contributed by Andrea Laliberte
UAS, also called Unmanned Aerial Vehicles (UAV)
Agency/Company Operating the Sensor
privately owned and operated
A UAS is an aircraft that is operated without a human on board. Unmanned aircraft are widely used in military applications for intelligence, surveillance, and reconnaissance missions, and more recently for armed missions. Civilian natural resources applications are a rapidly growing area for UAS due to their greater availability and the miniaturization of sensors, GPS, and associated hardware. Unmanned aircraft have been used to obtain remotely sensed imagery for fire and natural disaster monitoring, wildlife observations, and vegetation measurements in vineyards, crops, forests, and rangelands. The size and characteristics of UAS ranges widely, from micro-UAS, weighing less only grams, to large UAS, such as Predator and Global Hawk. Some of the smaller aircraft can be controlled remotely, similar to a model aircraft, but most can operate autonomously based on GPS and programmed flight plans.
Uses of UAS for Remote Sensing
UAS have been used successfully as platforms for remote sensing. In the natural resources sector, UAS have been used for estimating shrub utilization, mapping invasive species, measuring plant biomass and nitrogen, documenting water stress in crops, and for mapping rangeland vegetation. In rangeland and forest applications, unmanned aircraft allow for a landscape-level monitoring approach that offers potential for calculating landscape metrics that reflect changes in landscape processes and dynamics at very high resolutions. The quality and resolution of UAS-acquired imagery depends on flying height as well as sensor type and characteristics. For example, a UAS flying at 215 m above ground, equipped with a consumer camera can obtain imagery at approximately 6 cm pixel resolution. Sensors flown on UAS include video cameras, low-cost consumer cameras, multispectral and hyperspectral sensors, thermal imagers, synthetic aperture radar (SAR), and atmospheric sensors.
Imagery acquired from UAS are most similar to different kinds of aerial photography.
Advantages and Limitations
In terms of remote sensing, UAS are most similar to manned aircraft used for acquisition of digital aerial imagery. There are advantages and limitations to using UAS for these purposes.
- Ability to deploy the UAS relatively quickly and repeatedly for change detection
- Ability to fly at low altitudes, resulting in very high resolution imagery (depending on sensor and flying height)
- Lower image acquisition costs per image and for aircraft maintenance
- No pilot on board
- Initial acquisition cost (depending on size and complexity of UAS)
- Crew training requirements
- FAA regulations for flying a UAS in the National Airspace
- Limitation of suitable and lightweight image sensors
- Image processing can be more difficult due to lower stability of aircraft and low-cost sensors
Costs of UAS Operation
Due to the wide range of UAS, acquisition and maintenance costs are highly variable. A low-cost approach ($1000-3000) is the conversion and modification of a model aircraft by fitting a low-cost, light-weight consumer camera in the aircraft. Additional modifications may include automatic triggering of the camera based on GPS waypoints. Acquisition costs for small UAS (30 lbs), complete with ground station and launcher can range from the tens of thousands of dollars up to $100,000.
Another cost is associated with crew training. Personnel have to be trained in the safe operation of the UAS and have to observe FAA regulations (see below), which include requirements for private pilot ground school and/or private pilot licensing, and FAA medical certification.
Unmanned aircraft operation in the National Airspace (NAS) fall under the jurisdiction of the Federal Aviation Administration (FAA). Public entities (local, state and federal agencies) have to apply for a Certificate of Authorization (COA); civil entities require a Special Airworthiness Certificate (SAC). Application for a COA takes 3-6 months. The COA provides guidelines for operator qualifications, airworthiness, aircraft maintenance, flying altitudes, communication with air traffic control, visual line of sight, and visual observer requirements. Current regulations limit UAS flights to visual line of sight, even though many UAS are capable of operating autonomously for several hours and at large distances to the ground station. UAS regulations are subject to continuous review and are updated as required. The FAA maintains a website with the latest UAS regulations and policies at http://www.faa.gov/about/initiatives/uas/reg/.
Future Uses of UAS
There is a growing interest in using UAS for remote sensing applications in natural resources, but there are some limitations. In order to make this technology usable and operational for mapping and monitoring purposes similar to manned aerial photography missions, better integration into the National Airspace is required for UAS. Current FAA regulations impose restrictions that result in limitations for the size of area that can be mapped and in additional crew training costs. However, the regulations are in flux, and it is anticipated that future UAS operations will become less stringent.
Small and lightweight cameras and other sensors suitable for UAS are being developed, in conjunction with high quality GPS and INS (inertial navigation systems), which allow for higher accuracy in image georeferencing, required for orthorectification and mosaic-ing of UAS imagery.
Example Rangeland Application
At the USDA Agricultural Research Service (ARS) Jornada Experimental Range (JER) in southern New Mexico, ongoing research is aimed at determining the utility of UAS for rangeland mapping and monitoring, and to develop a workflow for acquisition, processing, and analyzing UAV imagery. We operate two MLB BAT 3 UAS, with a weight of 10 kg and a 1.8m wingspan. The UAS acquires imagery with a Canon SD900 10-megapixel digital camera at a flying height of 215 m above ground, resulting in a pixel resolution of approx. 6 cm. The images are orthorectified and mosaicked, and vegetation classifications are obtained using object-based image analysis techniques.
- Berni, J.A.J., P.J. Zarco-Tejada, L. Suarez, and E. Fereres, 2009. Thermal and narrowband multispectral remote sensing for vegetation monitoring from an unmanned aerial vehicle, IEEE Transactions on Geoscience and Remote Sensing, 47(3):722-738. Use of a UAS equipped with thermal and multispectral sensors for estimating water stress in fruit crops in Spain.
- Grenzdoerffer, G., A. Engel, and B. Teichert. 2008. The photogrammetric potential of low-cost UAVS in forestry and agriculture, International Archives of the Photogrammetry, Remote Sensing, and Spatial Information Sciences, XXXVII. Part B1, ISPRS Congress, Beijing, China, 1207-1213.
- Hardin, P.J., and M.W. Jackson, 2005. An unmanned aerial vehicle for rangeland photography, Rangeland Ecology and Management, 58:439-442. A small modified model aircraft was used to map knapweed in Utah rangelands.
- Hunt, E.R., M. Cavigelli, C.S.T. Daugherty, J. McMurtrey III, and C.L. Walthall, 2005. Evaluation of digital photography from model aircraft for remote sensing of crop biomass and nitrogen status, Precision Agriculture, 6:359-378. Use of a model aircraft for measuring biomass and nitrogen in agricultural crops.
- Laliberte, A.S., and A. Rango, 2009. Texture and scale in object-based analysis of sub-decimeter resolution unmanned aerial vehicle (UAV) imagery, IEEE Transactions on Geoscience and Remote Sensing, 47(3):761-770. Use of unmanned aircraft for mapping rangeland vegetation at sub-decimeter resolution.
- Laliberte, A.S., J.E. Herrick, A. Rango, and C. Winters. Acquisition, orthorectification, and object-based classification of unmanned aerial vehicle (UAV) imagery for rangeland monitoring. Photogrammetric Engineering and Remote Sensing (In press). Image acquisition, processing and classification of rangeland vegetation from RGB imagery acquired with a UAS in Idaho.
- Rango, A., A.S. Laliberte, C. Steele, J.E. Herrick, B. Bestelmeyer, T. Schmugge, A. Roanhorse, and V. Jenkins, 2006. Using unmanned aerial vehicles for rangelands: current applications and future potentials, Environmental Practice, 8:159-168. An overview of the use of unmanned aircraft for rangeland applications.
- Rango, A., and A.S. Laliberte. Impact of flight regulations on effective use of unmanned aerial vehicles for natural resources applications. Journal of Applied Remote Sensing (In review). Review of current FAA regulation for UAS use in the National Airspace for natural resource applications.
- Zhou, G.Q., 2009. Near real-time orthorectification and mosaic of small UAV video flow for time-critical event response, IEEE Transactions on Geoscience and Remote Sensing, 47(3):739-747. Use of a small UAS for acquiring video imagery and orthorectification of the imagery for natural disaster response.