Methods of Local Survey between Space Geodetic Observation

測地学会誌,第48巻,第2号

(2002),85-100頁

Journal of the Geodetic Society of Japan Vol. 48, No. 2, (2002), pp, 85-100

Methods of Local Survey between Space Geodetic Observation Systems

at a Collocation Site

Hiroshi Hasegawa 1), Shuhui Xia 1), Hitoshi Tamura 1), Junya Ooizumi 1), Taizoh Yoshino3),

Hiroo Kunimori 2), Jun Amagai 2), Futaba Katsuo 2), Yasuhiro Koyama 3), Tetsuro Kondoo 3)

1) Kokusai Kogyo Co., Ltd.

2) Communications Research Laboratory

3) KSRC, Communications Research Laboratory

(Received September 20, 2001; Revised May 7, 2002; Accepted June 25, 2002)

コロケーション局における宇宙測地観測システム間の

地上測量方法

長谷川浩司1)・夏淑輝1)・田村斉1)・大泉純也1)・吉野泰造3)

国森裕生2)・雨谷純2)・勝尾双葉2)・小山泰弘3)・近藤哲朗3)

1)国際航業株式会社

2)通信総合研究所

3)通信総合研究所鹿島宇宙通信研究センター

(2001年9月20日受付,2002年5月7日改訂,2002年6月25日受理)

要旨

　複数の宇宙測地観測システムを総合的に用いるコロケーション観測において,各システムの位

置を結合する精密地上測量は重要である.しかし,地上システムの基準点を結ぶ地上測量の方法は

必ずしも確立されていない.そこで,典型的なコロケーション局であるKey Stone Projectの4つ

の観測局で地上測量方法の確立を試みた.システムの基準点決定で直接測量法でも間接測量法でも

実験の結果,VLBI,SLR,GPSの宇宙観測システムの基準点および測量の基準となる固定基準点

において,標準偏差で1.5mm以内の測量精度が得られた.

Abstract

At space geodesy sites with collocated multiple observation systems, a precision local sur-vey is important to link the reference points of each system. However a standard method of local survey has not been well-established. Hence, we attempted to do so at the Key Stone sites, which are typical collocation sites of space geodetic systems. The reference points of VLBI, SLR GPS and monuments were measured to within 1.5 mm (S.D.) in both the direct method and the indirect method of determining the reference points of the VLBI and the SLR systems.

86 Hiroshi Hasegawa et al.

1. Introduction

In the last decade, the number of collocation sites for space geodetic observation system

has increased in the world. Collocation sites operate various observation systems such as

Satellite Laser Ranging (SLR), Very Long Baseline Interferometer (VLBI) and Global Posi-

tioning System (GPS). These observation systems are independent of each other.

The collocation of these observation systems gives several benefits that are to improve the

performance of individual observation systems and to improve the terrestrial reference frame

and to obtain integrated solution. To achieve above benefits, high accuracy terrestrial ground

survey between these observation systems are very important. But methods of ground survey

were unclear. These problems of ground survey for collocation have already been indicated by

J. M. Bosworth (1999) and by T. Yoshino (1999), that is, "Imprecise or poorly defined or undocu-

mented survey ties from the technique measurement point to a common ground monument"

and "the surveying method to tie the reference point of space geodetic system is not visible be-

cause the technique was conventional". To establish the international space geodetic and

gravimetric network (ISGN) for the future, this problem is also discussed (H. Drewes,1999). Determination of a local survey network depends on the area, terrestrial conditions and

visibility. ISGN and NASA standard conditions for setting up a local survey network at a col-

location site are as follows:

1) Three dimensional relative coordinates of the reference point of VLBI, SLR and GPS and

the monuments of survey should be determined within 1-3 mm precision, which is equiva

lent or better than the precision of space geodetic observation systems.

2) The local survey network should be placed within about 50-100 m of the center of the site

in order to ensure uniform geological and meteorological conditions.

3) The ground monuments for the local survey network should be set around the space geo-

detic observation systems. The ground monuments must be stabile and all monuments

must be visible from any monuments.

4) Survey instruments should be commercially available and calibrated.

5) The monuments should serve as platforms to re-survey for monitoring of stability of collo-

cation sites.

A ground survey for collocation at the FS-wettzell has been reported by Schlueter et al.

(1999). The local network is extension of 200 m across the station area. There, the ground sur-

vey was carried out by triangulation and trilateration using high precision theodolite (T3000),

distancemeter (ME5000), level (Ni002) and GPS at 1996. The maximum value of standard de-

viations obtained from 3D adjustment in local network is 1.75 mm. Method of reference point

of VLBI antenna or SLR telescope was determined by method of using the target moving on a

sphere reported by Thomas Kiesen (1990).

This paper describes a standard method we propose to establish terrestrial ground surveys

for collocation and the results of an experiment to verify its practicality. The method consists

of three steps: a local survey network to combine ITRF, the establishment of a local survey

Methods of Local Survey between Space Geodetic Observation Systems 87

network, a survey to determine the reference points of the space geodetic observation systems . The result of the standard deviation obtained from three dimensional network adjustments at

the experimental sites is within 1.5 mm.

2. Proposed methods of the establishment of a local survey network

The standard methods of a local survey network we proposed consist of three procedures,

that is, the method of the local survey network to combine ITRF and the method of establish-

ment of local survey network and the method of surveying for determination of reference

points of space geodetic observation systems.

2.1 Methods of local survey network to combine ITRF

The local survey network should be based on a clearly defined reference frame , because the collocation of space geodetic observation systems is carried out on the same reference frame . ITRF is one of the reference frames and most space geodetic observation systems are based on . In addition, most collocation sites have a permanent GPS survey network or a survey network

based on ITRF such as the International GPS Service (IGS) tracking network .The methods of local survey network to combine a reference frame are as follows:

We use the GPS network to combine a reference frame . We determine the coordinates of

one of the monuments and the azimuth angle of a point (the azimuth marker) far away from

a monument by GPS. The azimuth marker is used to orient the network with respect to the

north. To make certain that the orientation error is smaller than 1 mm over the site , we have to determine the azimuth angle to within 2 seconds , because 2 seconds corresponds to 1.0 mm over the distance of 100 m.

The relative accuracy of the horizontal position given by GPS is about 1 cm , if the GPS

data is good and large enough. Therefore when the distance from station datum to the azi-

muth marker is longer than 1000 m, the accuracy of the azimuth angle measured by GPS is bet-

ter than 2 seconds. Thus, the azimuth marker should be placed where the distance from one

of the monuments to the azimuth marker is longer than 1000 m , and GPS observation should

done for 24 hours. In this case, we can orientate the network to the north to within 1 mm

within a site.

2.2 Method of establishment of local survey network

(1) Observation of local survey network.

Local survey network is observed between the monuments and ground markers (Figure

1). Usually, high precision distancemeters and theodolites are used in turns on the monu-

ments. We propose to use a Total-Station (TS), which measures a distance to within 1 mm ac-

curacy by using a sheet-type reflective target. TS is efficient for survey without changing a

distancemeter with a theodolite. In addition the sheet type target is light and easy to use . But before surveying, to get 1 mm accuracy the surveying instruments are verified and calibrated

by the authorized verification. Furthermore those are checked on site by comparing several

surveying instruments.


Fig. 1 Map of the local survey network. Fig. 2 Map of the calculation points of geoid

undulation.

The horizontal and vertical angles and the distance between monuments and the ground

marks are measured by TS. Usually these observations are done simultaneously, but for high-

er accuracy, these observations should be done separately. The local survey network is meas-

ured by using integrated three dimensional triangulation and trilateration (Figure 1).

(2) Method of measuring the height component at the highest accuracy

To measure the height component accurately, we use a high accuracy leveling and im-

prove the method of measurement of the instruments' height and the targets' height.

A high accuracy leveling is used for the monuments and the ground markers. The instru-

ments' height and targets' height are usually measured by using steel tape. However it is dif-

ficult to get accuracy better than 1 mm with this method. Instead we attach a sheet-type

target on the mark of the instrument's height, then we measure the target directly by another

TS. In this manner, we can easily measure the instruments' heights with an accuracy of less

than 1 mm.

(3) Correction of geoid undulation

In some collocation sites, the geoid undulation is too large to disregard. If the plum line

is inclined at about 5 seconds, the plum lines' inclination corresponds to about 2.4 mm over 100

m.

If a precise geoid model whose long frequency component accuracy is better than several

cm over 1 km baseline can be obtained, the geoid undulation can be corrected as follows:

The geoid model is used to calculate the geoidal height at four points (such as northern,

southern, eastern and western points) 500 m away from the center of site (Figure 2). Then dif-

ference in geoidal heights from the northern point to the southern point for the N-S compo-

nents of deflection of the plumb line and difference in geoidal heights from the eastern point

to the western point for the E-W components of it are calculated. Because we assume the col-

location site is smaller than several hundreds meters across, the first order component of incli-

nation of geoid undulation has same value over the entire site.

We correct the geoid undulation by rotating coordinates. We calculate the rotation using

from (1), where ƒÌ is N-S component and n is E-W components of the deflections.

•¬(1)

Methods of Local Survey between Space Geodetic Observation Systems89

Fig. 3 Setting target of direct method on a VLBI .

2.3 Method of surveying the reference points of space geodetic observation systems

The reference point of VLBI or SLR is the intersection point of the azimuth axis and the

elevation axis. Depending on the observation system , in some cases azimuth axis is repre-

sented by the mark on the pedestal, and elevation axis is represented by the mark of elevation

axis. In some cases, however there are no azimuth-axis and elevation-axis marks .

The direct method described below is for when marks are present and indirect method is

for when there are no marks present .

(1) Direct method

Here, the reference point of each observation system is directly measured by TS from the

monument. This method can be applied when the target can be set on the reference point of

each system. The procedure is as follows.

The target is set on the azimuth axis. For example , a tripod is set on the pedestal and the

target is set on the mark's plumb direction that corresponds to the azimuth axis. When the tar-

get is set on the mark, the antenna is fixed. But it is necessary to check whether the mark is

moving or not according to antenna rotating , when the mark is set.

Next, the target is set on the elevation axis . For example, the height of target is set at the

same height as the wire that corresponds to the elevation axis . Figure 3 shows how the target

can be set.

Then, the target is measured directly by TS from the monuments . It is advisable that the

target should be measured from at least two different monuments to detect and estimate error.

(2) Indirect method

The indirect method uses the principle that a center of sphere can be determined by using

four or more points on the sphere. This method can determine the coordinates of the reference

point without measuring directly the reference point in such cases as that the reference point

is intersection point of azimuth axis and elevation axis . Therefore the indirect method is also

applied even if the target cannot be set on the reference point of each system .

The procedure is as follows.


Fig. 4 Setting target of the indirect method on a VLBI.

Fig. 5 Measuring positions in indirect method.

The target is set at a proper place on the VLBI antenna or SLR telescope (Figure 4). A tar-

get position should be within several meters of the reference point, because the shape of the

VLBI antenna or SLR telescope will deform slightly during rotation.

Secondly, VLBI antenna or SLR telescope is rotated around the azimuth axis and around

the elevation axis separately. The target should be moved on a sphere.

Thirdly, depending on the geographical conditions, a target attached on a VLBI antenna or

a SLR telescope should be measured at even interval in 3 - 6 directions around the azimuth

axis and in 3 directions around the elevation axis.

At least two ground markers are needed, because as the VLBI antenna (SLR telescope) ro-

tates around the azimuth axis, the target will become hidden from one of the ground marker.

And in a relative position of two ground markers, opposite direction is better than rectangular

direction for accuracy of coordinates such as ground marker A and B in Figure 5.

Furthermore, every target position should be measured from the two ground markers,

which are placed within about 2 - 3 m each other to get redundant data and to detect errors in

real time.

If 9 -18 target positions will be obtained, the position of the VLBI or SLR reference point

as well as the radius of the sphere can be estimated by the least squares method. Using equa-

tion is as follows.

r2=(xi-x0)2+(yi-y0)2+(zi-z0)2 (2)


Fig. 6 Monuments of the KSP.

Where, (x0, y0, z0) are the coordinates of VLBI or SLR reference point and (xi , yi, zi) are the measured coordinates of the target at different positions i= 1, 2, 3, ....

3. Survey at the Keystone sites

3.1 Conditions of KSP sites

The proposed method was applied in the stations of Key Stone Project (KSP) operated by

the Communications Research Laboratory in Japan . KSP has four space geodetic observation

sites (Koganei, Kashima, Miura, Tateyama) in the Tokyo metropolitan area. Each site has

three space geodetic observation systems: a VLBI with 11 m dish antenna , a SLR with 75 cm telescope in a dome, and a GPS.

In the case of KSP, the required standard deviations of coordinates of the monuments and

VLBI, SLR and GPS reference points are within 1.5 mm for the horizontal component and

within 2.0 mm for the height component. Because of these values are equivalent or better than

the precision of space geodetic observation systems.

The KSP site has several pillars for SLR calibration and for the ground-surveying monu-

ment surround SLR observation systems. The pillars have a rigid foundation in the ground , and are made of invar, whose thermal expansion coefficient is low. The pillars are covered to

stabilize their expansion and contractions due changes in temperature and to protect them

(Figure 6). No pillars are set around the VLBI, so ground markers (temporary base points)

were set around the VLBI.

Concerning the visibility of the pillars, while most pillars have a clear line of sight to the

other pillars, some line of sights are interfered by the observation systems and the buildings .

In this case, ground markers were placed between monuments.

VLBI, SLR and GPS are located at within 100 m in diameter area at all sites , except Kashima. The Kashima site has VLBI (26 m) and VLBI (34 m) in addition to VLBI (11 m) , and SLR and GPS, therefore Kashima site's area is larger to five hundreds meters . VLBI, SLR and GPS are construction on the same level flat ground except the Kashima site , where the differ-ence in ground height between VLBI and SLR is about 10 m.


Table 1. Specifications of main instruments

Fig. 7 GPS network for local survey network connection to ITRF.

Survey instruments are requested to be able to perform high precision. Also, survey in-

struments are requested to be easily usable and to be commercially available. Because of the

purposes of this survey are to be for high precision, efficiency and standardization. The speci-

fications and features of the main instruments are shown in Table 1.

3.2 Local survey network connection to ITRF94

KSP's local survey networks were connected to ITRF94. In Japan, nationwide array of

GPS (GEONET) is operated by Geographical Survey Institute (GSI). GPS offers observation

data and their coordinates in ITRF94 at epoch 1997.0. Therefore, we combined the local survey

network with ITRF94 by using three nearby stations of GEONET (Figure 7).

Station datum, which is a point of the local survey network, was measured for 24 hours by

GPS. When the station datum was not suitable for surveying by GPS, another point was meas-

ured. The azimuth marker, which is used for orienting the local network to the north, was

measured at the same time by GPS.

The distance from station datum to azimuth marker was longer than 1 km for all sites.

Table 2 compares the range measured by GPS and that by TS. These distances are rectified to

the slope distance between the monument and marker. Both results have good consistency

within themselves accuracy. The standard deviations of the station datum coordinates ob-

tained by network adjustment are shown in Table 3. The horizontal components are less than

5 mm. This indicates the accuracy of relative position of the GPS survey is better than 1 cm.

We estimated that the accuracy of the azimuth direction was better than 2 seconds, even


Table 4. Standard deviations of monuments in 1999 (mm)

blank entries indicate fixed components.

We have surveyed at KSP sites four times between 1996 and 1999. The changes in the co-

ordinates of the monuments during these periods at the Koganei site, at the Kashima site , at the

Miura site, and at the Tateyama site are shown in Figure 9, Figure 10, Figure 11, Figure 12, re-

spectively. The survey methods are slightly different year by year, that is, the configurations

of the local survey network, number of observations and orientation of the coordinates are not

constant. Therefore, the survey data has to be re-calculated based on the 1999 coordinate sys-

tem.

The data of Miura site indicates that some systematic changed occurred. The reason for

the change is not clear yet, but some possible reasons are as follows:

Three years elapsed from first survey to latest survey, so that we cannot also deny that the

local movement of the area occurs. The measurement method was not consistent in terms of

configuration of the local survey network and the quantity of observation .

3.4 Results of correction of geoid undulation

If correction of geoid undulation is processed, it is necessary to check geoid model. In the

KSP case, "Geiod96" Software made by GSI was applied for the geoid model. "Geoid96" was checked b

y comparison of the geoidal height calculating by using GPS

measurements and leveling between station datum and ground marker, whose distance was 488

m at the Kashima site. Geoidal height was calculated by subtracting the orthometric height

measured by leveling from ellipsoidal height measured by GPS . Comparison of two geoidal

hights is shown in Table 5.

Deflections of the plumb line using "geoid96" at KSP sites are shown in Table 6 . At the

Miura site where geoid undulation is the smallest of the KSP sites , the deflection of the plumb

line is about 9 seconds, which corresponds to 4 m over distance of 100 m for the Up-Down

component. At the Kashima site where geoid undulation is the largest of the KSP sites, the de-

flection of the plumb line is about 24 seconds, which corresponds to 12 mm over distance of 100

m for the Up-Down component.

These values were too large to disregard. Therefore correction of geoid undulation was

necessary and was tested by rotating coordinates.


Fig. 9 Changes in coordinates of monuments from 1996 to 1999 at the Koganei site.

Fig. 10 Changes in coordinates of monuments from 1996 to 1999 at the Kashima site .

Fig. 11 Changes in coordinates of monuments from 1996 to 1999 at the Miura site .

Fig. 12 Changes in coordinates of monuments from 1996 to 1999 at the Tateyama site.

Table 5. Comparison of geoid96 and GPS-leveling

Table 6. Deflections of the plumb line


Table 7. Standard deviation of the VLBI (11 m) reference point

Table 8. Difference of coordinates of the VLBI (11 m) reference point in 19961999

3.5 Results of surveying for the reference points of VLBI and SLR

(1) Direct method

The direct method for VLBI (11 m) was applied in 1996, 1998 and 1999. The standard devia-

tions of the VLBI (11 m) reference points by network adjustment are shown in Table 7. The

maximum standard deviation is 1.0 mm. The differences of the coordinates of the VLBI (11 m)

reference point after a year are shown in Table 8. Here, data for 1997 was obtained by the in-

direct method. The column of ( ) indicates a comparison of direct method result with indi-

rect method result.

Some of the differences are larger than 1 mm and indicate systematic changes. For exam-

ple, difference of the X component at the Miura site had been changing by almost same amount

year by year. The reason for the systematic change is not clear, but we think that land has

shifted or that change of configurations of the local survey network between the years has in-

fluenced.

The direct method was also used to measure the SLR reference point from 1996 to 1998.

However, it is difficult to set a target on the reference point, because the reference point is on

or around the tertiary mirror. Therefore, the indirect method was used in 1999.

Concerning the efficiency of work, direct method required one or two hours to get meas-

urements from the monument, and calculation and checking were easy.

(2) Indirect method

The indirect method was used for the VLBI (11 m) antenna in 1997 and for the SLR (75 cm)

telescope in 1999. At the Kashima site, it was also used for the VLBI (26 m) antenna in 1999

and VLBI (34 m) antenna in 1998 and 1999.

The targets were placed about 0.4 m, 0.2 m, 5.6 m and 4.9 m away from the reference point

of VLBI (11 m), SLR (75 cm), VLBI (26 m) and VLBI (34 m) respectively. VLBI (11 m) and


Table 9. Accuracy of the reference points measured by indirect method

Table 10. The accuracy of the reference point by indirect method

VLBI (26 m) and VLBI (34 m) were measured in 6 directions around the azimuth axis and 3 di-

rections around the elevation axis at about even intervals. We could simultaneously measure

a target position from two ground markers, so we could get redundant data. VLBI were out-

side of first order network, therefore VLBI antenna were measured from second order network.

The KSP SLR telescope is covered by a dome, so the target was measured from only three

points (on long pillars through the escape hatch), except at the Koganei site. Therefore the

SLR telescope was measured in three directions around the azimuth axis and three directions

around the elevation axis. At the Koganei site the long pillar is taller than the other site's pil-

lars, which made it difficult to measure the target from the long pillars through the escape

hatch. Hence three ground markers were placed on the roof of building and targets were meas-

ured from them.

The maximum residual of the observation data and the standard deviations of the coordi-

nates of the VLBI and SLR reference points (calculated by least square method) are shown in

Table 9. In the case of the SLR, the maximum residual of the observation data is less than 0.2

mm and the maximum standard deviation is less than 0.3 mm. In the case of the VLBI (11 m),

the maximum residual of the observation data is less than 1.4 mm and the maximum standard

deviation is less than 0.4 mm.

The maximum residual of observation data and the standard deviation of the coordinates

of the reference points of the VLBI (26 m) and VLBI (34 m) are shown in Table 10.

In the case of the VLBI (11 m, 26 m, 34 m), the maximum residual of observation data is

about 1.4 mm and their maximum standard deviation of all components is better than 0.4 mm.

The maximum residual of observation data is larger than in the case of SLR. The reasons that

maximum residuals of the VLBI (11 m, 26 m, 34 m) are larger than that of the SLR are that base


Table 11. Change in coordinates from 1998 to 1999

Fig. 13 VLBI (34 m) and remote-controlled target.

points for measurement of the target are included second order network points and a little de-

formation of antenna occurred, because maximum residuals are dependent on the size of the

antenna or the telescope.

The changes in the coordinates of the VLBI (34 m) reference points between 1998 and 1999

are shown in Table 11. The coordinates have changed by about 1 mm. Although the VLBI (34

m) is about 200 m away from the station datum, repeatability is almost the same as in other

systems in this case.

In addition, when the VLBI antenna is larger than about 20 m, a remote-controlled target

that can orient its face toward the instrument is used because it is safer and more efficient

(Figure 13).

In concerning efficiency of work, in most cases, the indirect methods took one or two days

to take measurements from the monuments or ground markers and needed more base points

compared with the direct method to measure the target. The indirect method took a day in the

office to calculate and check.

4. Discussion

We discuss precision, efficiency and features of standard methods we proposed from these

experiment.

At the Wettzell, local survey network was connected to ITRF using 7 parameters-trans-

formation by Lang (1996). At the KSP, local survey network was connected to ITRF94 by GPS


based on GEONET. The coordinates of station datum and azimuth angle of azimuth marker

were obtained by GPS. The distances between these points were more than 1.5 km. Therefore local survey network could be orientated to the north of the GRS80 ellipsoid based on ITRF94

within about 2 seconds. This means precision of orientation of the local survey network was

about 1 mm, because KSP sites areas are within 100 m across (except Kashima site) . For the local survey network, usually a high precision distancemeter and theodolite are

used such as at the Wettzell. At the KSP, a high precision TS and an easy-control target , that

are easy to use and available commercially , are used. Furthermore, we used leveling and ap-

plied alternative method of instrument height measuring to get a higher precision for height

component. The standard deviations of the horizontal and height components of the monu-

ments by least squares method are respectively within 1.5 mm and 2.0 mm except for those of

the Kashima site that is about 500 m wide. Surveying by TS is so efficient that local survey

network was measured in only one or two days. But it is necessary to verify and calibrate TS

by the authorized verification. Furthermore those are checked on site by comparing several

TS. Heights of monuments are stable and differences of heights over years are smaller than

1 mm. Therefore, leveling and alternative method of instrument height measuring are effec-

tive to get a higher precision for height component.

We attempted to correct the geoid undulation. The effect of geoid undulation for the up-

down component at the Kashima site from calculating by `geoid96' is about 7 cm over a 488 m

baseline. This value is almost as consistent as the survey result of GPS/Leveling . Thus the effect of geoid undulation in a collocation site like the Kashima site is too large to ignore . Therefore if a high precision geoid model such as `geoid96' and/or gravity data is used , the

geoid undulation can be corrected. However, it is careful for us to process it. At the KSP, we

checked `geoid96' by GPS/Leveling, but even if the effect of geoid undulation is as small as

1 cm, it is difficult for us to check it, because the GPS error is of the same size . We tested two surveying methods for measuring the reference point of space geodetic ob-

servation systems. The coordinate errors of most of the references points from least square ad-

justment are better than 1.5 mm by using them. We discuss two methods by comparison them.

Concerning the precision of the reference points , direct method and indirect method have no significant differences. The precision of the reference point measured by the direct method

depends on how precisely the target is set on the reference point . A precision of the reference

point measured by the indirect method depends on the amount of deformation of the VLBI an-

tenna or SLR telescope and errors of base points such as ground markers in most cases . In the

direct method, it is difficult to detect setting errors, so we recommend that the indirect method

should be carried out at least once in respect of errors detection.

Concerning the possibility of application, the direct method can only be used when a refer-

ence point can be represented by a mark of the reference point, but the indirect method is used

in most cases when the target can be set. Therefore, the indirect method is better than the di-

rect method. For example, in the KSP case, the SLR telescope was surveyed by direct method

at the beginning, but we change the method to indirect method. Because the reference point


was on or around the tertiary mirror, it is difficult to set a target at the reference point.

Concerning efficiency of the survey, the direct method is more efficient than the indirect

method, because it is simpler and easier.

5. Conclusion

We established method of a local survey for collocation that consists of three procedures:

the methods for combining local survey network with ITRF and the method for establishment

of a local survey network and the methods for determination of the reference points of the

space geodetic observation systems. These methods are quite general and the instruments are

commercially available, and thus, special techniques of operates are not needed. Therefore,

these methods can be used as a standard method.

Experiments to evaluate the above method were done at KSP sites. The standard devia-

tions obtained from 3D adjustment by the local survey network are within 1.5 mm. Both the

direct method and the indirect method have no significant differences when measuring the ref-

erence points of space geodetic observation systems. We add that when the mark of reference

point is clear and in the right position, we recommend adopting the direct method. When the

space geodetic observation system can be stopped for about two days, we recommend adopting

the indirect method.

Acknowledgments

We thank the Geographical Survey Institute of Japan for providing the GPS data from

GEONET.

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Documents

Methods of Local Survey between Space Geodetic Observation