UAV-based technologies are evolving and improving at a rapid pace. The abundance of solutions and systems available today can make it difficult to identify the best option for construction and civil projects. The purpose of this literature review is to examine the benefits and limitations of UAV-based sensing systems in the context of construction management and civil engineering, with a focus on camera-based and laser-based systems. The risk factors associated with UAV operations at construction sites are also considered.

Coastal environments are some of the most dynamic environments in the world. As they are constantly changing, so are the technologies and techniques we use to map and monitor them. The rapid advancement of sUAS-based remote sensing calls for rigorous field and processing workflows so that more reliable and consistent sUAS projects of coastal environments are carried out. Here, we synthesize the best practices to create sUAS photo-based surveying and processing workflows that can be used and modified by coastal scientists, depending on their project objective. While we aim to simplify the complexity of these workflows, we note that the nature of this work is a craft that carefully combines art, science, and technology. sUAS LiDAR is the next advancement in mapping and monitoring coastal environments. Therefore, future work should consider synthesizing best practices to develop rigorous field and data processing workflows used for sUAS LiDAR-based projects of coastal environments.

Small unmanned aerial systems (UAS) have been increasingly popular in surveying and mapping tasks. While photogrammetry has been the primary UAS sensing technology in other industries, construction activities can also benefit from accurate surveying measurements from airborne LIDAR. This paper discusses a custom-designed low-cost UAS-based LIDAR system that can effectively measure construction excavation and bulk piles. The system is designed with open interfaces that can be easily upgraded and expanded. An error model was developed to predict the horizontal and vertical errors of single point geo-registration for a generic UAS-LIDAR. This model was validated for the proposed UAS-LIDAR system using calibration targets and real-world measurements from different scenarios. The results indicated random errors from LIDAR at approximately 0.1 m and systematic errors at or below centimeter level. Additional pre-processing of the raw point cloud can further reduce the random errors in LIDAR measurements of bulk piles.

There is a demand for noncontact, high-accuracy, high-spatial-resolution, wireless sensing technologies for various water level and coastal monitoring applications. This paper presents a low-cost, compact, easily configurable interferometry radar for noncontact water level monitoring, including its hardware design, signal processing algorithms, and wireless communication strategies. Interferometry radar measures distance by comparing the phase lag between reflected and transmitted signals. Water level measurements using this approach have been demonstrated in a solitary wave laboratory experiment, a field deployment observing wave run-up near Ponte Vedra, Florida, and a field deployment observing waves and tides in the Sparkill Creek located in Piermont, New York. The experimental results from the radars with millimeter-level accuracy have been compared with reference sensors and demonstrate the potential of continuous wave radar for water level observations. There is a demand for noncontact, high-accuracy, high-spatial-resolution, wireless sensing technologies for various water level and coastal monitoring applications. This paper presents a low-cost, compact, easily configurable interferometry radar for noncontact water level monitoring, including its hardware design, signal processing algorithms, and wireless communication strategies. Interferometry radar measures distance by comparing the phase lag between reflected and transmitted signals. Water level measurements using this approach have been demonstrated in a solitary wave laboratory experiment, a field deployment observing wave run-up near Ponte Vedra, Florida, and a field deployment observing waves and tides in the Sparkill Creek located in Piermont, New York. The experimental results from the radars with millimeter-level accuracy have been compared with reference sensors and demonstrate the potential of continuous wave radar for water level observations.

Object detection in high-resolution aerial images is a challenging task because of 1) the large variation in object size, and 2) non-uniform distribution of objects. A common solution is to divide the large aerial image into small (uniform) crops and then apply object detection on each small crop. In this paper, we investigate the image cropping strategy to address these challenges. Specifically, we propose a Density-Map guided object detection Network (DMNet), which is inspired from the observation that the object density map of an image presents how objects distribute in terms of the pixel intensity of the map. As pixel intensity varies, it is able to tell whether a region has objects or not, which in turn provides guidance for cropping images statistically. DMNet has three key components: a density map generation module, an image cropping module and an object detector. DMNet generates a density map and learns scale information based on density intensities to form cropping regions. Extensive experiments show that DMNet achieves state-of-the-art performance on two popular aerial image datasets, i.e. VisionDrone and UAVDT.