UAS deployment of LIDAR to evaluate Coastal flood Risk

Abstract

Light detection and ranging (LIDAR) technologies have been in use over the last decades in the efforts to enhance the disaster management platforms. Its coupling with the unmanned Aircraft systems (UAS) it has become even cheaper, accurate and easier to use in the recent times. The two technologies have been of great influence in the disaster management cycle with their use being instrumental during the reduction, readiness, and response and recovery phases of disaster management. The combination of the two technologies has further enabled the stakeholders to achieve more efficient and accurate geospatial information. The LIDAR mapping systems consist of three very efficient components that make it stand out in all other remote sensing technologies. It contains the laser ranging system, an inertial measurement unit (IMU) and the global positioning system (GPS). Just like any other systems and technological pieces, the LIDAR and the UAS systems are marred with challenges and shortcomings of their own. However, the technologies have witnessed growth in the recent times with more software and hardware upgrade being adopted to increase the accuracy and efficiency of the system. The effort to enhance the systems is as a result of identification of the system as the leading technology in the survey and mapping industry

 

 

 

 

 

Acronyms used in the research

LIDAR- Light detection and ranging

UAS- Unmanned Aircraft systems

IMU- Inertial measurement unit

GPS- Global positioning system

NWS- National Weather Service

DEM- Digital elevation model

USGS- United States Geological Survey

NOAA- National Oceanic and Atmospheric Administration

USA- United States of America

 

 

 

 

 

 

 

Introduction

In the United States alone, flooding kills more people in the long-term than any other weather related disasters witnessed in the country. Floods are capable of destroying buildings, roads, schools, uproot trees, cause mudslides, destroy crops and further threaten human life (NOAA/NWS, 2005). On a large scale floods are difficult to monitor and have been sources of a head ache to many geological experts and disaster management agencies around the world over the years. They are even more sophisticated in monitoring due to their determination by some other local conditions such as the slope of the terrain, drainage networks, protective structures, land cover and even precipitation among other factors. There is, therefore, the need to monitor every other coastal area and even the rivers at different places along their course which can be difficult. Some floods happen periodically whereas others happen on an annual basis with other happening at random and unpredictable times (Harman et al., 2014).

According to the National Weather Service (NWS), the flooding severity may also vary from minor flooding, moderate flooding and major flooding (2005). The minor flooding results to minimal damages to property but may pose a threat to the public or cause some inconveniences. Moderate flooding causes some destruction on buildings, and there may need to evacuate the residents in the event of its occurrence. Major flooding, on the other hand, is very intense causing extensive damage to infrastructure and may require major evacuate of the human population to higher areas.  In the case of seawater, the disaster can be far more reaching (Webster et. al., 2006)

The flooding in coastal regions occurs when the sea height exceeds the elevation of the land usually where there is a form of a natural barrier such as dune system acting as the sea level. There are also some human-constructed barriers such as levees may be overpowered by swell conditions of the sea during storms or unusually high tides. The barriers may also be breached especially on the open spaces along the coast. The steady water flow may result in significant destruction and loss of life along the coastal region. Horizontally, the water surge may fan out for hundreds of miles along the coastline. The higher the intensity of a storm and the closer a community lives to the coast, the bigger the impact of the flooding that results from the upsurge of the waters (NOAA/NHC, 2014).

Coastal areas have always been at a very high risk of flooding, but there is a likelihood of increased the risk of flooding shortly due to the anticipated impacts of climate change. Such changes may be the rise of the sea level and also the increased rainfall intensity around the world. The changes will likely cause the areas that were previously flooding to flood more frequently or the effects of the flooding felt more than ever. It may also result in the witnessing of flooding in other areas that were previously not experiencing the flooding. Hence, the need to employ more technology and approaches that enable evaluation of the coastal flood risks in an attempt to be prepared and also sufficiently address and manage the inevitable disaster that comes with flooding (NOAA/NHC, 2014).

Since the acquisition of the aerial photography from a hot air balloon in 1858 over Paris in France man has made significant progress in the acquisition of remote sense data using platforms of aircraft, satellite, space shuttles, model planes and the famous unmanned aircraft systems (UAS). With the analysis of data from remote sensing data obtained through methods such as Light Detection and Ranging (LIDAR), we can now be in a position to parameterize the flood models, delineate the extent of the floods and also estimate the damage of the flood. Coupling the UAS and the LIDAR systems we can now not only act in a reactive manner during a flooding event but can also is proactive through the flood risk analysis and mitigation made possible by the technologies (NOAA/NHC, 2014). The flood hazards, exposure as well as the vulnerability levels can be able to be motored and assesses through remote sensing made possible by the LIDAR mounted on UAS. The flood risk management, as well as disaster management strategies towards the flooding menace, have been empowered and made possible through the technologies of the drone as well as the advancement in remote sensing systems.

The UAS is a faster method of data collection that fits between the vast areas satellite and smaller coverage. Mounting a LIDAR on the UAS makes it possible to take to the skies virtually at any point the experts feel like collecting the necessarily referenced images required without the hassle of having to wait for manned aircraft or satellite imagery. The UAS has offered the all necessary accurate aerial data that has been in demand especially among the disaster management agencies (Klemas, 2013). The LIDAR system deployed through the UAS incorporates its remote sensing method that uses light in the form of pulsed laser to measure the ranges to the Earth. It is the light pulses coupled with other data recorded by the airborne system that generates the precise, three-dimensional information necessary for disaster management among them the evaluation of coastal flood risk. Therefore, the UAS deployment of LIDAR is the most effective method of assessing the coastal flood risk making flood risk management easier and more efficient. 

 

 

 

Usage of the UAS deployment of LIDAR to evaluate Coastal flood Risk

            The usage of UAS deployment of LIDAR to evaluate Coastal flood risk has revolutionized flood risk management in the world. The concept of flood risk management is widely embraced over the past decade, and more and more nations are adopting the idea. It has led to the deliberate changes in decision-making practice highlighting the risk management as a potentially more complex but efficient and dynamic model of addressing the problem of flooding. The requirements of protection and belief in the people’s ability to control floods started increasing in to dominate the attempts to deal with flooding. The emergence of the flood risk management came with it the perception of the flood management as not only an engineering pursuit but as a social endeavor (Klemas, 2015). Throughout the 1960s, the attempts to address the flooding menace remained on more physical flood control efforts such as the building of levees, dikes, dams, diversion channels and other related structures. However, as the population grew over the years, the impact of flooding continued to increase and hence the need to do things in another approach. There was the need for an approach to that would utilize the concept of risk management in the decision-making process. It is this that encouraged the incorporation of technology to the disaster management and risk management endeavor. It led to the findings on the use of UAS and the LIDAR to be able to predict and mitigate flooding. With the employment of the technologies, it has resulted in an increased efficiency of risk management especially to flooding among other disaster management endeavors (Webster et. al., 2006). 

The LIDAR system as a remote sensing method has played a significant role in the disaster management cycle. Emergency management planning usually structured around the disaster management cycle. The cycle is composed of 4 major stages namely the reduction, readiness, response, and recovery. The remotely sensed data collected through the LIDAR deployed through the UAS can provide the valuable source of information at each stage helping one to understand the spatial phenomenon. It also provides the scientists and the relevant authorities with the objective data sources essential for decision making (Webster et. al., 2006). The major challenge faced by disaster management is the inherent unpredictability and range of hazards that does not allow for a single all-encompassing solution that needs to be developed and also explored. However, it offers a variety of differing remote sensing platforms and sensors employed for image acquisition.

The LIDAR remote sensing system can be used to assist in reducing the risk through the identification of hazardous zones associated with floods. It may also be used to verify the hazard models by measuring the location as well as the magnitude of the actual events. Imagery obtained through the LIDAR deployed by the UAS can be used by the meteorologist for providing weather forecasting and also provide warnings of potentially severe weather events providing the public and the emergency responders with the right information that can assist in making decisions around the short-term readiness. The imagery of disasters such as flooding is widely shared in all forms of media as a way to offer warning and caution to the affected persons. With the aid of the images, people that are at risk can understand and acknowledge the severity or extremes of the lingering disaster and therefore can take the relevant preparedness, mechanisms. For those that respond to disasters, the images obtained may offer them the right form of information necessary for preparing to mitigate and the impact of the disaster including evacuation efforts if there is perceived an extensive threat to human life. Remote sensing through the LIDAR can also be sued to provide the indication of the rate of recovery in a given area post-disaster based on the indicators such as vegetation re-growth and reconstruction which is crucial for planning and emergency preparedness.

The LIDAR systems deployed by the UAS can be very instrumental in the 4 phases of the disaster management cycle as follows:

Phase 1: Reduction

Disasters have been proven to be social constructs in that social driver have a role to play in the happening of such catastrophes. Some of the social constructs include migration, conflict, modification of natural systems, and overreliance on scarce resources, urban pressure, artificial protection structures as well as economic and political vulnerability. All these constructs are contributors to the people’s vulnerability to the hazards. LIDAR as a remote sensing technology can be very instrumental in addressing some of the disaster drivers through the proviso of data required to assist the planners, and others tasked with emergency management. The reduction or risk leads to the reduction of the probability of a disaster to happen a very crucial part of disaster management cycle. The LIDAR system can be paramount at a reduction of risk through identification and the understanding of the hazards. It is the knowledge obtained that is used to put in place some mitigation measures such as engineering structures, planning and analyzing the consequences of the risks which is fundamental to reducing vulnerability to such disasters (Webster et. al., 2006).

Understanding the magnitude, frequency, duration, location, manifestation and range of a hazard is essential for all disaster management endeavors. In as much as the social factors amplify the occurrence of a catastrophe, improved knowledge of such hazards and their potential consequences are essential to shaping up decision making about the modification of hazardous characteristics. It can also be sued to derive hazard-independent information that is critical to disaster reduction such as baseline building and topographic mapping (Webster & Forbes, 2006). LIDAR mapping for active fault location has been in use over time effectively. Conventionally, fault location was conducted with stereo aerial photography interpretation that was followed by intensive field survey. However, with the use of LIDAR, there is horizontal and vertical resolution provided by the airborne LIDAR imagery through its deployment in a UAS that provides the capability for identifying the faulty traces and also extracting elevation offsets with digital data in a very objective manner. The LIDAR technology has been used over the course of time in useful ways. Such examples may range from the Bridgewater Town LIDAR survey to assess the flood risk of the town in 2012 among other cities such as Lunenburg County in 2009. It is this evidence that echoes the efficiency of the model (Webster & Forbes, 2006).

Phase 2: Readiness

With the realization that residual risk from hazards has the potential to create emergencies and in some cases disasters, some readiness planning and activities are embarked on. Readiness is the process of the identification and also the development of the necessary systems, resources and skills before the happening of a hazardous event. The aim of readiness is to ensure that the response to the hazard is more coordinated and efficient to make sure that the community experience lesser trauma and recover on time (Webster & Forbes, 2006). Some of the readiness attempt employed by a community or disaster preparedness agency are public education, training and exercising, evacuation planning, developing hazard monitoring strategies and public alerting systems as well as instituting state and international plans and agreements for aid and assistance. It is such readiness resulting that leads to the reduction of the impact of a disaster on the community.

The information provided by the LIDAR systems is essential and acts as asset information that makes the possibility of readiness to the hazard attainable. Gaining familiarity with the most up to date spatial information such as imagery as is provided for by the UAS deployed LIDAR is crucial at assessing the damage during the response and recovery phases. LIDAR is used to produce high-resolution hazard and risk maps to the communities. It is the information provided by the remote sensing system that enables individuals as well as disaster management agencies to have the information about the location and range of hazards. If communities have the crucial information on the risks, then readiness is possible hence mitigating the impact and danger of such a happening.

Phase 3: Response

The response endeavors majorly focus on protecting property as well as the lives of the people in case of a disaster. Such activities include evacuations, sandbagging along the coastal lines, search and rescue operations, evaluating the safety of buildings in the event of flooding, establishing immediate emergency shelters as well as setting up command post among other quick responses that come with response phase. LIDAR a remote sensing technology may be very crucial in this phase at providing the immediate damage assessment if the data is provided promptly. Incorporating the UAS technology with the LIDAR system makes the assessment faster than ever before since it is easier and quicker. The LIDAR systems contain information and data that is crucial to enabling the making of evacuation plans through the combination of observing the weather patterns and the hazard behavior.

Ideally, the recovery activities all commence with the beginning of the response phase that is made possible by the imagery and other data collected by the UAS deployment of LIDAR to evaluate the flood risk. It is at this point that process of recovery is kick-started in a holistic manner. It means that the assessment of damages undertaken through the remote sensing during the response phase is integral to the recovery phase as well. At the stage of recovery, the temporal relevancy of the LIDAR provided information is very critical to allowing disaster managers to make effective plans for mitigation on the dynamic solutions readily available to them. The near real-time information from the system offers the coastal risk management to plan how to address the flooding menace and as a result leads to the saving of resources and time ultimately saving lives as well. The information that is usually of sufficient spatial resolution also allows the detailed tactical assessments and decision-making ion the flooding condition.

Phase 4: Recovery 

The use of the remote sensing technology such as LIDAR in the recovery efforts is the least developed technology in this area. However, the remote sensing can make critical contributions to the provision of objective time series over a large area that have both high and medium levels of spatial detail. In other specialization, the time series analysis of the remotely sensed data is a well-established practice. In the disaster management and primarily the recovery phase, some very clear indicators can be easily measured and also monitored with LIDAR imaging made possible by its deployment by the use of a UAS. Some of the indicators may include the construction and the following removal of the medium and long-term emergency shelters, removal of debris, starting and-and completion of construction or reconstruction of infrastructure such as buildings, roads and bridges, re-growth of vegetation and also the reduction of siltation from the waterways following a flooding event.

By the use of spatial resolution provided b y the LIDAR systems, the amount of housing reconstruction can, at least, be visually identified in the presence and also the absence of blue tarpaulins covering the roofs following the devastating Hurricane Katrina event (Webster & Forbes, 2006). The development of the UAS to deploy the LIDAR is a step in the right direction at enabling an automated detection method that is less time consuming to identify quickly and repeatedly in a series of data and time set. Moreover, the analysis if time series imagery could also be crucial at monitoring the efficiency of the various strategies. By extracting the recovery rates from the data gathered at time intervals could help in assessment and also assist in guiding future events of similar nature, it could also contribute to identifying some of the areas of residual risk that may require further monitoring until the physical recovery process is completed.

 

Advantages of UAS deployment of LIDAR to disaster management

LIDAR has the spatial density and also the vertical precision that is required to map coastal areas at risk of flooding and other disasters. The high resolution of the of the LIDAR digital elevation model (DEM) can easily be in a good position to capture embankments such as raised roadbeds that could prevent flooding towards inland causing risk to the population settling along the coastal lines. The use of the UAS makes it easy and even efficient at nothing the DEM across roadbeds to stimulate the connection between the oceans and the upstream low lying areas especially in sections where connectivity was present due to culverts or bridges (Sayers et. al., 2013). The LIDAR data is also used to evaluate the potential for overtopping and also dune erosion on a large coastal spit since the UAS has enhanced the coverage of such areas with ease and speed. It can also derive maps that could be crucial to the communities living in a disaster-prone area as well as the regional planners for use in the planning process and also assist them in the development of long-term adaptation strategies that are informed and updated.

The combination and use of the UAS and LIDAR technologies had made it easy and also possible to conduct topographic surveys for area impact assessment as well as reconstruction in the case of any disaster. The USGS has taken advantage of the LIDAR technology to carry out studies. Using the remote sensing technology that is remotely deployed using the UAS can be in a position to collect very high-resolution elevation data that support scientific studies related to hurricane impact, flooding impact and other disasters that may be glaring the country. It has also made it possible for recovery and rebuilding process, emergency response assessment as well as planning, post-disaster documentation as well as other resource management activities. The USGS has over the year taken advantage of the technology at collecting and compiling data for the coastal and inland areas as the basis of the extent of Hurricane Katrina and also the age and quality of the valuable data. The LIDAR has also been an instrumental tool at the USGS-led multiagency initiative to systematically acquire improved, high-resolution data across the United States.

Accurate aerial data demand is on the rise in all areas of disaster management as well as response. The use of the UAS technology came to solve the problems that previously faced scientists and risk managers in all field. The unmanned aircraft system (UAS) offers numerous advantages especially when it has a LIDAR attached to it while taking up to the skies. The UAS is capable of delivery in that it allows the experts to take up to the skies virtually at any time that they plan to collect geo-referenced images one requires. It is hustle free since it eliminates the bureaucracy of having to book and wait for the manned aircraft or even satellite imagery that may be time-consuming in some instances. The UAS is as easy as planning, fly and download the images and process the data immediately (Klemas, 2015). Moreover, the resolution of the UAS is significantly higher and even accurate than any other satellite and even than that of the manned aircraft can achieve. Also, the altitudes that the UAS can fly the issue of cloud cover is eliminated meaning that there are fewer weather delays it experienced and as a result there is less unusual imagery. Whatever the field that any experts may be concerned with, whether in forestry, asset management, agriculture, environmental protection, humanitarian, oil and gas, remote sensing and any other that may require risk management and disaster mitigation, the UAS offer the real benefits. It provides the most accurate data in a quick and cost-effective way.

The LIDAR mapping systems consist of three very efficient components that make it stand out in all other remote sensing technologies. It contains the laser ranging system, an inertial measurement unit (IMU) and the global positioning system (GPS) (Er. Rahul, 2016). The three systems are integrated to offer the horizontal coordinates as well as the elevation of each laser return. The earlier LIDAR systems were capable of recording a single return that was either the first or last pulse that was reflected by the target. The latest LIDAR sensors that are in sued in the current society are capable of recording multiple returns, typically, at least, the first and last pulse, with some sensors recording up to four immediate returns and even in some cases can record the intensity of the reflected pulses (Er. Rahul, 2016). The combination of the UAS and the LIDAR technologies has made the technology even more efficient and effective at the disaster and emergency management making it possible to accurately and efficiently, map out threats and also plan and execute recovery and emergency responses in cases of a catastrophe.

The remote sensing technology in the form of LIDAR systems incorporated in a UAS can be used to inform many aspects of the disaster management cycle. It is fundamental to consider all the aspects of disaster management as well as emergency management rather than focusing in emergency response alone. The LIDAR system can provide such comprehensive data and information that is crucial at going through the four cycles of disaster management. By incorporating the LIDAR system as into the reduction and readiness activities, it can also educate both the emergency management staff and the community about the type of information so that they are familiar with its use under response. The fundamental element of the usefulness of remote sensing data obtained by the LIDAR systems in support of the disaster management entities can provide the appropriate information in a manner that is spectral, temporality and spatially relevant. Also, there is a need to be aware of the information requirements of the disaster management community and also to tailor the remote sensing information to meet the needs (Sayers et. al., 2013). The achievement of this can only be done through the incorporation and collaboration of the disaster management community and the remote sensing or the geospatial community. The information gathered is fundamental to creating the readiness to the inherent hazards, reduction of the intensity as well as the impact of the disaster or risk, response to the dangers once they occur and also to the recovery process. By taking advantage of the information provided by the geospatial community that may be using the LIDAR systems the intensity and adversity of hazards can be reduced and also lead to sufficient planning and execution of plans to mitigate and also recovery from a disaster. Therefore, the technology has led to a massive saving of lives, property and even resulted in the creation of sufficient and efficient plans to address emergency management (Harman et al., 2014).

Another significant advantage of the LIDAR systems especially when coupled with the UAS technologies is that it is unobtrusive and environmentally friendly. Unlike other ground survey techniques that may be employed the airborne LIDAR can fly over the areas where access is limited undesirable or even impossible. It can avoid unnecessary tree cutting and other activities that may result in harming the environment all in an attempt to get the work done. It also has flexibility since the data obtained through the system can be used for anything. It is due to the immense point density that it achieves from LIDAR its accuracy and also its ability to penetrate the ground through foliage even in vegetated areas. As a result of its versatility and speed at collecting data, it can save clients a lot of money and time. It can be sued for many projects where DEMs are required and hence reduce the survey time and efforts directly translating to saving the clients the costs as well (Sayers et. al., 2013).

 

Disadvantages and opportunities for improvement for the UAS deployed LIDAR systems

The expected accuracies of the airborne LIDAR may be affected due to the shortcomings that the system components that is the GPS, IMU, and laser face they all have accuracy limitations which for the most part are understandable and in some cases predictable. Other factors affect the product accuracy of the LIDAR that arises from flight planning and flying conditions of the UAS, the atmospheric effects, the terrain undulation as well as the vegetation cover. As a result of the possible shortcomings of the system, there is need to hire and engage LIDAR practitioners that are careful and experienced at assessing the factors that may affect the system. There is also the necessity of incorporating and contracting agencies that can establish quality controls plans with contractors to include the sufficient ground survey checks. Having to contract and also engage some of these experts may increase the cost of using the system further than if the system was accurate at its work. The quality control experts are the ones that have to validate data obtained from the project area by the LIDAR system which also may lead to consuming of more time. Bearing in mind that disasters at times come at unplanned or unanticipated moments, the time was taken to validate such data may mean that it may leave the emergency management agencies limited time to respond or at times are caught up while still in the process of verifying and analyzing the data (Klemas, 2015).

Some of the other factors that may affect the accuracy of the LIDAR may include:

•         The quality of the hardware and the software that is in use is a major factor that could have an impact on accuracy of the LIDAR system. There is, therefore, the need for the experts to enhance and also accurately monitor such hardware and software. The experts should also engage in trying to improve the quality and the reliability of such hardware and software used by the LIDAR system (Harman et al., 2014).

•         The knowledge of the planners, office staff and the operators are also a factor that may affect the accuracy of the data obtained in an airborne LIDAR. It is because some of the errors of the LIDAR system are ascertainable and therefore those involved in analyzing and assessing such data need to be very qualified and experienced in the field. There is a need to enhance the system to offer higher accuracy so that it cannot be reliant on the judgment and the knowledge of individuals who are in some cases bound to make mistakes due to other external factors and may lead to very costly errors in the disaster management cycle.

•         The flying height may also be a factor. With the UAS, the flying height is not limited but with areas densely populated with very tall buildings or forest cover, it may necessitate the device to fly higher which may leave room for errors.

•         The scan angle may also affect the accuracy of the data obtained. It is important in the penetration of vegetation and therefore those that operate and use the LIDAR system ought to be useful at the choice of the scan angles.

The UAS also experiences shortcomings ion that it has limited abilities. They cannot communicate with the civilians or the experts for more detailed intelligence or information other t6han what they are programmed to focus on at a given time. The UAS cannot also be used to map out a particular thing since they concentrate on assigned areas and not the specific details. They are also not in a position to make informed choices or decisions that may be a manned aircraft would in cases of unforeseen circumstances. They totally rely on the judgment and the decisions made by the operators that may not have the clarity of the situation as the manned aircraft would have if they can see the situation firsthand (Harman et al., 2014). They are also a very expensive technological advancement and therefore, a majority of the developing countries may not be in a position typo afford such technologies coupled with the LIDAR systems to engage in disaster management.

 

 

 

 

Is the UAS deployed LIDAR technology growing or not?

The LIDAR system has revolutionized the survey and mapping world over the course of time with its increased advancements over time. The hydrographic LIDAR has been a viable survey tool since the 1980s. With the initiation of a full constellation of GPS in the early 1990s, the LIDAR system took a giant leap forward in being able to provide accurate data even for tough survey operations (Yadav et. al., 2013). The LIDAR systems have also evolved from relative physics experiment to a useable and reliable survey tool. More people are buying the LIDAR for mapping and survey, and the inclusion of the UAS technology to the LIDAR has made the system even more appellate growth over time increasing its efficiency and accuracy of data collection in all disaster management efforts. It has further grown due to its ability to acquire, process and quality control data within a very short time frame while at the same time minimizing costs, saving time and efforts of the users. It has further empowered clients and its users due to the speed at which data is collected making it ideal for use in disaster management, and it is this that has led to the growth of the technology further.

There are also ongoing initiatives in a direct effort to identify the areas that the technology allows for value added products to be generated or where it offer marginal cost reductions over traditional survey methods. In conclusion, the LIDAR technology coupled with the UAS has led to significant impact on the survey and mapping industry. There are also significant societal and economic benefits that accrue to the users through its use. Therefore, the UAS deployment of LIDAR is the most effective method of assessing the coastal flood risk making flood risk management easier and more efficient.