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Chandler and annual wobbles based on space-geodetic measurements: In this study, we examine the major components of polar motion, focusing on quantifying their temporal variability. In particular, by using the combined Earth orientation series SPACE99 computed by the Jet Propulsion Laboratory (JPL) from 1976 to 2000 at daily intervals, the Chandler and annual wobbles are separated by recursive band-pass filtering of the χ1- and χ2 -components. Then, for the trigonometric, exponential, and elliptic forms of representation, the parameters including their uncertainties are computed at epochs using quarterly sampling. The characteristics and temporal evolution of the wobbles are presented, as well as a summary of estimates of different parameters for four epochs. Polar motions with a half-Chandler period and less in their temporal variability: Our study focuses on the observed higher-frequency polar motions that are substantially smaller than the Chandler and annual wobbles. Here, the combined Earth orientation series SPACE99 from 1976 to 2000 with one-day sampling is used as input data, after removing the low-frequency, the Chandler and annual terms. We applied a data processing procedure including four steps, each computing the amplitude spectrum by a Fast Fourier Transform in order to reveal the periodic signals in the residual motions, and then separating their components from the residual time series by band-pass filtering. In particular, the oscillations have the following periods: Semi-Chandler and semi-annual periods and those of order four, three, two, and one and a half months, as well as quasi-biennial and 300-day periods. We show to what extent the observed polar motions are irregularly occurring. A very small polar motion signal with the period of one month is still found in the remaining motions.

Compared to the Chandler and annual wobbles, the higher-frequency components of polar motion (PM) have substantially smaller amplitudes. Therefore, their study had to wait until higher-quality time series with high temporal resolution, as measured by space geodetic techniques, became available. Based on the combined Earth orientation series SPACE99 computed by the Jet Propulsion Laboratory (JPL) from 1976 to 2000 at daily intervals, we have separated the periodic PM terms by band-pass filtering and found that the persistence of oscillations becomes less with increasing frequency (Höpfner 2001a, b). In order to quantify and better describe the parameter variability of these PM components over time, particularly of eight oscillations with periods ranging between about 650 and 45 days, we computed the radii, direction angles and period lengths from the periodic terms filtered out from the time series. The results clearly show the characteristics and time evolution of the periodic PM components that are important for geophysical interpretations., Scientific Technical Report STR ; 02/01

The history of the study of Polar Motion began with the derivation of the equations for the rotation of a rigid body by Euler published in 1758. This was followed by further theoretical contributions made by Lagrange (1788) and Poinsot (1834). To confirm the existence of the polar motion of the Earth in terms of a variation of latitude, intensive efforts were undertaken at several observatories toward the end of the 19th century. During the 7th General Conference of the European Arc Measurement in Rome in October 1883, Fergola had already suggested to investigate the problem. The latitude variation was detected by K¨ustner at the Berlin Observatory in 1888. Following this, during the Annual Conference of the Permanent Commission of the ”Internationale Erdmessung” in Salzburg in September 1888, Foerster proposed to consider the variation of latitude more systematically by a Special Commission. Activities began quickly, and after considerable effort the International Latitude Service (ILS) started in September 1899. The paper reviews, in which way the Geodetic Institute Potsdam contributed to the foundation of the ILS and took part in its activities through the work of Helmert, Albrecht,Wanach and Mahnkopf. Based on international scientific cooperation, the results were the rectangular coordinates of the Polar Motion from 1890.0 to 1922.7 at 0.1 year intervals, in particular those derived from the latitude observations at independent stations from 1890.0 to 1899.8, and those derived from the latitude observations at the ILS stations from 1899.9 to 1922.7

Scientific Technical Report STR ; 99/07

Scientific Technical Report STR ; 98/10

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Es wurden die Ergebnisse der Zeitbestimmungen auf Homogenität der Gruppenvarianzen, Normalverteilung der Beobachtungen, Unterschiede für die Ausgleichungsverianten und systematische Abweichung der Ortssternzeiten der Haupt- und Parallelbeobachtungen untersucht. Nachdem die Einzelergebnisse der Längenbestimmung als zweiseitige L!ingenunterschiede und einseitige Längen gegen Greenwich berechnet waren, wurden verschiedene Verfahren (allgemeine arithmetische Mittelbildung, Verfahren der Regressionsanalyse nach SCHÄDLICH, "direktes" Verfahren nach RADECKI) angewandt, um Endergebnisse der Längenbestimmung zu erhalten. Diese wurden durch Vergleich eingeschätzt. Dann ergaben eich die definitiven Ergebnisse für die Längenunterschiede und Längen auf Grund der obenerwähnten Untersuchungen. Aus ihrem Vergleich mit den Ergebnissen früherer Längenbestimmungen (1903, 1929, 1960) folgte, daß keine systematischen Fehleranteile in den definitiven Längenunterschieden zu erkennen sind. Somit können die erhaltenen mittleren Fehler von ≤ 3,5 ms als wahre äußere Genauigkeiten betrachtet werden. Als Schlußfolgerung ergibt sich, daß auch die Beobachtungsergebnisse an Passageinstrument.en zum Studium rezenter horizontaler Erdkrustenbewegungen beitragen können., The results of time determinations obtained at Borowiec, Dresden and Potsdam statione in 1966 were tested with reapect to homogeneity of group variances, normal distribution of observationa, differences for adjuatment variante, and ayatematic deviations between the local sidereal timea of principal and parallel observatiQns. After having calculated the individual results of longitude determination in terms of two-sided longitude differences and of one-sided longitudea referred to Greenwich, several methode (general arithmetic mean calculation, method of regreasion analysis by SCHÄDLICH, "direct" method by RADECKI) were employed to obtain final results of longitude determination. The latter were eatimated by comparison. The definitive results for the longitude differenees and the longitudes of the stations were obtained on the base o:f the above-mentioned examinations. These results were compared with previous measurements (1903, 1929, 1960). There do not seem to be any systematic deviations between the definitive longitude differences of the various measurements. Therefore, the obtained mean equare errors of ≤ 3,5 ms can be regarded as real external accuracies. The conciusion is drawn that observations performed by means of tranait instruments also can contribute to the investigation of recent horizontal crustal movements., Veröffentlichungen des Zentralinstituts Physik der Erde; 11