As the GPS survey directly determines the height of the Earth's surface from a reference ellipsoid, its combination with ordinary leveling and/or gravity measurements provides us several kinds of the gravity field quantities such as gravity anomaly, gravity disturbance and geoid height. Although these quantities have the same importance as the gravity field data, theoretically, it is meaningful to investigate the best practical ways of treating the data. We therefore present first a proper formulation by the least squares collocation as a mean to apply GPS, leveling and gravity data for a local problem, and then investigate the degree variances of the gravity field in Japan. We discuss subsequently the error estimates of the combined measurements, and finally conclude that the combined use of GPS and gravity data is quite efficient for both gravity surveys and height determinations.

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A special approach to adjust geodetic network in which GPS surveys are frequently repeated is performed with the aid of four-dimensional integrated adjustment technique. We take global Cartesian coordinate as a reference system, and assume not only coordinate unknowns but also rate of deformation signal linear with time. Observation equation for the repeated baseline measurements is proved to be a type of fundamental observation equation in least squares collocation. We deduced the solutions of deterministic approach for three cases in which (1) both design matrix and signal coefficient matrix are singular, (2) only design matrix is singular, and (3) signal coefficient matrix is singular. In solving the observation equation, we apply reduced normal equation for case (2) and (3). Further we discussed the solution of stochastic approach. In case of singular normal equation, we apply inner constrain matrix both for parameters and signals in order to obtain the unknowns. The adjusted results are transformed into the numerical values based on local Cartesian coordinate. Finally, horizontal strains are deduced from overdetermined horizontal displacement vectors at the GPS stations.

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In September, 1990, the Weilheim (Germany) 30 m antenna was configured for geodetic VLBI by transporting a K-4 back-end system from Japan and the first observations were accomplished between Weilheim, Kashima (Japan) and Nobeyama (Japan). Quality of observations at Weilheim is good, although a crystal quartz clock phase-locked to a Cs frequency standard was used. It is demonstrated that a K-4 back-end system has good transportability and mechanical reliability in international VLBI observations. The data of the Weilheim-Kashima baseline are analyzed to determine the coordinates of the Weilheim antenna. Internal precision of the estimated coordinates is about 10 cm which is much better than the hitherto known precision from surveying.

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We carried out test observation of crustal strain by two extensometers on common bases in an observation vault of Takajo observatory at Miyazaki prefecture in Southwest Kyushu, Japan. These extensometers are composed of two different type invarrods, one of which is conventional super-invar (S-I) and the other is new super-invar whose coefficint of expansion is extremely lower than that of conventional one. The new S-I extensometer is less influenced by temperature changes in the vault. Especially in the periods showing large drift after installation of instruments and for the duration of rainfall disturbances, when the air temperature in the vault changes rapidly, the availability of the low coefficient of new S-I reveals evidently. Coefficient of linear expansion of both materials were numerically estimated from the observation data in the period of initial drift and from the heating experiments data. The coefficient of expansion of conventional S-I is about 1×10^-6/°C and that of new S-I is less than 1×10^-7/°C, sign of which changes according to the temperature.

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The baseline for Electronic Distance Meters (EDM) in the Commonwealth Scientific and Industrial Research Organisation (CSIRO) was measured with a distance meter made by the National Research Laboratory of Metrology (NRLM) which utilises an intermode beat of a Ire-Ne laser. The measurements were carried out at distances between 20 m and 649 m and a repeatability of ±0.3 mm was obtained in measurements of 649 m after correction for refractive index and cyclic error. The measurement results were compared with other measurements using high precision commercial instruments. The compatibility of long distance standards between Japan and Australia has been verified from the calibration results of the beat distance meter in the NRLM tunnel both before and after these measurements.

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A geodetic network adjustment method under the constraint condition using the maximum shear strains has been developed as a new method for estimating displacement vectors. This adjustment method enables fixation of a network automatically without prior physical models or distortion of the network. Moreover, this method can be applied to networks on the ellipsoid and allows for the free selection of points which are under constraint. This method was applied to a small GPS network around Unzen Volcano and a 12 cm westward movement of the point on Mt. Fugendake was detected between November 1990 and February 1991. The method was also applied to the nationwide first order triangulation network of Japan using the data from the old first order triangulation (1882-1909) as well as the Primary Precice Geodetic Survey (1973-1989). As a result, crustal movements which are considered to have been caused by the plate motions were detected and a difference in patterns of displacement vectors was found between the northeastern and southwestern parts of the Japanese Islands. Furthermore, by converting the displacement vectors to those relative to a selected fixed point, crustal movements were studied in regions where a plate boundary or a tectonic line is assumed to exist. The results show notable features in crustal movements in the vicinity of the Suruga Trough in the Tokai district, the Itoigawa-Shizuoka Tectonic Line, the Oga-Ojika Tectonic Line in the Tohoku district and the Beppu-Shimabara Graben in Kyushu.

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In observing crustal deformations, strain and tilt data are usually recorded in a continuous manner with a telemetry system using leased lines. However, this system is often disrupted by such troubles as interruptions in the power supply and problems with the leased line. In order to alleviate these problems, an automated measuring system has been designed. The system consists of a microcomputer containing a newly designed interface circuit and a panel meter for analog-to-digital (AID) conversion. The system operates with low power consumption and supports a long-term continuous observation utilizing only a car battery. The system is inexpensive, easy to handle. The data recorded by the system agrees well with that by the telemetry system, and the former is reliable not only for use of tidal analysis but also for use over long periods.

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In order to fully understand the state of the Earth's environment, extensive scientific efforts for detecting various phenomena on a global scale are necessary. Since geodesy is the science for measuring the Earth's configuration and deformation, its contribution to the Earth's environmental study is, as a matter of course, expected. At present, a number of institutions in Japan are engaged in such geodetical works as tidal measurement, leveling, space technology-based surveys (VLBI, SLR, GPS), absolute gravity measurement, superconducting gravity measurement, satellite altimetry, Earth rotation and polar motion measurement, and so on. They are also participating in numerous international observation programs and services. Considering the important role expected of these geodetic works, we recommend that they should be more effectively applied to the environmental study of the Earth.

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Baseline vectors on Takayama-Hachijo baseline (412 km) were determined from daily GPS measurements using the GSI precise ephemerides. Results were compared with those determined using broadcast ephemerides in the period from April 1992 to January 1993. Longterm repeatability for ten months were improved to 14 mm (3.4×10^-8) from 18 mm in N-S component, to 22 mm (5.3×10^-8) from 57 mm in E-W, and to 63 mm (1.5×10^-7) from 117 mm in U-D.

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