spotter
/ˈspɒtə(r)/noun
often in combination
1- a person that looks for or observes a particular thing as a hobby or job喜欢（或专门）寻找（或观察）…的人：
bus-spotters.
大汽车观察爱好者。
1.1
- an aviator or aircraft employed in locating or observing enemy positions航空侦察员; 侦察机：
as modifier spotter planes.侦察机。
1.2
- US informal a person employed by a company or business to keep watch on employees or customers〈美, 非正式〉（公司雇佣针对员工或顾客的）秘密监视员。
1.3
- (in gymnastics, weight training, etc.) a person stationed to observe the performer and minimize the risk of accidents or injuries（体操、举重训练等中保障运动员安全的）现场监护人员。