Overview of the 16th TDC Meeting

Mamoru Sekido (sekido(AT)nict.go.jp)
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-0012, Japan

The 16th meeting of the Technology Development Center was held on February 7, 2000 at the Communications Research Laboratory.


CRL members Special members Following special members could not attend: Observers


1. Opening Greeting

Takao Morikawa, director of IVS TDC at the Communications Research Laboratory (CRL), greeted meeting holding. He made self-introduction of succeeding to chief of TDC from December of 1999. Now VLBI research in CRL is on the turning point just before reformation of CRL from Government Institute to Independent Agency. We hope to have candid opinion for guidance of our future plan, he said.

2. Technical Development Center Activity Reports

2.1 Introduction of IVS Activities (Tetsuro Kondo)

Overview of International VLBI Service for Geodesy and Astrometry (IVS) was introduced. In order to build the international organization like International GPS Service (IGS) which was successful in GPS society, the establishment of IVS was discussed by VLBI subcommittee of the CSTG (Commission on International Coordination of Space Techniques for Geodesy and Geodynamics) under IAG (International Association of Geodesy). And the IVS was inaugurated from March 1 of the last year. The aim of the IVS is producing high quality data used for research of geodesy and astrometry. Position of the IVS is as follows. An organization called Advanced Space Technology is under the IAG, and IGS, ILRS, and the IVS exist under it. The IERS is an earth rotation research related organization over both IAG and the IAU, and position of the IVS is equivalent to that of the IERS. Structure of the IVS consists of the analysis, technology development, network, operation, correlator, data, and coordinating center, and each of the technology, network, and analysis coordinators exist. Four organizations of the CRL, Geographical Survey Institute (GSI), National Astronomical Observatory (NAO), and National Institute of Polar Research( NIPR) have participated in the IVS from Japan. The CRL has become one of the TDCs of the IVS from that of the IERS since March 1999. Activities of TDC at CRL such as issue of TDC News, contributions to specification of VLBI Standard Interface (VSI), geodetic test experiments with Giga-bit VLBI system (GIFT Experiment), and real-time VLBI experiment (GALAXY) were introduced as the progress report from the last March.

Q: Do you see a prospect authorization of the VSI at the IVS General Meeting (2/20)?
A: Coordination of VSI specification has been done by Dr. A.Whitney, and it will be discussed in TDC report in the meeting.
Q What is the position of the development of the VSI in the IVS?
A: Each component of the IVS, such as network, analysis, and technical development set their own themes and they are working for that. The VSI has been set as theme of technology development component.
Q: Is the purpose of IVS TDC narrower comparing with that of former IERS, isn't it?
A: The field of former IERS has divided into IGS, ILRS, and IVS. The IVS is working by relating other organizations, IAU etc.
Q: Although various institutes are nominated as a component of IVS in Japan, has domestic cooperation been done between them?
A: CRL is aware of the responsibility of coordination of domestic IVS components.
C: I want to encourage and expect the activity as a role of a leader domestic IVS components to CRL.

2.2 VLBI Standard Interface (Yasuhiro Koyama)

The VLBI Standard Interface (VSI) is the epoch-making trial to unify the interface of various kind of VLBI terminal, whose incompatibility used to be observational restriction in the world VLBI community. And the VSI specification also put real-time VLBI operation into the view. The VSI specification include interface among formatter, recorder, and correlator.
Circumstances Explanation: It was proposed by A.Whitney at the time of GEMSTONE meeting in January 1999 at Tokyo, and work was started. The VSI specification has been discussed through various occasions, a domestic meeting, the IVS Directing board, URSI, and international telephone conference. (A conclusion will be expected soon.)
Overview of the VSI: The specification is for future system but compatibility with traditional VLBI system will be taken into account as much as possible. Current target will be 1024Mbps VLBI system. Compatibility among several kinds of VLBI system, which will be developed at each TDC, should be maintained at observation, correlation, and data copying operations. Data Transfer System (DTS) will be made as transparent as possible from viewpoint of Data Acquisition System (DAS) and Data Processing System (DPS).
Prospect to fix the specification: Endorsement of VSI specification by IVS is expected soon. We hope to realize the specification in Giga-bit VLBI system in the CRL and in VERA project in the NAO. I believe Japanese group will be at the nearest position to realization of the VSI. Works of standardization of a command, a protocol, and a data format, a connector, etc. are remain.

Q: Unless high-tech is more incorporated in the standardization, it is not connected with a breakthrough, is it?
A: Japanese group is in a direction to standardize the present equipment for wider VLBI network performance. Of course we are going to use optical communication technology in the VSI for real-time VLBI.
Q: It is very difficult to make a transparent system. Don't you think that you had better to devide the way of Internet VLBI and VSI?
A: Yes, we are going to make equipment for Internet VLBI for various tests. Then we will make it correspond to VSI one by one.
C: When VSI is realized, its benefit is very large, for example correlation processing become possible by any correlation system, which is compliant to VSI. We are now planning 2 Giga-bit system and I want to apply the VSI specification to our system. It is very important!
Q: Is standardization of a real-time system examined from now on?
C: Yes. We hope to consider with including distributed type data processing system.
Q: Although there are various modes (clock rate etc.) in VSI proposal, which should be adapted receiver side or sending side?
A: It is the compromise of adaptation in a part of modes as a result. Only a hard wire is decided by the present specification, but the compatibility in each mode is also a future argument subject.
Q: Don't you think that certain modes should be guaranteed at least?
A: I think that it is established at a future step. First of all, the first decision will be necessary. I think that probably such subject will be discussed in the next directing board.

2.3 Gigabit VLBI System Development Report (Yasuhiro Koyama)

Needlessness of Pcal (phase calibration) signal and Bandwidth synthesis is the peculiar feature of a Giga-bit VLBI system. A 3-m small VLBI mobile antenna was moved to Gifu University, and execution of the geodetic VLBI experiment with Giga-bit VLBI system is planned. Several test experiments had already been done or planned. A test geodetic VLBI experiment with the Giga-bit VLBI system was carried out on October 19, 1999 bu using a KSP baseline, and two GIFT (Gifu University Telescope) experiments were carried out in January and February, 2000. Baseline analysis was done for the experiment on October 19. Although 256 Mbps VLBI system technology is also advanced in the world, Geodetic VLBI by 1 Gbps system is top level technology in the world. However there is still 3 times larger variation of baseline analysis residual comparing with that of K4 (KSP). Collocation with GPS and Ionospheric delay correction with GPS are also thought to be a subject of study. Multi channel observation with higher order sampling technique for bandwidth synthesis will be considered in near future.

Q: Although SNR will be almost the same between KSP 10m pair and 34m - 3m pair, is the geodetic VLBI error of 183ps large, isn't it?
A: Software should be improved.
Q: Doesn't the reason of bad accuracy of the analysis result of Giga-bit system owing to lack of Bandwidth synthesis?
A: Cause of the problem is under study. It may be improved by making multi channel system.
Q: Doesn't the inappropriate phase characteristic in the band cause the bad accuracy of the analysis result?
A: It may be. It will be investigated.
Q: Since it is single frequency observation, I think that the ionospheric delay correction will be required. How do you obtain the ionospheric delay between TEC sampling points by GPS on the sky?
A: We obtain the ionospheric delay by interpolating and extrapolating TEC data using a model.

3. Proposals from the Special Members

Misao Ishihara (GSI)

We are perplexed by the financial and political problem that VLBI group of CRL is faced. Since our VLBI technology is based on that of CRL and we could have 32 m antenna at present. If there are no group which have the technology to lead us, it will be troubled. In our case, performing 50 times international VLBI experiments and four times domestic experiment per year is authorized by our institute. Operation of GEONET (GPS network) is also authorized as an routine project for several years. I would like you to make aware that only our gourp in 2nd geodetic Div. and Mr. Matsuzaka in Geography and Crustal Dynamics Research Center are doing VLBI technology related work in Geographical Survey Institute. Since we have been using VLBI system developed by CRL as an end user, we are expecting CRL to lead the VLBI technology development. Especially, theoretical work in geodetic VLBI, development of water vapor delay model, compact VLBI system, Giga-bit VLBI system, and real-time VLBI system are expected from us.

C: It is good if Geographical Survey Institute becomes the big sponsor of geodetic VLBI technology development in Japan. Supporting institute will be required from now on.

Arata Sengoku (HD/JCG) (Kunimori read for him)

Advantage of SLR: The data accumulation of long period of time of SLR and an immobility point is geometrically stable. Demerit of SLR: Expensive (equipment, and staff cost). There are few observing points. Observation is dependent on the weather. Achievement: Measurement of center of the Earth and gravity field. Verification of the theory of relativity by Lunar Laser Ranging (subject for future) etc. Time comparison, orbit determination of GPS and GLONASS satellites. Pursuit of a altimeter satellite. Collocation of space geodetic measurement system. What should be done from now on: To make LLR highly precise and supporting gravity missions. What is expected to CRL: To increase precision of SLR observation technology, real-time, full automation, development of eye safe system, supporting SLR station in Asia, technology of reverse laser ranging, and ranging among satellites.

Q: Is the LLR possible with present KSP system?
A: Improvement of the system (1 order of magnitude powerful laser and larger diameter) is required. Pointing (1 arc second) is also difficult, because guiding system is not present. So it is difficult in the present condition.
Q: What do you think about to use similar technique like VLBI for eye safe system? i.e. using weak continuum signal instead of pulse and improve SNR by the accumulation of signal.
A: Such a method is also considered although there are some methods in eye safe system.

Noriyuki Kawaguchi (NAO)

I would like CRL to develop the observation technology of Giga-bit VLBI system. 10G - 20Gbps system is also desired from astronomical observation. I also expect high-speed data transmission. I want to expect higher speed and more stabilized data transmission technology at a lower price not only with ATM. Moreover, it is kind if CRL provide us more reliable and user-friendly correlation processing technology. In the future, space craft observation technology, the data transmission technology in the space by optical communication, and correlation processing technology are expected. I also hope development of the high-precision position determination technology of space craft by GPS. Probably, high-precision radiometer technology will be also big contribution for geodetic measurement. Now phase stability measurement of VERA (VLBI Exploration of Radio Astrometry) project is cooperated. I hope contribution of low phase noise oscillator, receiver, low price atomic standard (cost down will change the VLBI circumstance drastically), and Earth orientation observation (we assumes Earth Orientation Parameter as known).

C: When the technology of CRL is required in the project of NAO, such as VSOP2, I want it to examine whether collaboration by cooperation is possible or not.
Q: Does the earth orientation parameters required in VERA project?
A: The accuracy is more important than real-time.
C: There is a merit that real time can perform data processing quickly, and it is connected with the improvement in accuracy.
Q: What accuracy is required as VERA?
A: It is under examination now. The present accuracy is the minimum necessity. Furthermore, it is better as accuracy raises.

4. The project proposed from CRL

4.1 Application of the Space Geodetic Measurement Technology in the Space (Taizoh Yoshino)

I want to consider position determination in the space. The demand of position determination, such as a satellite, is increasing in connection with development of space observation technology (Gravity-related satellite missions etc.). Although, conventional space geodetic measurement technology was aimed up to the space near the Earth, now position measurement by using radio or optical link are considered. Lunar laser ranging in SELENE-2 mission by using active optical transponder is considered as an idea.

Q: How long will it take to develop an active optical transponder?
A: It is not yet clarified.
Q: Is it possible to transmit atomic standard signal from the satellite to user satellite?
A: Since it is still under examination, the concrete satellite has not been planned.
Q: If the position of VSOP satellite is decided with sufficient accuracy, astrometric observation become possible. Can position measurement of a satellite be achieved in mm or cm accuracy?
A: By designing exactly by defining the purpose, I think that it will probably be possible in cm accuracy.
A: Since a satellite orbit can be determined by dynamics, if observation by the laser ranging and by VLBI can be performed, its position can be determined with sufficient accuracy even if the satellite is complex shape like VSOP satellite.
C: The NASA has a plan of space optical interferometer with several meter baseline length for astrometry, in which the baseline length is to be measured within order of micro meter. High accuracy determination of satellite orbit is great benefit for astrometric observation.
Q: What is the purpose of the astrometry?
A: By measuring accurate position and the distance of maser sources, 3 dimensional dynamic motions become clear, and it will lead to determine the gravity field of the galaxy.

4.2 Advanced Precise Positioning System: APPS (Yasuhiro Koyama)

A position is decided with high accuracy with GPS by analysis of specialist. APPS is a system which enables anyone to get high precision positioning information. In the APPS system, a user will obtain GPS observation data with a geodetic GPS receiver and send them to an APPS analysis server. The data are then processed automatically and analyzed results are sent back to the user. In this way, the user can obtain reliable and accurate coordinates of the GPS receiver. Expected effects would be standardization of position information, accumulation of data on water vapor and ionospheric distribution. Technical developments for fine phase characteristic GPS antenna, automatic GPS data analysis technique, earth orientation parameters, water vapor model, and improvements of ionosphere modeland a numerical weather model will be required.

Q: Although it will be good for a user, there are few development elements, aren't they?
Q: What amount of user can you assume?
C: Probably, it will be used by researchers in universities.
C: It will differ by setting filed of service for Japan or for the world. Although RTK (Real Time Kinematic)-GPS achieves 1 cm accuracy under good satellite arrangement condition, number of user is small comparing with single positioning. If the accuracy is about 1-10m order, I think there are many users.
A: The system is not limited to Japan. Although there might be few development elements, CRL performs the development of the first framework and a commercial company will realize the entire system. CRL is also responsible for the highly precise earth orientation information service.
C: Will it be performed by IERS and IVS?
C: It will be difficult to evaluate the demand before you present service price and doing market research.
C: Since the geodetic survey performed now becomes unnecessary, I think that remarkable demand can be expected.
C: Probably, it will become a point how the receiver element can be minimized.
C: How about compounding with communication positioning?

4.3 Real-time Earth Orientation Determination System (Tetsuro Kondo)

In research of the space and time standard development project being planned at CRL, VLBI will determine the Earth orientation in real-time. As an actual proof experiment plan, Kashima-Okinawa baseline (1600 km) will be promising from viewpoint of network. Various kinds of scientific results are also expectable. Technology of realizing that is Giga-bit VLBI and real- time VLBI. Two kinds of real-time system is considered as VLBI. One is VLBI over the ATM, and the other is using the internet protocol (IP). IP-VLBI targets for multi-channel, 16Mbps data rate, and software correlation with distributed processing. High-speed data transmission system used in KSP is characterized by 256 Mbps data rate and special correlation processor. Internet VLBI may extend a base of VLBI community. Research will also be activated if a number of young researchers increases in this field. Multicasting of the signal received by 34m and feed back of observed data from distinct observatory to a central station will be an attractive idea.

Q: Does communication cost (cost per bit) fall down by using IP?
C: Although the ATM is cheaper as cost performance at present, it can be expected that the way of IP system becomes cheap for a scale merit.
C: We can't generally say that ATM suits astronomy and IP suits geodesy, can we?
Q: Although there are various geodetic measurement system such as GPS and VLBI, VLBI is most inappropriate for real-time, isn't it? Why do you persist in VLBI?
C: Although GPS requires time for orbital determination, VLBI does not have it. This point should be claimed more.

4.4 Proposal of Space Positioning Technology Development Center (Tetsuro Kondo)

Communications Research Laboratory possesses many kind of technology neccessary for space positioning technique and its development is expected from outside. We have began to propose Space Positioning Technology Development Center (SPDC) dedicated to stable technological development. Frank discussions are welcome. The purpose of the SPDC is as follows. There are various kinds of demand of positioning depending on the accuracy from Earth surface to space around the Moon. These kind of positioning system will be considered in the SPDC. Overviews of the project, demand depending on its accuracy, organization plan were introduced.

C: It should be necessary to make clear whether the benefit pay for the huge cost for that. Just searching for improvement of the accuracy will be difficult to be understood by people certainly and even by researchers (it will be thought maniac.). Since higher accuracy and lower cost are not compatible, demand survey for accuracy will be necessary.
C: This comment is important. If the target is not clearly defined, it is difficult to be permitted in CRL. Target and role, which CRL has to do, should be made clear.
C: I have the same opinion. It is related with a subject whether government has to do. If there are demands and it makes money, somebody will do. Problem in the scientific field is that if pure science is made only at universities, we cannot have a big project. Not only pursuing high accuracy and scientific purposes, viewpoint of searching for seed of future commercial technology is necessary.
A: Although, time and space standardizing project is aimed for high accuracy, explanation that VLBI is necessary for high accuracy became difficult in CRL.
C: The important field that is not included here in earth science is the survey of bottom of the sea. Unless geodetic measurement of sea bed is not included, scientific demand is not satisfied.
Q: Even though the basis is the same, the approach should be quite different in developing a system between higher accuracy system and lower cost system. How do you think about this?
A: I am not sure about that. Radio wave propagation medium has to be taken into account in the case of low cost approach also. The algorithm is similar in both cases. The concept of the proposal is center for research and development with stimulating each other. What kind of approach is the best will be also a subject to be discussed in the center. Budgetary compensations will be possible by combination of variety of elements.
C: From my experience of space science, orbit determination technology in Japan is very behind in the world. If CRL can do that, it is desirable. If determination of satellite attitude is achieved, itself has very big impact.
C: Research is either needs oriented or seeds oriented. Since this is seeds oriented, you should have a self-confidence.
A: Currently, seeds do not produce needs.
C: It is necessary to search for what kind of needs is possible from the seeds.
C: Extending to a variety of fileds such as infra-red will be necessary.

5. Closing Greeting

Hiroshi Kumagai, the vice-director of the IVS TDC at CRL, greeted the closing. He thanks to a serious argument over the long time. Furthermore, he mentioned that considering that will be also important, what should be done, what is superior to the other, or what is pleasant.

The social gathering was held after the meeting and discussions continued further.

Return to CONTENTS