Passive sensors are devices that detect and measure energy emitted from natural sources, such as sunlight or thermal radiation. Unlike active sensors, which emit their own signals to gather data, passive sensors rely on existing energy in the environment. Common examples include cameras that capture visible light and infrared sensors that detect heat. These sensors are widely used in various fields, including remote sensing, meteorology, and environmental monitoring. They provide valuable information without interfering with the natural conditions of the environment, making them essential for applications like satellite imaging and wildlife observation.