Technology

Reflectivity

diffusereflectiveI came across this valuable explanation of reflectivity on Pulsed Light’s website. They explain that there are three types – A. Diffuse Reflective B. Specular, and C. Retro-reflective.

In the case of purely diffuse surfaces, we are talking about materials that have a textured quality that causes reflected energy to disperse uniformly. This tendency results in a relatively predictable percentage of the dispersed laser energy finding its way back to the LIDAR-Lite receiver. As a result, these materials tend to read very well.

Specular surfaces, on the other hand, are difficult or impossible for the LIDAR-Lite to recognize because radiated energy is not dispersed. Reflections off of specular surfaces tend to reflect with little dispersion which causes the reflected beam to remain small and, if not reflected directly back to the receiver, to miss the receiver altogether. Examples of specular surfaces are mirrors and glass viewed off-axis.

Retro-reflective surfaces return a very high percentage of radiated energy to the receiver due to their reflective properties. Light hitting a retro-reflective surface will return to the receiver without much signal loss so retro-reflective surfaces are typically very good targets for the LIDAR-Lite. Paint used to mark roadways, animals’ eyes, license plates and road signs are examples of retro-reflective surfaces.

1 Comment

  • Actual reflectance (reflectivity) is some combination of all three of these rather spatial cases: Specular reflectance, diffuse reflectance, and corner reflectance. The polarization of the reflected spectral radiance can also be a issue (might be a benefit) as it is with respect to active microwave interactions with materials. Many use a reflectance called the reflectance factor (RF) which is the spectral exitance divided by the spectral irradiance. This is a passive remote-sensing term that is, in fact, very difficult to measure based on imagery that has recorded the upwelling spectral radiance only in one direction (from the surface object to the camera).

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