Radar cross section is how well a target is able to reflect ultrasonic waves back to the transducer. Curved objects or tilted objects may scatter the majority of ultrasonic waves transmitted towards the object, which provides a weak echo response. Surfaces that yield the strongest echo response when facing the sensor are:

• Large
• Dense
• Flat
• Smooth

Objects that meet these criteria, like a wall or floor, yield the best responses. Small objects, or objects that partially deflect sound (like people, animals, or plants), will reduce the sensing response. A flat object should face the sensor at a 90° angle, when possible, to maximize sensing response. Round or rigid surfaces enable larger angular deviations. Figure 3-4 shows the reflected ultrasonic wave from the surface of a target based on the target's shape.

Figure 3-4 Ultrasonic Echoes Based on Target Shape

Equation 7 defines the radar cross section of a target (σ):

Equation 7.