Optical Erasure and Reconfiguration of Surface‐Relief‐Gratings of Azo Polymer and Azo Molecular Glass: A Comparative Study on Soft‐Lithographic Duplicates

Surface‐relief‐gratings (SRGs) of azo polymers and azo molecular glasses have attracted considerable interest for their erasable and reconfigurable characteristics. Herein, the optical erasure of soft‐lithographically duplicated SRGs of an azo polymer (BP‐AZ‐CN) and an azo molecular glass (IAC‐4) is investigated to tackle a long‐standing problem from “memory” effect existing in optically inscribed SRGs. The optical erasure is performed by single laser beam irradiation at wavelength of 488 nm with different polarizations, and the erasing behavior is thoroughly investigated by real‐time diffraction efficiency measurement and atomic force microscopy (AFM) observation. Showing no obvious dependence on the light polarizations, the optical erasure of IAC‐4 grating is a relatively fast process, and the original one can be completely erased and recreated. In contrast, the erasure of BP‐AZ‐CN grating is not only much slower, but also strongly correlated with the light polarizations. Upon the p‐polarized light irradiation, the grating profiles are substantially distorted during the erasure with a significant difference in that of the s‐polarized light irradiation. The gratings cannot be completely erased by the lights with all the polarizations. The erasure behavior is found to be determined by the effects of surface tension and mass transfer along the light polarization direction to different extents

Timing performance evaluation of Radio Determination Satellite Service (RDSS) for Beidou system

Radio Determination Satellite Service (RDSS) is the advantage and particular characteristics of Beidou, which is different from other satellite navigation systems. According to the rare existing researches of its timing service, this article evaluates timing performance of one-way and two-way using the time series analysis method. Moreover, this paper systematically studies the one-way timing and two-way timing principle and introduces Beidou measured data and analysis method. By analyzing the clock error total curve, the mean value segment, noise situation and timing accuracy, we have the conclusions: (1) one-way timing accuracy is less than 30 ns, and its Root Mean Square (RMS) is less than 6.81 ns; (2) two-way timing accuracy is less than 20 ns, and its Root Mean Square (RMS) is less than 3.60 ns; (3) there exist period switching phenomenon of timing data of one-way and two-way in each beam, and stratification of one-way timing data. These conclusions can be used for the difference compensation of Radio Determination Satellite Service (RDSS), which can provide reference for the clock error consistency of Beidou system, and then improve the system service precision

Seismic Impact of Large Earthquakes on Estimating Global Mean Ocean Mass Change from GRACE

We analyze the impact of large earthquakes on the estimation of the global mean ocean mass (GMOM) change rate over the 13-year period (January 2003 to December 2015) using the Gravity Recovery and Climate Experiment (GRACE) Release-06 (RL06) monthly gravity solutions released by the Center for Space Research (CSR). We take into account the effects of the December 2004 Mw9.1 and April 2012 Mw8.6 Sumatra earthquakes, the March 2011 Mw9.0 Tohoku-Oki earthquake, and the February 2010 Mw8.8 Chile earthquake. After removing the co- and post-seismic effects of these earthquakes in the oceanic areas by least squares fitting, we estimate the GMOM rate from GRACE monthly observations. Results show that GRACE-observed GMOM rate before the seismic correction is 2.12 ± 0.30 mm/year, while after correction the rate is 2.05 ± 0.30 mm/year. Even though the −0.07 ± 0.02 mm/year seismic influence on GRACE GMOM rate is small on a global scale, it is a systematic bias and should be considered for improved quantification and understanding of the global sea level change

Geophysical interpretation of GPS loading deformation over western Europe using GRACE measurements

We analyze more than 10 years of Global Positioning System (GPS) height residuals and vertical displacements predicted from surface mass loading observed by the Gravity Recovery and Climate Experiment (GRACE) for 36 International GNSS Service (IGS) stations over Europe. Seasonal surface displacements, mostly due to atmospheric and hydrological loading, are significant in both GPS and GRACE measurements. With an extended time period, our new analysis based on release 05 GRACE data from Center for Space Research (CSR) shows considerably improved agreement between GPS and GRACE than that from previous studies, for not only annual but also interannual signals. The GPS height residual series at most stations exhibit reduced weighted root-mean-squares (WRMS) after removing GRACE-derived vertical displacements, which is attributed to improved accuracy of both GPS and GRACE data products. Furthermore, we demonstrate the necessity of reducing leakage bias in GRACE estimates for the study of surface loading deformation using GRACE satellite gravity observations