CHAPTER 12WEATHER RADARThis chapter will be devoted to the discussion ofvarious types of radar, their characteristics, principles,and elements.The first portion of our discussion will deal withcharacteristics 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.NONDOPPLER RADARLEARNING OBJECTIVES: Interpret theeffects of wavelength on nondoppler radar.Recognize principles of wavelength onnondoppler weather radars.Evaluatenondoppler radar beam characteristics.Now let’s begin our discussion of nondoppler radar.For additional information, refer to the FederalMeteorological Handbook No. 7, Weather RadarObservations, Part B, NAVAIR 50-1D-7.EFFECTS OF WAVELENGTH ANDFREQUENCY ON RADAR PERFORMANCEThe concept of energy moving as waves through amedium such as water is easily understood because wecan observe the oscillation of the material. Bothelectrical and magnetic energy are transmitted by thesewaves. Viewed along the direction of transmission, theenvelope containing vectors representing anelectromagnetic field appears in wave form. Figure12-1 shows the common method for representingwaves. The radio energy waves have some semblanceto water waves in that they retain their size while alltraveling at the same speed. Therefore, they could alsobe represented as concentric circles about the generatingdevice, as seen in figure 12-2. In this case, we could saythat the circles represent wave fronts that move awayfrom the source. In the case of focused waves, such aswe have with weather radars, we could show the wavefronts moving along the beam path, as in figure 12-3. Inall three illustrations, the distance from wave front towave front, and from any part of a wave to thecorresponding part of the next wave, remains constant.This distance is determined by two factors, the speedwith which the waves move and the rapidity with whichthe generating device operates. The generating deviceis said to oscillate, and could be thought of as movingup and down, or back and forth. Each completeoscillation produces one complete wave. The wavesmove away from the oscillator as they are beinggenerated so that the wave front will be 1 wavelengthaway from the oscillator when the next wave front is justbeing formed.Because the speed of wave travelremains constant, there is a constant, inverserelationship between the frequency of the oscillationand 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.12-1