水路部研究報告第31 号平成7 年 3 月24 日 17 REPORT OF HYDROGRAPHIC RESEARCHES No.31March,1995

PRECISE DETERMINATION OF STATION COORDINATES

OF LORAN 睡 C NORTHWEST PACIFIC CHAIN t

Teruo KANAZAWA 存

Abstract Abstract

The government of Japan took over the operation of Loran-C northwest Padfic chain from the government of the United States of America in 1994. Because the Barrigada (Guam) station which located located in the territory of the US was not transferred to Japan, the configuration of the stations was changed, changed, that is, the master station was moved from Iwojima to Niijima in October 1994 and the Iwojima station was terminated. The precise coordinates of these stations except Guam one in WGS 84 as as well as in Tokyo Datum are determined on the basis of the results for the marine geodetic control network of the Hydrographic Department of Japan. keywords : Loran-C, northwest Pacific chain, coordinates

veys veys of the transmitting antennas of these sta- 1. 1. Introduction tions tions were conducted by the Hydrographic Several Several years ago, the government of the Department of Japan (JHD) based on the results United United States of America declared that the opera- of control points determined in the project of tion tion of Loran ”C system except in the territory of establishing the marine geodetic control network. its its own country would be terminated by the end of The method and results are described in this 1994. 1994. The government of Japan negotiated with report. the the US and the Maritime Safety Agency of Japan

took over the operation of Loran 明 C northwest Pacific Pacific chain in 1994. Since Since the Bar 廿gada (Guam) station was not transferred transferred to Japan and was terminated in 1993, it it was decided to change the configuration of the stations stations (Fig. 1.) The master station was newly ， = constructed constructed at Niijima and the operation began in ・＇司 ．！ ．！ October October 1994. Iwojima station was terminated instead. instead. ・5 －、 r In In order to utilize the new system with suffi- Gesashi Minami- cient cient precision and to cooperate with other cou ル torishima tries, tries, precise coordinates of these stations in the Fig. 1. New configuration of Loran-C northwest Pacific Pacific chain. world-wide world-wide geodetic system are needed and sur ”

t Ace 巴pted 23th January 1995 ＊航法測地課 Geodesy and Geophysics Division 18 18 Teruo KANAZA WA

static static differential method. 2. 2. Method of position determination (2) (2) Differences of coordinate systems

(1) (1) Marine geodetic control network Constructing a world-wide geodetic system Regulations Regulations to delineate the boundaries of the became realized after launches of artificial satel- jurisdictional jurisdictional sea such as the territorial sea or the lites and many kinds of world-wide geodetic sys- exclusive exclusive economic zone are provided in the terns have been reported since then. Differences United United Nations Convention on the Law of the among recent models are less than one meter and Sea. Sea. JHD commenced a project to establish the efforts to improve these systems are continuing marine geodetic control network in 1980 utilizing according to the increase of satellite observa- methods of satellite geodesy (Kubo, 1988). tional data. Among them two systems are used In In this project, satellite laser ranging (SLR) is frequently. One is WGS 84 which is used for GPS, conducted conducted at Simosato Hydrographic Observa- NNSS and Loran-C operated by US (DMA, 1991). tory tory (located in Wakayama prefecture) in coop- The other is IERS Terrestrial Reference Frame eration eration with other SLR stations distributed (ITRF) used in the scientific community world-wide world-wide and the coordinates of the fiducial (Boucher and Altamimi, 1989). IERS stands for point point at Simosato Hydrographic Observatory are International Earth Rotation Service. determined determined precisely in the world-wide coordinate The coordinate system used for the reduction of system. system. satellite data in JHD (called JHDSC) is almost First First order control points in off- lying islands of identical to ITRF. Differences between them are Japanese Japanese territory are connected to the fiducial within ten centimeters level (Sengoku, 1992). point point at Simosato by simultaneous SLR observa- WGS 84 is also nearly identical to ITRF and tions tions of Japanese geodetic satellite Ajisai. Second differences between them are reported to be fifty order order control points are connected to first order centimeters level (McCarthy, 1992). While these control control points by simultaneous observations of three coordinate systems are different in the Navy Navigational Satellite System (NNSS) and scientific sense, they can be regarded as identical of of Global Positioning System (GPS) lately. The in the practical sense considering the precision of coordinates coordinates of first and second order control positioning by Loran-C. So, we take the results of points points are thus determined in the world-wide marine geodetic control network as the coordi- coordinate coordinate system. nates in WGS 84 in this report. Among the stations of Loran 心 northwest In Japan, a unique coordinate system which Pacific Pacific chain, Tokachibuto (Hokkaido), Gesashi covers the mainland and a part of Okinawa (Okinawa), (Okinawa), Minamitorishima (Marcus island), islands was developed and is called Tokyo Datum and the former Iwojima station are placed near (TD). Since the coordinates of the origin of TD first first order control points and the coordinates of was determined by astronomical observations, these these nearby first order control points have the adopted values are known to have a differ- already already been determined by SLR method. ence from the values in world-wide coordinate The position of the new master station at system which amount to ten seconds of arc in Niijima Niijima was determined by GPS observations of both latitude and longitude. In addition to these PRECISE DETERMINATION OF STATION COORDINATES 19

differences, differences, because TD was constructed through Uchiyama, 1994). Coordinates of Loran ”C antenna conventional conventional triangulation method, there are dis- at Tokachibuto had been surveyed in TD from tortions tortions of triangulation network which are the nearest triangulation point in 1983 (Takemu ” known to reach more than ten meters in ra and Sawa, 1985). The results are also listed in Hokkaido and Okinawa regions. Table 1. Relations Relations between TD and the world-wide coor- (3) Gesashi (Okinawa) dinate dinate system can be obtained if both coordinates Observations of first order control point in are are known at the same point. We adopt the trans- Okinawa were conducted in 1989 and coordinates lation lation parameters obtained at Simosato (Tatsuno of the point were obtained (Sengoku et al., 1992). and Fujita, 1994). Coordinates of Loran ”C antenna at Gesashi had Coordinates Coordinates which are transformed from the been surveyed in TD from the nearest triangula- world-wide world-wide coordinate system by using these tion point in 1992 by the 11th Maritime Safety translation translation parameters are close to the coordi- Regional Headquarters. The results are listed in nates nates of TD but differs from TD because of the Table 1. distortions distortions existing in TD. We call this trans- (4) Minamitorishima (Marcus island) formed coordinate system as Corrected Tokyo Observations of first order control point in Datum (TDC) to distinguish it from TD in this Minamitorishima were conducted in 1989 and report. report. coordinates of the point were obtained (Sengoku et et al., 1992). Relations between newly established

3. 3. Observations of coordinates of Loran 胃 C control control point and the Loran-C antenna at antennas Minamitorishima Minamitorishima had been surveyed in 1982 (1) (1) Niijima (Takemura and Kanazawa, 1984) and were sur- GPS Observations to connect a triangulation veyed again in 1989. Because the position of this point point in Niijima to GPS network of our Depart- isolated island had been determined independent ment in Sagami Bay area were conducted in 1992 from TD, coordinates of Loran-C antenna in (Takanashi (Takanashi et al., 1994). Coordinates of the GPS Minamitorishima are listed in WGS 84 and in antennas antennas in Sagami Bay area had been deter ” TDC in Table 1. mined through other GPS observations with (5) Iwojima Simosato in 1992. Coordinates of Loran-C antenna Observations of first order control point in at at Niijima from the nearest triangulation point Iwojima were conducted in 1992 and coordinates were surveyed by the 3rd Maritime Safety of the point were obtained (Sengoku and Regional Regional Headquarters in 1992. The coordinates Uchiyama, 1994). Coordinates of Loran-C antenna of of Loran ”C antenna in Niijima in WGS 84, TDC had been surveyed in the local datum in 1982 and TD are listed in Table 1. (Takemura and Kanazawa, 1984). The coordi-

(2) (2) Tokachibuto (Hokkaido) nates of the former Loran ”C antenna in Iwojima Observations Observations of first order control point in in WGS 84 and in TDC are listed in Table 1. Tokachi were conducted in 1991 and coordinates of of the point were obtained (Sengoku and 20 20 Teruo KANAZA WA

Table Table 1. Coordinates of Loran-C antennas including the former Iwojima station in WGS 84, TDC and TD.

WGS84 WGS84 TDC TD Niijima latitude(N) 34' 24 ’ 11. 942 ” 34' 23 ’ 59. 778 ” 34' 23 ・59. 71 1” Iong i tu de (E) 139 16 19. 478 139 16 30. 802 139 16 30. 844

Takach ibu to latitude(N) 42 44 37. 219 42 44 28. 041 42 44 28.013 Iong i tu de (E) 143 43 09. 754 143 43 23. 940 143 43 23. 722

Gesashi Gesashi latitude(N) 26 36 25. 038 26 36 10. 624 26 36 11. 041 I ong i tu de (E) 128 08 56. 92 日 128 09 04. 096 128 09 03. 779

Hinam1- latitude(N) 24 17 08. 007 24 16 50. 922 torishima I ong i tu de (E) 153 58 53. 779 153 59 07. 679

Iwojima Iwojima latitude(N) 24 48 03. 661 24 47 47. 782 longitude longitude (E) 141 19 30. 814 141 19 41. 669

4. 4. Discussions References

As stated in section 2 (2), we neglected the Boucher, C. and Z. Altamimi : The initial IERS differences differences among JHDSC, ITRF and WGS 84 in Terrestrial Reference Frame, IERS Tech- this this report. Strictly speaking, any coordinate nical Note 1, (1989). system established on the surface of the earth is DMA : Department of Defense World Geodetic changing changing all the time because of plate motions on System 1984, DMA Technical Report world-wide world-wide scale and crustal deformations on 8350. 2, second edition, (1991). regional regional scale. If we stick to the accuracy of Kubo, Y. : Satellite laser ranging at Hydro- centimeter centimeter level, we must indicate the time that graphic Department, launch of Japanese the the coordinate system is referred such as ITRF geodetic satellite Ajisai and establishment 90, 90, ITRF 91 etc. Time differences of observations of satellite geodesy office, Data Rep. of of first order control points are also neglected in Hydrogr ・. Obs., series of satellite geodesy, 1, this this report. 1-18, (1988). Japan is located in an especially active tectonic McCarthy, D. D. : IERS Standards (1992), IERS region. region. Recent monitoring of crustal deforma- Technical Note 13, 16-24, (1992). tions tions by static DGPS observations revealed that Sengoku, A. : On the conventional terrestr 匂 1 ref- crustal crustal deformations associated with major earth- erence frames determined by Hydro- quakes often reach tens of centimeters even if graphic Department of Japan (in

epicenters epicenters are under sea 司 bottom hundreds of Japanese), Rep. Hydrogr. Res., 28, 309 321, kilometers kilometers apart from coast. Considering such (1992). circumstances, circumstances, we must repeat observations of Sengoku, A. and T. Uchiyama : Positioning of the these these positions and revise the results at appropri- first order control points (Tokati and Iwo

ate ate intervals in order to keep up accuracy of Sima) in the marine geodetic control net 国 coordinates coordinates of Loran-C antennas in ten centi- work (in Japanese), Data Rep. Hydrogr. meters meters level. Obs., series of satellite geodesy, 7, 35 48, (1994). (1994). Sengoku, Sengoku, A., T. Uchiyama and E. Nishimura: PRECISE DETERMINATION OF STATION COORDINATES 21

Positioning Positioning of the first order control points of astronomy and geodesy, 19, 85-98, in in the marine geodetic control network in (1985). 1989 1989 (in Japanese), Data Rep. Hydrogr. Tatsuno, T. and M. Fujita : Determination of the Obs., Obs., series of satellite geodesy, 5, 43 64, position of the mainland control point in (1992). (1992). the marine geodetic control network (in Takanashi, Takanashi, Y., K. Kawai and y, Watanabe : Japanese), Data Rep. Hydrogr. Obs., series Survey of geodetic position of Nii Sima by of satellite geodesy, 7, 102 106, (1994). using using GPS (in Japanese), Data Rep. Hydrogr. Hydrogr. Obs., series of satellite geodesy, 7, ロラン C 北西太平洋チェーン局の正確な位置の決定 89 89 94, (1994). （要旨） Takemura, T. and T. Kanazawa : Satellite 金沢輝雄 Doppler Doppler positioning of off-lying islands in ロラン C 北西太平洋チェーン局の配置は、米国か 1982 1982 (in Japanese), Data Rep. Hydrogr. ら臼本への移管に伴い、 1994 年に変更された。水路 Obs., Obs., series of astronomy and geodesy, 18, 部では、海洋測地の推進業務の中で得られた離島の 42 42 54, (1984). 基準点の位置を基に、これらのロラン C 局の正確な Takemura, T. and M. Sawa : Satellite Doppler 位置を世界測地系と日本測地系の双方で決定したの positioning positioning of off-lying islands in 1983 (in で、その手法と成果について報告する。 Japanese), Japanese), Data Rep. Hydrogr. Obs., series