Ryuichi Ichikawa

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Precise satellite orbits and clock information for global navigation satellite systems (GNSS) allow zero-difference position solutions, also known as precise point positioning (PPP) to be calculated. In recent years numerical weather models (NWM) have undergone an improvement of spatial and temporal resolution. This makes them not only useful for the(More)
Numerical weather models offer the possibility to compute corrections for a variety of space geodetic applications , including remote sensing techniques like interfer-ometric SAR. Due to the computational complexity, exact ray-tracing is avoided in many cases and mapping approaches are applied to transform vertically integrated delay corrections into slant(More)
—The computation of ray-traced troposphere delays which can be utilized for space geodetic applications is a time-consuming effort when a large number of rays has to be calculated. On the other hand, computation time can be tremendously reduced when algorithms are capable of supporting parallel processing architectures. Thus, by the use of an off-the-shelf(More)
At NICT, Japan, research and developments for the time and frequency standards are performed by the Space-Time Standards Group. The objectives of this group are to establish standards and reference of space and time as the fundamental basis for various fields of activities in science, engineering, and social activities, and to provide easy access to these(More)
Communications Research Laboratory has established four space geodetic observation sites in and around Tokyo, Japan under the Key Stone Project. At each of the four sites, an 11-m antenna VLBI system, a 75-cm telescope SLR system, and a geodetic GPS receiver are collocated closely. Site coordinates of the four VLBI stations have been connected to the ITRF96(More)
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