Commercial Multirotor UAV Campaign on Data Acquisition for Disaster Management

UAV usage and interest have shown great popularity recently, especially for commercial multirotor. It is cheap, easy to use, flexible, and has many capabilities. That is why multirotor is widely chosen in disaster management. As a technology, it possesses certain aspects. Review of how the implementation of multirotor UAV in disaster management is important to gain improvement in the technology and evaluate at how we use it. This paper provides insight into commercial multirotor UAV campaign in disaster management through literature study and personal experience in a related theme. Similar ideas on the development of UAV and its application in disaster management then combine with personal experience was used to identify the advantage, disadvantages, challenges, and opportunities of multirotor drone applications. The result suggested that multirotor UAV has limited capability in conducting disaster management campaigns. The weakness in deploying multirotor is related to the lack of technology which may be overcome in the future as the development in hardware and software technology.


Introduction
Rapid data assessment in every fieldwork related to any field is preferable. Since a long time ago, methods on data collection has developed to have adequate data with less time, effort, and capital. In the earlier times, data assessment for post-disaster relief was done manually by laboring surveyor to collect a large amount of data. This traditional method is time consuming, painstaking, and expensive. Another method comprising satellite imagery and aerial photograph has long been used for disaster management comprising pre-and post-disastrous campaign [1], [2].
Earth`s surface data acquisition or earth observation by satellite image for disaster management rapidly increases because of its rapidness and detail [3]. Technological advance in sensors and satellite is the factor of the increasing demand for satellite imagery. Satellite as part of aerospace technology, plays an important role in disaster risk reduction, thus rapid data acquisition, high temporal resolution, and all-weather capability is a must [4]. Satellite imagery and its wide options of sensors have the requirement mentioned by Verstappen. The satellite also has its advantages by its wide-area coverage, and the selection of sensors which some area weatherproof. Despite the advantages, satellite imagery is lacking on temporal resolution (only some have high temporal resolution) For non-radar sensors, most of the sensors are depended on the weather, which means that the cloud will be a big interference for

Methods
Commercial drone experience and its related data on disaster management were obtained not only from authors experience and previous research but also depends on the literature studies. Previous research selected in this study were disaster management covering multi-type of hazard which utilize drone/UAV/UAS for their data acquisition.
As literature study in this study is part of a narrative study which represent a generalization of ideas or cumulative knowledge [19], [20], [21] on the topic of disaster management with the utilization of multirotor drone for data acquisition. Cumulative ideas presented in a table to be easily recognized. Conclusion on the application of multirotor UAV synthesized from the shared ideas among the previous studies to find the benefit, disadvantages, challenges, and opportunities in the future.
This method was chosen as much data are available outside of the author`s possession. They came in books and journals. The only way to reach and collect the information was through the literature study as presented by several works in the various theme of drone [22], [23], [24]. There are several steps to obtaining the information and drawing conclusions. The first step was literature retrieval in the form of  [25], [27] In the US, multirotor, especially quadcopter is the most favourable among the hobbyist. DJI, one of many drone corporations still becomes the ruler of drone market share globally (Mordor Intelegence, 2020) with multirotor as the biggest type of drones in the market. Multirotor drone tends to have a more stable image capturing which increase the accuracy and number of the image due to the low-speed flight coupled with the ease of vertical take-off and landing [28]. A comparison of the basics of technical properties of multirotor drones that commonly used for survey and mapping is sown in Table 1. The table show variety of multirotor drone, from the small recreational drone, up to the big-heavy-dutyindustrial purposed drone. The price also varies between hundreds to thousands of dollars. Some are originated for recreation purposes but can be enhanced into survey and mapping with the addition of mapping and surveying software.  The recreational purpose for several drones is mainly for image capturing and video recording with the enhance of the capability of the drone such as following objects, following points or tracks, fly in circles, or following several rules. Enhanced software for mapping is introduced by several developers. The software has two main functions, first is to plan the flight track and properties such as speed, altitude, overlapped size, type of orthophoto, and camera angle. Second, the software is used to aid the image processing process and analysis, for example, to produce the mosaic, DEM, or analysis on the vegetation. Some software has multi-platform use, desktop (pc-based), and mobile (installed the mobile device). To have better assistance from the software developer, the user must make a payment subscription, unless only basic or time-limited service can be provided by the developer. Several software developers provide free service for flight planner in a mobile platform, and it can be used only for several drone manufacturers. Some software for flight planning and analysis are available such as Pix4D, dronedeploy, DJI ground station pro, Map pilot, etc. That software can enable the autonomous and semi-autonomous flight over planned track/points with the ability to override the control during the flight. In mobile platforms, some software can be run under android or iOS which is come handy for most users.

UAV Operation on disaster management.
Data demand right after the occurrence of a disaster covering the abrupt changes of the affected area is one of the top priorities in disaster management, so rapid data assessment is crucial [29] to provide data to improve the response and mitigation of the disaster [30]. Rapid data assessment after the onset of disaster can be covering a large sector including access and security, demographics, community resources, health, water, sanitation, food and non-food items, and shelters [31], and most of the data can be obtained from remote sensing survey [29], including the deployment of UAV. Aside from rapid data assessment, a UAV survey in a disaster can be applied to mitigation as a pre-disaster event. This application is widely used and reported by many researchers (see Table 2).
A previous study inferred that UAV campaign for disaster management is a sophisticated method that enables users to achieve data easily and rapidly with less effort and resources. Its ability to take off and land in limited space is also a key factor for the vast campaign of multirotor in disaster management. Various method of hazard management application, algorithm, and modelling has been developed to enhance the success of disaster management. Modelling and monitoring regarding mass movement have been conducted, so any changes in the environment that can trigger the landslide could be detected early to minimize the damage and loss [12]. The same concept also applied in mitigation of volcanic eruption of Stromboli Volcano by utilizing thermal images to produce 3 dimensional model of the volcano [14].
Frequently, UAV is mobilized due to assessing the surface conditions in the post-disaster event. Multirotor can also be deploy in this kind of event due to its flexibility. A study on the utilization of commercial quadcopter for mapping in the impact of landslide onset was carried in Banyumanik [42] and in Bangli, Bali as the result of flood and landslide a day before [32]. Based on the study carried by Azeriansyah, Prasetyo, & Yuwono, they can identify the affected area with good accuracy compared to the standard issued by Geospatial Information Agency (BIG/Badan Informasi Geospasial) under the regulation of the head of Geospatial Information Agency Number 15/2014. While based on the study by Wulan et al., they did not specify the technical result related to the data accuracy as they did not focus on that issue. Their study mainly focused on the mapping of the area affected by the flood and landslide. Another utilization of UAV and on landslide data measurement in India resulted in 5% difference between measurement using data assessed form UAV and data obtained from field measurement using a total station [13].
Disaster comes in many forms and triggering factor. Man-made structure and technology also exposed to a certain possibility of failure due to natural and artificial events. UAV mission for monitoring and assessing data on technology/engineering failure is common nowadays. Certain UAV deployment on an artificial structure is regularly made to investigate damage and verdict future possibilities and steps in disaster management. The sample of this work presented by Leizer  in 2017, when the utilize drone in the railway accident and disaster. Their work was motivated by the large amount of hazardous substances being transported using trains, and often accidents occur in the process of transporting the substance. They develop a method to monitor and assess the data utilizing RFID (Radio Frequency Identification) to identify the transported goods, their company, and any other data. They also revealed that deployment of drones, especially multirotor gave a huge benefit as their sensors are interchangeable and cheap. identification of hazardous radioactive waste or substance also can be monitored using a thermal sensor-equipped drone. Assessment on a structure which has high potential of danger requires the assistance of drone. If the result of drone assessment suggested detail manual observation, then human intervention is needed. The example of this work was done by Aiello et al. in 2020, they promote the use of mini-UAV in an inspection as to its participation in mitigation. Based on their study, mini-UAV with MTOW (Maximum Taking off Wight) is less than 300 grams, has a high potential in the monitoring stage of mitigating disaster risk in an industrial complex.
Even after several weeks of disaster occurrence, UAV participation is still possible. Works on tsunami impact and its inundation distribution and run-up heights did 1 month after the onset was conducted in Sulawesi as the response of landslide-generated tsunami triggered by an earthquake [38]. Based on the study, Mikami and his team able to identified the run-up height, inundation distribution, damage pattern. They conclude that the topographical factor plays an important role in the distribution of inundation. Another example of UAV deployment after the earthquake presented by Qi et al in 2015 after the Lushan earthquake in china. He deployed rotary-wing UAV to assist in SAR (search and rescue) process by capturing and processing data through low altitude flying. The mission proves its applicability and saves time by utilizing the rotary-wing UAV.
UAV comes in many sizes, capability, and prices. Each drone is unique due to its characteristics. Large size UAV with high capability and endurance may be used as a logistic carrier during the postdisaster campaign. This idea is brought by Estrada   Some disaster requires height data, such as for tsunami, mass movement, flood/inundation, liquefaction, etc. Height data is obtained by photogrammetry of the overlapping photograph from an aerial acquisition. Aerial image captured by UAV can be processed using various software developed by various developers such as global mapper, esri, Agisoft, dronedeploy, pix4d, etc. Many analyses and properties regarding the process can be adjusted. More accuracy in georeferencing can be enhanced  Figure 2.
Height data extracted from the photogrammetric analysis will be in a DSM (digital surface model). DSM still including the height of land covers such as trees and buildings, while DTM only represents the bare earth [43]. Based on DSM dan DTM, some analysis and modelling can be conducted for mitigation and damage assessment. Meanwhile, an aerial photograph is used to interpret the surface properties such as land use and land cover, structural damage, affected area, and resources identification.

Discussion
Based on the result derived from the literature study and personal experience in utilizing commercial multirotor UAV in disaster management, several aspects can be identified respectively as seen in Table  3 with the following discussion. The good thing coming from multirotor UAV is its many benefits. Many commercial multirotor available in the market are small, even foldable, and some can fit in a pocket. Its practicality will come handy during fieldwork where we have to carry so many additional equipments. We often use small size foldable UAVs such as DJI Mavic Pro. Its often used during our research and fieldwork to assess the environmental condition or reach inaccessible points from a safe place [44] and conduct aerial mapping to obtain a surface elevation model. Commercial multirotor can be controlled easily using a remote control or remote control with a mobile device connected to the controller. Some models provide double remote control as pilot control the movements and cameraman control the camera/sensor. To have consistent speed and direction, a flight plan for fly autonomously/semi is made. From the software flight pattern and properties can be adjusted to ensure the best overlap and result of the aerial photograph [45]. The many reasons why multirotor is chosen is for its price, easy to control, and maneuverability. Its VTOL (Vertical take-off-landing) capability assures the flexibility in any field and terrain of operation. Some small multirotor UAV can take -and land in the face of a palm. Movement of the UAV during flight contributes to the accuracy of the data it obtained. One movement that can only be done by multirotor than fix wing is hover maneuver. It is a still flight condition mid-air. This maneuver is beneficial as we can concentrate and examine objects without moving. The movement of multirotor UAV ensures the stability of data capturing [28], [46] which resulted in a better aerial image and accuracy [28]. Several missions require a custom-made apparatus to be mounted on a drone. Such as  [15], [16], [17], [18] and radiation monitoring [47], [48], [49].

Disadvantage.
Despite multirotor advantage, as opposites, it possesses several weaknesses that in the future may be overcome with the introduction of new technology. As for today, many commercial drones are lack of flight time, range, covered area, wind-resistance, payloads, and sensor. In several occasion, mapping mission using our quadcopter create a horrifying moment. As we have several mappings done in the windy coastal area, our quadcopter cannot meet the maximum flight duration. Once, we experienced only less than 5% battery remained with flight time less than the maximum duration. Based on our colleague`s experience, they have lost drones due to a signal lost on the hilly and forested area. It is not only happened in multirotor, fix wing also experienced similar events sometimes. This event demonstrates the deployment of multirotor UAV carrying risks. Topographic barrier, high and dense vegetation cover may disrupt the signal. The maximum range and flight time may be reached under preferable conditions. Problems in several cameras found in several commercial multirotor. The camera tends to condensate and produce blurry and misty images due to changes in atmospheric pressure and temperature during flight. This mist will be gone as the UAV stay longer in the air. The example of the blurry and misty image can be seen in Figure 3. The introduction of UAV is a revolutionary thing [6]. Introduction of a drone to the rapidly changing society carries a great challenge. Issues on terrorism, crime, and invasion of privacy emerge related to drone deployment. To prevent misuse and protect the community, several regulations are made due to the application of UAV and the use of air space to ensure flight safety. Pilot as the controller and decision-maker in the drone deployment needs to be well educated on flight safety, regulation, and understand the use of air space as well as a responsible individual. Every UAV deployment is using air space that must be shared for some interest such as commercial, recreation, and military. Each air space has its regulation that needs to be followed by the user and the UAV pilot. Besides that, drones development is facing a level where a new novel drone is expected with the ability to fly autonomously in every condition for many purposes [9]. Related to disaster, UAS need to be developed to enhance the effectivity, flexibility, and the rate of success of UAV deployment in the field to support disaster  [50] and data safety [51].

Opportunity.
Technological development has created a vast possibility for multirotor drone to advance. From sensors, flight systems, power sources, and capability [52] that will open new opportunities of UAV, especially multirotor new mission and field. Also transformable multiotor UAV has been developed to increase its manuverable, movement, and flexibility [53]. Based on current technology, UAV has been applied in the field of disaster management, crime prevention, law enforcement, border police, life safety and healthcare service, military service, commercial, construction, private uses, education, research, entertainment, sport, logistic, firefighter, agriculture, geology, astronomy, meteorology, and environment [34], [36]. Commercial drone, especially for multirotor, has shown a huge interest in the market and provide a huge amount of profit. Business on drone become a new prospect. The huge drone technology will be achieved for the next decade as computer technology is greatly advancing [54].

Conclusion
Multirotor technology provides new insight into the possibilities of UAV deployment in many fields of interest. Furthermore, the large usage of multirotor UAV has risen alarms on privacy, safety, air space usage, and regulatory system. In needs time for UAV to be fully accepted in daily life. Multirotor is widely used in daily activity because of its advantages, from price, flexibility, and capability. The weakness of multirotor for a disaster management survey is related to the technological aspect related to the software and hardware. Those weaknesses can be overcome with the future advance of technology. As the technology in multirotor UAV is advancing, market interest will grow in its resemblance. Overall, according to the literature study and personal experience, commercial multirotor UAV has a proper but limited capability in disaster management campaigns due to its weakness. The high usage of multirotor UAV for disaster management represents its benefit as a system, as it provides many benefits and promises a high possibility in future technological development.

Acknowledment
This paper is a generalization and summarize of our several previous researches and projects for the previous 5 years. The researches and projects were done with the supports of many sources of funding and backed by student from Institut Teknologi Yogyakarta (ITY), Amikom University, and surveyors from many places for.