第２０回宇治固体地球コロキウムを以下のとおり開催します。
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-------------- 第２０回 宇治固体地球コロキウム -------------

日程：　３月１５日（金）
時間：　午後４時半〜６時
会場：　ZoomによるOnline

講演者：　徐 培亮
Title：　高周波GNSS PPPから計算型加速度センサーの技術発明まで
　　　　From High-rate GNSS to the Technological Invention of Computerized Accelerometers
要旨：
This talk will consist of two parts. Part I will briefly report our effort of high-rate GNSS research, both theoretically and experimentally, in the past 10 years or so to demonstrate that very high-rate GNSS PPP can measure positions and displacements at the precision of mm-level within a few minutes, though PPP has been almost always reported in the GNSS literature to be of only cm-level. Our findings are clearly attributed to profound differences between PPP short- (up to a few minutes) and long-term performances (up to hours and days). PPP short-term performance is essential for applications in many areas of science and engineering, which is not only datum-free (irrelevant to any fixed/reference GNSS station) in one hand but also is able to provide precise displacements, for example, in the case of large and mega-earthquakes, in particular, those close to the epicenter. We will first explain why very high-rate GNSS can achieve mm-level precision theoretically and then make experiments to confirm and validate the theoretical development. We then apply very high-rate GNSS to the 2011 Tohoku Mw9.0 earthquake and demonstrate that it is feasible to use PPP to study rotational motions due to large and mega-earthquakes. In Part II, we will talk about the road for us to technologically invent computerized accelerometers. Although difference methods are always used to determine velocity and acceleration from GNSS precise positioning. We demonstrate that they are approximately valid on the implicit assumption of a low sampling rate of GNSS measurements and tend to lead to physically meaningless results of velocity and acceleration with the increase of sampling rates. The reason is that the random errors of GNSS-based velocity and acceleration are proportional to the sampling rate in the case of velocity or square-proportional to the sampling rate in the case of acceleration. Bearing in mind that a high sampling rate of PPP becomes routinely available, nowadays and in the future, it is extremely important to meet this challenge in the GNSS determination of velocity and acceleration. More precisely, we are faced with a number of critical technological problems in GNSS accelerometry: (i) with the increase of sampling rate, measurement errors are significantly amplified such that computed velocity and acceleration are completely immersed into noise and of no physical significance; (ii) down-sampling very high-rate GNSS precise positioning measurements directly results in a lower resolution of velocity and acceleration, a larger aliasing effect and signal distortion, the extent of which depend on that specific rate of sampling; and (iii) a low sampling rate also implies impossibility to provide instantaneous velocity and acceleration. Therefore, we present a regularization method to compute velocity and acceleration and its apparatus and apply it to the 2013 Lushan Mw7.0 earthquake. More surprisingly, the solution to these critical technological problems finally leads us to a technological invention of computerized accelerometers patented in Japan and China.