45 μm for a single epoch, exceeds the capability
of the current state of the art SLR systems. 相似文献
1