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The Observation Network Created by the Earthquake Proves Useful for Accurate Timekeeping (Part One of Two)

On a visit to Furuno Electric's headquarters in Nishinomiya City, Hyogo Prefecture, I took a slight detour to walk along the banks of the Mukogawa River. The river, which flows between Nishinomiya and Amagasaki down to Osaka Bay, offered a perfect walking course with groups of ducks leisurely floating on the water and thoughtful herons standing still. However, my purpose for the detour was not a stroll but a visit to the "electronic reference point" (electronic control point) located on an elementary school playground, just across the road from the riverbank.

For those unfamiliar with the term, let me explain a bit about the "electronic reference point."

Though named a "point," its actual form is a reasonably large metal pillar, typically about 5 meters tall and built on public land, such as school grounds or gymnasium parking lots. The top is covered with a white plastic dome, housing a GNSS antenna. Inside the pillar are GNSS receivers, communication devices, batteries, and other electronic equipment, though these are not visible from the outside. The only indications of its existence are a commercial power line and the sound of a cooling fan in the summer. A utility pole connected to the power line has a panel marked "Geospatial Information Authority of Japan," identifying the equipment manager.

The Geospatial Information Authority of Japan has installed approximately 1,300 of these electronic reference points across the country. The term "electronic reference point" is derived from the electronic engineering method of receiving and analyzing positioning signals from satellites, similar to triangulation points and benchmarks used in maps and surveys. The more common term is "GNSS Continuous Observation Points," and in English, it is known as CORS (Continuous Observational Reference Station), emphasizing its status as a permanent observation facility.
In Japan, full-scale development of the electronic reference point network began in 1993 with a national budget allocation. In December of that year, the United States declared the start of initial GPS operations, having completed the deployment of 26 satellites in orbit. The concept of the electronic reference point, paired with pioneering positioning satellites like GPS, thus has a long-standing history.

In October 1994, the electronic reference point network began operating at 210 points nationwide. The network was divided into two systems with different purposes. Of the 210 points, 110 were concentrated in the South Kanto and Tokai regions to observe crustal movements, while the remaining 100 points were uniformly distributed nationwide at intervals of about 120 km for surveying purposes. An unforeseen opportunity to prove the robust and useful capabilities of these electronic reference points arrived soon after.
It was the Great Hanshin-Awaji Earthquake that occurred on January 17, 1995.

Proving its usefulness as a surveying standard

Furthermore, the Great Hanshin-Awaji Earthquake provided an opportunity for experts to recognize the importance of surveying standards. The restoration and reconstruction required extensive construction work, including civil engineering to prepare the land for building foundations. Surveying the land's shape and elevation is essential before civil engineering, necessitating reliable reference points for accurate coordinates. However, due to the seismic shifts, the coordinates of previously used triangulation points and benchmarks became uncertain. Therefore, eight temporary electronic reference points were established in the affected areas to serve as reliable new benchmarks. According to the documentation, "Using electronic reference points as known points allows GPS surveying to be conducted directly on new points (unknown points), significantly improving efficiency and reducing labor." The observation data from these eight temporary electronic reference points were distributed via computer communication and utilized in practical surveying.

The initially two networks were integrated into GEONET (GPS Earth Observation Network System), and its expansion has led to approximately 1,300 points being operational nationwide. Each electronic reference point is assigned a station number, with the first two digits representing the last two digits of the installation year. The "95" electronic reference points, initiated as a result of this earthquake, number 402 out of about 1,300, including "Nishinomiya" (950355), mentioned at the beginning of the article.