Scatter {MCBackscattering}

Scattering of Single Photon in Media

Description

Scattering is the interaction event in the media when photon hits structural elements and changes direction as a result of collision.

Usage

Scatter(myObject)

Arguments

myObject

The mandatory parameter of this function is the MCBS class created by MCBS constructor function.

Details

The Scatter function, alias Scatter.MCBS, calculates the new direction of photon travel. In isotropic media, any new 3D direction can occur with equal probability. In anisotropic media, the new direction is decided according to the Heyney-Greenstein phase function. The isotropic and anisotropic behavior of media is shown by anisotropy factor (g). The anisotropy factor is zero (g = 0) for isotropic media, g = -1 means backward reflection (backscattering) is the most likely, while g = +1 means the most likely result is that photon continues forward (forward scattering). Biological tissues were reported to have high positive anisotropy factor g > 0.8.

Value

The Scatter function returns an MCBS object as class. Typically the same object is used in argument and result. As a result of Scatter function, new direction is given by c(u,v,w). These values are used in function Move to calculate next position.

u

3D vector coordinate along x-axis

v

3D vector coordinate along y-axis

w

3D vector coordinate along z-axis

Note

Please note that this function is designed to be used in Simulation function. You may use it separately in case you design your own procedure. In such a case, please note that function Randomize prepares trajectory data for each photon and iterations are done using move index myObject$midx. Results of Scatter function are used in Move function.

References

Henyey, L.G., Greenstein, J.L. (1941) Diffuse Radiation in the Galaxy. Astrophysical Journal, 93, 70–83. doi: 10.1086/144246.

Jacques, S.L. (1998) Light Distributions from Point, Line and Plane Sources for Photochemical Reactions and Fluorescence in Turbid Biological Tissues. Photochemistry and Photobiology, 67(1): 23-–32. doi: 10.1111/j.1751-1097.1998.tb05161.x.

See Also

MCBS for construction of object with initial input parameters. Simulation for running the simulation with adjusted parameters. Chart for plot of calculated photon flux profile. Export for export of photon flux with corresponding radii. Setup for initial computation of specular reflection and transport albedo. Randomize for adjustment of random trajectory vectors. Launch for start position of single photon and initial direction in media. Bounce for interaction with surface and computation of photon flux leaving media. Move for moving single photon forward. Absorb for absorption of single photon energy in interaction with media.

Examples

## Apple simulation data according to Qin and Lu (2006).
## DOI: 10.13031/2013.20862

# create object
cfgMedia <- c(0.63,30,0,1.4)
cfgSimulation <- c(1e6,0.05,1e-9,3,0.012)
apple <- MCBS(cfgMedia,cfgSimulation)
apple <- Setup(apple)
apple <- Randomize(apple)

# launch with 10° incident angle and move first photon
apple$idx <- 1
apple <- Launch(apple)

# first interaction event
cat("Direction",apple$u,":",apple$v,":",apple$w,"\n")
apple$midx <- 1
apple <- Scatter(apple)
cat("Direction",apple$u,":",apple$v,":",apple$w,"\n")