Overview and Current Status of Remote Sensing Applications Based on Unmanned Aerial Vehicles (UAVs) Gonzalo Pajares Abstract Remotely Piloted Aircraft (RPA) is presently in continuous battery or energy system’s capabilities. There are vehicles with development at a rapid pace. Unmanned Aerial Vehicles the ability to fly at medium and high altitudes with flight dura- (UAVs) or more extensively Unmanned Aerial Systems (UAS) tions ranging from minutes to hours, i.e., from five minutes are platforms considered under the RPAs paradigm. Simulta- to 30 hours. The horizontal range of the different platforms neously, the development of sensors and instruments to be is also limited by the power of the communications system, installed onboard such platforms is growing exponentially. which should ensure contact with a ground station, again These two factors together have led to the increasing use of ranging from meters to kilometers. Communications using sat- these platforms and sensors for remote sensing applications ellite input can also be used, expanding the operational range. with new potential. Thus, the overall goal of this paper is There are several different categorizations for unmanned aerial to provide a panoramic overview about the current status platforms depending on the criterion applied (Nonami et al., of remote sensing applications based on unmanned aerial 2010). Perhaps the most extensive and current classifications platforms equipped with a set of specific sensors and instru- can be found in Blyenburgh (2014) with annual revisions. ments. First, some examples of typical platforms used in An auto platform or remotely controlled platform through remote sensing are provided. Second, a description of sensors a remote station together with a communication system, and technologies is explored which are onboard instruments including the corresponding protocol, constitutes what is specifically intended to capture data for remote sensing ap- known an Unmanned Aircraft System (UAS) (Gertler, 2012). plications. Third, multi-UAVs in collaboration, coordination, According to Yan et al. (2009) and Gupta et al. (2013), UAS and cooperation in remote sensing are considered. Finally, are considered as the full system, including the aircraft, the a collection of applications in several areas are proposed,Delivered by Ingentaremote control station and all of the ground support elements, where the combination of unmannedIP: 192.168.39.151platforms and sensors, On: Sat, 25communication Sep 2021 13:24:12 links, air traffic control, and launching and together with methods, Copyright:algorithms, Americanand procedures Society provide for Photogrammetry recovery system, and Remote as may beSensing required (this is the opinion of the overview in very different remote sensing applications. the Civil Aviation Authority (CAA, 2015)). Unmanned Aerial This paper presents an overview of different areas, each inde- Vehicles (UAVs) are included in the category of UAS, i.e., they pendent from the others, so that the reader does not need to can fly autonomously, although they can be also remotely read the full paper when a specific application is of interest. controlled (The UAV, 2015). From the standpoint of remote sensing, the equipment of UAS is required for capturing information, which is later conveniently handled (processed, Introduction analyzed, or stored), but the term “UAV” is commonly used in Remote sensing refers to the technique of capturing informa- remote sensing. Therefore, in this paper, we will refer to UAVs tion at a distance (remotely) by specific instruments (sen- under the perspective of remote sensing operations, includ- sors). Traditionally, remote sensing has been associated with ing drones, gliders, (quad-, hexa-, octo-) copters, helicopters, satellites or manned aircraft with a set of airborne sensors. In balloon-launched gliders, airships, or stratospheric balloon the last decade, the increasing developments and improve- systems and more broadly, any unmanned vehicle with the ments in unmanned platforms, together with the development ability to fly auto-controlled using processors onboard, re- of sensing technologies installed onboard of such platforms, motely controlled with human supervision based on a ground provide excellent opportunities for remote sensing applica- station (remotely piloted aircraft; RPA) or through another aeri- tions. Indeed, they can offer high versatility and flexibility, as al vehicle under coordination. Certainly, from a strict point of compared to airborne systems or satellites, and can oper- view, all these systems should be considered as RPA systems, ate rapidly without planned scheduling. In remote sensing because they need human supervision; full autonomy is not operations with high human risk, lives can be safeguarded. generally yet achieved. Nevertheless, as mentioned earlier, Additionally, they can fly at low altitudes and slowly, with throughout this paper we will refer to them as UAVs. This the ability of acquiring spatial and temporal high resolution overview is focused on remote sensing applications based on data, representing important advantages against conventional small UAVs of different categories flying at relatively low alti- platforms that have been broadly used over the years. tudes with different take-off and landing systems, including Watts et al. (2012), Dalamagkidis et al. (2012), and Ander- Vertical-Take-Off-and-Landing (VTOL), where UAVs operate in son and Gaston (2013) provided a classification and use of different scenarios and situations. The potential use of UAVs platforms where an important issue that determines this clas- sification is the altitude they can fly, ranging from a few meters up to 9,000 m or more. Micro- and nano- air vehicles can fly Photogrammetric Engineering & Remote Sensing at low attitudes with limited flight duration because of their Vol. 81, No. 4, April 2015, pp. 281–329. 0099-1112/15/281–329 Department of Software Engineering and Artificial Intelligence, © 2015 American Society for Photogrammetry Faculty of Informatics, University Complutense of Madrid, and Remote Sensing Madrid 28040, Spain ([email protected]). doi: 10.14358/PERS.81.4.281 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING April 2015 281 in remote sensing has been reported in many works with high with a set of specific sensor technologies and also with performance exploring areas of different sizes, sometimes several UAVs working in concert with each other. With such hazardous, with assumable costs as compared to traditional purpose, as far as it has been possible, we have collected most airborne or satellite systems (Jardin and Jensen, 2013). The recent technological advances, especially in the last decade, range of applications makes UAVs suitable tools in remote where the boom has occurred. Nevertheless, apologies to au- sensing with an apparent market, which is to be consolidated, thors or possible references if some of them were not cited. when UAVs are widespread, which will likely be the turning Different worldwide international associations and forums point in remote sensing, as pointed out by Esler (2010) and have emerged related to UAVs, providing ideas, information Hardin and Jensen (2011) several years ago. and opportunities for members, users, and researchers while UAVs must navigate to perform the remote sensing mission; they cover most fields and application areas, including any re- for this reason they are equipped with different instruments lated to remote sensing. Commercial benefits are also consid- and sensors, such as, Global Positioning Sensors (GPS), Inertial ered without ruling out the use of all available resources for Navigation Sensors (INS), Micro-Electro-Mechanical Systems immediate humanitarian interventions protection or search (MEMS) gyroscopes and accelerometers, Altitude Sensors (AS) and rescue in disasters. Additional member relations, oppor- (Quinchia et al., 2013) or even camera-based sensors, among tunities, and training are offered, where remote sensing is an others (Shabayek et al., 2011; Bristeau et al., 2011), where important activity (UAS Vision, 2015; UAVa, 2015; UAVc, 2015; multisensory fusion techniques are required (Oh, 2010). Obvi- UAPA, 2015, UAVS, 2015; AUVSI, 2015). Also, local associations, ously, UAVs are generally configured with control strategies for at the country or region level, become more or less active autonomous navigation that must follow a previously planned from the remote sensing point of view. path, with the ability to make autonomous decisions. Obstacle In 2006, the NASA Civil UAV Assessment Team (Yuhas, avoidance is also required during navigation. Ultrasonic sen- 2006), defined Earth observation missions for UAVs, based sors (Bristeau et al., 2011) or 3D laser scanners (Holz, 2013) on user-defined needs to determine technologies, platform are sometimes also used for safe navigation, where they can capabilities, and a comprehensive civil UAV roadmap. Later, be used for detecting other UAVs around them. Also, dynamic Colomina et al. (2008) established some fundamental issues strategies for positioning, landing, and take-off, including of UAV-based photogrammetry and remote sensing as a para- VTOL, as part of the full path planning, is necessary in normal digm, identifying challenges and specific advantages. and adverse environmental conditions, where aircraft control Many institutions, research centers and companies world- in wind conditions is essential. Moreover, UAVs require ad- wide have addressed the challenge