CMOS Based. The CMOS based sensor uses a CMOS camera chip to capture the images.
3DRobotics PX4FLOW KIT with MT9V034 machine vision CMOS sensor with global shutter
Vision Positioning System
The Vision Positioning System present in the DJI Inspire 1 uses a combination of Ultrasonic sensors and Optical Flow Technology to control the position of the UAV in environments where GPS signals cannot reach. It can hold its position and stop when the RC controls are released.
DJI Inspire 1 Vision Positioning System –  Two sonar sensors  One binocular camera.
The Intel RealSense is a new depth-capturing camera technology designed to be incorporated into the latest laptop and tablet technology. It has the ability, thanks to its specialised lens array, to alter the focus of photographs after they have been taken, like the Lytro Illum. It can also track hand gestures to control the computer systems and 3D scan real world objects.
The new Astech Trinity Autopilot system incorporates 6 Intel RealSense cameras enabling 360˚ motion capture and obstacle avoidance .
The Astech Trinity Autopilot will be incorporated into the AscTec Firefly later this year.
A lot of technical development has gone into the idea of drone swarms where multiples drones fly together in cooperation. Amongst the applications considered for their use are search and rescue, crop pollination, surveillance, monitoring traffic and as a distributed computing and communications network in disaster areas. Work at the GRASP (General Robotics, Automation, Sensing & Perception) Lab at the University of Pennsylvania has included navigating obstacles, Simultaneous Localization and Mapping (SLAM) using a Microsoft Kinnect and Laser Rangefinder, flying formation by monitoring each other’s position and co-operation in building structures.
Within Archaeological and Cultural Heritage recording this has the potential for a swarm of UAVs to record areas in co-operation reducing the time taken, as well as the potential of using different technologies to record at the same time.
A UAV can act as a platform for a number of different recording technologies that can be employed in the recording of Archaeology and Cultural Heritage.
Photogrammetry is a technique for taking measurements from photographs and can be used to create a number of different results.
The type of camera system used depends on the type of UAV system employed, the more powerful the system the heavier and more powerful the camera that it can carry.
Weight is an important consideration; cheaper UAV systems are designed to only carry the GoPro or another extreme sports camera. While the more expensive/powerful systems can carry higher powered digital SLR cameras which record in much higher levels of detail and without lens distortion. The better quality the camera the more details are recorded.
A number of 360° camera systems have been released which can be attached to the bottom of UAV systems. These have the potential to record many more photos than a single camera, this could potentially speed up photogramemtric recording as well as providing immersive experiences using VR (Virtual Reality) technology such as the Oculus Rift.
360Heros 360° GoPro mount
UAVs are used for mapping within a number of industries, and have already begun to be used in the mapping of archaeological sites. They provide an ideal platform for the creation of DTM (Digital Terrain Model) and DSM (Digital Surface Model) models which can be used in GIS (Geographical Information Systems) applications.
This is the ideal project for a fixed wing UAV which can be deployed to fly over the area under study with a downward facing camera. The major benefits of such a systems is the stability, the amount of time that they can fly and hence the amount of recording that they can do in one flight.
Using autopilot systems and software for programming the autopilot, such as Mission Planner, the flight plan for the UAV can be programmed.
Setting out a UAV light pattern in the Mission Planner Software
Such software has the ability to create a grid flight pattern using the study area selected in the map interface, the altitude flown, the image overlap and the characteristics of the camera being used. Any alteration in the altitude, image overlap or camera specification (such as lens used) will alter the grid pattern to accommodate the alterations.
Setting out a grid UAV flight pattern in the Mission Planner software
A grid of circular paper targets can be set up on the ground with each target being surveyed in using a GPS (Global Positioning System) which both increased the accuracy of the photogrammetry model and georeferences the results so they can incorporated with other data within a GIS system
Standing Building Recording
Photogrammetry has a long history in standing building recording which has be enhanced by the ability of the Total Station to survey points accurately. Limitations of ground based photogrammetry include the ability to record information high above the ground or masked from view. Traditionally this has been solved by using scaffolding, but his is an expensive and time consuming system which can also be dangerous.
Another option is to use standard building photogrammetric recording techniques to record structures in high detail using a UAV to fly the camera at set heights parallel to the structure. This would mean that high quality imagery could be created using standard methods. The UAV can act as a mobile camera platform/tripod which has the ability to take to camera to heights not easily accessible by other means. Certain points on the building surface would need surveying in using a total station to georeference the 3D model created by the photogrammetry process and to make it more accurate. Orthophotos (geometrically corrected images) can be created from the images taken which are an important element in building recording.
Increasing development in autonomous flight can be used to automate the flight patterns having the UAV automatically record buildings.
HDR (High Dynamic Range)
High Dynamic Range photography is a technique where multiple images are taken with different exposures (bracketing), these are then merged together using computer software to form an image with all of the detail from the images. Many modern digital camera have an auto-exposure bracketing (AEB) setting which allows this to set up on the camera to be done automatically. There are also dedicated HDR cameras. It provides images which are close to what the human eye can see and with more information than standard photographs.
The problem with using UAVs for this technology is that the images need to be taken while the camera is perfectly still, and even with a camera gimbal a UAV is likely to move slightly between the photographs being taken.
HDR photographs can also be used in photogrammetry.
The video capabilities of most cameras that UAVs carry mean that they can record videos. As we have already seen the ‘Follow-Me’ technology has the potential within archaeology or cultural heritage to record a site tour, filming the tour guide as they walk around site, with a separate digital recording system recording the audio which can later be combined with the video footage in post-production. The Hexo+ UAV Director’s Toolkit allows different filming scenarios such as crane; pan, tilt, crab, dolly, 360° around you, and far-to-close/close-to-far.
The UAV has the potential to create immersive fly through videos of sites thanks to the recent introduction of multi-camera systems or systems with multi-lens cameras, this can aid in public interaction and interest.
Lidar (Light Detection And Ranging)
LIDAR is a technology which has already proved useful in Archaeology and Cultural Heritage, it works by firing a pulsed laser beam at the ground and recording the returned beams, the time it takes for the beam to return is recorded and this is used to determine the distance. It is tied to the flight instruments of the light aircraft carrying the LIDAR and accurately records the 3D position and height of the results creating a dense point-cloud of the topography being recorded. The resulting LIDAR point data can be loaded in GIS systems.
It has the potential to discover archaeological remain under woodland by removing points from the LIDAR point-cloud leaving only the points that hit the ground between the forest cover.
Although not a cheap technology a number of LIDAR systems have recently been developed which can be carried as a payload on UAV systems. This includes the Phoenix Aerial Systems AL3 S1000 Copter which combines a DJI S1000 Octocopter with their AL3 technology which includes the Velodyne HDL-32 high definition LiDAR sensor.
Phoenix Aerial Systme – AL3 S1000 Copter
If the UAV system recorded high quality photographs as well, these could be recorded in a separate flight using the same flight path, these could be used to overlay the LIDAR data.
LIDAR can be analysed with a number of computer tools enabling more information to be visualised.
LiDAR Data with Multiple Hillshades and with Principal Component Analysis (PCA).
Multi-Spectral and Hyper-Spectral Imaging
Multi-Spectral and Hyper-Spectral imaging involves the recording of the electromagnetic spectrum outside the visible spectrum, this includes the infrared which can detect differences in ground moisture helping to determine what is below the ground level.
Traditionally this has been done using satellites but spectral imagers are also available for UAV platforms.
Comparative multispectral imagery of prehistoric field systems near Stonehenge © Historic England.NMR; Source Environment Agency
Ground Penetrating Radar (GPR)
Ground Penetrating Radar is a technology that is used within field archaeology to discover buried features, it works by recording reflected radio waves that have been transmitted into the ground. GPR can be used on areas such as concrete, stone and tarmac where other geophysical techniques won’t work.
MSc students from the University of Southampton carrying out a GPR survey in the vicinity of the Episcopio, between Portus and the Isola Sacra, Italy (https://kdstrutt.wordpress.com)
The potential of having UAVs carry Ground Penetrating Radar recording equipment has already been tested in a number of fields including the detection of IEDs (Improvised Explosive Devices) and mines and the characterization of soil properties. But studies, including one at the University of Leicester, are looking into the potential of GPR carrying UAVs in archaeological recording.
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