The Beer-Bouguer-Lambert Law defines the attenuation of an optical signal traveling through an optically homogeneous medium, based on propagation distance and an extinction coefficient specific to medium and signal. STK's implementation allows you to divide the atmosphere into concentric homogeneous spheres, or layers, each having different optical properties. The propagation loss for each layer is then computed using the Beer-Bouguer-Lambert Law.
To apply the atmospheric loss model to a laser receiver, go to the Laser Receiver's Basic Definition properties page, select the Propagation Loss Models tab->Atmospheric Loss tab, and select Enable.
The top row in the table for the Beer-Bouguer-Lambert Law Model corresponds to the top layer of the atmosphere; similarly, the bottom row corresponds the layer closest to the object’s central body.
| Field | Description |
|---|---|
|
Maximum Altitude |
Valid if Evenly Spaced Layer Heights is enabled. Defines the upper most height of the atmosphere. The layers will be evenly distributed between the maximum altitude and the surface of the central body such that all layers will have equal thickness. |
| Layer Top | Writable if Evenly Spaced Layer Heights is disabled. Allows you to define a thickness for each layer. The thickness is determined by specifying the top of the layer which is relative to the surface of the object’s central body.
To change the height for a particular layer, select the layer and change its Layer Top value. The Top of Layer value is an accumulation of the selected layer and all the layers below it. Each Layer Top value is relative to the surface of the spheroid. If Evenly Spaced Layer Heights is disabled and you adjusted the Layer Top values, enabling Evenly Spaced Layer Heights will recompute all the Layer Top values. |
| Extinction Coefficient | Constant describing the attenuation of an optical signal of a specific wavelength in a particular medium. |
| Add/Remove |
Use to add and remove layers. Additional layers are always added closest to the object’s central body. If Evenly Spaced Layer Heights is enabled, all Layer Top values will be recalculated to evenly distribute the layers. The Layer Top values must increase from the layer closest to the central body up to the top layer of the atmosphere. To remove a particular layer, highlight the layer to be removed and click Remove. If Evenly Spaced Layer Heights is enabled, all Layer Top values will be recomputed. |
Beer-Bouguer-Lambert Law Atmosphere Model
The Beer-Bouguer-Lambert Law atmosphere model is for use in the NIR/VIS/UV range of the spectrum and can be found only on Laser Receivers. It is a monochromatic model assuming a homogeneous medium within a given atmospheric layer. It assumes scattering effects are negligible and that the intensity lines within each layer are independent.
The Beer-Bouguer-Lambert atmosphere model must be populated with an Extinction Coefficient. The extinction coefficient is typically known for a given wavelength and extinction medium. The loss due to the Beer-Bouguer-Lambert model is given by the following equation:
where k is your extinction coefficient and d is the effective distance thru the atmosphere.
For more information on the Beer-Bouguer-Lambert Law, see K.N. Liou An Introduction to Atmospheric Radiation: Second Edition, 2002.