Yasuhiro Koyama - Academia.edu (original) (raw)
Papers by Yasuhiro Koyama
Graphics processing units provide lowcost massive parallel computing performance, which can be ut... more Graphics processing units provide lowcost massive parallel computing performance, which can be utilized for the implementation of a GPS software receiver. In order to realize a realtime capable system the crucial stages of the receiver should be optimized to suit the requirements of a parallel processor. First results from such a receiver development are presented together with a short overview of the hard-and software systems.
GALAXY is a research project on advanced VLBI technology, jointly conducted by CRL, NAO, and NTT.... more GALAXY is a research project on advanced VLBI technology, jointly conducted by CRL, NAO, and NTT. The testbed of the project is a 2.5-Gb/s ultra-high speed network using Asynchronous Transfer Mode (ATM). One of the aims of this project is to achieve high-sensitivity VLBI observation with this gigabit class network. GALAXY network consists of KSP and OLIVE networks provided by NTT and spans 200km range. The sensitivity achieved in our current observation system is comparable to the world-highest class (approx. 10mJy) using conventional VLBI samplers. This short baseline and high sensitivity make GALAXY a unique VLBI network for astronomy in the world. Here we describe the properties of GALAXY network and observations focusing on some unique results that can be achieved with the capability of GALAXY. Developments of new networking technology such as Internet Protocol UP) with GALAXY network are also presented,
Egs General Assembly Conference Abstracts, 2002
In the Keystone project, crustal deformation has been observed around Tokyo area de- ploying four... more In the Keystone project, crustal deformation has been observed around Tokyo area de- ploying four space geodetic stations. The observing system consists of VLBI, SLR and GPS, which are collocated at each site. To compare the observation results and to con- tribute the reference frame improvement, the reference point of each system is tied by 1.5 mm precision by the local survey. Using the survey data, baseline length observed by the independent techniques is compared. During the extraordinary volcanic event happened ca. 150 km south of Tokyo in the summer of 2000, the significant crustal deformation whose change was as large as ca. 5 cm in two months in some baselines in the Keystone network, was observed using the independent systems. Daily solution is available from the real-time VLBI system. SLR solution provides the 15 days so- lution. GPS result is available regularly from the Japanese nation wide GPS network maintained by the Geographical Survey Institute. They coincides within formal error. The observed baseline length change will be compared and discussed.
Radio signal delays associated with the neutral atmosphere are one of the major error sources of ... more Radio signal delays associated with the neutral atmosphere are one of the major error sources of space geodesy such as GPS, GLONASS, GALILEO, VLBI, In-SAR measurements. We have developed a state-of-art tool to estimate the atmospheric path delays by ray-tracing through JMA meso-scale analysis (MANAL data) data. The tools, which we have named 'KAshima RAytracing Tools (KARAT)', are capable of calculating total slant delays and ray-bending angles considering real atmospheric phenomena. Numerical weather models such as MANAL data have undergone a significant improvement of accuracy and spatial resolution, which makes it feasible to utilize them for the correction of atmosphere excess path delays. In the previous studies for evaluating KARAT performance, the KARAT solutions are slightly better than the solutions using VMF1 and GMF with linear gradient model for horizontal and height positions. Based on these results we have started the web-based online service, 'KAshima RAytracing Service (KARATS)' for providing the atmospheric delay correction of RINEX files on Jan 27th, 2010. The KARATS receives user's RINEX data via a proper web site (http://vps.nict.go.jp/karats/index.html) and processes user's data files using KARAT for reducing atmospheric slant delays. The reduced RINEX files are archived in the specific directory for each user on the KARATS server. Once the processing is finished the information of data archive is sent privately via email to each user. If user want to process a large amount of data files, user can prepare own server which archives them. The KARATS can get these files from the user's server using GNU ¥emph{wget} and performs ray-traced corrections. We will present a brief status of the KARATS and summarize first experiences gained after this service went operational in December 2009. In addition, we will also demonstrate the newest KARAT performance based on the 5km MANAL data which has been operational from April 7th, 2009 and an outlook on future developments of KARATS.
We performed differential VLBI (Δ VLBI) experiments for tracking of the interplanetary spacecraft... more We performed differential VLBI (Δ VLBI) experiments for tracking of the interplanetary spacecraft. Our main goal is to obtain the precise and quasi-realtime navigation technique of the spacecraft using Δ VLBI technique. With VLBI time delay measurements, differenced between the spacecraft and angularly nearby quasars to cancel common measurement errors such as the propagation delays due to the ionosphere and the neutral atmosphere. However, we can't always observe desirable quasars. Unfortunately, sometimes we have no choice but to use quasars which are angularly far from the spacecraft. Then, we tried to evaluate the reduction effect by subtracting the group delays of the reference radio source from those of the spacecraft. Two HAYABUSA Δ VLBI experiments were carried out in order to evaluate reducing propagation delays on October, 2004. The spacecraft HAYABUSA has been flying steadily towards an asteroid named ``Itokawa'' and it will orbit the asteroid as of September 2005, land on it, and bring back a sample from its surface. The HAYABUSA spacecraft and an angularly nearby quasar ``2126-158'' were observed sequentially, not simultaneously, during each period with various time intervals of data acquisition. The maximum angular separations of the spacecraft from the quasar are less than 3 degrees. We estimated the zenith path delay due to the water vapor (ZWD: Zenith Wet Delay) using the data sets of the GPS stations which are adjacent to each VLBI antenna. A principle observable feature of VLBI is the difference in arrival times of radio signals between two stations. Then, we calculated difference between the slant path delays which are values as a ZWDs at each station multiplied by a mapping function. We defined this ``differential wet delay''. If the angular separation is sufficiently small, the differential wet delays for both radio sources are almost equal. Then, these are canceled out by the difference procedure. However, if these are different, the differences between them is added directly to the observables as an error source. According to our analysis, a large difference value of up to 10 cm of the differential wet delay for the Kashima-Uchinoura baseline was estimated in spite of a small separation angle between the HAYABUSA spacecraft and quasar. Such large value was mainly caused by the humid condition around Uchinoura due to the typhoon approaching. Moreover, the east-west direction of the baseline vector and the large difference in elevation angle of radio source between both stations helped to enlarge the difference value.
Iau Colloq 140 Astronomy With Millimeter and Submillimeter Wave Interferometry, 1994
International Vlbi Service For Geodesy and Astrometry 2004 General Meeting Proceedings, Jun 1, 2004
ABSTRACT The ray tracing tools, which we have named ’KAshima RAytracing Tools (KARAT)’, are capab... more ABSTRACT The ray tracing tools, which we have named ’KAshima RAytracing Tools (KARAT)’, are capable of calculating total slant delays and ray-bending angles considering real atmospheric phenomena. We compared PPP solutions using KARAT with that using the Global Mapping Function (GMF) and Vienna Mapping Function 1 (VMF1) for GPS sites of the GEONET (GPS Earth Observation Network System) operated by Geographical Survey Institute (GSI). Our comparisons show the KARAT solutions are almost identical or slightly better than the solutions using VMF1 and GMF with linear gradient model for horizontal and height positions. In addition we have started the web-base service “KARATS” for reducing atmospheric delay error from the RINEX file.
We give a short overview on the current status of near real-time monitoring of UT1 with geodetic ... more We give a short overview on the current status of near real-time monitoring of UT1 with geodetic VLBI. The use of real-time data transfer together with automated correlation and data analysis makes it possible to derive final dUT1-results with very low latency. The agreement with IERS C04 results is on the level of 30 µsec. It is even possible to determine time series of dUT1 during ongoing 24 h IVS-sessions. The concept is highly relevant for future VLBI2010 operations.
Nict Technology Development Center News, 2008
... Thanks to the high speed research (shared) net-work and real-time Tsunami protocol, observed ... more ... Thanks to the high speed research (shared) net-work and real-time Tsunami protocol, observed data at ... Figure 2: Automatic data processing with distributed computing environment ... This leads to an im-provement of compatibility of the systems and helps to boost data conversion ...
Agu Fall Meeting Abstracts, Dec 1, 2008
The Japan Meteorological Agency (JMA) meso-scale analysis data (MANAL data) which we used in our ... more The Japan Meteorological Agency (JMA) meso-scale analysis data (MANAL data) which we used in our study provides temperature, humidity, and pressure values at the surface and at 21 height levels (which vary between several tens of meters and about 31 km), for each node in a 10km by 10 km grid that covers Japan islands, the surrounding ocean and eastern Eurasia. The 3-hourly operational products are available by JMA since March, 2006. We have simultaneously evaluated atmospheric parameters (equivalent zenith total delay and linear horizontal delay gradients) and position errors derived from slant path delays obtained by the KAshima RAytracing Tools (KARAT) through the MANAL data. Most of the early mapping functions developed for VLBI and GPS were based on the assumption of azimuthal isotropy. On the other hand, the recent geodetic analyses are carried out by applying the modern mapping functions based on the numerical weather analysis fields. The Global Mapping Function (GMF) by Boehm et al. (2006), and Vienna Mapping Function (VMF) by Boehm and Schuh (2004) have been successfully applied to remove the zenith hydrostatic delay in the recent years. In addition, the lateral spatial variation of wet delay is reduced by linear gradient estimation. Comparisons between KARAT-based slant delay and empirical mapping functions indicate large biases ranging from 18 to 90 mm, which is considered to be caused by significant variability of water vapor. Position error simulation reveal that the highly variability of the errors is clearly associated with severe atmospheric phenomena. Such simulation are very useful to investigate the characteristics of positioning errors generated by local atmospheric disturbances. Finally, we compared PPP processed position solutions using KARAT with those using the latest mapping functions covering a period of two week GEONET data. The KARAT solution is almost identical to the solution using GMF with linear gradient model, but some cases tends to be slightly worse under the extreme atmospheric condition. Though we need further investigations to evaluate the capability of KARAT to reduce atmospheric path delay under the various topographic and meteorological regimes, KARAT will promise an efficient reduction of atmospheric path delays considering that the numerical weather model will be improved concerning spatial and temporal resolution.
... 2008 in cooperation with the Geographical Survey Institute (GSI) and Onsala Space Observatory... more ... 2008 in cooperation with the Geographical Survey Institute (GSI) and Onsala Space Observatory have shown that accurate automatized estimates of UT1 can be obtained when MK3TOOLS ... I s / / / -Ih Post-correlator output (MKS) MK3 database Post-correlator output (K5) 4 fit! ...
Earth Planets and Space, 2008
Journal of Atmospheric and Solar Terrestrial Physics, Feb 1, 2010
Space geodetic applications require to model troposphere delays as good as possible in order to a... more Space geodetic applications require to model troposphere delays as good as possible in order to achieve highly accurate positioning estimates. However, these models are not capable to consider complex refractivity fields which are likely to occur during extreme weather situations like typhoons, storms, heavy rain-fall, etc. Thus it has been investigated how positioning results can be improved if information from numerical weather models is taken into account. It will be demonstrated that positioning errors can be significantly reduced by the usage of ray-traced slant delays. Therefore, meso-scale and fine-mesh numerical weather models are utilized and their impact on the positioning results will be measured. The approach has been evaluated during a typhoon passage using global positioning service (GPS) observations of 72 receivers located around Tokyo, proving the usefulness of ray-traced slant delays for positioning applications. Thereby, it is possible reduce virtual station movements as well as improve station height repeatabilities by up to 30% w.r.t. standard processing techniques. Additionally the advantages and caveats of numerical weather models will be discussed and it will be shown how fine-mesh numerical weather models, which are restricted in their spatial extent, have to be handled in order to provide useful corrections.
Caused by historical separation and driven by the requirements of the PC gaming industry, Graphic... more Caused by historical separation and driven by the requirements of the PC gaming industry, Graphics Processing Units (GPUs) have evolved to massive parallel processing systems which entered the area of non-graphic related applications. Although a single processing core on the GPU is much slower and provides less functionality than its counterpart on the CPU, the huge number of these small processing entities outperforms the classical processors when the application can be parallelized. Thus, in recent years various radio astronomical projects have started to make use of this technology either to realize the correlator on this platform or to establish the post-processing pipeline with GPUs. Therefore, the feasibility of GPUs as a choice for a VLBI correlator is being investigated, including pros and cons of this technology. Additionally, a GPU based software correlator will be reviewed with respect to energy consumption/GFlop/sec and cost/GFlop/sec.
Graphics processing units provide lowcost massive parallel computing performance, which can be ut... more Graphics processing units provide lowcost massive parallel computing performance, which can be utilized for the implementation of a GPS software receiver. In order to realize a realtime capable system the crucial stages of the receiver should be optimized to suit the requirements of a parallel processor. First results from such a receiver development are presented together with a short overview of the hard-and software systems.
GALAXY is a research project on advanced VLBI technology, jointly conducted by CRL, NAO, and NTT.... more GALAXY is a research project on advanced VLBI technology, jointly conducted by CRL, NAO, and NTT. The testbed of the project is a 2.5-Gb/s ultra-high speed network using Asynchronous Transfer Mode (ATM). One of the aims of this project is to achieve high-sensitivity VLBI observation with this gigabit class network. GALAXY network consists of KSP and OLIVE networks provided by NTT and spans 200km range. The sensitivity achieved in our current observation system is comparable to the world-highest class (approx. 10mJy) using conventional VLBI samplers. This short baseline and high sensitivity make GALAXY a unique VLBI network for astronomy in the world. Here we describe the properties of GALAXY network and observations focusing on some unique results that can be achieved with the capability of GALAXY. Developments of new networking technology such as Internet Protocol UP) with GALAXY network are also presented,
Egs General Assembly Conference Abstracts, 2002
In the Keystone project, crustal deformation has been observed around Tokyo area de- ploying four... more In the Keystone project, crustal deformation has been observed around Tokyo area de- ploying four space geodetic stations. The observing system consists of VLBI, SLR and GPS, which are collocated at each site. To compare the observation results and to con- tribute the reference frame improvement, the reference point of each system is tied by 1.5 mm precision by the local survey. Using the survey data, baseline length observed by the independent techniques is compared. During the extraordinary volcanic event happened ca. 150 km south of Tokyo in the summer of 2000, the significant crustal deformation whose change was as large as ca. 5 cm in two months in some baselines in the Keystone network, was observed using the independent systems. Daily solution is available from the real-time VLBI system. SLR solution provides the 15 days so- lution. GPS result is available regularly from the Japanese nation wide GPS network maintained by the Geographical Survey Institute. They coincides within formal error. The observed baseline length change will be compared and discussed.
Radio signal delays associated with the neutral atmosphere are one of the major error sources of ... more Radio signal delays associated with the neutral atmosphere are one of the major error sources of space geodesy such as GPS, GLONASS, GALILEO, VLBI, In-SAR measurements. We have developed a state-of-art tool to estimate the atmospheric path delays by ray-tracing through JMA meso-scale analysis (MANAL data) data. The tools, which we have named 'KAshima RAytracing Tools (KARAT)', are capable of calculating total slant delays and ray-bending angles considering real atmospheric phenomena. Numerical weather models such as MANAL data have undergone a significant improvement of accuracy and spatial resolution, which makes it feasible to utilize them for the correction of atmosphere excess path delays. In the previous studies for evaluating KARAT performance, the KARAT solutions are slightly better than the solutions using VMF1 and GMF with linear gradient model for horizontal and height positions. Based on these results we have started the web-based online service, 'KAshima RAytracing Service (KARATS)' for providing the atmospheric delay correction of RINEX files on Jan 27th, 2010. The KARATS receives user's RINEX data via a proper web site (http://vps.nict.go.jp/karats/index.html) and processes user's data files using KARAT for reducing atmospheric slant delays. The reduced RINEX files are archived in the specific directory for each user on the KARATS server. Once the processing is finished the information of data archive is sent privately via email to each user. If user want to process a large amount of data files, user can prepare own server which archives them. The KARATS can get these files from the user's server using GNU ¥emph{wget} and performs ray-traced corrections. We will present a brief status of the KARATS and summarize first experiences gained after this service went operational in December 2009. In addition, we will also demonstrate the newest KARAT performance based on the 5km MANAL data which has been operational from April 7th, 2009 and an outlook on future developments of KARATS.
We performed differential VLBI (Δ VLBI) experiments for tracking of the interplanetary spacecraft... more We performed differential VLBI (Δ VLBI) experiments for tracking of the interplanetary spacecraft. Our main goal is to obtain the precise and quasi-realtime navigation technique of the spacecraft using Δ VLBI technique. With VLBI time delay measurements, differenced between the spacecraft and angularly nearby quasars to cancel common measurement errors such as the propagation delays due to the ionosphere and the neutral atmosphere. However, we can't always observe desirable quasars. Unfortunately, sometimes we have no choice but to use quasars which are angularly far from the spacecraft. Then, we tried to evaluate the reduction effect by subtracting the group delays of the reference radio source from those of the spacecraft. Two HAYABUSA Δ VLBI experiments were carried out in order to evaluate reducing propagation delays on October, 2004. The spacecraft HAYABUSA has been flying steadily towards an asteroid named ``Itokawa'' and it will orbit the asteroid as of September 2005, land on it, and bring back a sample from its surface. The HAYABUSA spacecraft and an angularly nearby quasar ``2126-158'' were observed sequentially, not simultaneously, during each period with various time intervals of data acquisition. The maximum angular separations of the spacecraft from the quasar are less than 3 degrees. We estimated the zenith path delay due to the water vapor (ZWD: Zenith Wet Delay) using the data sets of the GPS stations which are adjacent to each VLBI antenna. A principle observable feature of VLBI is the difference in arrival times of radio signals between two stations. Then, we calculated difference between the slant path delays which are values as a ZWDs at each station multiplied by a mapping function. We defined this ``differential wet delay''. If the angular separation is sufficiently small, the differential wet delays for both radio sources are almost equal. Then, these are canceled out by the difference procedure. However, if these are different, the differences between them is added directly to the observables as an error source. According to our analysis, a large difference value of up to 10 cm of the differential wet delay for the Kashima-Uchinoura baseline was estimated in spite of a small separation angle between the HAYABUSA spacecraft and quasar. Such large value was mainly caused by the humid condition around Uchinoura due to the typhoon approaching. Moreover, the east-west direction of the baseline vector and the large difference in elevation angle of radio source between both stations helped to enlarge the difference value.
Iau Colloq 140 Astronomy With Millimeter and Submillimeter Wave Interferometry, 1994
International Vlbi Service For Geodesy and Astrometry 2004 General Meeting Proceedings, Jun 1, 2004
ABSTRACT The ray tracing tools, which we have named ’KAshima RAytracing Tools (KARAT)’, are capab... more ABSTRACT The ray tracing tools, which we have named ’KAshima RAytracing Tools (KARAT)’, are capable of calculating total slant delays and ray-bending angles considering real atmospheric phenomena. We compared PPP solutions using KARAT with that using the Global Mapping Function (GMF) and Vienna Mapping Function 1 (VMF1) for GPS sites of the GEONET (GPS Earth Observation Network System) operated by Geographical Survey Institute (GSI). Our comparisons show the KARAT solutions are almost identical or slightly better than the solutions using VMF1 and GMF with linear gradient model for horizontal and height positions. In addition we have started the web-base service “KARATS” for reducing atmospheric delay error from the RINEX file.
We give a short overview on the current status of near real-time monitoring of UT1 with geodetic ... more We give a short overview on the current status of near real-time monitoring of UT1 with geodetic VLBI. The use of real-time data transfer together with automated correlation and data analysis makes it possible to derive final dUT1-results with very low latency. The agreement with IERS C04 results is on the level of 30 µsec. It is even possible to determine time series of dUT1 during ongoing 24 h IVS-sessions. The concept is highly relevant for future VLBI2010 operations.
Nict Technology Development Center News, 2008
... Thanks to the high speed research (shared) net-work and real-time Tsunami protocol, observed ... more ... Thanks to the high speed research (shared) net-work and real-time Tsunami protocol, observed data at ... Figure 2: Automatic data processing with distributed computing environment ... This leads to an im-provement of compatibility of the systems and helps to boost data conversion ...
Agu Fall Meeting Abstracts, Dec 1, 2008
The Japan Meteorological Agency (JMA) meso-scale analysis data (MANAL data) which we used in our ... more The Japan Meteorological Agency (JMA) meso-scale analysis data (MANAL data) which we used in our study provides temperature, humidity, and pressure values at the surface and at 21 height levels (which vary between several tens of meters and about 31 km), for each node in a 10km by 10 km grid that covers Japan islands, the surrounding ocean and eastern Eurasia. The 3-hourly operational products are available by JMA since March, 2006. We have simultaneously evaluated atmospheric parameters (equivalent zenith total delay and linear horizontal delay gradients) and position errors derived from slant path delays obtained by the KAshima RAytracing Tools (KARAT) through the MANAL data. Most of the early mapping functions developed for VLBI and GPS were based on the assumption of azimuthal isotropy. On the other hand, the recent geodetic analyses are carried out by applying the modern mapping functions based on the numerical weather analysis fields. The Global Mapping Function (GMF) by Boehm et al. (2006), and Vienna Mapping Function (VMF) by Boehm and Schuh (2004) have been successfully applied to remove the zenith hydrostatic delay in the recent years. In addition, the lateral spatial variation of wet delay is reduced by linear gradient estimation. Comparisons between KARAT-based slant delay and empirical mapping functions indicate large biases ranging from 18 to 90 mm, which is considered to be caused by significant variability of water vapor. Position error simulation reveal that the highly variability of the errors is clearly associated with severe atmospheric phenomena. Such simulation are very useful to investigate the characteristics of positioning errors generated by local atmospheric disturbances. Finally, we compared PPP processed position solutions using KARAT with those using the latest mapping functions covering a period of two week GEONET data. The KARAT solution is almost identical to the solution using GMF with linear gradient model, but some cases tends to be slightly worse under the extreme atmospheric condition. Though we need further investigations to evaluate the capability of KARAT to reduce atmospheric path delay under the various topographic and meteorological regimes, KARAT will promise an efficient reduction of atmospheric path delays considering that the numerical weather model will be improved concerning spatial and temporal resolution.
... 2008 in cooperation with the Geographical Survey Institute (GSI) and Onsala Space Observatory... more ... 2008 in cooperation with the Geographical Survey Institute (GSI) and Onsala Space Observatory have shown that accurate automatized estimates of UT1 can be obtained when MK3TOOLS ... I s / / / -Ih Post-correlator output (MKS) MK3 database Post-correlator output (K5) 4 fit! ...
Earth Planets and Space, 2008
Journal of Atmospheric and Solar Terrestrial Physics, Feb 1, 2010
Space geodetic applications require to model troposphere delays as good as possible in order to a... more Space geodetic applications require to model troposphere delays as good as possible in order to achieve highly accurate positioning estimates. However, these models are not capable to consider complex refractivity fields which are likely to occur during extreme weather situations like typhoons, storms, heavy rain-fall, etc. Thus it has been investigated how positioning results can be improved if information from numerical weather models is taken into account. It will be demonstrated that positioning errors can be significantly reduced by the usage of ray-traced slant delays. Therefore, meso-scale and fine-mesh numerical weather models are utilized and their impact on the positioning results will be measured. The approach has been evaluated during a typhoon passage using global positioning service (GPS) observations of 72 receivers located around Tokyo, proving the usefulness of ray-traced slant delays for positioning applications. Thereby, it is possible reduce virtual station movements as well as improve station height repeatabilities by up to 30% w.r.t. standard processing techniques. Additionally the advantages and caveats of numerical weather models will be discussed and it will be shown how fine-mesh numerical weather models, which are restricted in their spatial extent, have to be handled in order to provide useful corrections.
Caused by historical separation and driven by the requirements of the PC gaming industry, Graphic... more Caused by historical separation and driven by the requirements of the PC gaming industry, Graphics Processing Units (GPUs) have evolved to massive parallel processing systems which entered the area of non-graphic related applications. Although a single processing core on the GPU is much slower and provides less functionality than its counterpart on the CPU, the huge number of these small processing entities outperforms the classical processors when the application can be parallelized. Thus, in recent years various radio astronomical projects have started to make use of this technology either to realize the correlator on this platform or to establish the post-processing pipeline with GPUs. Therefore, the feasibility of GPUs as a choice for a VLBI correlator is being investigated, including pros and cons of this technology. Additionally, a GPU based software correlator will be reviewed with respect to energy consumption/GFlop/sec and cost/GFlop/sec.