# Reflection of particles and light: different reflection surface types

• HP123
In summary, the speaker is seeking help with two problems related to the reflection of particles and light off surfaces. The first problem involves modeling the reflection of rigid particles off a sedimentary surface and calculating coefficients of restitution. The second problem is modeling the reflection of light off a rough surface and determining a way to connect the surface's roughness to the range of possible reflection angles. The speaker is specifically looking for information on a distribution function to characterize the range of angles. Another person suggests looking into the Bidirectional Reflectance Distribution Function and mentions other rough surface reflection models.
HP123
Hi,

I'm interested in reflection of both particles and light off surfaces. My problem is associated with a model that I'm working on and can be divided into two parts as far as I see it.

The first problem is the reflection of particles off the surface and the change in velocity due to energy losses associated with the reflection or bounce itself. I'm trying to model rigid particles bouncing off a sedimentary surface, e.g., mud, sand, gravel, or rock, but have had difficulty finding any means of calculating coefficients of restitution for different surfaces using known physical properties of the materials or even simply values that have been obtained experimentally. Does anyone know of any means of modelling this kind of process acurately?

The second issue that I'm having is modeling the reflection of light off a rough surface. I understand that if light reflects off a surface that is smooth then the angle of incidence is the same as the angle of reflection and everything is very easy. However, if the surface is not smooth, e.g., sandpaper, then for one beam of light hitting the surface at a given angle of incidence there must be a range of possible angles of reflection due to the range of possible orientations of the surface due to the roughness elements. Is anyone aware of a means of connecting the roughness of a surface to the range of possible reflection angles? I imagine that this range of angles could be characterised by some sort of distribution function like a normal distribution where for a given angle of incidence there are angles of reflection that are more common than others, hence the distribution.

Thanks.

HP123 said:
<snip>
The second issue that I'm having is modeling the reflection of light off a rough surface. I understand that if light reflects off a surface that is smooth then the angle of incidence is the same as the angle of reflection and everything is very easy. However, if the surface is not smooth, e.g., sandpaper, then for one beam of light hitting the surface at a given angle of incidence there must be a range of possible angles of reflection due to the range of possible orientations of the surface due to the roughness elements. Is anyone aware of a means of connecting the roughness of a surface to the range of possible reflection angles? I imagine that this range of angles could be characterised by some sort of distribution function like a normal distribution where for a given angle of incidence there are angles of reflection that are more common than others, hence the distribution.

Thanks.

Google 'Bidirectional reflectance distribution function'. There are many rough surface reflection models- Lambertian, Kubelka-Munk, Cook-Torrance, etc.

Hi Andy,
Thanks for that response regarding my second issue. That's exactly what I need!
Cheers!

## 1. What is reflection of particles and light?

Reflection is the process by which particles or light waves bounce off a surface at an angle equal to the angle at which they hit the surface.

## 2. What are the different types of reflection surfaces?

The three main types of reflection surfaces are specular, diffuse, and retroreflective. Specular surfaces reflect light in a single direction, while diffuse surfaces scatter light in multiple directions. Retroreflective surfaces reflect light back in the direction it came from.

## 3. How does the type of reflection surface affect the direction of reflected light?

The type of reflection surface determines the angle at which light is reflected. Specular surfaces reflect light at the same angle as the incident angle, while diffuse surfaces reflect light in various directions. Retroreflective surfaces reflect light back in the direction it came from, regardless of the angle of incidence.

## 4. What are some examples of specular, diffuse, and retroreflective surfaces?

Examples of specular surfaces include mirrors, polished metal, and still water. Diffuse surfaces include paper, fabrics, and matte surfaces. Retroreflective surfaces include road signs, safety vests, and reflective tape.

## 5. How is the law of reflection applied to the reflection of particles and light?

The law of reflection states that the angle of incidence is equal to the angle of reflection. This means that the direction of reflected light particles or waves can be predicted based on the angle at which they hit the surface.

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