ALBERT

Description: Precise nautical charts have become indispensable both for determination of the outer limit of jurisdictional sea and for the safety at sea. It is because the United Nations Law of the Sea has come into effect in many countries and also because of the advent of GPS that enables navigators to obtain precise position even in the middle of the ocean. Since 1980, the Hydrographic Department of Japan has carried out space geodetic observations, such as satellite laser ranging (SLR) and global positioning system (GPS), to establish geodetic control network in Japanese islands. This paper briefly reviews our activities and several results in space geodesy for precise nautical charts.

Description: Published

Description: An algorithm for estimation of geodetic parameters by means of a linear estimation theory applying to Satellite Laser Ranging (SLR) data was presented in the former paper of this publication series by the author (Sasaki 1984). The procedure and expression to determine the precise position of SLR site in the geocentric rectangular coordinate, the geocentric constant of gravitation (GM), the dynamical form factor of the earth(J2) and a ballistic air-drag coefficient (β） were given. A preliminary results for the precise location of the Simosato Hydrographic Observatory and the datum shift correction from the Tokyo Datum to a global geodetic system were also presented in the paper by applying the algorithm to SLR data obtained in worldwide observation sites. In succession from the former paper an algorithm to have results of the earth rotation parameters of pole position ( xp. yp,) and excessive angular velocity (Δω) and geodetic coordinates of observation sites expressed in latitude, longitude and height from a reference ellipsoid（ φ,λ,h) is given in this paper in order to use the algorithm for the analysis of SLR data in the Hydrographic Department and so on. Key words, Satellite laser ranging, Earth rotation, Geodetic coordinate

Description: Published

Description: The optimum orbits of the geodetic satellite GS-1, expected to be launched after 1982, are here investigated. The satellite is a balloon, approx. 10 m in diameter, which can be observed by both photography and laser ranging so that its direction and distance can be determined simultaneously. The role of the satellite is to determine the positions of the isolated islands around Japan, with an accuracy of ±1～2 m, with respect to an unified geodetic system for establishing the marine geodetic network which is to be a positioning reference system in all scientific investigations in the sea area, and to correct the national triangulation network on land. In order to accomplish these programs the satellite orbit should be selected in such a way that will satisfy the following conditions : i) the satellite can be photographed with a moderate size astrograph to determine its direction and time, ii) laser ranging is possible with a comparatively simple device, iii〕there are plenty of chances for simultaneous observation from two stations approx. 2000 km apart, iv) the satellite will remain in orbit for five years or more during which the observations can he completed as scheduled, and v) there is little difficulty in the problems of safety and technique needed the satellite into the orbit. From the standpoint of planning the observation program, and the efficiency of the observations, it is desirable that the orbit be circular. The optimum values of the orbital height and inclination, which directly affect the chances of observation, have been investigated through numerical analysis and simulation, taking the conditions enumerated above into account. Through the analysis the relationships among the satellite irradiation, observable area on the earth’s surface, and the occurrence of observation chances, have been evaluated by providing a varied orbital height and observable elevation angle limit. During the simulation the positioning accuracy and the observation times have been evaluated by using the sham observation values derived from the normal random numbers. The conclusions are as follows : Concerning the orbital height, although the positioning accuracy of the observation stations depends on the accuracy of a single observation, due to the satellite height and direction, such an effect is smaller than the effect which the height has on the number of observation chances. The number of the observation chances also depends on the optical capacity of the astrograph. The lower the optical limit of the observable elevation angle the more the observation chances, although scintillation becomes significant in the lower elevations. If the astrograph is effective for all areas above some fixed angle between 20°and 30°, it is better to adopt a higher orbit, within the limit of the laser ranging. If there is a lower limit in the elevation angle, at approx. 30°, there is not so much difference in the observation chances for heights of 1400～1600 km. If the optical capacity of the astrograph is insufficient, it appears to be better to adopt a lower orbit. But this is no more desirable because of the decrease of the absolute amount of the chances. For the inclination, the simulation shows that there are no remarkable differences in the chances due to an inclination between 45° and 55° in the case of observation in Japan and its surrounding area. Hence an inclination should be decided, which will minimize any error in height at the launching, optimize the period of observable seasons, and, if necessary, enable the use of the satellite by stations in other regions of higher latitudes. Key words: satellite geodesy.

Description: Published

Description: A satellite laser ranging system was installed at the Simosato Hydrographic Observatory and the satellite observation has been continued since March, 1982. To process the range data and to obtain satellite orbits and geodetic parameters, an orbital processor using numerical integration has been developed. The processor includes the terms of the non-spherical force due to the geopotential, lunisolar and planetary forces, radiation pressure, atmospheric drag and tidal effects of the solid earth and ocean. The algorithm and formation of the processor are described here. The processor is applied to the range data obtained at the observatory and other laser sites in the world to determine the position of Simosato site in the global geocentric coordinate system. The coordinate of the intersecting point of azimuth and elevation axes of the laser ranging system at Simosato site is obtained on the basis of the LPM 81.12 coordinate system. The preliminary result is 33° 34’39”. 697N (latitude),135° 56’13”. 156E (longitude) and 100.66 meters (height from the reference ellipsoid: A=6378 137.0 m, 1/f=298.257). The comparison of the result with the geodetic coordinate surveyed in the Tokyo Datum derives the datum shift correction from the Tokyo Datum to the LPM 81.12 system as ΔU=-142.5 m，ΔV=+510.4 m and ΔW= +681.2 m. If the position of the origin of the Tokyo Datum is expressed in the LPM 81.12 system by using the datum shift correction, the values of the position is shifted by +11”. 71 in latitude and -11”.83 in longitude on the basis of the values expressed in the Tokyo Datum and the shift amounts to 468 meters to the direction of 321 degrees in azimuth. According to the results of the lunar laser ranging, an eastward rotation of the LPM 81.12 system of 0”.197 makes the same longitude for the reference point of the 2. 7 meter telescope at the McDonald Observatory. If it is applied to the longitude of Simosato site, the datum shift correction changes to ΔU=-146.0 m，ΔV=+506.7 m and ΔW=＋681.2 m.The new expression for the position of the origin of the Tokyo Datum obtained by using this datum shift correction on the basis of the lunar longitude system is given as 35° 39’29”. 217N (latitude), 139° 44’28”. 878E (longitude). Key words: Orbital determination, Minimum Variance estimate, Satellite laser ranging, Tokyo Datum

Description: Published

Description: Published

Description: Since mid-1970’s three Satellite Laser Ranging (SLR) systems were completed in Japan. An experimental system was developed by the Hydrographic Department of Japan (JHD) and the Geographical Survey Institute (GSI) in cooperation and was installed at an observatory of GSI. Another SLR system was installed at the Simosato Hydrographic Observatory and observations have been continued there since 1982. A transportable SLR system was also developed by JHD and field observations in isolated islands have been continued since early 1988. The author has been deeply involved in planning, development, observation and data preprocessing for the three systems. An orbital processor/ analyzer based on the linear estimation theory has been developed by the author and was named HYDRANGEA. Applying the HYDRANGEA to SLR data, the earth rotation, coordinates of SLR stations, baseline lengths among SLR stations and some geophysical parameters as GM, J2, and so on were determined. Namely, it is shown that a specific short arc method with use of SLR data obtained simultaneously at plural stations for successive passes of a satellite is extremely effective to determine baseline lengths among SLR stations. The precisions of the resultant lengths of straight baselines of Simosato・ Titi Sime (938 km) and Simosato-Minamitori Sima (2025 km) determined by using the processor/analyzer with use of LAGEOS and AJISAI SLR data attain to 4 mm and 7mm， respectively. The semi-long arc method is also applied. By using a number of LAGEOS five-day-arcs and GEM-Tl gravity field, two geophysical parameters are derived as GM= 398600. 4453 ± 0. 0003 km3/s2 and J 2 = (1082.571±0.015）× 10-s. The pole position (xp, yp) and excess rotation per day （Δω)of the earth in five day intervals from September 1983 to October 1984 are estimated by means of 85 five-day-arcs of LAGEOS SLR data. The mean systematic difference of this result from a result of ERP (CSR) 85L07 derived by the Center for Space Research (CSR) of the University of Texas at Austin is ( δxp， δyp, δω)= (-0.51 milliarc- seconds(mas), -0.13 mas, -0.87ms/d) and the standard deviation of each five-day-result is Δxp, ΔYP，Δω ）=（ ±1.1 mas，±1.4 mas, ±0.42 ms/d). The coordinates of worldwide SLR stations at epochs of 1984.80, 1986.76 and 1988.11 are derived from LAGEOS SLR data. The internal errors of three dimensional rectangular coordinates determined for positions of 14 stations at 1984.80 are (2.6 cm, 2.4 cm, 2.9 cm) and the systematic difference of the result from the set of CSR coordinates of LSC 85L07 and mean individual difference between the result and the CSR result are ( +0.5 cm, +0.5 cm，+3.1 cm) and (3.4 cm, 3.1 cm, 5.1 cm), respectively. From the differences of each corresponding baseline arc lengths on the earth’s surface between several SLR stations for three epochs above, plate motions among Simosato, Hawaii, Monument Peak (California) and so on are derived as Simosato-Hawaii: -11.9 cm/y, Simosato-Mon. Peak : 5.7 cm/y, Simosato-Quincy : -1.1 cm/y, Simosato-Wettzell:-3.1 cm/y, Simosato-Yaragadee: -6.2 cm/y, Hawaii-Mon. Peak: +1.3 cm/y, Hawaii-Quincy: +0.6 cm/y, Hawaii-Wettzell：一7.0cm/y, Hawaii-Yaragadee: 10.9 cm/y, Mon. Peak-Wettzell: 0.0 cm/y and Mon. Peak-Yaragadee: 9.6 cm. Almost all the results except for the baseline between Simosato and Wettzell well coincide with the estimation of AM0-2 model given by Minster/Jordan [1978]. The change of arc length between Simosato and Wettzell is estimated as -3.1 cm (contraction) despite of the both stations being believed on the same Eurasian plate. This phenomenon is considered to be the result of the movement of the Philippine Sea plate which is under thrusting the Japanese Islands.

Description: Published

Description: Published

Description: A satellite laser ranging system has been made under cooperation with the Hydrographic Department and the Geographical Survey Institute. The receiving telescope is of a Cassegrain type with 40 cm diameter installed on 3-axes type mountings which are driven by pulse motors in combination with encorders in three different tracking modes : manual, programing and automatic. A 0. 1 nsec-resolution counter is prepared for measuring flight time. The system has a 500 MHz oscilloscope with a remote controlled camera which makes it possible to study the shapes of the transmitted and received light for accomplishing high ranging accuracy. According to the test operations the transmitted laser energy attains to 3. 3 Joules and the pulse width is 21 nsec. These correspond to 160 MW at peak. In the case of using an electro-optical shutter which is adopted for sharpening the transmitting light, those values become 0. 2 Joule, 6 nsec and 43 MW, respectively. It has been definitely shown by some experiments and test operations that the developed system is valid for precise ranging. Key words : laser ranging system

Description: Published