High-precision position records that keep positioning uninterrupted during disasters! How the Quasi-Zenith Satellite supports them

When large-scale disasters such as earthquakes or heavy rains occur, communication infrastructure outages and power failures can make it difficult to grasp location information. However, accurate understanding of the affected conditions and rapid formulation of recovery plans require on-site high-precision position records. At the center of attention is Japan’s Quasi-Zenith Satellite System (QZSS, "Michibiki"). Quasi-zenith satellites provide a powerful means to maintain positioning even when communications are cut and to record positions with centimeter-level accuracy (half-inch accuracy). This article explains what quasi-zenith satellites are, how they help during disasters, and their mechanisms and practical on-site uses in detail. Aimed at municipal employees, surveyors, and disaster management personnel, we present the latest on high-precision positioning that is useful in disaster response and points for use in normal times.

What is a quasi-zenith satellite, and why is it strong in disasters?

The Quasi-Zenith Satellite System (English name: QZSS, nickname: Michibiki) is a satellite positioning system operated independently by Japan. Its greatest feature is the adoption of a special orbit called the “quasi-zenith.” The satellites are designed to remain almost directly overhead of Japan (near the zenith) for long periods, making it easier to receive signals at high elevation angles even in mountainous areas or among tall buildings. As a result, Michibiki’s presence overhead stabilizes positioning in locations where conventional GPS alone had difficulty acquiring satellites. Currently, four satellites cover all of Japan, and the system is planned to expand to seven satellites in the future (Michibiki is expected to enable standalone positioning around 2025). By complementing and strengthening GPS, this mechanism dramatically improves positioning errors that were normally several meters (several ft) to, under the right conditions, several centimeters (a few in). In this way, the Quasi-Zenith Satellite System, which can always secure a satellite almost directly over Japan, exerts great power in disasters. For example, even immediately after an earthquake causes terrain changes, Michibiki’s overhead presence ensures the required number of satellites is available, and positioning is less likely to be interrupted even if aftershocks change the surrounding environment. Designed specifically for Japan, Michibiki provides a foundation that dramatically increases the availability of positioning in emergencies.

CLAS: Satellite corrections that enable high-precision positioning even under communication outages

Normally, achieving centimeter-level accuracy requires RTK positioning, which corrects GNSS errors using a nearby reference station. However, RTK requires continuous transmission of correction information from a base station, so high-precision positioning cannot be achieved where base stations are not available. Traditionally, users either set up their own local base stations that transmit corrections wirelessly on-site or obtained correction data via the internet from national or private reference station networks (GNSS continuously operating reference stations or VRS services). In large-scale disasters, however, these communication infrastructures can be severed, and real-time precision positioning has been impossible in practice.

To solve this problem, Michibiki offers the Centimeter-Level Augmentation Service (CLAS). CLAS distributes high-precision correction information from the quasi-zenith satellites across Japan; users with compatible receivers can receive this correction signal (L6 band) directly from the satellites and apply it to their positioning to obtain centimeter-level accuracy (half-inch accuracy) in real time. Simply put, it is a “satellite-broadcast RTK correction,” delivering data from the government-maintained network of reference stations from above. This groundbreaking service removes the need for users to prepare their own base stations and also makes communication lines for obtaining corrections unnecessary. Imagine correction data raining down directly from the overhead Michibiki satellites: even if mobile phone signals are out of range, high-precision positioning can continue. In fact, during the 2023 Noto Peninsula earthquake, CLAS-capable positioning devices proved highly effective for field surveying in affected areas where mobile communications were cut off. Michibiki CLAS provides an accessible high-precision positioning infrastructure that can be used by anyone, anywhere as an emergency backup.

Note that CLAS requires a compatible GNSS receiver; typical smartphone GPS chips cannot receive the L6 signal. However, in recent years small CLAS-capable receivers that can pair with smartphones have become available from various manufacturers, making it possible to introduce centimeter-level positioning on-site without expensive fixed equipment.

Comparison with traditional RTK: Strengths of a self-contained positioning system

The main differences between traditional communication-dependent RTK (which requires base stations or mobile networks) and self-contained positioning using QZSS CLAS are as follows:

• Dependence on communication infrastructure: Traditional RTK requires internet connectivity or radio communication, whereas CLAS receives correction information directly from satellites, eliminating the need for communication lines. Positioning is possible in mountainous areas or during communication outages.

• Need for a base station: Traditional RTK requires the user to set up a reference station or use an external reference station service. With CLAS, users do not need to prepare a base station; the receiver alone is sufficient.

• Positioning range: Local RTK accuracy degrades as the distance from the base station increases, but CLAS provides nearly uniform accuracy across Japan. High precision is available even on remote islands or offshore.

• Cost: Networked RTK services may incur monthly service fees from private providers, whereas CLAS is provided as a public service free of charge, eliminating usage fees. This lowers the cost of expensive equipment purchases and running costs, making adoption easier for small municipalities and companies.

• Resilience in disasters: If base stations are damaged or communications are severed in a large-scale disaster, traditional RTK becomes nonfunctional. In contrast, CLAS-capable devices can receive correction signals independently as long as the satellite is visible, maintaining centimeter-level positioning from immediately after the disaster. This self-contained capability is the greatest strength for keeping positioning from being "interrupted" during disasters.

What location records are required at disaster sites: capturing "where, when, and how much"

In large-scale disaster response, the first challenge is to accurately record "where and what happened." If the locations of road breaks, landslide initiation points, and inundation areas are not correctly identified, it is difficult to prioritize rescue and recovery. Equally important is information on "when it occurred and how extensive it was." Even for the same landslide, whether it occurred immediately at the time of the event or expanded due to subsequent rain, and how much soil moved, changes the measures to be taken and the materials required. To grasp these on-site, it is essential to reliably record location, time, and scale data together.

Conventionally, field teams marked damaged spots on paper maps or jotted location notes by hand on photos. In chaotic situations, such methods are prone to omissions and mistaken locations, causing confusion during later aggregation. If high-precision location records are saved as digital data, human errors can be greatly reduced and decisions can be made based on reliable information.

Moreover, multiple teams and agencies operate simultaneously during disaster response. Keeping a location history of "who was where" makes it immediately clear which areas have been surveyed by whom, preventing missed areas or duplicate surveys. Even amid the chaos immediately after a disaster, when each person records and shares high-precision location data, everyone can rely on a common map to understand the situation. Location records are not mere notes; they are fundamental data that support decision-making in disaster response.

Using high-precision positioning at evacuation centers, emergency hubs, and damage sites

High-precision positioning is useful in all areas of an affected region. For example, when evacuation centers or temporary emergency hubs are established, measuring and recording their exact positions provides a reliable basis for planning evacuation support routes and supply transportation on maps. Even if address signs or road markings are lost to damage, coordinates from satellite positioning allow rescue teams and support teams from other regions to find locations accurately. Disaster response requires action based on objective location data rather than guesswork or hearsay, so correctly sharing the positions of evacuation centers and command posts is extremely important.

On damaged sites, high-precision positioning is powerful for situational awareness and information sharing. Measuring the positions of collapsed buildings, the sections of severed roads, or the extents of collapsed slopes with CLAS-capable devices yields accurate coordinate-stamped records on the spot. Measurement results can be saved as digital data together with photos and notes, so it remains clear later which point the data refers to. Sharing this data with stakeholders allows remote headquarters to intuitively grasp damage on a map. For example, if photos taken at the disaster site have high-precision latitude and longitude and camera orientation tagged, headquarters can precisely understand "which direction the photo was taken," preventing reporting omissions and misunderstandings. Even when multiple teams divide up surveys of damaged points, integrating all positioning data on a map allows rapid grasp of the overall damage and distribution. By measuring on-site and immediately sharing, the speed and accuracy of disaster response improve dramatically. Even if communication means cannot be secured at the site, recorded data can be uploaded later from a place with connectivity. Information accumulated by satellite positioning does not lose accuracy over time, giving the reassurance that data can be organized and transmitted calmly after leaving the site.

LRTK: Simple positioning, recording, AR, and sharing anyone can do

LRTK is a compact high-precision GNSS receiver that can be attached to smartphones or tablets. Attach it to the back of a smartphone and launch the dedicated app, and centimeter-level positioning (half-inch accuracy) can start immediately on-site. No special settings or expertise are required; it is designed so anyone can operate it with intuitive controls. Because LRTK supports the CLAS service mentioned earlier, it can perform high-precision positioning independently even outside mobile coverage. The small device weighs only a few hundred grams and can fit in a pocket, enabling easy smartphone surveying.

This smartphone plus quasi-zenith satellite positioning combination allows tasks that previously required experienced surveyors to be performed by anyone on-site. For example, attaching a smartphone to a telescoping monopod allows one person to measure ground elevation or measure coordinates at a distance from a safe location. This reduces the need for many people to enter dangerous disaster sites, enabling one person to safely and quickly perform surveying and recording. LRTK apps also include an AR (augmented reality) display feature that overlays design drawings or pre-prepared 3D models on the site view. For example, in restoring a collapsed revetment, an AR-projected design model can be compared on-site with current conditions to check deviations. Being able to visually compare the “intended position” and the “current position” on the spot helps prevent mistakes and supports quality control.

Furthermore, the LRTK system can integrate with the cloud to instantly share positioning data and photos. Measured points and high-precision photos can be uploaded to the cloud for team-wide viewing. This allows the field and headquarters to synchronize the latest information and collaborate efficiently. By using LRTK as described, anyone can easily perform the series of processes to “measure,” “record,” and “communicate” at disaster sites, strongly supporting everything from initial response to recovery work.

Examples of use by disaster response phase (from initial response to recovery)

• Initial response (immediately after the disaster): In the early stages after an event, life-saving and damage assessment are top priorities. Using LRTK, a minimal number of people can enter hazardous sites affected by aftershocks or bad weather and measure damage with high precision. You can immediately assess the scale of a collapsed slope with point-cloud scans to estimate the number of heavy machines needed, or measure the length and position of severed roads to consider candidate emergency routes—collecting vital decision-making information quickly during the time-critical initial phase. Because positioning data can be recorded without communication infrastructure, teams can reliably bring back on-site information from mountainous areas or isolated communities.

• Temporary recovery phase: When temporary repairs and recovery work begin to prevent further damage, high-precision positioning is effective for provisional construction and secondary disaster prevention measures. For instance, when constructing a temporary detour road, LRTK can measure terrain on-site to formulate the optimal route. When placing sandbags or provisional reinforcement on a collapsed revetment, on-site measurement can confirm whether the required height and thickness are being maintained. Sharing measured data to the cloud during work allows experts at headquarters to advise, enabling high-quality temporary response even with limited personnel.

• Full recovery and reconstruction phase: During full-scale recovery work and reconstruction, precise surveying and feedback into design are indispensable to restore infrastructure and buildings to pre-disaster conditions. LRTK allows rapid re-surveying of lost control points and fast surveying for new design references. During construction, the actual shape of completed works can be measured to check deviations from design drawings, and AR can overlay design models on-site to check construction accuracy in real time—useful for quality control. All such data are saved in time series, aiding post-recovery verification and report preparation. High-precision positioning tools support the site through the final stages of reconstruction.

Use and preparedness in normal times

High-precision positioning tools that are powerful in disasters achieve their true effectiveness when used in normal times. Regularly practicing smartphone surveying and operating CLAS-capable devices will ensure smooth operation on-site when needed. Fortunately, these high-precision positioning technologies are useful not only in disaster response but also in everyday surveying and inspection tasks. For example, you can record dimensions and displacements during regular road and river inspections or use smartphone surveying for as-built verification in small-scale construction to improve efficiency and digitization. Such initiatives are attracting attention as part of disaster prevention DX (digital transformation).

Moreover, if important infrastructure and terrain are measured and recorded with high precision in advance, comparing “before and after” after a disaster enables quantitative damage assessment. For example, if the heights of levees or bridge piers are checked in advance, you can immediately determine how much subsidence or deformation occurred after an earthquake or flood. Pre-event data accumulation thus helps prevent overlooking damaged locations and supports rapid recovery planning.

In practice, progressive municipalities such as Fukui City have introduced high-precision positioning systems using smartphones in the disaster prevention field, achieving faster initial response and reduced surveying costs. Some municipalities have adopted LRTK for routine maintenance tasks so that staff become familiar with high-precision positioning. National disaster management agencies are also paying attention to smartphone-based positioning technologies, and case studies of their use at disaster sites are being introduced in publications from the Ministry of Internal Affairs and Communications and the Ministry of Land, Infrastructure, Transport and Tourism. In light of this trend, establishing a system in normal times so that “anyone can measure” is becoming important as organizational preparedness. High-precision positioning tools are not special devices but should be established as tools that extend naturally from everyday work, which becomes a strength in times of need.

Conclusion

The high-precision positioning infrastructure provided by the Quasi-Zenith Satellite "Michibiki" and technologies such as LRTK that put it to practical use on-site are greatly advancing information collection and recovery in disasters. Securing an environment where “positioning is not interrupted” becomes the foundation that supports decision-making across all phases, from damage assessment to quality control of recovery work. Moreover, Michibiki is scheduled to be strengthened to a seven-satellite system and to see enhancements to the CLAS service, so positioning accuracy and reliability are expected to further improve. With technological progress, it will be possible to gain a greater sense of security that “positioning will never be interrupted” in a wider range of situations in the future.

By utilizing these technologies in normal times and advancing human resource development and system preparedness, organizations should be able to respond calmly in emergencies. Please consider taking this opportunity to explore the introduction of smart positioning that leverages the Quasi-Zenith Satellite. It could be the first step in preparing for future disasters.