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Tuesday, February 17, 2009
Sunday, February 08, 2009
Notebook wireless switch failure.
I found I cannot switch on the wireless radio today. It turns out to be the result of accidentally deleting of HP Wireless Assistant software (which I though useless) several days ago. Furthermore, I found that the hardware switch on the keyboard should be first turned on, then one could turn on/off the wireless in HP Wireless Assistant. Thus, it's a good idea to always keep the hardware radio switch on and use the software switch to enable or disable the wireless signal.
Is Tibet Plateau uplifting?
According to one newest published paper in GRL, the Tibet Plateau is uplifting with a rate of about 1.14 mm/yr.
"4. GPS Data Reveal Uplift of the Tibetan Plateau
[7] We use GPS data at the three stations to obtain the vertical displacement rate. Since the early 1990s, several GPS networks for tectonic studies have been established in China and neighboring regions [Wang et al., 2001]. Especially, 25 permanent GPS stations have been established and continuous observations have been made to the present day [Gan et al., 2007] The Lhasa, Kunming, and Dali stations belong to parts of the permanent network; high-quality data are obtained. Here we use GIPSY software to reduce phase and pseudorange data into a site position. The GPS data collected at ca. 20 IGS stations throughout Asia and 18 continuous sites within China are organized into discrete 24 h segments and are processed simultaneously to yield a daily network solution. The precise satellite orbit and clock are fixed to the non-fiducial products provided by the JPL. We solve for 3D coordinates, clock biases, and atmospheric refraction per site with loose constraints. Phase ambiguities are also estimated, but no ambiguity resolution was done (phase ambiguities are estimated as real number and not fixed to integers). We apply azimuth and elevation-dependent antenna phase center models, following the tables recommended by the IGS. We select a subset of IGS sites with a longer time span for definition of reference frame, and rotate the loosely constrained daily solutions onto the ITRF2000 by seven-parameter similarity transformation. We then obtain a time series of vertical components of each site. The time series is then fit in a weighted least-squares sense to a linear function that includes the initial coordinate plus the secular motion rate. Furthermore, assuming a time series characterized by a white noise process, we derive a post-fit RMS of 1.1–1.5 mm for the vertical component of site position and standard deviation of <0.1 mm/yr (1 sigma) for the vertical rate. The rate uncertainty might be overoptimistic because of neglect of the time-correlated noise inherited in the geodetic time series. The rate error might be underestimated by a factor of 5–11 if a pure white noise model is assumed for the coordinate time series [Mao et al., 1999]. Zhang et al. [1997] found that the rate uncertainty might be 2–4 time larger than that for fractional white noise and 3–6 for white plus flicker noises. We adopt a moderate scale factor of five because the time-correlation noise averaged down gradually over time. Multiplying the standard deviation of 0.1 mm/yr by five engenders the rate uncertainty of ca. 0.5 mm/yr, which is comparable with vertical rate precision of 0.4–0.6 mm/yr assigned by Prawirodirdjo and Bock [2004] and Calais et al. [2006]. Finally, we obtain the aggregate station coordinates of the three stations and plot them in Figure 2 (right). Results show that all three stations exhibit positive displacements vertically, implying that the Tibetan Plateau is continuing its uplift. The uplift rates are, respectively, +0.8 ± 0.5, +2.3 ± 0.5 and +0.5 ± 0.5 mm/yr for Lhasa, Kunming, and Dali. Such a mean vertical displacement rate of 1.2 mm/yr agrees well with the conclusion (1.14 mm/yr) obtained on a geological scale [Rowley and Currie, 2006]."
Is this really the case?
"4. GPS Data Reveal Uplift of the Tibetan Plateau
[7] We use GPS data at the three stations to obtain the vertical displacement rate. Since the early 1990s, several GPS networks for tectonic studies have been established in China and neighboring regions [Wang et al., 2001]. Especially, 25 permanent GPS stations have been established and continuous observations have been made to the present day [Gan et al., 2007] The Lhasa, Kunming, and Dali stations belong to parts of the permanent network; high-quality data are obtained. Here we use GIPSY software to reduce phase and pseudorange data into a site position. The GPS data collected at ca. 20 IGS stations throughout Asia and 18 continuous sites within China are organized into discrete 24 h segments and are processed simultaneously to yield a daily network solution. The precise satellite orbit and clock are fixed to the non-fiducial products provided by the JPL. We solve for 3D coordinates, clock biases, and atmospheric refraction per site with loose constraints. Phase ambiguities are also estimated, but no ambiguity resolution was done (phase ambiguities are estimated as real number and not fixed to integers). We apply azimuth and elevation-dependent antenna phase center models, following the tables recommended by the IGS. We select a subset of IGS sites with a longer time span for definition of reference frame, and rotate the loosely constrained daily solutions onto the ITRF2000 by seven-parameter similarity transformation. We then obtain a time series of vertical components of each site. The time series is then fit in a weighted least-squares sense to a linear function that includes the initial coordinate plus the secular motion rate. Furthermore, assuming a time series characterized by a white noise process, we derive a post-fit RMS of 1.1–1.5 mm for the vertical component of site position and standard deviation of <0.1 mm/yr (1 sigma) for the vertical rate. The rate uncertainty might be overoptimistic because of neglect of the time-correlated noise inherited in the geodetic time series. The rate error might be underestimated by a factor of 5–11 if a pure white noise model is assumed for the coordinate time series [Mao et al., 1999]. Zhang et al. [1997] found that the rate uncertainty might be 2–4 time larger than that for fractional white noise and 3–6 for white plus flicker noises. We adopt a moderate scale factor of five because the time-correlation noise averaged down gradually over time. Multiplying the standard deviation of 0.1 mm/yr by five engenders the rate uncertainty of ca. 0.5 mm/yr, which is comparable with vertical rate precision of 0.4–0.6 mm/yr assigned by Prawirodirdjo and Bock [2004] and Calais et al. [2006]. Finally, we obtain the aggregate station coordinates of the three stations and plot them in Figure 2 (right). Results show that all three stations exhibit positive displacements vertically, implying that the Tibetan Plateau is continuing its uplift. The uplift rates are, respectively, +0.8 ± 0.5, +2.3 ± 0.5 and +0.5 ± 0.5 mm/yr for Lhasa, Kunming, and Dali. Such a mean vertical displacement rate of 1.2 mm/yr agrees well with the conclusion (1.14 mm/yr) obtained on a geological scale [Rowley and Currie, 2006]."
Is this really the case?
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