Residual structure of secular change by pulse model fitting has been explained through several examples of leveling and gravity measurements. The pulse residual variance corresponding with various errors will be required in discussing the secular change of the physical quantity in bench marks. In a one-point-fixed geodetic network, it is generally known that great secular influence of a temporary fixed point is exercised upon the estimated values in each bench mark. It is difficult to distinguish explicitly the true change from a measurement error, Thus, a pulse model has been proposed in this paper against a time series in the geodetic network based upon the idea of Walsh's orthogonal decomposition. The variation of the part not to be fitted by the pulse model is called the pulse residual variance; it will be treated as a new "rule". Also the pulse information criterion, PIC, has been proposed as a criterion to evaluate the goodness in fitting of the pulse model. Geophysical and dynamic suppositions have been shown when the pulse model is fitted to the time series. By applying a pulse model to the results of leveling measurements in Niigata and Shikoku and also to the results of gravity measurements around Lake Biwa as examples, no contradictions were detected when compared with other geophysical results. The change of a temporary fixed point has been quantified by the residual variance in an observation field. This implies that the extraction of more stabilized temporary fixed points will be possible without using mean sea level analysis in the future. Actual values of the residual and error variances are investigated from various directions. The performance evaluation of the pulse model by means of computer simulation has also been dealt with. Although this method is not always the optimal method for leveling and gravity measurements, it is possible to evaluate uniformly the error or residual in each bench mark. There is a high probability that any abnormality or data error in the time series will be detected, and any stabilization or moving states will be noticed as early as possible. Concerning treatments of time series error, no peculiar methods are needed compared with the case of the leveling and gravity measurements when applying the pulse model to the geodetic measurements using GPS. With respect to continuous observation as well, it is considered that this method can be applied with adequate sampling to general geodetic networks, mean sea level analysis or analysis of other regions without modification.

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Geoid undulation differences were determined in a region of 600 km×300 km in the southwestern part of Japan by employing data of GPS (Global Positioning System) measurements and levelling surveys carried out at 54 sites in this region during the period from 1989 to 1992. Amang them, data at 27 sites were newly obtained in the present study. As the measurement region was widely extended, five sites at which coordinates were accurately determined were adopted as reference ones during GPS measurements in order to retain the precision of GPS measurements without degrading. The precision of the GPS/levelling geoid differences determined was estimated to be about 11 cm in which the precision of an ellipsoidal height difference measured by employing GPS, that of an orthometric height difference measured by levelling and others were included. The GPS/levelling geoid differences determined were compared with the ORI-89 geoid estimated by Fukuda. The comparison showed discrepancies of several tens of centimeters in Chugoku and Shikoku Districts. We consider such discrepancies are mainly caused by peculiar errors in the ORI-89 geoid.

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The mathematical model for a new adjustment of the Japanese Datum derived by the author previously is a rigorously three-dimensional system. The mathematical specifications for observations, reductions, and observation equations of terrestrial surveys are given. The final set of normal equation coefficients can be accumulated by summing over the partial normal equations. The equations for elimination of orientation unknowns and those for handling of the observation equations for Laplace azimuths, trigonometric leveling, and astrogravimetric leveling are derived.

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This document is the quadrennial report of gravimetric works made in Japan during the period from April 1990 to March 1994. It is to be submitted to the International Gravity Commission of the International Association of Geodesy at the Joint Meeting with the In ternational GGeoid Commission, to be held in Graz, Austria from September 11 to 17, 1994. A few of works and publications not included in the previous report to the 13th meeting are also supplemented. It summarizes gravimetric works such as international and domestic connections of gravity networks, absolute and relative gravity measurements, tidal and non-tidal gravity changes, gravity surveys in Japan and foreign countries, data handling and mapping, geophysical interpretation of gravity data, theoretical researches of gravity field, etc. Complete references of the related articles are found in the bibliography. The report was made by compiling manuscripts of various Research Institutes and Uni versity research groups. The editors are grateful to Drs. Y. Ehara, Y. Ganeko, Y . Hagiwara, T. Hashimoto, K. Kaminuma, M. Komazawa, Y. Kono, M. Kosuga, M. Mishina, H. Mu rakami, M. Murakami, I. Nakagawa, S. Nakai, K. Nakamura, J. Nishida, I. Ohno, M. Ooe, M. Satomura, J. Segawa, R. Shichi, S. Takemoto, T. Yabuki, A. Yamamoto and A. Yoshida.

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