TABLE OF CONTENTS Variance in the irradiance from a beam caused by turbulence can be estimated as follows for the special case of a horizontal beam path:
| where | ? 2 t | = 0.31 C n 2 k 7/6 L 11/6 |
| C n 2 | = index of refraction structure constant discussed in the rule called " C n 2" | |
| k | | |
| L | = propagation path length in the turbulent medium | |
| ? | = wavelength |
Combining the equations above, we get
The standard deviation variation in irradiance is the square root of the term on the right.
This type of simplifying analysis of beam propagation in the atmosphere has been spearheaded by both the military, which is interested in laser beam propagation, and the astronomical community, which is very much concerned with the disturbance that the atmosphere imposes on light collected by terrestrial telescopes. Of course, the latter group has little use for analysis of horizontal propagation of light, but the underlying theory that results in the equations above derives from a more general theory that applies to all cases.
A basic assumption used in the development of the results for the horizontal-beam case is that the value of C n 2 is constant over the path. This is generally not the case, as C n 2 is the manifestation of temperature variations in the atmosphere. However, this simplifying assumption is often used for horizontal beams and has been qualitatively confirmed in many experiments. When C
