## 3 Review of Sensor Requirements for A3R
### ODD Considerations  
The tasks required for A3R are conducted in the context of the ODD presented in Section 2.4. The ODD provides one example of how requirements and test matrices can be methodically constructed. The information in the ODD is largely driven by the concept of employment (CONEMPS), which represents the intended mission and requirements to complete that mission, for the UA. The requirements derived from the ODD may also be used to determine the requirements for sensors installed on the UA.  
Consider the physical domain of the ODD. This physical domain includes the type of tankers, refueling stores, position of the basket (wing or fuselage mounted), altitude, and airspeed, which will be driven by the intended tanker and informed by NATO SRDs [17]. The main considerations associated with the sensors onboard the UA will be the ability to complete all phases of A3R within the required domains. Additionally, it will be important to train and verify the CV system to recognize the critical objects for each tanker and refueling store configuration. Anticipated environmental conditions, such as all-weather operations or clear day only, will drive the requirement of an illumination source for the CV or the adoption of a specific camera system.  
For the connectivity portion of the ODD, the CV system may necessitate a HOTL for additional assurance, especially in early deployments. Therefore, if the CONEMPS for early operations require a human monitor, a BLOS or LOS data link would be a requirement for the UA to facilitate the required monitoring. Therefore, even if operational deployment would not require a BLOS or LOS data link, early development may require the inclusion of that capability.  
Column five of the ODD (Figure 10), environmental conditions, takes into consideration the environmental conditions that a UA may encounter when completing A3R. These environmental conditions will largely be determined by the requirements for the UA to complete the primary mission. If the UA will be required to operate in daytime only under visual flight rules (VFR) weather minimums [2], then the UA will only require sensors that can operate in those weather conditions. In modern militaries, almost all platforms will be cleared to operate in both day and nighttime, as well as most weather conditions. Therefore, the sensors onboard the UA must be able to process information throughout the entire anticipated domain of environmental conditions.  
The environmental conditions portion of the ODD will consist of multiple layers to account for all the permutations of conditions the UA may encounter conducting A3R. For example, the weather may include wind, rain, snow, or sleet [46], if the flight envelope of the UA allows for flight through all of these conditions, and these different conditions will have degradation on multiple systems, especially the CV system, as demonstrated by object detection to support autonomous driving [102]. For background, understanding, the types of clouds the UA may encounter will determine the requirements of multiple sensors onboard the UA to include the IRST or A/A Radar [103] or the CV system [104]. In a similar fashion to crewed refueling [97], lighting in the domain, both natural and artificial, must be considered when determining the requirements of the CV system.  
The ODD presented provides one example of the factors that need to be defined, the example ODD would be appropriate for a system design and deployment to support the collection of training data and for evaluating the system performance throughout the anticipated domain. The ODD should be designed prior to defining sensor requirements for the UA to ensure that limitations associated with different sensors covered in this paper do not result in unintended limitations of the platform.