## 3 Discussion  
### Regulations Governing UAS Use  
The majority of published studies regarding use of UAS for scientific research or other public-use missions do not discuss laws regarding use of unmanned aircraft in the airspace above the study site. This commonality conforms to conventions of scientific journals--some of which are beginning to require evidence of adherence to regulations by authors using UAS in their studies--but it belies the importance of considering regulations when planning an operation that may involve UAS. Mostjurisdictions that regulate manned-aircraft flight in their airspace also restrict some aspect of unmanned aircraft use. Motivations behind these restrictions include safety of people on the ground and aloft as well as security against the misuse of UAS. These regulations evolve in response to emerging technology and potential accidents, but general concepts that underlie new rules tend to be stable despite changing political and technological landscapes. In the United States, the FAA oversees both manned and unmanned aircraft operations, providing regulations and guidance on airspace restrictions, pilot requirements, and equipment and performance requirements. Since the FAA's main concern about UAS operations in the US National Airspace System (NAS) is safety, it is critical that UAS do not endanger current users of the NAS, including manned or other unmanned aircraft, nor compromise the safety of personnel and property on the ground. Therefore, the FAA has instituted rules restricting UAS operations in the NAS. In 2007, FAA clarified UAS regulations requiring that all UAS aircraft must apply for flight operations through a UAS Certificate of Authorization or Waiver (COA [16]). The FAA COA is an authorization issued by the FAA Air Traffic organization (ATO) to a public operator for a specific activity. After a complete application is submitted, FAA conducts a comprehensive operational and technical review. If necessary, provisions or limitations may be imposed as part of the approval to ensure the UAS can operate safely with other airspace users. The COA process is available to public entities (including military, law enforcement, and other government agencies) who want to fly UAS in civil airspace. The FAA issues a COA generally based on three main restrictions. First, the COA authorizes an operator to defined airspace and includes special provisions unique to the proposed operation (such as requirement to only operate under Visual Flight Rules (VFR)). Most COAs are issued for a specific time period (up to one year, in most cases). Second, most COAs require coordination with the appropriate air traffic control facility and may require the UAS to have a transponder to operate in certain types of airspace. Third, due to the inability of UAS to comply with \"see-and-avoid\" rules, a visual observer or an accompanying chase aircraft must maintain visual contact with the UAS and serve as its \"eyes\" when operating outside restricted airspace [17]. A Special Airworthiness Certificate in the Experimental Category (SAC-EC) is an additional route available to obtain approval for UAS operations in the NAS. Its regulations stipulate that the aircraft cannot carry personnel or property for compensation or hire. The SAC-EC does allow operations for research and development, market survey and crew training, but effectively prohibits commercial UAS operations in the US. UAS can operate within the guidelines of an active Restricted Area (RA), within active Warning Areas (WA) or within active prohibited areas, when authorized, such as a Military Operating Area (MOA), under specific guidance and direction by the holders of the RA/MOA. Both areas (RA/MOA) are generally under the control of government DoD operators (military bases, _etc._), and are responsible for their own airspace and regulate the airspace of all aircraft that are in that space. If military operations or facilities are involved in UAS flights (such as a MOA), prior coordination with the appropriate DoD office is required [18].