CHAPTER 6 



RADAR AND SATELLITE EQUIPMENT 



Two of the biggest forecasting aids that 

 present immediate pictorial depiction of me- 

 teorological data to the meteorologist are sat- 

 ellites and weather radars. This chapter 

 is devoted to introducing the Aerographer's Mate 

 to the various types of satellites and weather 

 radar equipment being used by Naval Weather 

 Service personnel today. 



RADAR EQUIPMENT 



Radar and weather are very closely allied. 

 The use of radar has provided meteorologists 

 with a tool which permits the collection of at- 

 mospheric data under conditions when the more 

 orthodox methods fail. On the other hand, a 

 knowledge of atmospheric conditions provides 

 the radar operator with information vital to the 

 accuracy of his results. 



The word radar is an acronym for "radio 

 detection and ranging." Fundamentally, all radar 

 depends upon the emission of a short, sharp 

 pulse of electromagnetic energy in a given 

 direction. This pulse on intercepting a target is 

 scattered in all directions. That part of the 

 energy which is scattered in the direction of 

 the radar is picked up by the radar antenna, 

 producing an echo or "blip" on the receiver 

 scope. The time taken for the pulse to cover 

 the path to the target and return is a measure 

 of the range to the target. Azimuth and eleva- 

 tion of the target are determined from the di- 

 rection in which the pulse is emitted and returned. 



Since the electromagnetic pulse travels with 

 the speed of light, range is determined by 

 a timing procedure. At the instant the pulse 

 leaves the antenna, a timing device starts count- 

 ing. When the return echo reaches the antenna, 

 the counting is stopped. The distance to the 

 target is equal to one-half the distance traveled 

 by the pulse. 



Meteorological radar provides a unique means 

 of obtaining meteorological data for use by the 

 forecaster when issuing warnings and environ- 

 mental forecasts. As weather requirements con- 

 tinue to expand and change, new designs and 

 modifications to meteorological radar will con- 

 tinue to appear in the effort to improve and 

 keep pace. 



The Meteorological Radar Set AN/FPS-106 

 is the newest model of radar designed for 

 meteorological use. The AN/FPS-81 meteoro- 

 logical radar is the most common set in use 

 in the Navy today. 



RADAR INDICATORS 



The purpose of the indicator (cathode ray 

 tubes) in a radar is to display information to 

 the Aerographer's Mates about the range, bear- 

 ing, and elevation of surrounding targets. In 

 general, information is presented piecemeal, and 

 a single viewing of an indicator gives only a 

 small part of the picture. Different types of 

 radar scans are employed to display wanted 

 information from returning echoes on the dif- 

 ferent indicators. 



A-Scan Presentation 



The simplest type of display is the A-scan 

 presentation, which is illustrated in figure 6-1. 

 The display is one which gives return signal 

 intensity against range. This display shows only 

 the range to a target. 



The bearing of the target can be found by 

 moving the antenna horizontally to the position 

 of maximum signal intensity (highest pip). Chang- 

 ing the angle of elevation of the antenna to get 

 maximum signal intensity provides information 

 concerning the elevation of the target. The 

 horizontal and vertical limits of a rainstorm 

 can be found in much the same way by noting 

 the positions of the antenna at which the re- 

 turn drops below a detectable level. 



102 



