Quickly Locate Benchmarks Buried in Snow – Coordinate Guidance Technology Useful Immediately After Disasters

Table of contents

• Benchmarks indispensable for disaster recovery

• Challenges posed by benchmarks buried in snow

• Traditional search methods and their limits

• What is coordinate guidance technology?

• Rapid benchmark search using high-precision GNSS

• Benefits of coordinate guidance technology

• Simple surveying with LRTK

• FAQ

Immediately after a disaster, benchmarks for accurate surveying are the lifeline of recovery work. However, in addition to ground deformation caused by heavy rain or earthquakes, when benchmarks are buried in snow by heavy snowfall or avalanches and become invisible, conventional methods can take time to locate them, potentially delaying recovery. This article focuses on the challenge of searching for benchmarks that are buried and invisible in snow, and explains how the latest coordinate guidance technology can speed up the process. Finally, we touch on simple surveying using a new surveying solution called LRTK and introduce how these technologies can be used immediately after a disaster.

Benchmarks indispensable for disaster recovery

When large-scale disasters such as earthquakes, heavy rain, or landslides occur, roads and structures are damaged and terrain deforms across wide areas. To carry out recovery work smoothly, it is necessary to accurately grasp the positions of terrain and structures before and after the disaster. The reference for this is the benchmark (a known point that serves as a surveying starting point). Using the benchmark’s coordinate values as a reference makes it possible to accurately measure the position and elevation of damaged areas and to use that information for recovery planning and damage reports.

For example, at a site where a cliff collapse has occurred, it is necessary to re-survey the slope terrain in order to calculate the volume of displaced soil. Likewise, when bridges or roads have shifted or subsided, accurate survey data are required for comparison with pre-disaster drawings. These surveying tasks are founded on the on-site benchmarks. If the benchmarks are solid, the post-disaster situation can be recorded precisely, and planning and progress management of recovery work proceed smoothly. Conversely, if benchmarks are unclear, surveying and restoration design at the site can incur errors, causing rework in later stages. Note that for large-scale disasters, damage reports may be required within a few weeks of occurrence, so delays in initial response due to absent benchmarks can be critical.

Challenges posed by benchmarks buried in snow

Imagine a large-scale landslide occurring in a mountainous area in the middle of winter. The entire site is covered by thick snow, and survey stakes or reference stones that are normally visible cannot be seen at all. Under such heavy snowfall conditions, benchmark markers become buried and visual confirmation becomes difficult. In fact, immediately after heavy snow or an avalanche, surface markers are often completely covered in white, making it impossible to tell where benchmarks are located. This presents a major obstacle to recovery work.

When a benchmark is invisible, there is no fixed starting point for surveying, and measurement of the damaged area or construction surveying cannot begin. For example, boundary stakes or leveling points placed along a road become unidentifiable under snow, leaving surveyors uncertain where to start. Disaster response often requires urgent action, so time spent searching for benchmarks can directly translate into delays in recovery. Moreover, if surveying begins with uncertain assumptions, positional errors can grow, increasing the risk of mistakes and rework in subsequent restoration work.

Furthermore, the search itself in heavy-snow environments is hazardous. In areas where snow depths range from tens of centimeters (tens of in) to several meters (several ft), workers may slip and fall, or fall due to hidden terrain features. Long searches over snow drain workers’ stamina and increase health risks such as hypothermia. For these reasons, how to find benchmarks buried in snow safely and quickly is a critical challenge in disaster recovery in cold regions.

Traditional search methods and their limits

Traditionally, finding benchmarks under snow has relied on analog methods based on experience and intuition. Field personnel use past records and drawings as clues to make an educated guess like “the benchmark should be around here,” and then dig through the snow with shovels. When the benchmark uses a metal stake, a metal detector may be used as well. But these methods require a great deal of time and labor and lack reliability.

A veteran technician may find the benchmark by instinct to some extent, but due to the amount of snow or changes in terrain, benchmarks may have been carried to unexpected locations. Especially when the ground has shifted in a disaster, the benchmark itself may be lost or destroyed. In that case, it is necessary to re-establish new benchmarks (re-survey), which can lead to major delays in recovery plans.

To re-establish new benchmarks from a distant undamaged point, a surveying team must observe multiple points with a total station or GNSS equipment and tie them into a known coordinate system. That process takes time and delays overall understanding of the affected area. There have been reports from the field saying, “Because benchmarks were buried in snow and unusable, we had to urgently re-survey benchmarks with GNSS,” highlighting the limits of conventional methods.

Sometimes the only option is to clear snow and wait for thawing. Of course, such leisurely measures are unacceptable in disaster recovery, and alternative ways to rapidly identify positions have been sought.

What is coordinate guidance technology?

A promising new solution to break this impasse is coordinate guidance technology. Coordinate guidance technology refers to methods that guide you to a target location based on numerical coordinates, without relying on visible markers. The latitude and longitude (coordinate values) of a known target point are entered into a device in advance, and the device navigates you to that location.

For example, smartphone map apps can guide a person to a specified point. However, typical map apps and car navigation GPS have position accuracies on the order of a few meters (a few ft), and thus can only guide you near the target. Coordinate guidance technology differs in that it combines higher-precision positioning techniques to enable arrival at the target point with errors on the order of centimeters (inch-level). In other words, if the exact coordinates of a benchmark are known, entering them into a device and starting guidance can bring you very close—right above—a benchmark buried in snow.

Rapid benchmark search using high-precision GNSS

The key to achieving coordinate guidance is high-precision GNSS positioning (satellite positioning) technology. GNSS is a general term for global navigation satellite systems including GPS, and multiple satellite networks, including Japan’s quasi-zenith satellite system “Michibiki,” are available today. GPS built into ordinary smartphones or car navigation systems has position errors of several meters (several ft), making it unsuitable for precise benchmark searches. However, in recent years, with the advent of correction techniques called RTK (Real-Time Kinematic) and centimeter-class augmentation services (CLAS) provided by Michibiki, centimeter-class positioning (half-inch-class positioning) has become possible even with small devices.

RTK is a method that achieves high accuracy by simultaneously observing satellite signals at a reference station and a rover and correcting errors from their differences. Previously, dedicated expensive surveying equipment was required, but technological advances have led to miniaturization and cost reduction, and today RTK positioning can be performed using smartphones or tablets with external devices. In Japan, by using augmentation signals distributed from the quasi-zenith satellite Michibiki (CLAS), real-time corrections are possible even in mountainous areas out of cellular coverage. Thanks to these mechanisms, stable centimeter-level positioning (inch-level positioning) can increasingly be maintained even at disaster sites without mobile reception.

By utilizing high-precision GNSS positioning, a receiver can reduce the positional error between its current location and the known benchmark coordinates to a few centimeters (a few in), indicating the target almost pinpoint. Specifically, a worker’s handheld positioning device displays the bearing and distance to the target in real time on the screen, and by walking in the direction the arrow indicates, they can reach the benchmark location. Tasks that used to be performed by experienced surveyors using transits and rods for staking and point setting are now being replaced by digital devices.

Benefits of coordinate guidance technology

Using high-precision coordinate guidance technology brings the following benefits for searching benchmarks buried in snow:

• Significant reduction in search time: Relying on coordinates and taking the shortest route to the target eliminates the need to probe and dig across a wide area. Benchmarks can be found quickly, improving the speed of initial response.

• Reduction in labor and personnel: Because you simply follow digital navigation, searches can be carried out by one person without specialists. There is no need to deploy heavy equipment or many workers, making it easier to respond even with limited manpower.

• Improved safety: There is no need to spend long periods on snow or search dangerous slopes. Since you can reach the target with minimal movement, workers’ exposure time is reduced and the risk of secondary disasters such as avalanches or falls is lowered.

• Effectiveness under adverse conditions: Because it does not rely on physical markers, guidance is possible in snow as well as at night or in dense fog when visibility is poor.

• Maintenance of survey accuracy: Since guidance is based on digital coordinates, the located benchmark has almost no positional offset, preserving the accuracy of subsequent surveying. Compared with searches based on intuition, this prevents construction errors due to accumulated errors.

In this way, coordinate guidance technology offers major advantages over traditional methods in terms of both efficiency and safety. Especially at disaster sites that cover wide areas, searching for benchmarks manually one by one is impractical. Leveraging digital technology to reduce labor and speed up processes is strongly demanded in modern disaster prevention and mitigation.

Simple surveying with LRTK

One accessible solution to implement the above coordinate guidance technology in the field is simple surveying using smartphones with LRTK. LRTK (Local Real-Time Kinematic) is the name of a series of ultra-compact RTK-GNSS receivers developed by a startup originating from the Tokyo Institute of Technology. By attaching this LRTK device to a smartphone such as an iPhone and using a dedicated app, a regular smartphone is quickly transformed into a surveying instrument capable of centimeter-class positioning (half-inch-class positioning). The fact that a palm-sized device achieves positioning accuracy comparable to traditional large surveying equipment is revolutionary.

Compared with procuring dedicated expensive surveying equipment, LRTK has the advantage of being lower-cost and easier to introduce because it can leverage existing smartphones.

The LRTK system includes a navigation function that guides the user to specified coordinates. The operation is simple: input the coordinates of recorded benchmarks or stake positions into the app and start guidance. The screen displays the direction and distance to the target, and by following the arrow you can accurately reach a benchmark that is buried and invisible in snow. With an error of only a few centimeters (a few in), guidance brings you almost directly above the point, after which a small amount of snow removal will reveal the benchmark marker. There are no complicated operations; it is intuitive to use and can be immediately utilized on-site by staff without surveying expertise.

LRTK also supports the centimeter-class augmentation service (CLAS) provided by Japan’s quasi-zenith satellite Michibiki, allowing stable high-precision positioning even in areas without mobile reception. By combining a smartphone with a small GNSS device like this, benchmarks can be rapidly recovered and utilized even under the harsh conditions immediately after a disaster. In fact, municipalities in snowy regions have begun adopting LRTK for infrastructure inspections during heavy snowfall and for surveying damaged areas. The simple equipment configuration makes it easy to handle in emergencies, and field operators appreciate how much it reduces the burden of arduous searches.

As disaster prevention technology continues to advance, smartphone-based positioning solutions like LRTK are expected to become a new-era tool that enables anyone to quickly perform surveying and location identification. If such coordinate guidance technologies become widespread, surveying tasks in future disaster responses will become dramatically more efficient and safer. For the challenge of rapidly locating benchmarks buried in snow, coordinate guidance via LRTK could become the trump card of on-site DX (digital transformation).

FAQ

Q: What is a benchmark? A: A benchmark is a point that has a defined coordinate value used as a reference in surveying. It includes triangulation points and leveling benchmarks installed by the Geospatial Information Authority of Japan, as well as temporary benchmarks set arbitrarily at construction sites. Surveying is conducted from these benchmarks, so they play an important role as the basis for accurate positioning and elevation.

Q: Why are benchmarks necessary during disasters? A: During disasters, terrain changes and visual markers can be lost, so a reference is essential to accurately understand the damage. With benchmarks, the extent and volume of damage can be measured quantitatively. Reliable survey data based on trusted benchmarks are indispensable for comparing with original designs and verifying boundaries during recovery work.

Q: How should a benchmark buried in snow be located? A: The most effective method is to use coordinate guidance technology. If benchmark coordinates are known in advance, high-precision GNSS devices can guide you to those coordinates, enabling accurate location identification even under snow. This avoids the need to dig across wide areas or use manpower-intensive searches, allowing discovery in a short time and safely.

Q: Do you need to know the benchmark’s coordinates in advance to use coordinate guidance? A: Yes. To search for a benchmark via coordinate guidance, you need to know the exact coordinate values of the target benchmark. When benchmarks are established and surveyed in normal times, it is important to record and store their coordinate data. With such preparations, you can immediately identify positions by coordinate guidance even if benchmarks are buried in snow. If coordinate data are unavailable, it is possible to derive coordinates from nearby benchmarks or GNSS reference stations, but that requires extra effort and time, so data management during peacetime is recommended. In snowy regions, erecting tall marker poles (snow poles) near benchmarks helps identifying positions in snow. However, physical markers can be washed away or damaged, so combining them with data-based management is more reliable.

Q: Do you need special equipment for coordinate guidance? A: Yes. For high-precision coordinate guidance at the centimeter level, a positioning device capable of centimeter-class measurements is required. Specifically, use a receiver compatible with RTK-GNSS or a device that incorporates it (for example, a smartphone-mounted device like LRTK). Ordinary smartphone GPS has large errors, so equipment or services capable of receiving dedicated correction information are essential.

Q: Is high-precision coordinate guidance possible when communications infrastructure is down? A: Even without a communication line, high-precision positioning is possible by using augmentation signals from satellites. In Japan, devices that can receive the quasi-zenith satellite Michibiki’s centimeter-class augmentation service (CLAS) can perform centimeter-class positioning without network connectivity. In practice, using CLAS-compatible devices like LRTK allows stable coordinate guidance in mountainous areas out of cellular coverage or in regions where base stations are unusable due to a disaster.

Q: What is LRTK and what are its features? A: LRTK is a surveying solution consisting of a small high-precision GNSS receiver device and a dedicated app. Combined with a smartphone, it enables easy RTK surveying (Real-Time Kinematic). Its features include centimeter-class positioning (half-inch-class positioning), intuitive navigation functions, and cloud-linked data management. This means that even without specialized surveying equipment, anyone can quickly perform surveying and location identification.

Q: Is coordinate guidance technology useful in situations other than snow? A: Yes. Coordinate guidance can be applied in many situations. For example, when looking for boundary markers hidden by dense vegetation, coordinate guidance can pinpoint the exact location. It is also useful for setting survey points at night or in dense fog when visibility is poor, and for locating buried utilities (provided their positions were recorded in coordinates beforehand). Beyond disaster response, it contributes to efficiency in routine surveying and inspection tasks.