The environment in which a sensor is expected to operate exerts a strong influence on its performance. The effects include interactions of the acoustic or electromagnetic radiation with the target and its surrounds (the background), and particularly with the atmosphere through which the beam must travel between the target and the sensor. These interactions include attenuation by the atmosphere and attenuation and scattering by hydrometeors and other suspended particulates. For electromagnetic sensors, clear-air attenuation is mostly caused by molecular absorption and scattering by oxygen and water.

Chapter Contents:

• 7.1 The Sensing Environment
• 7.2 Attenuation of Electromagnetic Waves
• 7.2.1 Clear Weather Attenuation
• 7.2.2 Effect of Atmospheric Pressure (air density)
• 7.2.3 Effect of Rain
• 7.2.4 Effect of Fog and Clouds
• 7.2.5 Overall Attenuation
• 7.2.6 Attenuation through Dust and Smoke
• 7.2.6.1 Attenuation of Radar Signals
• 7.2.6.2 Attenuation of Laser Signals
• 7.2.7 Effect of atmosphere composition
• 7.2.8 Electromagnetic propagation through solid
• 7.3 Refraction of Electromagnetic Waves
• 7.4 Acoustics and Vibration
• 7.4.1 Characteristic Impedance (Z) and Sound Pressure
• 7.4.2 Sound Intensity (I)
• 7.4.3 Sound Propagation in Gases
• 7.4.3.1 Worked Example: Effect of Molecular Weight on Speed of Sound
• 7.4.3.2 Effect of Temperature and Pressure
• 7.4.4 Sound Propagation in Water
• 7.4.5 Sound Propagation in Solids
• 7.4.6 Attenuation of Sound in Air
• 7.5 Attenuation of Sound in Water
• 7.6 Reflection and Refraction of Sound
• 7.6.1 Waves normal to the Interface
• 7.6.2 Waves at an angle to the Interface
• 7.6.3 Refraction and Refraction
• 7.7 Multipath Effects
• 7.7.1 Mechanism
• 7.7.2 Multipath Lobing
• 7.7.3 Multipath Fading
• 7.7.4 Multipath Tracking
• 7.7.5 Effects on Imaging
• 7.8 References

Inspec keywords: electromagnetic wave scattering; atmospheric electromagnetic wave propagation; electromagnetic wave absorption; hydrometers

Other keywords: hydrometers; acoustic radiation; electromagnetic atmospheric attenuation; clear-air attenuation; molecular absorption; electromagnetic radiation interaction; signal propagation; electromagnetic atmospheric scattering; electromagnetic sensors

Subjects: Electromagnetic wave propagation; Electromagnetic waves: theory; Electromagnetic wave propagation and interactions in the lower atmosphere