The atmospheric excess path delay is a major contributor to the error budget of space geodetic applications and should therefore be reduced to the maximum possible extent. Numerical weather models are undergoing improvements with regard to their spatial resolution, which enables compensation of troposphere propagation errors by applying corrections obtained from ray-tracing through three-dimensional meteorologic fields. Such correction can be applied utilized for GNSS positioning, removal of troposphere artifacts in InSAR images or even help to improve Earth orientation parameters determined from VLBI measurements.

View full abstract

 On 13th August 1986, The Japanese geodetic satellite, “AJISAI” (Hydrangea-1986-061A) was launched into orbit by Japan’s first experimental rocket, H-I. The satellite has functioned well for 25 years despite the fact that its spin rate has slowed. The satellite is made of GFRP (Glass Fiber Reinforced Plastic) spherical body. The surface is covered with 120 laser retroreflector assemblages (cube corner reflectors, 1,436 ea) for distance survey, and 318 pieces of mirrors (solar light reflectors) for angled survey of the observation site. The mesurements are: mass 685.2 kg, 2.15 m in diameter, orbital altitude 1,500 km, orbital inclination 50 deg. The spin rate originally started at 40 rpm and gradually slowed to its present rate of 28 rpm.
 Initially, JAXA (formaly NASDA) received the proposal of the satellite plan from GSI (GeoSpatial Information Authority of Japan) and JCG (Japan Coast Guard) to launch a balloon shaped satellite in the 1970s, and began to do an experimentation study on the project. However, in 1980, a solid type satellite was decided on instead of the balloon type, which significantly lower the cost of the entire project.
 While GSI is observing “AJISAI” by means of an optical telescope to analyze the spin, JCG is using SLR (Satellite Laser Ranging) system, as well as the telescope for marine geodesy. Today, NICT (National Institute of Information and Communications Technology), JAXA and SLR-Stations around the world survey earth with “AJISAI” as many times as 10,000 passes in the year 2010 alone.
 This article describes the history of the project, the performance of the satellite, and its great contribution to the study of earth.

View full abstract

  A new method for smoothing tide gauge data is proposed to monitor temporal changes of mean sea level combined with vertical land motion at the tidal stations. The method consists of two stages of processing. First, ocean tides and oceanic response to atmospheric pressure are estimated and removed from hourly measurements of tidal heights and atmospheric pressure. Daily averages taken from the hourly values so processed are used afterward. In the second stage time series of the daily averages are analyzed with the semi-discrete wavelet transform and the coherent fluctuation components between the time series at a pair of adjacent tidal stations, which are common to one another due to seasonal steric changes and oceanic currents, etc., are removed respectively from the time series, yielding time series of smoothed mean tidal heights. The method is applied to data obtained at four tidal stations around Tokyo Bay and the results demonstrate its effectiveness in smoothing superior to previous approaches. Combined with crustal land motion derived from GPS continuous observation, the time series of smoothed mean tidal heights reveals temporally linear change in mean sea level, the rate of which is consistent with that estimated from satellite altimetry measurements.

View full abstract