Can Drone Surveying Be Done After Rain? 6 On-site Decision Points

When it rains on a day a drone survey is scheduled, many people in charge are unsure whether to proceed or postpone. Especially on civil engineering, land development, exterior works, and maintenance sites, schedules are tight, so it is not uncommon for teams to want to fly "if it can be flown" even immediately after the rain stops. On the other hand, it is also true that drone surveying after rain is prone to failure if you judge solely on whether the aircraft can fly. Even if the aircraft can take off, reflections may appear in photos and reduce processing quality, and muddy ground can prevent the terrain you want to know from being captured accurately. Furthermore, residual moisture at the site can affect safety and work efficiency, so it is necessary to increase the number of decision criteria and consider more factors than usual.

To conclude, drone surveying can sometimes be carried out after rain. However, that does not mean “it’s okay because the rain has stopped.” What matters is to separate three considerations: whether flight is possible, whether the required accuracy can be met, and whether there is a risk of having to re-shoot. On site, often only flight permissibility is discussed, but in practical terms the more important question is whether the intended deliverables can be produced without problems. The acceptable range for working after rain varies depending on whether you want to create orthomosaic images, generate point clouds, calculate earthwork volumes, or use the data for as-built management. In other words, even under the same post-rain conditions, some sites are suitable to proceed while others are better postponed.

In this article, we organize and explain six key points that field personnel should keep in mind to decide on-site whether to conduct drone surveying after rain. Rather than offering mere generalities, we delve into what to look for on site to make decisions, what kinds of failures are likely to occur, and how to judge whether to postpone. If you force execution to prioritize the schedule and end up redoing work, the timeline and costs will actually worsen. Conversely, if you clarify the conditions under which operations are feasible after rain, you can more easily balance accuracy and safety while avoiding unnecessary postponements.

Table of Contents

• Can drone surveying be performed after the rain?

• Why Surveying Quality Tends to Decline at Sites After Rain

• Point 1: Safety of takeoff and landing locations and underfoot conditions

• Point 2: Reflections from puddles and wet ground

• Point 3 Mud and ground surface stability

• Point 4: Moisture risks to the airframe and sensors

• Point 5 Wind and light recovery status

• Point 6 Deliverables and Acceptable Tolerances

• How to Avoid Failures When Conducting Drone Surveys After Rain

• Summary

Can drone surveying be performed after rain?

Drone surveying is not something that is uniformly canceled just because it has recently rained. It can be carried out if the site conditions and surveying objectives are compatible. For example, if the rain has stopped, the takeoff and landing areas are dry, there are no large puddles on the ground surface, the wind has calmed, and the deliverables are not strongly affected by photogrammetric processing, it can often proceed. Conversely, even if the aircraft itself is flyable, it is safer to postpone in situations where the ground is too wet and highly reflective, the target area is muddy, wet leaves or pavement shine and make feature points hard to capture, or surfaces intended as references for comparative measurements are unstable.

The important thing here is to consider separately whether you can fly and whether you can obtain measurements. Even if a drone can fly overhead, if you cannot obtain survey-quality data, carrying out the operation becomes of little value. For photo-based processing in particular, it is important that the ground surface appears uniform, that there are few unnatural reflections or glare on surfaces, and that the contours of target objects are consistently visible. Because conditions after rain tend to disrupt these factors, more cautious judgment is required than when it is dry.

Even after the same rainfall, the difficulty varies depending on the type of site. On sites with many paved surfaces, reflections from water films tend to be more pronounced, while at earthwork sites, mud and disturbances of the surface layer become problematic. On slopes and in areas with abundant vegetation, water droplets remaining on leaves and grass can cause the way they appear in images to be unstable. In other words, to successfully carry out drone surveying after rain, you must consider not only the weather but also the condition of the target features.

Reasons Why Surveying Quality Tends to Decline at Sites After Rain

The reason post-rain drone surveying is difficult is not simply that things are wet. It’s because the conditions that determine survey quality tend to deteriorate simultaneously. The first is visibility. Wet ground reflects light more easily, and when the sun appears some areas may become strongly overexposed while others appear unusually dark. Images with such large variations in brightness can make automated matching in post-processing unstable. In particular, puddles, wet pavement, dark soil, metal surfaces, and vinyl materials tend to change appearance easily and can affect image continuity.

The second is the stability of the ground surface. Immediately after rain, the soil can become soft, and only the surface may have flowed, altering fine surface features. At development sites, temporary roads, spoil storage areas, and similar locations, tire tracks can become deeper and the surface layer can slump slightly, making it difficult to compare with conditions when dry. When the purpose is to verify soil volumes or as-built geometry, these slight differences can skew assessments.

The third is safety. When the footing of the pilot or an assistant becomes poor, mistakes during takeoff and landing, mishandling of equipment, and delays in checking reference points are likely to occur. On-site, problems are often more likely to occur before and after takeoff and landing than during flight. Even simply losing your balance in the mud or having muddy water splash near the aircraft can, as a result, lead to reduced quality or an increased risk of damage.

The fourth is work efficiency. After rain, the "time available for flight" tends to be shorter. Even if conditions temporarily recover after a rain cloud passes, wind may remain, road surfaces may begin to glisten again, or the next rain may be approaching. If you try to cram tasks into the limited recovery time, revision of the flight plan becomes superficial, making missed shots or duplicated coverage more likely. At sites after rain, you need to be prepared to finish with high quality in a shorter time than on a normal day.

Point 1: Takeoff and Landing Locations and Foot Safety

The first thing to check is not the survey area itself but the takeoff and landing sites and the operational routes. On a site after rain, the ground can be more hazardous than the air. If the ground underfoot is muddy, it’s easy to slip when carrying the drone by hand, and if you lose your footing during takeoff or landing, the risk of propeller contact or the drone tipping over increases. Because the success of a survey depends as much on equipment handling before and after flight as on piloting during flight, you need to first confirm that there are places where you can stand safely, set the drone down safely, and recover it safely.

If the takeoff and landing surface is wet, mud and fine droplets being kicked up can also be a problem. If kicked-up mud or moisture adheres around the camera or sensors, image quality may decline even if the flight itself can continue. At some sites, the flight area may be fine overall while only the takeoff and landing point has poor conditions. In such cases, rather than forcing a nearby flight, it is effective to prepare a stable temporary surface, move to a drier location, or shorten the carrying distance to reduce the number of times equipment must be transported.

Also, the ease of auxiliary tasks must not be overlooked. After rainfall, tasks such as verifying control points, checking the surrounding area for safety, and inspecting for obstacles take longer than usual. When the on-site staff has to perform multiple roles alone, checks are more likely to be missed. For drone surveying after rain, it is important to confirm before starting the flight the movement route from the takeoff/landing site to the target area, ensuring lines of sight, and even the temporary placement of equipment. A site that cannot be started safely cannot be said to meet the conditions for operation, even if the sky is clear.

Point 2 Reflections on Puddles and Wet Ground

One thing that's especially easy to overlook in drone surveys after rain is reflections from puddles and wet ground. Even if it feels "just a little wet" on site, the effects of reflections can be much more pronounced from the air. Wet pavement, compacted soil, temporary metal structures, pale sheets, and shallow puddles can shine strongly depending on the angle, causing their appearance relative to the surroundings to change drastically. These changes can work against the photogrammetric processes that reconstruct terrain by overlapping photos. In other words, images can end up much harder to handle than the impressions you get from visual inspection on the ground.

Especially in projects that prioritize orthoimages, reflections are a major cause of quality degradation. When image readability is important—for example, checking pavement condition, mapping parcel layouts, inspecting areas near boundaries, or recording current site conditions—glare on wet surfaces is a significant obstacle. Even when creating point clouds or 3D models, in image-based workflows for deriving geometry, reflections can obscure some features. As a result, processing can be locally weakened and connectivity can become unstable.

The important point here is not to assess a site after rain solely from a ground-level perspective. Small puddles that are unnoticeable on the ground can appear as continuous bands of reflection from the air. Conversely, a surface that looks dry may still have a thin film of water on it that affects image quality. Therefore, when deciding whether to proceed, you need to consider as a set how much of the target area remains wet, where the wet areas are concentrated, and how much the reflections will impact the deliverables. If the wetness is limited to part of the surface, it may be possible to address it by adjusting the flight plan, but if a large proportion of the target area remains wet, postponement is a realistic option to consider.

Point 3: Mud and Stability of Surface Conditions

In drone surveying, attention tends to focus on photographing from the air, but the object being measured is the ground surface. After rain, the problem is not just how the surface looks, but that the surface itself can be unstable. In particular, at earthwork sites, natural ground before and after development, temporary yards, slope faces, and soil stockpiles, the surface condition is likely to change after rain. When the surface layer becomes soft, new ruts can form easily from vehicle or worker traffic, and drainage flow can create linear erosion features. Such changes are not merely a visual issue; they affect the interpretation of survey results.

For example, when you want to check earthwork volumes, what you need to know is the actual shape of the construction target. However, immediately after rain, the effects of surface moisture and trampling are strong, and it can be difficult to treat the surface as the normal shape. The same applies to as-built verification and progress comparisons: if the surface condition is very different between the previous and current measurements, it becomes hard to determine whether the difference is due to construction or to weather. In other words, after rain it's not that you "can't measure"—it's that the measured results are often "difficult to compare as-is."

Also, at sites with vegetation, after rain the leaves and grass may fall over or, conversely, spread as they absorb water, changing how the surface appears. This also makes it harder to grasp the current conditions. When the contours of the natural ground, the slope shoulder, the slope toe, and the boundaries of steps become difficult to see, decisions can vary later when mapping or verifying. Therefore, for drone surveys after rain it is important to determine whether the target surface has returned to a stable condition rather than simply whether the sky has cleared. If the ground surface is still moving, or its condition changes every time people or vehicles pass, it is generally better overall to wait a little and improve the conditions than to rush into the survey.

Point 4: Moisture Risk to the Airframe and Sensors

One thing you must not forget when conducting drone surveys after rain is the risk of moisture remaining on the aircraft and sensors. Even if the sky is clear, conditions can still be harsh for the equipment. Near grass or wet ground, fine moisture is easily kicked up during takeoff and landing, causing humidity to collect not only on the airframe but also around the camera and ventilation openings. Also, if there is a temperature difference between the storage location and the outdoors, condensation can form on the lens and inside the device. Condensation is troublesome because it can be hard to notice visually yet greatly reduces image sharpness.

In surveying, a single clean image is not sufficient. Only when multiple images can be acquired stably does post-processing produce consistent, well-formed deliverables. Therefore, it is important not only that the aircraft has good flight performance but also that the camera can maintain continuous, stable capture. If there is even slight fogging or moisture on the lens, it may look fine in the field but show reduced apparent sharpness when enlarged later. If this spreads across multiple images, it will affect the entire processing.

After rain, the working environment for battery replacement and memory card replacement also tends to deteriorate. Damp gloves, muddy hands, and a lack of temporary places to set things down can lead to problems around contact points and to management errors. These kinds of troubles may not be dramatic, but they can be a significant cause of survey failures. If you are conducting drone surveying after rain, check the condition of your equipment more thoroughly than usual, and rather than taking the equipment outdoors and flying immediately, let it acclimate to the environment while you check the imaging conditions. On site you are often pressed for time, but skipping this step increases the likelihood that you will need to re-shoot.

Point 5: Recovery Status of Wind and Light

It's dangerous to use only "the rain has stopped" as the criterion for judging conditions after a rain. What actually has a large impact on quality is how the wind and light recover afterward. Immediately after the rain clouds have passed, it may look calm at ground level while wind remains aloft. If the wind is unstable, aircraft attitude fluctuations increase, and shooting intervals and image appearance are more likely to vary. This is especially true for drone surveying, which requires photographing large areas under consistent conditions; if the light suddenly changes or the wind strengthens partway through, image continuity is easily compromised.

The return of light is equally important. After rain, strong sunlight can stream through gaps in the clouds, which at first glance may seem like favorable conditions. However, in practice the combination of strong sun and wet surfaces can worsen reflections. Also, when clouds move frequently, brightness can change easily even during the same flight, reducing image uniformity. Large contrasts in ground brightness can result in deliverables that are hard to interpret in post-processing or that reduce the legibility of boundaries.

Wind and light affect both the safety of the aircraft and the quality of the deliverables, so they are factors to be especially cautious about after rain. Even if the operation must be carried out for scheduling reasons, you need to consider not just "it's not raining now" but whether conditions are likely to remain stable throughout the entire flight. The decision changes between small sites that can be completed in a short time and sites that require multiple flights. For the latter, the risk that conditions will break down midway is higher, so if conditions at the start are even slightly unstable, postponing is the more reasonable option.

Point 6 Deliverables and Acceptable Tolerances

In drone surveying after rain, what ultimately determines the final decision is, after all, "what you want to accomplish." Even on the same site, acceptable conditions change depending on whether you only want to record the current conditions, use it for quantity verification, or use it for design and construction management. For example, if the main purpose is to grasp the broad situation or share progress over a wide area, you may be able to proceed even with some wet surfaces. However, for uses that prioritize accuracy and reproducibility—such as earthwork volumes, as-built verification, dimensional checks, or later comparative evaluations—you should be cautious immediately after rainfall.

A common mistake at this point is the judgment, "If it can fly, let's shoot first." Even if the footage can serve as a record, it may be difficult to use later as surveying deliverables. That then makes re-shooting necessary and doubles the work. On-site staff naturally want to push the day's tasks forward, but after rain it's less likely to fail if you first clarify the required quality level of the deliverables and decide based on whether you can meet that standard.

Also, when conducting comparative measurements, you need to pay attention to differences in conditions from the previous time. If the previous survey was conducted in dry conditions and the current one is after rain, both the appearance and the state of the ground surface will change. If you want to read the differences, having weather condition differences mixed in makes evaluation difficult. Therefore, whether to carry out the survey after rain should be decided not by flight conditions alone but by considering the desired deliverables, intended use, whether comparisons will be made, and the allowable error together. In practice, merely adopting this perspective can significantly reduce unnecessary rework.

How to Ensure Successful Drone Surveys After Rain

To successfully carry out drone surveying after rain, it is effective to fix the order in which decisions are made rather than deciding on the spur of the moment on the day. First check safety. If there are problems with the takeoff/landing area, operation routes, temporary equipment placement, or stability underfoot, you should decide not to proceed at that point. Next assess ground conditions: check for puddles, wet surfaces, mud, drainage marks, and flattened vegetation, and evaluate the extent and degree to which they might affect the deliverables. On that basis, consider whether wind and lighting will remain stable during the planned flight time, and finally make a decision on whether to proceed based on the mission objective and the allowable error.

If you think in that order, it's easier to judge whether it's worth doing before whether flying is possible. On site, when you're unsure you tend to focus only on aerial conditions and lean toward proceeding, but after rain the ground conditions are often the dominant factor. In particular, on sites involving earthwork volume calculations or as‑built verification, changes in surface conditions directly affect the results. Conversely, if the main purpose is sharing the current situation or creating a wide‑area overview record, it may be acceptable to proceed even if conditions are not perfect. The important thing is to match the conditions to the objective.

Furthermore, at sites after rain, it is important to adopt the mindset of not completing assessments based solely on aerial imaging. Having a system that can quickly perform reference checks on the ground helps stabilize the interpretation of the capture results. Being able to immediately confirm site coordinates, carry out additional checks where needed, and provide auxiliary positioning for the survey area makes it easier to compensate for uncertainties unique to post-rain conditions. In such cases, combining an iPhone-mounted GNSS high-precision positioning device like LRTK can streamline on-site position checks and auxiliary observations. Rather than relying only on drone surveying, having ground-based verification methods increases the reliability of post-rain assessments and deliverables.

Summary

Drone surveying can sometimes be carried out after rain, but the decision should not be based on whether the rain has stopped. It is important to check these six items in sequence on site: the safety of takeoff and landing areas; reflections from puddles and wet surfaces; the stability of ground conditions including mud; moisture risks to the aircraft and sensors; recovery of wind and light conditions; and the required deliverables and allowable tolerances. In practical operations, judging not only whether flight is permitted but whether the necessary results can be obtained is key to preventing failures.

After rainfall, conditions often vary far more than they appear. Rather than pushing ahead and ending up having to reshoot, it’s better to make a precise judgment—even if brief—so the overall workflow remains stable. Conversely, if you clarify the decision points in advance, you can avoid unnecessary cancellations and keep moving forward. To make drone surveying effective on site, it’s essential to look not only at the sky but also at the ground and the requirements for the deliverables as a set.

Moreover, the more difficult a site’s conditions are to interpret—such as after rain—the more effective it is to have a system that can quickly perform high-precision ground-based position checks and auxiliary observations in addition to aerial measurements. If you want to improve on-site decision accuracy and conduct surveying work in a more practical manner overall, combining drone surveying with an iPhone-mounted GNSS high-precision positioning device like LRTK can further enhance the usability of drone surveying.