International Polar Motion Service Research Articles

Corrected μβ for stars of Hipparcos catalogue from independent latitude observations over many decades

During the last century, there were many so-called independent latitude (IL) stations with the observations which were included into data of a few international organizations (like Bureau International de l'Heure - BIH, International Polar Motion Service - IPMS) and the Earth rotation programmes for determining the Earth Orientation Parameters - EOP. Because of this, nowadays, there are numerous astrometric ground-based observations (made over many decades) of some stars included in the Hipparcos Catalogue (ESA 1997). We used these latitude data for the inverse investigations - to improve the proper motions in declination ?? of the mentioned Hipparcos stars. We determined the corrections ??? and investigated agreement of our ?? and those from the catalogues Hipparcos and new Hipparcos (van Leeuwen 2007). To do this we used the latitude variations of 7 stations (Belgrade, Blagoveschtschensk, Irkutsk, Poltava, Pulkovo, Warsaw and Mizusawa), covering different intervals in the period 1904.7 - 1992.0, obtained with 6 visual and 1 floating zenith telescopes (Mizusawa). On the other hand, with regard that about two decades have elapsed since the Hipparcos ESA mission observations (the epoch of Hipparcos catalogue is 1991.25), the error of apparent places of Hipparcos stars has increased by nearly 20 mas because of proper motion errors. Also, the mission lasted less than four years which was not enough for a sufficient accuracy of proper motions of some stars (such as double or multiple ones). Our method of calculation, and the calculated ?? for the common IL/Hipparcos stars are presented here. We constructed an IL catalogue of 1200 stars: there are 707 stars in the first part (with at least 20 years of IL observations) and 493 stars in the second one (less than 20 years). In the case of ?? of IL stars observed at some stations (Blagoveschtschensk, Irkutsk, Mizusawa, Poltava and Pulkovo) we find the formal errors less than the corresponding Hipparcos ones and for some of them (stations Blagoveschtschensk and Irkutsk) even less than the new Hipparcos ones.

History of the International Polar Motion Service/International Latitude Service

AbstractThe history of the International Latitude Service and the International Polar Motion Service is described, with an emphasis on the evolution of the international cooperation for monitoring the Earth’s rotation. Also given is a brief description of the history of the Japanese geodetic and astronomical activities, as well as the future prospects.

The International Latitude Service A Historical Review, From The Beginning To Its Foundation In 1899 And The Period Until 1922

The study of Polar Motion (PM) is associated withthe work of the InternationalLatitude Service (ILS), the International PolarMotion Service (IPMS) and theBureau International de l'Heure (BIH), andthen the International Earth RotationService (IERS). After reviewing briefly thehistory of early PM research, thescientific objective of the ILS including itsrealizing, and the activities of all thecited services and giving information on thePM time series available from mid-19thcentury to the present, important details onthe events and results are presentedover the period until 1922. It is shown, inwhich way the Geodetic Institute Potsdamcontributed to the foundation of the ILS andtook part in its activities through thework of Helmert, Albrecht, Wanach and Mahnkopf.Based on international scientificcooperation, the results were the rectangularcoordinates of the Polar Motion from1890.0 to 1922.7 at 0.1 year intervals, inparticular those derived from the latitudeobservations at independent stations from 1890.0to 1899.8, and those derived fromthe latitude observations at the ILS stationsfrom 1899.9 to 1922.7.

北アメリカ大陸とユーラシア大陸における降水量変動と関連する極運動の10年変動

A hydrologic excitation of ten-yearly polar motion appearing in the combined five-daily polar motion data of International Polar Motion Service (IPMS) and SPACE94 during 1962-1995 is discussed. The discussion is based on time-dependent exponential decay models of land water storage supplied by precipitation, in which the National Oceanic and Atmospheric Administration (NOAA) monthly gridde precipitation anomaly data for 5° × 5° is used. The decay parameter of the land water storage τ d is determined when square of the difference between the observed ten-yearly polar motion and calculated one becomes minimum. Amplitude in the calculated polar motion can explain about 36 % of that in observed ten-yearly polar motion when τ d takes 3.7 months. The behavior of the calculated polar motion is similar to the observed one though the phase of the former leads that of the latter by about one year. When we do not consider the small phase difference, about 52 % of amplitude in the observed polar motion can be explained when τ d takes 5.1 months, suggesting a globally averaged decay time of the land water storage. The seesaw-like changes of precipitation that excite efficiently the ten-yearly polar motion are also confirmed between the North American continent and the western region of the Eurasian continent. These facts suggest a conceptual model of the feedback system on decadal hydrologic cycle centered in the North Atlantic Ocean, in which the system consists of atmospheric variations connected with the North Atlantic Oscillation, seesaw-like sea level changes, and precipitation changes in the North American and Eurasian continents.

Commission 41: History of Astronomy (Histoire de L’Astronomie)

During the XXth General Assembly the Commission agreed to support a motion by Commissions 19 and 31 that a history be prepared of the Bureau Internationale de l’Heure and the International Polar Motion Service; the rider wad added that the two authors proposed (B. Guinot and S. Yumi) obtain the services of a professional historian of astronomy, to advise and assist where possible.

Seth Carlo Chandler, Jr.: Discoveries in polar motion

On January 1, 1988, the new International Earth Rotation Service (IERS) will become operational. IERS will encompass the services provided by the International Latitude Service (ILS), the International Polar Motion Service (IPMS), and the Bureau International de l'Heure (BIH) for nearly a century and will provide improved services that will be particularly useful to scientific researchers. For example, the IERS will establish and maintain a conventional celestial reference frame defined by a selected set of extragalactic radio sources, establish and maintain a conventional terrestrial reference frame defined by a set of globally distributed stations marked by monuments, determine improved constants of precession and nutation, and collect and distribute ancillary data important to understanding earth rotation, such as atmospheric angular momentum time series.

Earth orientation from lunar laser ranging and an error analysis of polar motion services

The rotational orientation of the earth has been determined from lunar laser ranging (LLR) measurements acquired at McDonald Observatory in Texas. The values and uncertainties of UT0 are calculated from 1971 through May 1982 in four forms: raw results on 799 separate days, Kalman‐filtered values, Gaussian‐smoothed values, and Fourier‐smoothed values. The effects of the different smoothings are assessed. LLR, being dominated by a single‐station operation, is sensitive to one projection of polar motion: the component along the McDonald meridian. Variation‐of‐latitude results are presented. For the polar motion component along the McDonald meridian, analyses of the LLR data assess the errors of polar motion sources: Bureau Internationale de l'Heure (BIH), Defense Mapping Agency Hydrographic/Topographic Center (DMAHTC Doppler), the International Polar Motion Service (IPMS), LAGEOS/Goddard Space Flight Center (GSFC), LAGEOS/University of Texas (Texas), and the Lerch analysis of artificial satellite data. The rms errors, of both the LLR data and the determination of polar motion by the various services, decrease in recent times. For data taken from August 1976 through May 1982, Doppler and BIH values are of comparable quality (estimated error: Doppler, 20±5 cm; BIH, 22±4 cm), with IPMS results being somewhat larger (38±5 cm). LAGEOS polar motion error drops in early 1979 in both analyses (GSFC, 14±7 cm; Texas, 18±6 cm, for data from February 1979 through May 1981). This drop parallels instrumental improvements and the increased number of stations in the laser system. The Doppler polar motion error (17±5 cm) is especially low for the period May 1977 through February 1981; the analysis of Lerch (February 1979 through May 1981) gives an error estimate of 14±7 cm. All analyses are consistent with 11 cm as an estimate for the combined LLR modeling, fitting, and instrumental error (noise) for August 1976 to May 1982.

Comparison of Polar Motion Results Using Lunar Laser Ranging

AbstractA comparison of polar motion results from three sources [Bureau International de l’Heure (BIH), Defense Mapping Agency Hydrographic/Topographic Center (DMAHTC-Doppler), the International Polar Motion Service (IPMS)] was performed using lunar laser ranging (LLR) data. The rms errors, both of the LLR data and of the determinations of polar motion by the three services, decreased in recent times. The BIH and Doppler polar motion are comparable in quality (12 ± 6 cm for BIH values taken from August 1976 through May 1980, 14 ± 7 cm for Doppler results taken from June 1977 through May 1980). The IPMS errors were substantially larger (33 ± 7 cm for data taken from August 1976 through May 1980). All three analyses give 13 ± 3 cm as an estimate for the combined LLR modeling, fitting, and instrumental error (noise) for the last four years.

On the Adoption of a Terrestrial Reference Frame

AbstractThe report of the IAU Working Group on Nutation endorsed by Commissions 4, 8, 19 and 31 at the 1979 General Assembly points out that “… the complete theory of the general nutational motion of the Earth about its center of mass may be described by the sum of two components, astronomical nutation, commonly referred to as nutation, which is nutation with respect to a space-fixed coordinate system, and polar motion, which is nutation with respect to a body-fixed system …”. Unlike the situation for the space-fixed frame, there is not an adequate, formally accepted, body-fixed system for this purpose. The Conventional International Origin (CIO) as it is presently defined is no longer acceptable because of recent improvements in observational techniques. The effective lack of this type of terrestrial reference frame limits the complete description of the general nutational motion of the Earth. In the absence of a terrestrial reference frame suitable for specifying the orientation of the Earth, it is suggested that a body-fixed system could be represented formally in a manner analogous to that used to represent the space-fixed frame. This procedure would be quite similar to methods employed currently by the International Polar Motion Service and the Bureau International de l’Heure, and would allow for the use of observations from new techniques in the definition of a terrestrial reference frame to be used to specify the complete nutational motion of the Earth.

Analysis of star pair latitudes

Star pair latitude observations form the basis for the pole positions reported by the International Polar Motion Service (IPMS). The IPMS processes these observations to produce a mean pole position. However, the time series of observations contains high‐frequency information which is lost in the calculation of the mean pole. In this study, 2931 star pair observations are analyzed. A possible large excitation at one cycle per solar day is observed. The average power level in the frequency band of the tesseral tides is seen to be high, although the peaks cannot be conclusively identified as tidal phenomena.

Analysis of daily latitude variations

The daily latitude measurements of the International Polar Motion Service are analyzed. The annual oscillation in the data was modeled by separate oscillations in each observatory's latitude data. The separate oscillations varied in amplitude from 0.05″ to 0.15″ with standard deviations of about 0.007″. Within the resolution of the latitude residuals (150 cm), there is no indication of the sharp changes which might be associated with earthquake effects. Then, applying Schuster's test to a periodogram of the residuals indicates that there are probably several processes occurring at amplitudes between 0.007″ and 0.03″ whose solution awaits a more precise measurement technique.

Polar motion and Earth rotation

During the reporting period 1975–1978, the activity in the field of polar motion and Earth rotation in the United States has been concerned with the continuation of regular observations of polar motion and the rotational speed of the Earth, improvement in the present observational techniques, development of new observational techniques and the analysis of the observations in relation to geophysical phenomena. Significant work has been accomplished in each of these areas, and these efforts are summarized separately in this report.ObservationsClassical observations of the variation of astronomic latitude at the International Latitude Observatories at Gaithersburg, Maryland and Ukiah, California were continued by the National Geodetic Survey of the National Ocean Survey. These observations were made with the same visual zenith telescopes that have been used in the past observations. The data were transmitted to the Central Bureau of the International Polar Motion Service in Mizusawa, Japan, and to the Bureau International de l'Heure in Paris, France. Results are listed in the annual publications of the IPMS and the BIH.

Velocity of the Motion of the Terrestrial Pole

The results of the spectral analysis of the velocity of the polar motion based on the data of the International Latitude Service (ILS), International Polar Motion Service (IPMS),. Bureau International de l'Heure (BIH), and the Doppler Polar Motion Service (DPMS) are presented.

Recent Results of Radio Interferometric Determinations of a Transcontinental Baseline, Polar Motion, and Earth Rotation

Radio interferometric observations of extragalactic radio sources have been made with antennas at the Haystack Observatory in Massachusetts and the Owens Valley Radio Observatory in California during fourteen separate experiments distributed between September 1976 and May 1978. The components of the baseline vector and the coordinates of the sources were estimated from the data from each experiment separately. The root-weighted-mean-square scatter about the weighted mean (“repeatability”) of the estimates of the length of the 3900 km baseline was approximately 7 cm, and of the source coordinates, approximatelyor less, except for the declinations of low-declination sources. With the source coordinates all held fixed at the best available,a posteriori, values, and the analyses repeated for each experiment, the repeatability obtained for the estimate of baseline length was 4 cm. From analyses of the data from several experiments simultaneously, estimates were obtained of changes in the x component of pole position and in the Earth's rotation (UT1). Comparison with the corresponding results obtained by the Bureau International de l'Heure (BIH) discloses systematic differences. In particular, the trends in the radio interferometric determinations of the changes in pole position agree more closely with those from the International Polar Motion Service (IPMS) and from the Doppler observations of satellites than with those from the BIH.

Systematic Differences between Global or Local Solutions of Polar Motion Derived from Astronomical and Spatial Measurements

Global determinations of polar, motion are now made by two kinds of methods: the astronomical method as used by the International Polar Motion Service (IPMS) (Yumi, 1973) or by the Bureau International de l’Heure (BIH) (Guinot, Feissel and Granveaud, 1971), and the method based on Doppler measurements on artificial satellites as used by the Dahlgren Polar Monitoring Service (DPMS) since 1967 (Anderle,1970). In addition, there are local methods used to compute the latitude variations of isolated stations from laser or Doppler measurements.

The Calculation of the Nutations

It is well known that the knowledge of precession and nutation is essential for the computation of astronomical coordinates and the comparison of values obtained at different dates. It is therefore important to compute the nutations from the best available observations.Unfortunately, there are not many long series of reliable observations that can be used for the calculation of the several nutations. Nowadays, we need more accurate values and, therefore, it is fundamental to have observations reduced in an homogeneous way. For this purpose, Commission 19 (Rotation of the Earth) set up a ‘Working Group on Pole Coordinates’, during the last IAU meeting in 1970 (Vicente, 1972), with the objective of reducing the 70 years of variation of latitude observations done by the International Latitude Service (called the International Polar Motion Service at the present time) that constitute a remarkable set of astronomical data. It is expected to obtain more reliable values for the coordinates of the pole and be able to calculate the nutations.The Working Group on Pole Coordinates is transferring to punched cards all the observations registered in the original observation books and that involves nearly 2 million cards. This work has been hampered by financial difficulties, but it should be supported by the international astronomical community in order to obtain the best results from so many years of observations, done by international cooperation.The theoretical researches done in the last decades have shown that the values of the nutations depend on the structure of the Earth (Jeffreys and Vicente, 1957). Lately, the researches done in seismology have resulted in a better knowledge about the structure of the Earth, leading to the setting up of many Earth models due to the availability of computers. This fact has led to the situation where one cannot propose better theoretical values for the nutations because they depend on the model adopted for the structure of the Earth.

On the Separation of the Spectral Components of Polar Motion

Summary This paper presents a novel method for the separation of the annual and Chandler spectral components in astronomic latitude or polar motion data. The method relies upon the high resolving power of maximum entropy spectral analysis. This separation technique is applied to astronomic latitude data from 10 International Polar Motion Service stations for the time interval 1962.0 to 1971.0, and is also applied to the two orthogonal polar motion components as determined from the data of these 10 stations. The results of this separation technique are compared with those from a method used by S. Yumi of the International Polar Motion Service. There is good agreement between the methods for the annual component determination. It was found that the annual component amplitude and phase varied widely among the ten stations. There is not good agreement between the methods for the Chandler component determination. However, evidence is given that the results of the novel separation technique are more internally consistent than those for the previously used separation method. The Chandler polar motion is plotted for the 2 years 1963.0 to 1965.0. This Chandler polar motion was determined by a least-squares fit to the 10 IPMS stations’ data after the individually determined annual components were removed from each station'sdata.

Report of the International Polar Motion Service

Report of the International Polar Motion Service

Secular and Nonpolar Variation of Washington Latitude

Observations of astronomical latitude made at Washington are analyzed for a secular trend. Comparison with the variation of latitude based on the path of the rotational pole of the International Polar Motion Service shows linear trends in good agreement. No evidence is found for a 24 yr libration of the pole. Systematic differences between observed and derived latitudes indicate that there are nonpolar variations in Washington latitude. Evidence is presented for the correlation of seismic activity with abrupt changes in the nonpolar variation, and the consequences of a changing geopotential surface are discussed with regard to observations of the rotational pole of the Earth.