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UNIT 6LESSON 3 REFRACTIVITY OVERVIEW Define refraction, and identify the atmospheric properties that control it and the units used to measure it. Identify the methods used to determine N -values. Identify the four types of refractive conditions and the effects of each on radar. Identify the manual methods used to determine refractive conditions. Identify the manual methods used to determine whether trapping conditions are occurring. Define anomalous propagation. Identify refractivity computer programs and the capabilities of each. Identify the methods used to present refractive conditions. OUTLINE Atmospheric refraction Determining N -values Refractive conditions Determining refractive conditions Determining the probability of trapping Anomalous propagation Refractivity computer programs Methods of presenting refractive conditions REFRACTIVITY Electromagnetic energy (radiation) is defined as the emission and propagation of electromag-netic waves or particles through an electromag-netic field. Common examples of electromagnetic energy include light emitted from a searchlight, radio and television waves, and energy created by a microwave oven. Electromagnetic energy was previously discussed in Unit 1, Lesson 2 of the AG2, Volume 1. Before we go on, it may help if you review that material. Electromagnetic energy travels in waves and is most often characterized by wavelength and frequency. Wavelengths range from .001 micrometer to 10 centimeters, while frequencies range from approximately 10 Hz to 10 25 Hz.These ranges make up the electromagnetic spectrum. See figure 6-3-1. The electromag-netic spectrum is subdivided into eight major categories: (1) electric waves; (2) radio waves; (3) infrared; (4) optical; (5) ultraviolet; (6) X-rays; (7) gamma rays; and (8) cosmic rays. In this lesson we will look at the radio wave portion of the electromagnetic spectrum. More specifically, we will look at the effect of the atmosphere on radar (Radio Detection And Ranging) transmissions. The effects of the atmosphere on radar transmissions are very important, since radar is our primary means of long-range early detection of enemy aircraft, ships, missiles, and so forth.
Figure 6-3-1.-Electromagnetic spectrum. Learning Objective: Define refraction, and control it and the units used to measure it. |
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