This chapter will be devoted to the discussion of various types of radar, their characteristics, principles, and elements.

The first portion of our discussion will deal with characteristics and principles of nondoppler radar, followed by a discussion of principles, characteristics, and phenomena associated with doppler radar. Finally, we will look at the Next Generation Weather Radar (NEXRAD) system, principally the WSR-88D.

LEARNING OBJECTIVES: Interpret the effects of wavelength on nondoppler radar. Recognize principles of wavelength on nondoppler weather radars. Evaluate nondoppler radar beam characteristics.

Now lets begin our discussion of nondoppler radar. For additional information, refer to the Federal Meteorological Handbook No. 7, Weather Radar Observations, Part B, NAVAIR 50-1D-7.

EFFECTS OF WAVELENGTH AND FREQUENCY ON RADAR PERFORMANCE

The concept of energy moving as waves through a medium such as water is easily understood because we can observe the oscillation of the material. Both electrical and magnetic energy are transmitted by these waves. Viewed along the direction of transmission, the envelope containing vectors representing an electromagnetic field appears in wave form. Figure 12-1 shows the common method for representing waves. The radio energy waves have some semblance to water waves in that they retain their size while all traveling at the same speed. Therefore, they could also be represented as concentric circles about the generating device, as seen in figure 12-2. In this case, we could say that the circles represent wave fronts that move away from the source. In the case of focused waves, such as we have with weather radars, we could show the wave fronts moving along the beam path, as in figure 12-3. In all three illustrations, the distance from wave front to wave front, and from any part of a wave to the corresponding part of the next wave, remains constant. This distance is determined by two factors, the speed with which the waves move and the rapidity with which the generating device operates. The generating device is said to oscillate, and could be thought of as moving up and down, or back and forth. Each complete oscillation produces one complete wave. The waves move away from the oscillator as they are being generated so that the wave front will be 1 wavelength away from the oscillator when the next wave front is just being formed. Because the speed of wave travel remains constant,  there is a constant, inverse relationship between the frequency of the oscillation and the length of the wave; the faster the oscillation (higher frequency), the shorter the wavelength.

Figure 12-1.-Energy wave represented as oscillations. These are 5 cm long.

Figure 12-2.-Flve 1-cm energy waves represented as concentric circles around the wave emitttcr. 

Thus, radar waves can be described either in terms of frequency or wavelength. The two are related by the following equation:

FREQUENCY = : where k is the wavelength and c is the speed of light (300,000,000 meters per second or 3 x 10⁸).

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