Analysis of the high frequency components of Earth rotation demodulated from VLBI data

Transcription

1 Analysis of the high frequency components of Earth rotation demodulated from VLBI data Alesander Brzezińsi 1,2 and Sigrid Böhm 3 1) Warsaw University of Technology, Faculty of Geodesy and Cartography 2) Space Research Centre, Polish Academy of Sciences, Warsaw, Poland 3) Institute of Geodesy and Geophysics, Vienna University of Technology ale@cb.waw.pl Presented at Journées 211 Systèmes de Référence Spatio-Temporels Earth rotation, reference systems and celestial mechanics: Synergies of geodesy and astronomy September 211, Vienna, Austria

2 Introduction The problem In the recent wor Böhm, Brzezińsi and Schuh, submitted to J. Geodynamics, Special Issue on Earth Rotation we demonstrated the application of the complex demodulation technique to VLBI parameter estimation for determination of the high frequency signals in Earth rotation. It is expected that the diurnal and semidiurnal components of polar motion and UT1 contain the harmonic terms due to imperfections of the conventional model of the ocean tide influence less regular signals of atmospheric origin which are not included in the a priori models the terdiurnal and higher order terms do not contain any significant signal of geophysical origin Objectives of the presentation Here we present preliminary results of the analysis of the high frequency components of Earth rotation demodulated from VLBI data Brzezińsi and Böhm Journées 211, Vienna, September 211

3 Introduction Complex demodulation a method of extracting the high frequency signals from time series (Bingham et al., 1967) the output image of the high frequency signal is a low frequency, complex valued time series which is easy to handle in analysis the procedure preserves power spectrum of the original series while moving it only along the frequency axis in such a way that the demodulation frequency becomes zero first application for representation of diurnal and semidiurnal signals in VLBI observations of polar motion and UT1 was proposed by Herring and Dong (1994) applied by Brzezińsi (1994) to extract the retrograde diurnal component of the atmospheric excitation function with 6-hourly resolution extended on other high frequency components of geophysical excitation by e.g. Bizouard et al. (1998), Brzezińsi et al. (; ) recently, its features were used in an extended parametrization of polar motion and universal time which was implemented into a dedicated version of the Vienna VLBI Software VieVS Brzezińsi and Böhm Journées 211, Vienna, September 211

4 High frequency components of EOP demodulated from VLBI Alternative parameterisation of ERP as implemented in VieVS: demodulated time dependent amplitudes x y UT1 p p t t N x y N N 1 t t t sin t x y t t cos 1 t y x t t c s t u tcostu tsint cos y x sin t GMST Low frequency variations = (diurnal, semi-diurnal, ter-diurnal, quarter-diurnal band) Brzezińsi and Böhm Journées 211, Vienna, September 211

5 High frequency components of EOP demodulated from VLBI determine x p, y p, dut1 as a sum of x, y, x -2, y -2, x +1, y +1..., u c, u s, u c 1, u s 1,... only one value for each session Nutation parameters can(!) be estimated daily Fit tidal or other sub-diurnal terms to the amplitude time series, at the demodulated frequencies. E.g. Universal time diurnal band: UT1 n s c t cos U sin U cos i1 i i c u 1 t i i sin n i1 c U sin s Ui cos i u s 1 t i i Demodulated time variable amplitudes Brzezińsi and Böhm Journées 211, Vienna, September 211

6 c u 1 [µs] raw values 5 5 u 1 c [µs] smoothed values µs K1 cos (IERS) s u 1 [µs] raw values 5 5 u 1 s [µs] smoothed values µs K1 sin (IERS) time [yr] Raw and smoothed values of demodulated UT1 parameters u c 1 and u s 1. Cyan: series estimated including a priori high-frequency EOP models. Blac: series estimated without a priori high frequency EOP model. Brzezińsi and Böhm Journées 211, Vienna, September 211

7 PM from VLBI data demodulated at 3Ω PM from VLBI data demodulated at 4Ω PM from VLBI data demodulated at 1Ω 5 PM from VLBI data demodulated at 2Ω Demodulated high frequency components of retrograde polar motion with the a priori IERS models applied blac raw values, red smoothed values Brzezin si and Bo hm Journe es 211, Vienna, September 211

8 PM from VLBI data demodulated at +3Ω PM from VLBI data demodulated at +4Ω PM from VLBI data demodulated at +1Ω 5 PM from VLBI data demodulated at +2Ω Demodulated high frequency components of prograde polar motion with the a priori IERS models applied blac raw values, red smoothed Brzezin si and Bo hm Journe es 211, Vienna, September 211

9 UT1 from VLBI data demodulated at +3Ω UTsin and UTcos (µas) UTsin and UTcos (µas) UT1 from VLBI data demodulated at +4Ω UT1 from VLBI data demodulated at +1Ω 5 UTsin and UTcos (µas) UTsin and UTcos (µas) UT1 from VLBI data demodulated at +2Ω Demodulated high frequency components of UT1 with the a priori IERS models applied blac raw values, red smoothed Brzezin si and Bo hm Journe es 211, Vienna, September 211

10 Polar motion residual amplitude [µas] K1 S1 Q1 O1 P1 diurnal prograde zero terms semidiurnal prograde N2 M2 S2 Artz et al. (211) CD VieVS standard VieVS K2 zero terms semidiurnal retrograde N2 M2 S2 K2 zero terms Residuals of tidal polar motion amplitudes of CD VieVS, standard VieVS and Artz et al. (211) w.r.t. IERS21. The gray and blue dotted lines show the plain and threefold standard deviations belonging to CD VieVS. From (Böhm et al., 211, J. Geodynamics, submitted). Brzezińsi and Böhm Journées 211, Vienna, September 211

11 Universal time residual amplitude [µas] Q1 O1 S1 P1 diurnal K1 zero terms N2 Artz et al. (211) CD VieVS standard VieVS M2 S2 semidiurnal K2 zero terms Residuals of tidal UT1 amplitudes of CD VieVS, standard VieVS and Artz et al.(211) w.r.t. IERS21. The gray and blue dotted lines show the plain and threefold standard deviations belonging to CD VieVS. From (Böhm et al., 211, J. Geodynamics, submitted). Brzezińsi and Böhm Journées 211, Vienna, September 211

12 MEM PSD of PM demodulated at 1Ω MEM PSD of PM demodulated at 2Ω MEM PSD of PM demodulated at 3Ω MEM PSD of PM demodulated at 4Ω MEM PSD of PM demodulated at +1Ω MEM PSD of PM demodulated at +2Ω MEM PSD of PM demodulated at +3Ω MEM PSD of PM demodulated at +4Ω MEM PSD of UT1 demodulated at +1Ω MEM PSD of UT1 demodulated at +2Ω MEM PSD of UT1 demodulated at +3Ω MEM PSD of UT1 demodulated at +4Ω Maximum entropy power spectra of demodulated high frequency components of Earth rotation, blac with the a priori IERS models applied, red after additional removal of the residual tidal terms Brzezińsi and Böhm Journées 211, Vienna, September 211

13 Summary and conclusions The high frequency components of polar motion and UT1 (diurnal, semidiurnal, terdiurnal and quarterdiurnal) have been demodulated from VLBI data using the modified software VieVS. Our analysis shows demodulated data prior 199 is too noisy therefore should be not used for the time domain analysis and geophysical interpretation residual amplitudes of the tidal terms in diurnal and semidiurnal bands reach the level of 2 µas with the standard deviation of about 1.5 µas spectral analysis of the terdiurnal and quarterdiurnal terms does not reveal any sharp spectral line Next steps comparison of the residual S 1 and S 2 amplitudes to the nontidal atmospheric and oceanic contributions estimated from AAM/OAM data time domain comparison of the demodulated series with the residual tidal terms removed to the corresponding components demodulated from AAM/OAM data Brzezińsi and Böhm Journées 211, Vienna, September 211