Unmanned Aerial Systems (UAS) for environmental applications special issue preface

Drones are indeed a key new technology for remote sensing, and one that has grown rapidly in recent years. According to the database, Web of Science (published by Clarivate Analytics), the first significant use in IJRS of any of the terms UAS, unmanned aerial vehicle (UAV) or drones, for example, in the title, abstract, or keyword of an article, was in 2009, in a paper by Dunford et al. (2009). It was not until 2012 that another paper used one of those terms. After that, the numbers increased very quickly, and by 2017, IJRS published 68 papers that referenced these terms. Most notably, 2017 also saw the first IJRS special issue on UAS, titled ‘Unmanned aerial vehicles for environmental applications’ (The Editors 2017). This current special issue is a direct follow-on from that major collection of papers, and the fact that we are able to have two major special issues on this topic in the space of just over one year, is further evidence of its importance