14-9] INTRODUCTION TO WEATHER RADAR 759 



represents an ideal solution. Such a system combines, in a complementary 

 fashion, the highly accurate long-term velocity information furnished by 

 the doppler radar, which is also useful for airborne erection and damping of 

 the inertial system, and the highly accurate short-term velocity and vertical 

 information of the inertial platform, which can, in turn, aid the doppler 

 radar tracking and provide dynamic inertial memory. Hence, such a 

 combined system is capable of providing very accurate velocity and vertical 

 information (see references 1 5 and 1 6 of Bibliography at end of this chapter) , 



In another important example, if highly accurate position, and hence 

 directional, information is required for long periods, as in the case of long- 

 range vehicles, an ideal doppler-inertial interconnection is a system which 

 employs a doppler radar as part of a so-called doppler inertial compass, i.e., 

 with a platform which is interconnected so as to operate in a north-seeking 

 gyrocompass mode. In this mode of operation, the platform is kept pointed 

 north at all times. The necessary vehicle ground velocity information is of 

 course available in the system from the doppler radar. Such a system pro- 

 vides accurate information on long-term velocity from the doppler radar 

 and short term velocity, and verticality and long-term azimuth information 

 from the inertial platform. Thus it permits highly accurate determination 

 of position for long ranges and periods of time (reference 16). 



Another possible combined system configuration is a so-called doppler- 

 inertial-stellar system which uses a doppler radar for long-term velocity, an 

 inertial platform for short-term velocity, and an astrocompass for accurate 

 directional information and position correction. Various forms of such self- 

 contained combined systems using doppler radar have found application in 

 military vehicles. 



Doppler radars can also be used advantageously in other forms of com- 

 bined systems, such as in conjunction with certain ground-based radio 

 guidance systems. In such systems, the doppler radar provides continuity 

 of information but with an error which accumulates with distance, whereas 

 the ground-based radio system provides intermittent, but instantaneously 

 highly accurate, position fix information (references 14 and 17). 



It may be said in conclusion that the next ten to twenty years should see 

 tremendous application of doppler radar navigation systems in military as 

 well as in civil aviation. 



14-9 INTRODUCTION TO WEATHER RADAR 



Generally speaking, the designer of a radar system is concerned with 

 meteorological factors at radar wavelengths only insofar as they cause 

 detrimental effects to the prime function of the system. The designer of 

 weather mapping or weather avoidance radar, on the other hand, can profit 

 a great deal from an understanding of some of the basic meteorological 



