6 safety checks before surveying disaster recovery sites with an electronic total station

In disaster recovery sites, unlike ordinary land development or construction sites, there are many hazards that should be checked before surveying, such as loosened ground, risk of collapse, fallen or floating trees and debris, flooding, and unstable temporary roads. A total station can measure distances and angles from a distance, making it easier to assess conditions without approaching dangerous areas too closely. However, if the instrument’s setup location, line of sight, or the workers’ positions are incorrect, the surveying itself could become the trigger for secondary disasters. In this article, from the perspective of field practitioners, we organize the safety items to confirm before surveying disaster recovery sites with a total station.

Table of Contents

• Basics to cover before using a total station at a disaster recovery site

• Confirm site access and the risk of secondary disasters

• Verify the safety of instrument stations and work movement paths

• Check line of sight and measurement range with a safety margin

• Inspect ground and structural deformations

• Confirm changes in weather and water levels

• Confirm communication channels and evacuation decision criteria

• In disaster recovery surveying, balance safety checks with the quality of recorded data

Basics to Know Before Using a Total Station at Disaster Recovery Sites

The purpose of using a total station at disaster recovery sites is not merely to measure current positions and elevations. It is important to understand the condition of damaged roads, rivers, slopes, retaining walls, revetments, temporary yards, and other features, and to compile baseline information that can be used for restoration planning and construction decisions. Therefore, surveying work must not only consider accuracy but also whether the work can be completed safely and whether the measured results can be used in subsequent processes without misunderstanding.

On a typical site, the locations for setting up instruments, backsight points, survey points, and the work area are often organized to some extent. By contrast, on a disaster recovery site, access routes may be severed, existing reference points may have been lost, and even locations that appear stable may have been scoured underneath. In the early stages of recovery, access routes for heavy equipment and material storage areas are often temporary, and site conditions can change from day to day.

Because a total station can measure distant points using prisms or targets, there are situations where it allows inspection without directly stepping into hazardous areas. For example, by choosing measurement positions carefully you may be able to reduce close approaches to the top edge of a collapsed slope, deformed sections along a river, or the edge of a road where the shoulder has been lost. However, if you force line of sight to take a measurement or have workers carry a target into a dangerous location, the advantages of using a total station are lost.

In surveying at disaster recovery sites, it is important to first confirm safety and then determine the surveying method. Instead of deciding on the points you want to measure first and then forcing your way closer, consider what can be measured from locations where you can stand safely. If the required measurement points are within a hazardous area, you should not insist on direct measurement; make your decision by including observations from other directions, the establishment of auxiliary points, photographic records, or re-surveying at a later date.

In disaster recovery, surveying results are often urgently required. The more pressing the on-site decisions—such as lifting road closures, emergency restoration, designing temporary works, and assessing earthwork quantities—the more surveyors are required to carry out work in a short time. However, the more urgent the situation, the more likely oversights are to occur, and overlooking the selection of instrument points, evacuation routes, means of communication, or changes in weather can lead to accidents. Measuring quickly is not the same as omitting safety checks.

Before surveying a disaster recovery site with an optical surveying instrument, you need to organize not only measures to ensure surveying accuracy but also the areas where workers can safely stand, locations where equipment can be stably installed, hazards likely to change during measurement, and evacuation routes in case of abnormalities. The six items covered in this article are checkpoints useful not only for unstable sites immediately after a disaster but also for sites where recovery work is already underway.

Confirm whether entry to the site is permitted and the risk of secondary disasters

The first thing to confirm is whether survey personnel are even permitted to enter the site. At disaster recovery sites, road authorities, river authorities, facility managers, the prime contractor, the client, and local stakeholders may each hold information about the site. Rather than the survey team deciding to enter on its own, it is basic practice to verify in advance the areas where entry is permitted, areas where entry is prohibited, passable routes, permissible working hours, and whether a monitor is required before taking action.

The hazards at a disaster site are not limited to the visible areas of collapse. There are many factors that are difficult to assess from appearance alone: unstable soil left at the top of slopes, leaning trees, heaved pavement, scoured road shoulders, damaged gutters and culverts, and drop-offs hidden beneath turbid water. Especially at sites after heavy rain or earthquakes, even if the initial collapse appears to have stopped, aftershocks, rainfall, or vibration from heavy machinery can cause it to collapse again.

When using a total station, tasks are often divided between the person who sets up the instrument and the person who holds the target. For that reason, even if the instrument side is safe, it is meaningless if the target holder moves into a hazardous area. At disaster-recovery sites, the entire surveying team must share the same understanding of hazard zones and clearly define where entry is permitted and where it is not. In particular, when the point to be measured is near a collapse edge or the water’s edge, the footing of the worker holding the target is often the most at risk.

When confirming whether entry is allowed, it is important to first grasp the overall picture of the site. Rather than setting up equipment immediately upon arrival, observe from a distance the extent of the damage, areas under restoration, the movement paths of heavy machinery, the flow of water, and the locations of fallen rocks and trees. By surveying the whole site from a safe position, you can also identify instrument points suitable for surveying and evacuation routes. Conversely, if you only notice hazards after going deep into the site, your route back may be limited.

When assessing secondary disaster risk, also check whether the surveying work itself could increase danger. For example, setting up a tripod in a narrow passage can obstruct other workers or the movement of heavy equipment. Positioning a target close to heavy machinery engaged in recovery work can also make it difficult for the operator to see. If you observe for a long time near a collapse site, there is also a risk that evacuation decisions will be delayed.

At disaster recovery sites, expanding the survey area yields more information, but it also increases travel distances and opportunities to approach hazards. Rather than trying to measure everything from the outset, a practical approach is to organize the required deliverables and prioritize measurements starting from areas that can be accessed safely. By separating the minimum area needed for the recovery plan, points that can be obtained from lower-risk locations, and points that can be added in later stages, unnecessary entry can be reduced.

Confirming whether entry is permitted and assessing the risk of secondary hazards is not something that ends with the pre-survey check. If the weather changes during work, water levels rise, or small stones fall from slopes, you need to review your initial judgment. Even a location judged safe during surveying can have its conditions change over time. At disaster recovery sites, it is important to perform pre-survey checks together with continuous observation during work.

Verify the safety of equipment locations and workflow paths

Safe surveying with a total station depends greatly on the selection of the instrument point. An instrument point is the position where you set up the tripod and mount the total station. At disaster recovery sites you may be tempted to choose a location with good visibility, but if you prioritize sightlines alone you may end up placing it in unstable locations such as the edge of a collapse, the road shoulder, the lower part of a slope, the water’s edge, or near heavy equipment traffic routes. When choosing an instrument point, you need to consider not only the measurable range but also stability underfoot, hazards from the surroundings, and ease of evacuation.

When the ground on which a tripod is set is weak, the legs can sink during surveying, causing measurement errors. After a disaster, the ground may appear dry on the surface yet contain water internally, or voids may form beneath pavement. Before placing the instrument, check that the ground underfoot will not sink, that the pavement is not lifting or cracked, and that the tripod feet can be stably secured. In particular, at road shoulders or the edges of embankments, the surface may remain while the lower parts have been scoured away, so it is important not to position the tripod too close to the edge.

Near the instrument station there must also be space for the worker to stand. The person operating the total station may be concentrating on the screen and telescope during measurements and thus can have difficulty noticing changes in the surroundings. Therefore, the instrument station should be set where the worker has enough room to maintain a safe stance and can move away immediately if necessary. Places with a cliff or waterway directly behind, sloping footing, or areas where materials or debris make tripping likely should be avoided.

Verifying workers' movement routes is also essential. In surveying, crews move from the instrument setup point to survey points, and personnel carrying targets may visit multiple positions. At disaster recovery sites, the risk of falling or stepping through unstable ground while moving is high, and the travel route can be more hazardous than the measurement points themselves. Before surveying, you need to check the routes workers will walk and identify any level differences, mud, driftwood, rubble, temporary materials or structures, openings, drainage ditches, or collapsed pavement.

The risk of contact with heavy machinery and vehicles is also significant. At disaster recovery sites, earth removal, temporary road construction, and material delivery may proceed simultaneously. If the location where an optical total station is set up is close to the swing radius of heavy equipment or the route of dump trucks, danger can arise while workers are focused on their tasks. Instrument stations and target positions should be placed where heavy equipment operators can easily see them, and, where necessary, work areas should be separated and signalers positioned.

When selecting instrument points, also confirm evacuation routes. In the event of falling rocks from slopes, a sudden rise in water level, or interference with heavy equipment operations, decide in advance which direction to evacuate. If a safe evacuation location is too far away or there is only a single evacuation route, you should reconsider conducting long-duration surveys at that location. At disaster recovery sites, instrument points that are suitable for measurement accuracy may not coincide with those that are suitable for safety. In such cases, prioritize safety and consider compensating for accuracy by establishing auxiliary points.

Recording instrument points is also important. Survey results from disaster recovery work may be referenced later for additional surveys or construction management. Even if an instrument point is at a temporary location, documenting the surrounding conditions, the reason it was set up, the range over which line of sight was achieved, and the areas that could not be measured due to danger makes it easier to judge how the results can be used. If the number of survey points was reduced compared with normal practice because of safety constraints, leaving a record of that reason helps prevent misunderstandings in later stages.

Verify line of sight and measurement range on the safe side

An optical surveying instrument requires a clear line of sight from the instrument to the survey point as a precondition for measurement. At disaster recovery sites, fallen trees, driftwood, collapsed soil, temporary structures, heavy equipment, sandbags, guardrails, and other items can block the view. If workers move into dangerous positions or force their way close to obstacles to secure a line of sight, the risks of surveying operations increase. When confirming line of sight, it is important not only to check whether the point to be measured is visible, but also whether a position from which it can be seen safely can be selected.

When determining the measurement range, first check the affected area that can be seen from locations where you can safely stand. Rather than entering hazardous areas to measure everything directly, select points that can be observed from safe outer positions. Even when measuring collapsed slopes or deformation of revetments, prioritize points that can be measured from the opposite bank or from stable positions on the road, avoiding approaching the edge of the collapse. If it is necessary to place a target at the waterline or on collapsed soil, consider whether it is truly necessary to measure that point directly or whether it can be substituted by another method.

When taking measurements with a total station, it is also important to hold the target correctly. At disaster sites, footing is often poor, making it difficult for the worker holding the target to keep it level and plumb. Standing at a survey point on unstable footing not only poses a risk of falling but also reduces the reliability of the measurements. In locations where the person at the survey point cannot maintain a stable posture, do not rush the measurement; consider securing the footing or observing from a different position.

When there are obstructions to the line of sight, you may be tempted to fell trees or remove them to improve visibility. However, at disaster recovery sites, fallen trees or driftwood may be supporting other soil or debris, and temporary materials may be holding down unstable structures. Avoid touching obstacles solely for the purpose of surveying, and if removal is necessary, coordinate with the site manager and the crews responsible for the work. Decisions about ensuring line of sight should not be made by surveyors alone but should be handled within the overall site safety management.

Be careful not to take too wide a measurement range. At disaster recovery sites, there are situations where you want to grasp the entire affected area at once. However, long-distance measurements can affect measurement quality due to target identification, weather conditions, ease of sighting, personnel placement, and so on. Rather than having workers move into hazardous areas to measure distant points, it may be better to set up multiple instrument stations within a safe area. Plan measurements with not only efficiency but also safety and the stability of results in mind.

With a total station, communication between the observer and the target holder is important. Even with a clear line of sight, voices may not carry over long distances, and signals can be lost in the noise of heavy machinery or flowing water. If measurements are taken with ambiguous signals, the target may be recorded in the wrong position or measurements may be made while a worker is moving. At disaster recovery sites, signaling methods should be decided in advance, and signals for start of measurement, completion of measurement, start of movement, and evacuation should be clearly defined.

When confirming the safety of the measurement area, it is also important not to forcefully try to fill in places that could not be measured. If there are locations that are dangerous and cannot be approached, record the reasons why they were not measured and decide to perform additional surveying later once conditions improve. In the initial stages of disaster recovery, there are situations where securing the information that can be safely obtained at the present time takes priority over measuring everything completely. By clearly stating the safety-related constraints in the surveying results, users can correctly understand the scope of the deliverables.

Inspect ground and structural deformations

At disaster recovery sites, you must act on the assumption that the ground and structures are not in their normal condition. Before using an optical total station, check not only the survey target but also the ground and structures where workers will stand, where the instrument will be set up, and along the routes they will move for any changes or deformations. Cracks, differences in elevation, subsidence, bulging, tilting, wet soil, seepage or springs, scouring (undercutting), and signs of voiding may all be indicators of hazards during surveying operations.

At road disaster sites, even if the pavement remains, the roadbed or slopes may have been washed away. A shoulder that looks walkable can collapse under a person's weight if the area beneath has been undercut. When placing an instrument point near the shoulder, check for pavement cracks or settlement, missing or broken edges, and tilting of guard facilities, and decide not to approach any suspicious spots. Assuming it's safe to move close to the edge just a little for surveying can lead to accidents.

Be cautious of scouring and water level changes around rivers and waterways. Even after the water has receded, there may be voids behind revetments or changes in the riverbed that make footing unstable. In areas where turbid water remains, it is difficult to discern the depth underfoot or drops in level, posing a risk of misstepping or falling. When measuring points at the water’s edge with a total station, ensure the target holder does not approach the water’s edge too closely, and, if necessary, consider measuring a representative point from a safe position.

At slope and embankment sites, be careful of falling rocks and the movement of soil and debris from above. Even if a slope appears stable when viewed from below, there may be cracks at the top or loose rocks and fallen trees remaining. Observers using a light-wave surveying instrument look through the telescope, which makes it difficult to notice changes above. If observation from below the slope is unavoidable, avoid prolonged stays and consider safety measures such as assigning a spotter. When the risk is high, prioritize measuring from the opposite bank or another distant position rather than entering below the slope.

Structures such as retaining walls, revetments, bridge abutments, weirs, culverts, and drainage structures may also be deformed after a disaster. If tilting, cracking, opening of joints, washout of backfill, settlement, or scour around the foundations are observed, it is dangerous to set up instruments nearby or for workers to stand there for long periods. When surveying on or near these structures, it is important to confirm the judgment of the manager or engineer and to observe the permitted access limits.

Deformation of the ground or structures also affects survey results. At disaster sites, the very points intended for use as references may have shifted. Even when using existing nails, piles, markers, or corners of structures as references, you must confirm that they have not been displaced by the disaster. Using a point that may have moved as a reference will introduce errors throughout the entire set of survey results. Alongside safety checks, you need the perspective to determine whether a reference point can be trusted.

When inspecting for deformation, records taken before and after work are also helpful. Recording the locations of cracks, subsidence, seepage, and collapse edges found at the start of surveying makes it easier to determine whether changes occurred during the work. At disaster recovery sites, conditions can change even in a short time. If you notice sounds, increased turbidity, changes in water flow or volume, rockfalls, or widening of cracks that differ from the initially observed condition, you should suspend surveying and reconfirm safety.

Check changes in weather and water levels

Safety at disaster recovery sites is heavily influenced by weather conditions. Surveying with a total station can be affected by rain, wind, fog, strong sunlight, and temperature variations, but in disaster recovery it is necessary to place greater emphasis on changes in site safety than on impacts to measurement accuracy. In particular, at sites of heavy rain events, river-related disasters, or landslides, even a small amount of rain can loosen the ground or cause water levels to rise.

Before surveying, check not only the weather on the day but also rainfall up to the previous day, rainfall in the upstream area, and upcoming forecasts. Even if it is not raining near the site, heavy rain upstream can raise the water level of rivers and waterways. In mountainous or valley terrain, rainwater tends to concentrate and flow rates can increase suddenly. At sites where water levels are likely to change, it is important to minimize work that approaches the water’s edge during surveying and to set evacuation decision criteria early.

Checking the wind is also necessary. In strong winds, not only can tripods vibrate and targets become unstable, but there are also hazards from fallen trees, temporary structures or materials, signage, and flying debris. At disaster recovery sites, there may be materials that are not securely fixed and damaged structures remaining. Continuing observations in strong winds can result not only in unstable measurements but also in workers and equipment being put at risk. When winds are strong, it may be necessary to relocate the instrument station to a position less affected by wind, shorten working time, or postpone the work.

Be careful of slippery footing during rainy weather or after rainfall. Mud, wet pavement, moss-covered revetments, temporary boards, and sandbags can become slippery. Operators of total stations may have both hands occupied, and people holding targets also move while carrying poles or equipment. Moving on slippery surfaces increases the risk of falling more than usual. Before moving to a survey point, it is important to check the condition of your shoe soles, your walking route, and whether handrails or other supports are available.

Poor visibility caused by fog or rainfall makes it difficult to confirm measurement targets or reference points. Forcing measurements in low-visibility conditions can result in measuring the wrong point or losing sight of the person holding the target. On disaster recovery sites, poor visibility also impedes safety monitoring. Because it becomes harder to notice falling rocks, approaching heavy machinery, or changes in water level, when visibility is poor you need to decide whether to reduce the surveying area or temporarily suspend work.

Temperature, heat, and cold also affect work safety. At recovery sites, workers may spend long periods in areas with little shade, on paved surfaces that reflect strong heat, or along rivers with high humidity. Surveying requires standing and concentrating for long periods, making it difficult to notice heat- or cold-related illness. Confirm work hours, rest areas, hydration, and preparations for cold and heat protection, and establish procedures for responding if someone becomes unwell.

Checks of weather and water levels should continue not only before starting surveying but also during operations. Changes such as the sky changing color, wind suddenly strengthening, increased turbidity of the water, more driftwood, or water beginning to emerge from slopes may be signs that site conditions are deteriorating. There are situations where you should prioritize a safe withdrawal over completing the planned survey. At disaster recovery sites, sharing the criteria for stopping work in advance can prevent delays in decision-making.

Confirm communication arrangements and evacuation decision-making

Before using an optical total station at a disaster recovery site, establish a clear communication system. Survey crews often operate with few personnel, and those operating the instrument and the target may be apart. At some sites, noise from heavy machinery, flowing water, wind, or traffic can make verbal communication difficult. If work proceeds with inadequate signaling, it can lead not only to measurement errors but also to delays in conveying hazards.

As part of the communication protocol, we confirm not only signals within the survey team but also coordination with the entire site. We share the survey's scope and timing with the teams carrying out restoration work, heavy equipment operators, site managers, and safety observers. By confirming in advance where the survey team is, which direction they will move, and during which time periods they might interfere with heavy equipment operations, it becomes easier to prevent contact and overlapping entry.

Decisions about evacuation are particularly important in disaster recovery surveying. When danger is sensed during surveying, it is necessary to decide who will make the call to stop operations, where to evacuate to, and whether to abandon equipment and flee. When using expensive equipment, decision-making during withdrawal can be delayed by attempts to protect the gear. However, if there are hazards such as collapse, rising water levels, falling rocks, or the approach of heavy machinery, human life must be given top priority.

Evacuation locations should not be decided casually after arriving on site, but confirmed by everyone before starting surveying. Decide evacuation points according to the situation, such as safe high ground, stable roads, the location of support vehicles, the site office, or open areas. Check evacuation routes for level differences or drops, mud, narrow passages, edges prone to collapse, waterways, and so on. If an evacuation route is dangerous, it is necessary to reconsider the survey position itself.

Consider multiple means of communication to be safe. In addition to voice and hand signals, organize the methods you can use according to site conditions, such as radios, whistles, lights, and vehicle signals. However, it is dangerous to rely too much on communication equipment. In mountainous or valley terrain, reception can be weak, and rain or noise can make it hard to hear. Decide on actions to take if communication is cut off and on a rendezvous point if you cannot make contact for a set period, as this makes it less likely to become confused during a problem.

Clarify the division of roles within the survey team. If it remains unclear who operates the total station, who holds the target, who checks the records, and who monitors safety, communication can be delayed even when someone notices a hazard. Even with a small team, it is important to consciously separate the role of the person who focuses on measurements from the person who watches the surroundings. In particular, on downslope areas, at the water's edge, and near heavy-equipment travel routes, observers need to avoid becoming too absorbed in their instruments.

It is important to include site-specific conditions in the criteria for evacuation decisions. If small stones begin to fall, evacuate; if the water level passes a certain mark, stop operations; if the rain intensifies, withdraw; if heavy machinery work approaches, stop observations; if visibility worsens, reduce the work area — having concrete criteria makes judgment easier. At disaster recovery sites, it is crucial to act early when signs of danger appear rather than waiting until the danger becomes obvious.

Balancing safety checks and record quality in disaster recovery surveying

Before surveying a disaster recovery site with an electronic distance measuring (EDM) instrument, it is important to confirm whether entry to the site is permitted, instrument setup points and work flow paths, line of sight and measurement range, ground and structural deformations, weather and water levels, and the communication system and evacuation decision-making. These may appear as separate checklist items, but in the actual field they are interrelated. Without a safe instrument setup point, maintaining line of sight is difficult; if the weather changes, ground stability also changes. If the communication system is inadequate, workers cannot be notified immediately even if a hazard is detected.

In disaster recovery surveying, attention tends to focus on obtaining precise measurements. Restoration extent, earth volumes, slope geometry, locations of structures, road widths, elevation differences, and so on—survey results directly inform decisions in subsequent stages. However, results obtained at the expense of safety are not desirable for the site as a whole. Surveyors are responsible for distinguishing which points should be measured and which situations should not be measured, and for ensuring they reliably record results that can be obtained safely.

If there are points that cannot be measured for safety reasons, do not force an approach; instead, record the areas that could not be measured and the reasons. At recovery sites, additional surveys may be possible later once access or scaffolding is in place. In the initial survey, obtain an overall picture that can be safely acquired, and it may be necessary to limit documentation of hazardous locations to photographs, notes, and records of approximate positions. For those who will use the survey results, it is important to be able to tell which points are actual measured values and which areas are unmeasured or approximate.

A total station is an effective surveying method at disaster recovery sites. Its ability to measure from a distance, to determine positions by combining angles and distances, and its ease of integration into existing surveying procedures are major advantages. On the other hand, because instrument setup, line of sight, target positioning, and worker movement are required, safety checks are indispensable when site conditions are poor. Not only the equipment's performance but also the ability to assess the site and make operational judgments determine the quality of the results.

In recent years, situations in which it is necessary to record site information in a short time during the initial response to disasters and for situational awareness have been increasing. In addition to point measurements with total stations, combining photographs, videos, point cloud measurements, sketches, work records, and other inputs according to site conditions can sometimes make it easier to share the damage situation and verify subsequent processes. The idea of increasing the information that can be obtained from safe locations and reducing time spent on-site and approaches to hazardous areas is an important perspective in disaster recovery surveying.

When conducting surveys at disaster recovery sites, it is important not to let pre-survey safety checks end as mere formalities, but to link them to actual work decisions. By thoroughly enforcing the basics—do not enter hazardous areas, do not demand impossible lines of sight, do not overlook changes in weather or water levels, and do not hesitate to evacuate—you can safely leverage the advantages of total stations. If you record the results of safety checks together with the scope of the survey results, they will be easier to use for recovery decisions and serve as materials that are less likely to be misunderstood in subsequent processes.