Serial No. 20

June

2002

CONTENTS
Technical Reports
The Metsähovi Solution for Gigabit VLBI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Jouko Ritakari and Ari Mujunen
High speed network connectivity of VLBI stations in Japan . . . . . . . . . . . . . . . . . . . . . . 4
Yasuhiro Koyama
Development of Versatile Scientiﬁc Sampling Processor (VSSP) – A practical . . . . . . 7
approach
Hiro Osaki, Tetsuro Kondo, and Moritaka Kimura
Experimental observation of the GEOTAIL spacecraft using diﬀerential VLBI . . . . . 10
technique
Ryuichi Ichikawa, Tetsuro Kondo, Yasuhiro Koyama, Hiro Osaki,
and Hiroshi Ohkubo
Error estimation on VLBI measurement for spacecraft NOZOMI with con- . . . . . 12
tinuous phase tracking
Mamoru Sekido and Makoto Yoshikawa- News - News - News - News CRL VLBI group received award from the Geodetic Society of Japan . . . . . . . . . . . . . 18
2002 FIFA World Cup football games were held at Kashima . . . . . . . . . . . . . . . . . . . . . . 18
Highway bus service has connected Kashima to the world . . . . . . . . . . . . . . . . . . . . . . . . . 19

1

IVS CRL-TDC News No.20

2

The Metsähovi Solution for
Gigabit VLBI

cial eﬀort to design the system to be compatible
with the Mark5 system that is being developed at
Haystack Observatory.

Jouko Ritakari and Ari Mujunen

2.

Metsähovi Radio Observatory, Finland

1.

Introduction

MRO has developed a PC-based data acquisition
system for VLBI.
The system is based on the VSI standard
interface1 and is capable of recording any VSI-H
compliant data source, including both new CRLdeveloped gigabit VLBI sampler data and existing
VLBA or Mark IV data.
VSIB data I/O PCI board makes it possible to use conventional Linux PCs in continuously streaming high-throughput data acquisition and playback applications at data rates of
512 Mbits/s/PC and beyond. Furthermore, it iswell-suited to data acquisition systems consistingof multiple PCs running in parallel and/or chained,
resulting in both aggregate data rates of multiGbps and total on-line data volumes of several terabytes.
Because of board simplicity and low cost, andbecause of the use of standard PC hardware andlow-cost IDE hard disks, even high-volume, highthroughput data acquisition systems can be realized at exceptionally low cost. We have made spe-

Design Philosophy

We are using a fundamentally diﬀerent design
philosophy than the other teams that are developing disk-based data acquisition systems.
Early in our project we noticed that the common
PC technology has several bottlenecks that limit
the performance in data acquisition and transfer:• 32-bit PCI bus speed limits the performance
to 600-700 Mbit/s• Disk subsystem speed limits the performance
to 500-700 Mbit/s• Gigabit Ethernet speed limits the performance
to 600-700 Mbit/s
While the other teams are designing single-PC solutions for Gbit/s data acquisition, we try to get
the maximum performance from a commodity PC
and build a scalable system. If the performance ofa single unit is not one Gbit/s, that is no problem.
We can use two units or three.
3.

The VSI I/O Board for PC (VSIB)The VSI input board (illustrated in accompanying Figure) is a low-cost 32bit/33MHz PCI interface that stores the incoming VSI data stream
to microcomputer main memory with bus-master
DMA.

Figure 1. The VSIB data I/O PCI expansion board.
1 http://web.haystack.edu/vsi/index.html

June 2002
Data acquisition uses huge circular buﬀers in the
PC main memory and can operate without mainprocessor intervention.
The most important feature is that the VSIBs
have two bidirectional VSI ports and can be daisychained to capture high-speed data. In this way
the maximum sustainable speed of one computer
does not limit the speed of the system.
VSIB has been designed as a standard half-size
32-bit, 33 MHz PCI expansion board. It is compatible with both 5V and 3.3V bus signalling withits “universal” dual-slot PCI card edge connector
and it can thus be used also in most 64-bit, 64 MHz
PCI slots.

3

4.

Universal dual 40-pin cable to VSI converter (VSIC)

When we designed the VSI input board weneeded a test vector generator and a signal level
converter to capture real VLBI data.
We noticed that VLBI uses lots of cables with
diﬀerent pinouts and data polarity, but almost all
cables use the same 40-pin ﬂat cable connectors
and diﬀerential RS-422 or ECL signalling. The new
RS-422 line receivers have a common mode voltage
range that is large enough to capture ECL signals,
so we designed a universal VLBI cable to VSI converter that can interface to most of the cables usedin VLBI.
The VSIC can be connected to Mark IV or
3.1 On-Board Logic
VLBA formatter outputs or directly to VLBA samDiﬀerential LVDS signals are processed with bus pler outputs. If the 1PPS marker that is needed in
LVDS transceivers terminated with 100Ω resistors VSI is not available (for example in the formatterat both ends, ensuring that cable connections are output cables) the VSIC can regenerate the 1PPS
always correctly terminated. A Xilinx FPGA pro- signal from the information in the frame headers.
vides signal routing and processing, and a 4 kB
buﬀer FIFO memory between VSI and PCI bus in- 5. Project status
terface, ensuring continuous data ﬂow regardless of
At this moment three VSIBs and two VSICs have
PCI bus latencies.
been built and tested.
The Xilinx logic allows selection of all 32 VSI
Data capture has been extensively tested anddata bits, or a subset of 16 or 8 (VLBI “Mark 5A”
512 Mbit/s speed (for one unit) seems to be fullycompatibility). It also allows skipping VSI input
operational, which means that sustained 1 Gbit/s
data words with a counter in the range of 1..65535.
operation is possible with only two microcomputBoth of these features can be used to direct a single
ers.
VSIB to process a subset of the whole VSI data
Data playback has been tested at the JIVE corstream. For instance, four VSIB boards can be
relator and seems to be fully working at speed of
set up to repeatedly “demultiplex” four consecutive
256 Mbit/s per PC.
VSI data words to four VSIB boards in a chain,
The documentation (schematics, frequently
eﬀectively reducing the data rate requirements for
asked questions and PostScript ﬁles of the board
a single PC host to a quarter of the original datalayout) are available at “http://kurp-www.hut.
stream.
fi/vlbi/instr”.
3.2

PCI Bus Interface

For connecting to any 32-bit, 33 MHz PCI expansion bus, VSIB utilizes a PLX bus-mastering interface chip. The chip enables high-throughput scatter/gather bus-master DMA transfers to and from
PC main memory. Depending on motherboard
chipset performance, VSIB has been demonstrated
to sustain data transfers in excess of 700 MBits/s.
PC main memory, arranged in ring buﬀer fashion, is used to allow VSIB to operate in conventional Linux operating environment without theneed for any special real-time extensions. PCI bus
interface hardware takes care of depositing data inlarge main memory ring buﬀer where Linux software can ﬁnd it at its own pace.

IVS CRL-TDC News No.20

4High speed network connectiv- port summarizes the current situations of the highresearch networks and the connectivity of the
ity of VLBI stations in Japan speed
VLBI stations in Japan.
2.

Yasuhiro Koyama (koyama@crl.go.jp)
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-0012, Japan
1.

Introduction

In April 2002, an international workshop concentrating on the e-VLBI issues entitled “Connecting
the Global VLBI Array in the New Era of HighSpeed Networks” was held at Haystack Observatory. In the workshop, a lot of technical aspects
were discussed among many researchers participated from around the world. As one of the consequences of the workshop, a group of representatives
from regions and network researchers named as thee-VLBI task force was formed. The major purpose
to form the task force was to draft a document topromote and enhance the activities to achieve eVLBI observations at as many observing stations
as possible. To begin with, each member of thetask force was asked to investigate the current situation of the high speed network connectivity at
VLBI observing stations in each region. This re-High speed research networks in Japan

In Japan, dedicated ATM network for VLBI
observations was established under the collaboration between Communications Research Laboratory and NTT Laboratories in 1996. The network connected four Key Stone Project VLBI observation stations at Kashima, Koganei, Miura,and Tateyama with the maximum data rateof 2.4Gbps (OC-48) using ATM (AsynchronousTransfer Mode). 64m antenna at Usuda DeepSpace Center of the Institute of Space and Astronautical Science (ISAS) and 45m antenna at
Nobeyama Radio Observatory of National Astronomical Observatory (NAO) were connected to the
Mitaka Campus of NAO in 1996 under the collaboration between ISAS, NAO and NTT Laboratories. The network was called OLIVE networkand the maximum data rate was 2.4Gbps (OC-48)
using ATM. These two networks were connectedwith each other in 1999 and the entire network
was named as the Galaxy network (Figure 1). The
network was then partially modiﬁed to transport
IP (Internet Protocol) data stream between Usuda,
Kashima, Koganei, and Musashino (Figure 2).

Usuda(ISAS)
Kashima(CRL)

36 N

Latitude

Nobeyama(NAO)
Koganei(CRL)

Musashino(NTT)

Mitaka(NAO)

35 N

138 E

139 E

140 E

Longitude
Figure 1. The geographical conﬁguration of the Galaxy network.

141 E

June 2002

5

Usuda (ISAS)

Kashima (CRL)
M20

Antenna

BV-3000

GR2000-20

Antenna

ASX4000

BV-3000

ASX1200
under
construction

Nobeyama (NAO)
Antenna

BV-3000

M20
ASX4000
ATM Interface

Koganei (CRL)
GR2000-20

BV-3000R

ID1 Interface

Musashino (NTT)
Antenna

BV-3000

Correlator

BV-3000R

Gigabit Ether

ASX4000

BV-3000R

M160

ASX4000, ASX1200 : ATM-SW
M20, M160, GR2000-20 : Router
BV-3000, BV-3000R : ATM NW IF

Mitaka (NAO)

Figure 2. The logical conﬁguration of the Galaxy network.

In addition to the dedicated network for the realtime VLBI observations, there are high speed research networks in Japan. Super-SINET and JGN(Japan Giga-bit Network) are the two major networks for research and developments for information technology. Super-SINET is now being established by connecting Universities and national institutes. The maximum data rate is 2.4Gbps (OC48) and many VLBI observation stations are either
preparing or proposing to be connected to the closest network nodes.

tenna station at Kashima and 64m antenna station at Usuda. Recently, the 32m antenna station at Tsukuba has been connected to the SuperSINET at High Energy Accelerator Research Organization. Gifu university has a connection to the
JGN network and a proposal has been submitted
to the Super-SINET. Similarly, proposals are being
prepared to be submitted to the Super-SINET for
Tomakomai, Mizusawa, and Yamaguchi stations.
5.

Future Plan

Network infrastructure in Japan and international connectivity are improving very fast, andThere are at least three network routes to trans- the e-VLBI seems to be becoming feasible between
fer high speed data stream between United States Japan and the United States. VLBI observation
and Japan. One route is the GEMnet. GEMnet hardware systems for e-VLBI observations are also
is a research network owned by NTT corporation under developments. Using these opportunities,
and is connected to the Abilene network in the a plan has been initiated to perform a demonUnited States. The total data rate of the GEMnet stration experiment between Haystack Observais 33Mbps and 10Mbps is allocated to the connec- tory and Galaxy network stations. At noted intion with the Abilene network. The second route is the previous section, there are at least three routes
the Super-SINET. The Super-SINET is connected to realize the e-VLBI observations between Japan
with the Abilene network in the United States at and the United States. Within these three routes,
the speed of 155Mbps. The third route is the the GEMnet route seems to be the most promising
APAN/TransPAC connection. Two 622Mbps con- route to perform e-VLBI observations, since thenection lines are available between United States Galaxy and GEMnet networks are operated by theand Japan.
NTT corporations. The Super-SINET is also a candidate. Although it requires to settle technical and
4. High speed network connectivity at policy related issues, the use of the Super-SINETVLBI stations in Japan
will be pursued.
3.

International Connectivity

Current situation of the high speed network connectivity at VLBI station in Japan is summarized
in the Table 1. At present, Kashima, Koganei,
Usuda, and Nobayama are connected to the Galaxy
network. The network speed is 2.4Gbps and thereal-time VLBI observations at the data rate of
1024Mbps have been achieved between 34m an-

Acknowledgement: The author would like to appreciate many members of the Galaxy project and collaborators who provided the valuable information
to compile the current network connectivity of the
VLBI stations in Japan. Especially, the essence of
the Figure 1 was provided by Dr. Hisao Uose of
NTT Laboratories.

6

Table 1. Network connectivity status of VLBI stations in Japansite namediameter organi(meter) zation

Shintotsukawa
Tomakomai
Mizusawa
Mizusawa
Tsukuba
Usuda

3.8
11
10
20
32
64

Kashima34

KashimaKashima
Nobeyama
Koganei

receivers

distance toa network
node (km)statuslatitude longitude(deg. N) (deg. E)

no plan to be coneccted to networks
proposal is being prepared to Super-SINET
proposal is being prepared to Super-SINET
proposal is being prepared to Super-SINET
connected (2.488Gbps) : Super-SINET : ATM
connected (2.488Gbps) : Galaxy : ATM

43.5
42.7
39.1
39.1
36.1
36.1

141.8
141.6
141.1
141.1
140.1
138.4

0

connected (2.488Gbps) : Galaxy : ATM+IP

36.0

140.7

0
0
0
0

36.0
36.0
35.9
35.7

140.7
140.7
138.5
139.5

Gifu

11

GU

S/X

0

35.5

136.7

Gifu

3

GU

X

0

35.5

136.7

Yamaguchi
Aira
Iriki
Kagoshima
Ogasawara
Chichijima
Ishigaki

32
10
20
6
20
10
20

NAO
GSI
NAO
KU
NAO
GSI
NAO

X, 22GHz (planned)
S/X
S/X, 22GHz, 43GHz
22GHz, 43GHz
S/X, 22GHz, 43GHz
S/X
S/X, 22GHz, 43GHz

15
?
?
?
?
?
?

station will be closed in 2002
connected (2.488Gbps) : Galaxy : ATM+IP
connected (2.488Gbps) : Galaxy : ATM
connected (2.488Gbps) : Galaxy : ATM+IP
connected (30Mbps): SINET:IP
in addition, proposal has been submitted to SuperSINET (2.488 Gbps): fiber to the Super-SINET
node (~60km) will become available in 2002
proposal is being prepared to Super-SINET
no plan to be coneccted to networks
currently no plan to be coneccted to networks
no plan to be coneccted to networks
currently no plan to be coneccted to networks
no plan to be coneccted to networks
currently no plan to be coneccted to networks

34.2
31.8
31.7
31.5
27.1
27.1
24.4

131.6
130.6
130.4
130.5
142.2
142.2
124.2

acronyms

CRL
GSI
GU
HU
ISAS
KU
NAO

Communications Research Laboratory
Geographical Survey Institute
Gifu University
Hokkaido University
Institute of Space and Astronautical Science
Kagoshima University
National Astronomical Observatory of JapanIVS CRL-TDC News No.20

?
70
118
118
0
0

26
11
45
11

GSI
S/X
HU S/X, 22GHz (planned)
NAO S/X, 22GHz, 43GHzNAO S/X, 22GHz, 43GHz
GSI
S/X
ISAS
S/X, L, C, 22GHz
S/X, L, C, 22GHz,
CRL
43GHz
GSI
S/X
CRL
S/X
NAO 22GHz, 43GHz, etc.
CRL
S/X

June 2002

Development of Versatile
Scientiﬁc Sampling Processor(VSSP)– A Practical Approach
Hiro Osaki (osaki@crl.go.jp), Tetsuro Kondo,
and Moritaka Kimura
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-0012, Japan
1.

Introduction

Recently a 4-channel PCI-bus VLBI data sampler board has been developed by Communications Research Laboratory and Nihon Tsushinki
Co. Ltd. [Kondo et al, 2000] [Kondo et al, 2002].
This board gives us a chance to make a VLBI dataacquisition system based on a standard personal
computer (PC). The system will be useful not onlyin the VLBI community, but also in other scientiﬁc ﬁelds where accuracy of the timing of the data
sampling is required. This system, hence, is named“Versatile Scientiﬁc Sampling Processor (VSSP)”.
There are at least three advantages in developing
PC data recording system. Firstly, the price of thesystem is inexpensive compared to ordinary VLBI
recorder. Our system expected to be lower than
US$40,000. Secondly the system becomes ﬂexible
because the user can modify the software. Thirdly,
it is easy to adopt various computer technologies
to make the system more convenient. For example, if observation experiment is made using thisPC-based system, the data can be easily transported among the observation sites over the Internet. Moreover, developing computer technologies such as high-speed networks and distributed
computing may be adopted without diﬃculty. In
the present paper we will introduce a practical approach to produce this PC-based recording system.
2.

Requirements of the VSSP system

7

open PCI sockets are necessary to install the board.
Installing more than 1 set of the boards to 1 PC
is not supported. The maximum recording rate of
the sampler board is 64 Mbps (e.g. 4 channels × 16Mbps). In order to realize 256 Mbps (16 channels
× 16 Mbps) recording, hence, 1 VSSP system must
be composed of 4 PCs and 4 sampler boards.
We have prepared 480 GB data storage area oneach PC. The amount of the data storage area is decided as follows: during data recording at 64 Mbps,
the data on the PC increases by 8 MB per second.
If the system records one whole day continuously,
the amount of the data on the PC increases by 8
MB/s × 1 day ∼ 690 GB. However, in case of VLBI
observation we do not have to record continuously,
especially while the antenna is slewing. Hence, 480
GB will be practically suﬃcient for our purpose.
The storage area consists of four 120 GB IDE harddisk drives (HDDs). At present SCSI HDD is not
adopted as data storage device because of the expensive price and diﬃculty of purchasing large volume drives. USB HDD and IEEE-1394 HDD arealso rejected now because of the reliability of thedevice drivers on the operating system (OS) that
we are using.
It is noteworthy that IDE devices have at least
two limitations that the user should care. Firstly,a standard PC motherboard can adapt only 4 IDE
devices, which are primary master, primary slave,
secondary master, and secondary slave. Our system used four IDE HDDs for the data storage
area. We need another HDD for OS and user applications. For this purpose 20 GB SCSI HDD isadapted with on-board SCSI port. If the motherboard has additional IDE ports, the user can use
another IDE HDD instead of the SCSI HDD. Secondly, most of the motherboards available now cannot recognize IDE HDDs larger than 137 GB. If auser would like to adopt such HDDs, the user mustchoose one of the motherboards compliant with thislimit.
The other parts of the PC are as follows: 1
on-board 10/100Base-T Ethernet port, one 1 GHz
Pentium III CPU, and 512 MB RAM. This spec issimilar to that of a standard PC today. The specof our ﬁrst VSSP PC are summarized as Table 1.
The sampling board itself is expected to work on
rather obsolete system compared to this one.

The goal of the VSSP is to make a PC recording
system comparable with today’s standard VLBI
recorder. In other words, the system can record 16channel 256-Mbps 1-day VLBI observation data.
In this section we will describe essential properties 2.2 Software environmentsof the hardware and software necessary for this sysThe device driver software for this sampler boardtem.
is prepared for FreeBSD-4.x and MS-Windows
2000. Linux device driver will be available soon.
2.1 Requirements of the hardware
Our system adopts FreeBSD-4.5 as the OS. Some
The PCI sampler board is composed of a pair of data acquisition software and data analysis soft2 boards connected by a short ﬂat cable. Hence, 2 ware for VLBI observation are under development

IVS CRL-TDC News No.20

8

Table 1. Features of the ﬁrst VSSP computer.
CPU
RAM
HDD

SCSI port
Ether port
PCI busPentium III (1 GHz)
512 MB
four 120 GB IDE disks (7200rpm,
Ultra ATA/100 compliant)
20 GB SCSI disk
on-board SCSI controller
on-board 10/100 Base-T controller
2 open PCI sockets

on FreeBSD. Those applications can be ported toLinux system without diﬃculty, if the device driver
were available. Porting to MS-Windows 2000 may
require some eﬀort.
‘Soft-updates’ is enabled on our system. Softupdates is a ﬁlesystem adopted by FreeBSD, which
increases input/output (I/O) performance drastically. Originally FreeBSD ﬁlesystem has adopted
synchronous (sync) I/O, which is known as a robust
but slow I/O. Linux ﬁlesystem adopts another type
I/O, called asynchronous (async). Async is known
as a fast ﬁlesystem at the cost of the robustness
against sudden system crash. Soft-updates is developed based on sync I/O by taking in the advantageof the async I/O. That is expected to be as robust
as sync, and as fast as async. In the next section
we will show the eﬀectiveness of the soft-updates
on our system.
3.

Testing the eﬀectiveness of FreeBSD
soft-updates ﬁlesystem

In order to check the eﬀectiveness of softupdates, we have made a simple test on two identical PCs (PC-1 and PC-2). These two PCs
are almost the same, except the one is installed
FreeBSD-4.5 with soft-updates (PC-1), and theother is installed FreeBSD-4.3 without soft-updates(PC-2). The specs of the PCs are 1 GHz Pentium
III CPU, 128 MB RAM, and 46 GB IDE HDD(7200 rpm, Ultra ATA/100 compliant), which islower than that of the VSSP PC. The test is performed as follows: execute the following command,
wait for 10 seconds, and then terminate the task
by Ctrl-c.
cat /dev/zero > fooThis simple test will show the apparent datawriting rate onto the HDD. A dummy data ﬁle(here ‘foo’) is created on the HDD. The result isshown as Table 2.
This result implies that soft-updates doubled
I/O speed of PC-1. As it is already told in thepresent paper, VSSP requires 64 Mbps = 8 MB/s
data recording rate on each PC. Here PC-2 barely

Table 2. Performance of the system with/withoutsoft-updates.
OS version
Soft-updates
Resultant ﬁleafter 10 sec
Data writing rate

PC-1
FreeBSD-4.5
enable200MB

PC-2
FreeBSD-4.3
disable87MB

20MB/s

8.7MB/ssatisﬁes the requirement. If some other disk accessoccurs during data is being recorded, the recording may possibly fail. On the contrary, I/O speedof PC-1 will be suﬃcient for realizing VSSP system. Hence, soft-updates ﬁlesystem is adopted inour system.
4.

Miscellaneous notes on developing VSSP

4.1

The spec of the HDDs

The HDDs used in our VSSP system have a
speed of 7200 rpm. They are also compliant with
Ultra ATA/100 interface (an interface having a capability of 100 MB/sec data transport rate). Actually they are comparatively fast HDDs at present.
If a slower HDD is used, the recording rate becomes slower. This causes a trouble on the systemfrom time to time. For example, we have tested 64
Mbps recording using old 2 GB IDE HDD (5400rpm). Sometimes the system becomes out of orderwhile observation data is being recorded on thisHDD. Hence, it is advisable to choose faster HDDs
for the data storage area.
4.2

Amount of the RAM

Usually most operating systems do not write a
new ﬁle onto the HDD during the ﬁle is being processed. Instead, the RAM works as a disk cacheand the data is temporary stored on the RAM as
a ﬁle image. The ﬁle image is transported to the
HDD after a while. Hence if the system has large
RAM, there is enough space to be used as a disk
cache. For example, if 480 MB RAM can be used asa disk cache, 64 Mbps x 60 sec data can be stored
on the RAM. Although this eﬀect has not been
conﬁrmed by experiment, we can expect that thelarger the RAM is, the faster the practical recording rate becomes.
4.3

Internal spurious noise

In order to set up the ﬁrst VSSP unit, we prepared a 2U-size rack mount PC server. Figure 1
shows the front view of the PC server. A pair ofsampler boards is installed as shown on Figure 2.
Analyzing the data, some spurious noise was foundJune 2002

Figure 1. Front view of PC server.
on the ﬁrst and second channels of the board. We
examined the PC server and the sampler board,and concluded that the noise comes from the motherboard. In this thin 2U-size rack mount casethe sampler board and the motherboard is locatedclose to each other. The ﬁrst and second channelsof the board are close to some chips on the motherboard, which makes the spurious noise. We could
not avoid the noise because there was no enoughspace to install a shield to reject the noise. Or if
there had been some other PCI sockets, the sampler board might have been moved to one of thesockets where less spurious noise was found. We
will choose such PC case when developing the next
VSSP unit.
5.

Summary

9

Figure 2. A pair of sampler boards installed in PC
server.
HDDs and the amount of the RAM are also important factors.
Our ﬁrst VSSP unit was developed on U2-size
rack mount PC server. Testing this unit, we foundthat some spurious noise came from the motherboard. In order to avoid such noise, it is advisable
to choose a PC case with several excess PCI sockets, because the user can select one of the sockets
where less spurious noise is found. The excess PCI
socket space is also useful to install a shield to reject the noise.
The VSSP system is being developed as shownin the present paper. It is expected to work as
a central part of the future VLBI observation system for data recording, data transporting, and dataprocessing, by ﬂexibly taking in various computer
related technologies.

In this paper we reported on inexpensive andﬂexible VLBI data acquisition system using PCs
and PCI VLBI sampler boards. The system was Referencescomposed of 4 units, 1 of which consists of a stanKondo, T., Y. Koyama, M. Sekido, J. Nakajima, H.
dard spec PC, 480 GB data storage HDDs, andOkubo, H. Osaki, S. -I. Nakagawa, and Y. Ichikawa,
1 PCI VLBI sampler board. Now device driver
CRL IVS TDC news No. 17, pp. 22-24, 2000.
software of the sampler board has been prepared
Kondo, T., Y. Koyama, J. Nakajima, M. Sekido, R.
for FreeBSD and Microsoft Windows 2000. Linux
Ichikawa, E. Kawai, H. Okubo, H. Osaki, M. Kimura,device driver will be available soon. We made aand GALAXY Team, Second IVS General Meeting
simple test of the system with/without FreeBSD
at Tsukuba, Japan, February 4, 2002.
soft-updates ﬁlesystem. The eﬀectiveness of softupdates became apparent. To improve the performance of the system, the speed of the data storageIVS CRL-TDC News No.20

10

Experimental observation of to determine the precise orbit of the NOZOMI. We
a preliminary result of the observation in
the GEOTAIL spacecraft using describe
this short report.
diﬀerential VLBI technique2.

Data Recording System

We used a new VLBI system using Internet Protocol (IP) technology for data sampling and acquisition of the GEOTAIL spacecraft. This new system is one of the two kinds of the “IP-VLBI” underdevelopment at Communications Research LaboKashima Space Research Center
ratory (CRL) and it will enable real-time VLBI
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-0012, Japan observations anytime and, anywhere at a low cost
[Kondo et al., 2002]. The “IP-VLBI board” forthe system is designed so that all digital process1. Introduction
ing from signal sampling and, data transmission,
We performed a preliminary diﬀerential VLBI
to real-time correlation processing is preformed on(DVLBI) observation with National Astronomical
multiple personal computers (PCs). The experiObservatory (NAO) and the Institute of Space and mental observation of the GEOTAIL spacecraft is
Astronautical Science (ISAS) to determine prealso aimed to evaluate our IP-VLBI system.
cise orbit of the GEOTAIL spacecraft on June 4,
2002. The purpose of this observation is to estab- 3. Observation and Preliminary Result
lish the positioning technology for the interplaneWe performed a ﬁrst DVLBI observation for thetary spacecraft using diﬀerential VLBI in real-time.
GEOTAIL
spacecraft on June 4, 2002. An observOur main concern is to determine the PLANET-B
ing
schedule
is made based on a predicted space(NOZOMI) orbit just before the second swing-by
craft
trajectoryfrom 0630UT to 1400UT. In ouron next March [Yoshikawa et al., 2001]. It is signiﬁobservationaseriesof 2 short (about 30 minutes)
cantly important to get the timing to maneuver thesequencesofdiﬀerential
VLBI observations were inspacecraft before the swing-by. However, the usual
sertedintotheschedule,
using the sources, 3C279
range and range rate orbit determination will notand3C274.
A
sourcegeometryof the GEOTAIL
be available because it will be diﬃcult to point the
spacecraft
for
each
one
minuteepoch and radio
high-gain antenna mounted the spacecraft towardsourcesareillustratedin
Figure1.
We use Kashima
the earth at that time. So we need a new technique
ICHIKAWA Ryuichi (richi@crl.go.jp),
KONDO Tetsuro, KOYAMA Yasuhiro,
OSAKI Hiro, and OHKUBO Hiroshi

3C274

12

KASHIMA

Declination (J2000)

108
2002/06/04 0630UT

6
4
2002/06/04 1400UT

3C273

2
0
-2
13.2

13

12.8

12.6

12.4

12.2

12

Right Ascension (J2000)
Figure 1. Source geometry of the GEOTAIL spacecraft(solid circles) and the radiosources(open squares) on June 4, 2002. The sources of 3C273 and 3C274 are used forthe diﬀerential VLBI. Angular separations of the spacecraft from the two radio source areabout 4.0 degrees and 8.0 - 10.0 degrees, respectively.

June 2002

11

Figure 2. Observed fringes for the GEOTAIL S-band telemetry signals.
34-m and Kashima 11-m of CRL, and Usuda 64-m Referencesof ISAS antennas for DVLBI observations at S and
X-bands with the K4 and the IP-VLBI systems. Kondo, T., Koyama Y., Nakajima J., Sekido M.,
Ichikawa R., Kawai E., Okubo H., Osaki H., Kimura
Another system, RISE terminal systems were alsoM., Ichikawa Y., and GALAXY team, Real-time Giinstalled in these stations by the NAO group.
gabit VLBI System and Internet VLBI System, IVS
Figure 2 shows an example of the S-band fringes
2002 General Meeting Proceedings, p.142-146, 2002.
of the GEOTAIL, which was detected by using
Yoshikawa
M., Sekido M., Kawaguchi N., Fujisawa K.,
a preliminary VLBI data processing. This clear
Hanada H., Kono Y., Hirabayashi H., Murata Y.,
fringe suggests that a conventional analysis using
Sawada-Satoh S., Wajima K., Asaki Y., Kawaguchigroup delay data sets is available to determine theJ., Yamakawa H., Kato T., Ichikawa T., and Ohnishi
spacecraft orbit. We will try to determine the orbit
T., Present status and future problems of the orbit
based on these data sets and the further analysis
determination for Nozomi spacecraft, IVS Technicalwill be discussed in another report.
Development Center News, No. 19, p.37-40, 2001.

IVS CRL-TDC News No.20

12Error estimation on VLBI
methods. Due to less calibration capability of radio
propagation medium than phase switching method,measurement for spacecraft
the expected accuracy will be worse in the continNOZOMI with continuous phase uous phase tracking. Although, the requirementon spacecraft position measurement accuracy fromtracking
ISAS is order of 100 mas as a comparable accuracy expected from range and range rate technique(R&RR), then continuous phase tracking is still a
Mamoru Sekido (sekido@crl.go.jp) andcandidate of choices.
2
Makoto Yoshikawa
A test experiment was conducted for spacecraft
GEOTAIL
in June 2002 for checking data acqui1
Kashima Space Research Centersitionsystemand data processing. The results ofCommunications Research Laboratory
thisexperiment
may be reported somewhere.
893-1 Hirai, Kashima, Ibaraki 314-0012, JapanIn
thispaper,
we discuss the expected accuracy
2Institute of Space and Astronautical Sciencewiththecontinuous
phase tracking method with ﬁ3-1-1 Yoshinodai, Sagamihara,
nite
distance
VLBI(hereafterﬁnite-VLBI) model.
Kanagawa 229-8510, JapanWe
supposereferencesourcesselected from Inter3
Space Geodynamics Laboratory,
national
Celestial
Reference
Frame(ICRF) catalog
stfl.
4850 Keele Street 1
North York,areobserved
atthebeginningandend of the obOntario, M3J 3K1, Canada
servation for the purpose to solve clock parameter
in VLBI analysis. And we assume that coordinates
1. Introductionof the observation stations are well known on the
Possibility on VLBI observation of spacecraft International Terrestrial Reference Frame (ITRF),NOZOMI [1] has been discussed in joint working and ground based calibration data of atmospheregroup among VLBI related institute (Institute of (weather data) and ionosphere (GPS data) areSpace and Astronautical Science (ISAS), National available to reduce the systematic error of spaceAstronomical Observatory of Japan (NAOJ), Com- craft position as less as possible.
munications Research Laboratory (CRL), and soon).
Diﬀerential group delay VLBI observa- 2. Finite-VLBI modeltion with reference radio star (DDOR) is one of
the choices of VLBI observation methods. The 2.1 Diﬀerence between Finite-VLBI andnormal VLBIDDOR observation technique had been used by
JPL since 1980’s for interplanetary missions sucSpacecraft at a distance up to 30 light years
cessfully. This technique requires multiple sub- have to be treated as ﬁnite distant radio source
carrier signals spread in wide frequency range (sev- on in VLBI model since the curvature of the radio
eral MHz). The NOZOMI’s transponder was not wavefront cannot be ignored [2]. The maximum, however, originally designed for the wide range diﬀerence of geometrical delay between the ﬁnitesub-carrier transmission. Additionally radio link VLBI and inﬁnite (normal) VLBI delay model withcondition during the two swing-by ( Dec. 2002 and earth-radius baseline is several hundreds of nanoJune 2003) is supposed to become much poorer seconds at geocentric distance of 1AU (Figure 1).
than ordinary condition. This kicked a motiva- It corresponds to several thousands of wavelengthtion that VLBI is considered for space navigation at radio frequency 8.3 GHz. VLBI model of ﬁfor NOZOMI [1]. Then availability of DDOR for nite distance is presented by Sovers and Jacobs [2]NOZOMI has been examined by JPL and CRL, (1996) and Fukushima [3](1994). Here a set of parindependently. Another choice of VLBI observa- tial derivatives regarding right ascension, declination method is phase delay measurements. It only tion and geocentric distance is displayed by usingneed stable carrier signal from spacecraft, then it Fukushima’s model.
may rather suitable for the case of NOZOMI. Phaseswitching VLBI observation between target source 2.2 Partial Derivatives
and reference radio source has been sometimes used
Geometrical VLBI delay of ﬁnite distance rain astronomical VLBI observation. Diﬃculty in
dio source is expressed [3] by coordinates of radio
this method is phase connection between scan tosource x0 and station vector xi (i= 1,2) as:
scan for each target source and reference source. If
the phase connection is failed, no results are excτ = −k · B,
(1)pected from the observation. To eliminate this


r
+
r
01
02
risk, also continuous phase tracking for the tar- where k =, rij = |rij |, rij = xi − xj .
r
+
r
01
02
get source can be one choice of VLBI observation
1,3

June 2002

13

0.01

And partial derivative of delay rate with respect tothe radio source coordinates x0 is

Delay difference (second)

0.001
0.0001

∂2τ
1
=
×
∂t∂
x
1
+
β02
0

 .(6)(β02 +β20 )
k20(β01 +β10 )
k10


v1 −
v2 −
v0
v0
−
−
+
r01
r02
r20
r10

1AU

1e-05
1e-06

Here, terms of higher order than second order of βwere eliminated. By using this partial, partials interms of α, δ, and r are given as:

1e-07
1e-08
1e-09

1

10

100

1000

10000

100000

1e+06

1e+07

∂2τ
=
∂t∂r
∂2τ
=
∂t∂α
2
∂ τ
=
∂t∂δ

r/R

Figure 1. Maximum diﬀerence of geometrical delay
between ﬁnite-VLBI and inﬁnite (normal) VLBI
model. Horizontal axis is distance from geocenterwith unit of Earth radius. Vertical axis is delay
diﬀerence (sec.)
3.
Origin of the coordinates is placed at geocenter.
Partial derivative respect to source coordinates x0
is give by Fukushima [3] as,∂τ
1∗ {k02 − (1 + β12=)k01 } (2)∂x0(1 + β02 )c
where
r

v
∗
20 −β10= β1−β. (3)βij = kij · cj , kij = rijij , β1210This partial derivative approaches to zero when the
distances of the radio source increases r10 , r20 →∞. Partial derivatives of τ in terms of right ascension (α), declination (δ), on which VLBI has sensitivity, and geocentric distance of spacecraft (r)
are
∂τ
=
∂r

∂2τ 
· ir
∂t∂x0∂2τ 
r cos δ· iα∂t∂x02∂ τ r· iδ .
∂t∂x0(7)Error from propagation medium

Excess path delay comes from propagation
medium of atmosphere and ionosphere are the mostsigniﬁcant error source in continuous phase tracking observation. We suppose ground based calibration data are available to reduce systematic error ofspacecraft position as less as possible. Ionospheric
total electron content (TEC) data measured by
global or regional GPS network will be available
for ionospheric delay correction.
Here, we put an assumption that these groundbased calibration data give appropriate estimate ofeach excess path delay. In other words, excess path
length estimated from calibration data is supposed
to be distributed randomly around the true one.
Errors for each components are considered as follows:

∂τ 
· ir
∂x0
Dry troposphere Excess path length due to dry
1
∗ 


component of troposphere is 2.3 m in zenith{k02 − (1 + β12 )k01 } · ir=
(1 + β02 )c
direction. Since it is known that atmosphere∂τ ∂τobey hydrostatic equilibrium to a high degree= r cos δ
· iα
∂α
∂x0
(4)
of accuracy, most of dry component excess
r cos δ ∗ {k02 − (1 + β12=)k01 } · iαpath length can be predicted by ground-based(1 + β02 )cpressure measurement. One hecto-Pascal of
∂τ 
∂τ
= r
· iδ
ground pressure error corresponds 2.3 mm
∂δ
∂x0
r
zenith excess path. Factor of mapping func∗{k02 − (1 + β12 )k01 } · iδ=tion is about 6 at 10 degrees elevation angle.
(1 + β02 )c
Here we conservatively assume 3 cm as error
Where, ir is a unit vector from geocenter to theof dry component of excess path length .
radio source, and ,iα ,iδ are unit vectors in direc- Wet troposphere Excess path of water vapor
tions of right ascension and declination at the radio(hereafter we call as wet component of troposource on a celestial sphere.
sphere) is diﬃcult to predict accurately from
Delay rate of ﬁnite-VLBI is given by Fukushima
ground-based wether measurement, since it is[3] asnot well mixed in the air. Roughly wet tropospheric excess path length in zenith direction
β01 − β02 + β10 − β20∂τ=(5)changes with weather condition from 1 cm to∂t
1 + β02∗
30 cm. Here we put the error at 14 cm by
β01 − β02 + (1 − β10 )β12=.
including mapping function.
1 + β02

IVS CRL-TDC News No.20

14
80
60

Declination (deg.)

Ionosphere Excess path of the ionosphere has
dispersive characteristic, which means it depends on radio frequency inversely in proportion to square of radio frequency. When number of total electrons in the line of sight per
square meter is TEC (×1016 electrons/m2 )and radio frequency is f GHz, excess path
length at microwave frequency region is given
by 30.4T EC/f 2 cm. Total amount of inzenith direction TEC at middle latitude has
daily changes from 50 to 100 TEC Units (1016electron/m2 ) under small turbulence condition. Accuracy of global ionosphere model derived from GPS observation is around 3 TECU[4], which corresponds to excess path length of
1.3 cm√at 8.3GHz. By taking into account thefactor 2 from two ionosphere paths in VLBI
observable and factor of mapping function, we
assume error of ionospheric excess path as 11
cm.

40
20
0
-20
-40
-60
-80
02/11/01 02/12/01 03/01/01 03/02/01 03/03/01 03/04/01 03/05/01 03/06/01 03/07/01
Tue Jun 11 20:33:30 2002

Date

Figure 2. Declination of NOZOMI in the period
Nov. 2002 - Jun. 2003.
Table 1. Parameters of NOZOMI at three epochs.
The column of r/R is geocentric distance with unitof earth radius, and Vlos and dVdtlos are geocentric
velocity and acceleration of NOZOMI in line ofsight.

From the assumption that each calibration data
dVlos
Date
α
δ
r/R
Vlos
dt
is unbiased estimator of each excess path compo(deg) (deg)(km/s) (mm/s2 )
nent, total error
02/11/4
44-10 2.3e3-4.3
0.84√ caused from propagation medium
is evaluated 32 + 142 + 112 = 18 cm. This length
02/12/4
42-17 7.7e2
-3.2
0.076
03/ 2/2
277
66 1.8e3
2.3-0.47
correspond to about 1800 degrees of phase error at
8.3 GHz. This phase error is used in covarianceanalysis in the next section.
4.1 Phase delay measurement
Error of phase delay rate is evaluated with ,According to current orbit plan, right ascendz dδτdτ= δτ sec z tan z+
sec z,
δsion and declination coordinates of NOZOMI willdt
dt
dt
change with angular velocity of a few arc minwhere, z is zenith angle, and simple mapping func- utes per day even in stable period between thetion sec(z) was assumed. Since changing rate of two swing-byes (Figure 3). Then this large proper
zenith excess path ( second term of right had side) motion and radial distance from geocenter wereis not known, here we used only elevation change included in our parameterized observation model.
rate (ﬁrst term of right hand side) by using zenith Fringe phase as observable is given by residual ofexcess path error as δτ = 30 cm. When z=80 de- phase delay after subtraction of a priori phase degree, delay change rate is derived as 2.4 ps/s at lay model based on a priori space craft position.
equatorial region for zero declination radio source. Linearized observation equation for small variation
when middle latitude stations are observing middle of right ascension, declination, and geocentric disdeclination radio source, delay rate becomes 0.01 tance is given as follows:
Hz at 8.3 GHz.
∂τ{∆α0 + ∆α̇(t − t0 )}∆φ = 2πf∂α4. Covariance Analysis∂τ(8)+ 2πf {∆δ0 + ∆δ̇(t − t0 )}Spacecraft NOZOMI is planed to experience two∂δ∂τswing-byes with the Earth in December 2002 and in+ 2πf {∆r + ∆ṙ(t − t0 )} + δφ∂rJune 2003 [1]. Declination of NOZOMI from viewpoint of geocenter is around −10 ∼ −20 before the Partial derivatives were computed by using equaﬁrst swing-by (Figure 2) and it keeps high declina- tion (4) and a priori orbit information of NOZOMI.
tion (more than 60 degree) after the 1st swing-by Error of phase delay observable was assumed to betill to the 2nd swing-by. Covariance analysis on 1800 degrees as discussed in section 3. and obserVLBI measurement of NOZOMI was performed for vation time span was from rising up of the spacethree epochs: Nov. 4 2002 (decl. = -10 deg.), Dec. craft till to its setting in. Elevation cut oﬀ an4 (decl. = -17 deg.), and Feb. 2 2003 (decl. = 66 gle was set as 10 deg. Phase delay sampling indeg.). Parameters of NOZOMI at these epochs are terval is 30 min. Under these conditions, covariance matrices were computed on Kashima-Usuda
listed in Table 1.

June 2002

15

30

Proper motion (arc min/day)Right Ascention
Declination
20

10

0

-10

-20

-30
11/01/02 12/01/02 01/01/03 02/01/03 03/01/03 04/01/03 05/01/03 06/01/03 07/01/03

Date

Figure 3. Proper motion of NOZOMI : × indicatesproper motion in right ascension and ✷ indicatesproper motion in declination.
Table 2. Covariance matrix of phase delay observation of NOZOMI on each baselines (see text). Initial phase, right ascension, declination, geocentric
distance, and there time derivatives were used asmodeling parameters. Partial derivatives are computed based on orbit information at Feb. 2 2003. Figure 4. Variation of geometrical delay cause by
σ indicates estimation error and Ca,b is correlation change of radial distance based on orbit information of NOZOMI at Feb. 2, 2003. Upper panel
between parameter a and b.
is that of Kashima-Usuda baseline (200km) andBaseline
σα
σα̇
σδ
σδ̇
σφ
lower one is that of Kashima-Algonquin baseline(mas)(mas/h)(mas)(mas/h)(deg.)
K-U
190
18.7
207
38
600
(9100km).
K-A
K-G
Baseline

12.5
3.2
σr
(km)
7.6e4
7.4e3
5.1e3

1.2
1.4
σṙ
(km/s)
4.2
0.36
0.14

20.0
11.3

4.1
1.3

1300
1290

VLBI position measurements during this period.
The formal error of Table 2 shows that intercontinental baseline will achieve mas order of accuracy,
Ca,b
α̇
δ
δ̇
φ
r
ṙ
and even with domestic 200 km K-U baseline will
α
0.39
0.53
0.81
-0.32
-0.41
-0.71
α̇
1
0.73
0.15
0.03
-0.72
-0.05
satisfy 100 mas accuracy, which is required from
K-U
δ
–
1
0.29
0.20
-0.96
-0.23
–
–
1
-0.46
-0.12
-0.92
δ̇
ISAS, in declination.
φ
–
–
–
1
-0.01
0.19
It is interesting to see that estimated error of
r
–
–
–
–
1
0.05
α
-0.04
-0.35
0.98
-0.41
0.19
-0.97
the
spacecraft coordinates is larger on K-A baseα̇
1
0.74
0.04
0.42
-0.79
-0.12
K-A
δ
–
1
-0.27
0.90
-0.98
0.19
line
than that of K-G baseline, nevertheless pro–
–
1
-0.34
0.10
-1.00
δ̇
φ
–
–
–
1
0.0
0.29
jectedbaseline of K-A is longer than that of Kr
–
–
–
–
1
-0.03
α
-0.66
-0.52
0.55
0.57
0.51
-0.30
G. Long projected baseline gives higher angular
α̇
1
0.86
-0.58
-0.95
-0.87
0.12
K-G
δ
–
1
-0.41
-0.87
-0.99
-0.04
resolution and higher astrometric accuracy in nor–
–
1
0.40
0.36
-0.86
δ̇
φ
–
–
–
1
0.0
0.10
mal VLBI. This strange result is a characteristic
r
–
–
–
–
1
0.10
of ﬁnite-VLBI, and it was caused from that geocentric distance r and its time derivative dr
dt wereincludedintheobservation
model.
The
highcor(K-U), Kashima- Algonquin (K-A), and Kashimarelation(97%)
between
α
and
ṙ
on
K-A
baseline
Goldstone (K-G) baseline (Table 2). Although,covariance analysis was performed also for epochs will be responsible for that. Also high correlationof Nov. 4 and Dec. 4 of 2002, intercontinental between δ and r is remarkable on all baselines.
Two example of geometrical delay variation
baseline cannot keep enough mutual visibility incausedby change of radial distance based on NOthose epochs, and errors of spacecraft position were
ZOMI’sorbit information is displayed in Figure 4.
larger than arc second. Consequently they are not
These
examplesindicate that parameterized modpractically useful for navigation, thus their results
elingofradialdistance
is necessary for ﬁnite disare eliminated here. Fortunately spacecraft willtance
spaecraft
observation,
since change of radial
keep high declination between two swing-by epochs
distancecausessigniﬁcantchangeof geometrical(Figure 2), thus observation condition is better for
K-U
K-A
K-G

IVS CRL-TDC News No.20

16

Table 3. Covariance matrix of phase delay observation of NOZOMI on each baseline. Initial phase,right ascension, declination, and their time derivatives were used as modeling parameters. Partial
derivatives are computed with orbit information on
epoch Feb. 2 2003.
Baseline
K-U
K-A
K-G

Baseline

K-U

K-A

K-G

σα
(mas)
110
2.5
2.2

σα̇
(mas/h)
13
0.7
0.7

Ca,b
α
α̇
δ
δ̇
α
α̇
δ
δ̇
α
α̇
δ
δ̇

α
1
–
–
–
1
–
–
–
1
–
–
–

α̇
0.211
1
–
–
-0.40
1
–
–
-0.22
1
–
–

σδ
(mas)
42
1.2
1.1

δ
0.05
0.26
1
–
0.15
-0.40
1
–
0.09
-0.52
1
–

σδ̇
(mas/h)
14
0.3
0.2

δ̇
0.57
0.21
0.06
1
0.27
-0.74
0.52
1
0.00
-0.59
0.46
1

σφ
(deg.)
570
570
570

φ
-0.51
-0.23
-0.04
-0.89
0.32
-0.84
0.43
0.82
0.17
-0.88
0.51
0.64

Table 4. Covariance matrices of phase delay rate
observation for NOZOMI. Right ascension, declination, geocentric distance, and their derivatives
are used for modeling parameter. partial derivatives are computed with orbit information on Feb.
2 2003.
Baseline
K-U
K-A
K-G
Baseline
K-U
K-A
K-G
Baseline

K-U

K-A

delay in interferometric measurement. If they are
not included in the model, quasi-sinusoidal delay
will be absorbed in (α, δ) parameters, and they
will contain systematic error. In case the examples(Figure 4), 120 - 160 mas of systematic coordinates
error will be caused regardless of baseline length.
For comparison purpose, covariance matrix of thecase that r and dr
dt are excluded from modeling parameters is listed in Table 3. In this table, theformal error becomes smaller than the former caseand it become smaller on longer baseline as it is innormal VLBI.

K-G

σα )
(mas)
3200
100
98
σr
(km)
7.9e5
6.5e4
3.3e4

σα̇
(mas/h)
470
18
12
σṙ
(km/s)
48.3
3.2
1.9

Ca,b
α
α̇
δ
δ̇
r
α
α̇
δ
δ̇
r
α
α̇
δ
δ̇
r

α̇
0.18
1
–
–
–
-0.62
1
–
–
–
0.11
1
–
–
–

σδ
(mas)
7700
660
330

δ
-0.12
0.19
1
–
–
-0.37
0.57
1
–
–
0.02
0.59
1
–
–

δ̇
0.54
0.38
-0.02
1
–
0.73
-0.71
-0.06
1
–
0.71
-0.14
-0.07
1
–

σδ̇
(mas/h)
1300
110
61

r
0.18
-0.20
-0.99
0.10
1
0.35
-0.56
-1.00
0.04
1
-0.06
-0.59
-0.99
0.02
1

ṙ
-0.57
-0.38
0.07
-0.99
-0.15
-0.72
0.71
0.05
-1.00
-0.03
-0.72
0.13
-0.04
-1.00
0.01

Partial derivatives was computed with equation(7) based on orbit information of NOZOMI on
Feb. 2, 2003. Error of observable was assumed
to be 0.01 Hz at 8.3 GHz. Covariance matrices
were computed for each baseline : Kashima-Usuda(K-U), Kashima-Algonquin (K-A), and Kashima4.2 Phase delay rate measurement
Goldstone (K-G) are listed in Table 4.
An advantage of phase delay rate measurement
When phase delay rate is used as observable,
is that observable is ambiguity free. In contrast to only intercontinental baseline will be able to satisfy
that diﬀerential phase delay measurements has a the requirement of 100 mas accuracy. As it is therisk of insertion of phase ambiguity between scans, same with phase delay measurement, K-G baseline
phase delay rate observation allows intermittent gives better results than K-A baseline, neverthelessobservation without any risks. Thus switching ob- K-A baseline is longer than K-G.
servation with reference ICRF sources will be possible to calibrate phase delay rate error by propa- 5. Conclusion
gation medium. Drawback of this method is lower
Accuracy of coordinates measurement of NOspatial resolution than phase delay measurement.
ZOMI
with VLBI was discussed under the condiObservation model including ﬁrst time derivative
tions:(i) continuous tracking VLBI observation,of spacecraft position isand(ii)
single baseline VLBI observation, and as 
 2 
dφ
∂ τ
1
sumption(iii) propagation medium is the most sigδ= f{∆α + ∆α̇(t − t0 )}
2π
dt
∂t∂α
niﬁcant
error
source and ground based calibration
 2 

∂ τ
data
will
give
unbiased estimator of excess path∆δ + ∆δ̇(t − t0 ) (9)+ f∂t∂δlengthforeachcomponent of them. Phase delay
 2 
∂ τ
and
delay
rate
errorsare put at 1800 degree, and+ f{∆r + ∆ṙ(t − t0 )}∂t∂rJune 2002
0.01 Hz at 8.3 GHz. As results of covariance analysis with ﬁnite-VLBI model based on orbit dataof NOZOMI in Feb. 2003, following estimates are
obtained. (1) Phase delay measurement with intercontinental baseline will gives a few mas accuracy of spacecraft coordinates in the plane perpendicular to the line of sight. Even with domestic
baseline, 1 µ radian of accuracy will be available.
(2)Phase delay rate measurements has advantage
of ambiguity free, thus calibration of propagation
medium with switching observation with reference
source is easy. This method can achieve 0.1 arc
second accuracy with intercontinental baseline, butdomestic baseline is ineﬀective with this method.
Acknowledgement: Authors thank to member of
the NOZOMI VLBI observation working group (T. Kondo, R. Ichikawa, Y. Koyama, J. Nakajima,
E. Kawai, M. Kimura, H. Osaki, H. Ohkubo of
CRL, H. Hirabayashi, Y. Asaki, Y. Murata, J.
Kawaguchi, H. Yamakawa, T. Kato, T. Ichikawa,
S. Sawada-Satoh, K. Wajima of ISAS, N. Kawano,
Y. Kouno, H. Hanada, F. Kikuchi, N. Kawaguchi of

17

NAOJ, K. Fujisawa of Yamaguchi Univ., T. Iwata
of NASDA, and T. Ohnishi, S. Ishibashi of Fujitsu).
And we are thankful to W. Cannon and P. Ryanof York University Physics and Astronomy department for comment.
References[1] Yoshikawa M., et al., “Present status and future problems of the orbit determination for
Nozomi spacecraft”, CRL TDC News, No. 19
pp.37-40., 2001.
[2] Sovers O. J. and Jacobs C. S., “Observation Model and Parameter Partials for
the JPL VLBI parameter Estimation Software ‘MODEST’-1996”, JPL Publication 8339, Rev. 6, 1996
[3] Fukushima T, Astron. & Astrophys., Vol. 291,
pp.320-323, 1994.
[4] M.Sekido ,”Comparison of ionospheric delay
between GPS and VLBI (II)” ,TDS news No.
18, pp.7-9, 2001.

18

IVS CRL-TDC News No.20- News - News - News - News - News - News - News - News - News - News - News -CRL VLBI Group received Tsuboi Award from the Geodetic
Society of JapanThe VLBI group of Communications Research Laboratory received a Tsuboi award from the Geodetic
Society of Japan on May 30, 2002. The Tsuboi award, established in commemoration of the Japanesedistinguished geophysicist Prof. Chuji Tsuboi, is given to an individual or group who made a remarkableachievement in the ﬁeld of geodesy. The reason of the award for CRL VLBI group is the contribution to
VLBI technical development over many years and systematic research works of plate motion and crustal
deformation. In particular, the achievements accomplished in the period from 1980s to early 1990s areawardwd. Thus CRL VLBI group has a chance to receive an award again for later works, according to
the chair of the award selection committee who made a speech at the ceremony. (Tetsuro Kondo)

Photo 1. Accepting the award from the chairof the Geodetic Society of Japan.

Photo 2. The plaque of the Tsuboi award.

2002 FIFA World Cup football games were held at Kashima
Three matches of the stage 1 of the 2002 FIFA World Cup football games were held at the Kashima
Soccer Stadium in June. The stadium is located very close to the Kashima Space Research Center.
Teams of Argentina, Croatia, Germany, Ireland, Italy and Nigeria visited Kashima and showed us very
exciting games to around the world. If you noticed our antenna was broadcasted on TV, please let us
know! (Yasuhiro Koyama)June 2002

Photo 3. Kashima Soccer Stadium on June 5,
2002.

19

Photo 4. German vs Ireland on June 5 at
Kashima.

Highway bus service has connected Kashima to the world
The accessibility to the Kashima Space Research Center from around the world became much moreconvenient than ever! Two bus companies started regular highway bus service between New Tokyo
International Airport (NARITA) and Kashima. The bus runs 8 times a day and it takes only about ahour to and from the airport. The bus stops right front of the Kashima Space Research Center and theone way fare is 1000 yen if return ticket is purchased at the same time (otherwise 1200yen).
(Yasuhiro Koyama)

Photo 5. Bus stop for Kashima at
Narita airport.

Photo 6. Kashima Space Research Center anda bus for the Narita airport.

IVS CRL-TDC News No.20

20“IVS CRL Technology Development Center News” (IVS CRL-TDC News) published by theCommunications Research Laboratory (CRL) is the continuation of “International Earth Rotation Service - VLBI Technical Development Center News” (IERS TDC News) published by CRL.
In accordance with the establishment of the International VLBI Service (IVS) for Geodesy andAstrometry on March 1, 1999, the function of the IERS VLBI technical development center was
taken over by that of the IVS technology development center, and the name of center was changed
from “Technical Development Center” to “Technology Development Center”.
VLBI Technology Development Center (TDC) at CRL is supposed
1) to develop new observation techniques and new systems for advanced Earth’s rotation observations by VLBI and other space techniques,2) to promote research in Earth rotation using VLBI,
3) to distribute new VLBI technology,4) to contribute the standardization of VLBI interface, and5) to deploy the real-time VLBI technique.
The CRL TDC newsletter (IVS CRL-TDC News) is published biannually by CRL.

This news was edited by Tetsuro Kondo and Yasuhiro Koyama, Kashima Space Research Center,
who are editorial staﬀ members of TDC at the Communications Research Laboratory, Japan.
Inquires on this issue should be addressed to T. Kondo, Kashima Space Research Center, Communications Research Laboratory, 893-1 Hirai, Kashima, Ibaraki 314-0012, Japan, TEL : +81299-84-7137, FAX : +81-299-84-7159, e-mail : kondo@crl.go.jp.
Summaries of VLBI and related activities at the Communications Research Laboratory are on theWorld Wide Web (WWW). The URL to view the home page of the Radio Astronomy Applications
Section of the Kashima Space Research Center is : “http://www.crl.go.jp/ka/radioastro/”.

IVS CRL TECHNOLOGY DEVELOPMENT CENTER NEWS No.20, June 2002
International VLBI Service for Geodesy and Astrometry
CRL Technology Development Center News
published by
Communications Research Laboratory, 4-2-1 Nukui-kita, Koganei, Tokyo 184-8795, Japan