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Superrefraction Conditions When N decreases at a rate of 24 to 48 N-units per 1,000 feet, a SUPERREFRACTION condition exists. In this situation, the radar waves bend downward at a much faster rate than they do under normal conditions. Figure 6-3-6 illustrates the superrefraction condition. Trapping Conditions When the N-gradient is 48 N-units per 1,000 feet or greater, a condition known as TRAPPING occurs. With trapping, the refraction is extreme. The temperature and moisture conditions are such that the electromagnetic waves are sharply refracted back to the surface, where they are reflected back into the trapping zone. This process is repeated over and over. Little energy is lost in this process, and radar ranges are significantly extended when trapping conditions occur. Figure 6-3-7 illustrates the effect of trapping on radar. Learning Objective: Identify the manual conditions. DETERMINING REFRACTIVE CONDITIONS Refractive conditions can be determined manually by constructing an N-profile (curve) and
Figure 6-3-5.-Comparison of a subrefractive wave path to a normal wave path.
Figure 6-3-6.-Comparison of superrefractive wave path to normal wave path.
Figure 6-3-7.-Comparison of trapping wave path to normal wave path, and approximate difference in radar coverage. overlaying it with an N-gradient overlay, or by working up the data on a refractive index worksheet. |
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