Preface for the Special Issue of IJRS Drones section in conjunction with the 6th UAS4Enviro conference.

This special issue, which is published in conjunction with the new Drones section of the I International Journal of Remote Sensing i ( I IJRS i ), gathers five key papers from the 6 SP th sp I Small Unmanned Aerial Systems for Environmental Research i ( I UAS4Enviro i ) conference. The capability of optical UAS data to generate fine spatial resolution imagery, as well as Digital Elevation Models (DEMs), Digital Surface Models (DSMs), and Canopy Height Models (CHMs), are among the benefits of UAS data compared to satellite and airborne data. Although publicly available LiDAR data from airborne sensors is often a common choice over relatively costly custom-acquired data from UAS-based LiDAR sensors, UAS-mounted instruments are generally preferable for generating the very high spatial resolution required for site-specific surveys. Although UAS-borne LiDAR remains relatively expensive compared to multispectral UAS remote sensing, UAS technology holds much potential for making LiDAR data available in areas where airborne data is prohibitively expensive, especially in less developed countries. [Extracted from the article]