Surface Source Properties

purpose of the Surface Source Property is to allow you to accurately model real sources, with detailed angular and spectral behavior. When you create a new Surface Source Property, you can choose from the following spectral and angular types.

Spectral Types	Angular Types
Rectangular	Lambertian
Gaussian	Uniform
Solar	Gaussian
Table	Solar
	Table

You can choose any combination of spectral and angular type. The Spectral type and Angular type are independent of each other, unless you choose Table for both types. If you need to model a source that has different angular shape for different wavelengths (or different spectrum for different emission angles), then you need to create a Table Wavelength-Table Angle source. This choice will allow you to enter a separate table of emissivity versus angles for each wavelength.

Except for the Table-Table combination, the spectral and angular dependence are separable. In mathematical terms,

S(λ, θ, φ) = f1(λ)f2(θ, φ)

for all combinations except Table Wavelengths with Table Angles.This means that the same angular dependence applies to all wavelengths. The exception to this is theTable Wavelengths - Table Angles combination, which allows you complete flexibility to change the angular dependence with wavelength.

To use a Surface Source Property to define a surface source, select Emission Type = Source Property in the Apply Properties dialog box, Surface Source tab. Remember that the Property specifies the behavior of the source, but you can still choose what wavelengths will be traced to represent, or sample, the source. These wavelengths are entered in the Apply Properties dialog box, Surface Source tab.

Spectral types

Rectangular

To make a Rectangular Spectral Type surface property, you specify a minimum wavelength and a maximum wavelength. The emissivity is equal to the value in the table for wavelengths between the minimum and maximum, and zero otherwise.

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Technical Reference

FIGURE 7.13 - Rectangular Spectrum with Min wavelength = 1, Max wavelength = 2.

Gaussian

To make a Gaussian Spectral Type surface property, you specify a Central

wavelength and a 1/e2 half-width wavelength. The spectral emissivity has the shape

	–2		(λ – λcentral)		2
S(λ) = exp		------------------------------
			λ1
		--
			2

An example Gaussian spectrum with Center wavelength = 1 and half-width = 0.1 is shown in Figure 7.14.

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Surface Source Properties

FIGURE 7.14 - Gaussian Spectrum with Center wavelength = 1 and 1/e2 wavelength = 0.1. The red vertical lines show the half-width

wavelengths with emissivity value of 1/e2 = 0.1353.

Solar

The Solar Spectral Type uses a standard solar spectrum: ASTM E-490-00. It is the solar spectral irradiance incident on the Earth's upper atmosphere in SI units

of W/m2-μm. According to the standard, the total insolation irradiance is 1366.1 W/m2. Therefore, when you make a Solar Spectral Type property, it is a

Radiometric Irradiance source with Emission = 1366.1 W/m2. The spectrum extends from 0.1195 um to 1000 um. A portion of the spectrum is shown in Figure 7.15.

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