The sound source system consists of an acoustic projector, a power 

 supply, electronic circuitry, and a pressure-resistant housing. The 

 power supply and electronic circuitry are contained in the pressure- 

 resistant housing and the acoustic projector is attached to the top of 

 this housing. This package weighs about 10 pounds and is 23 inches long 

 and 3-1/2 inches in diameter. It is designed to screw onto the stud at 

 the upper end of the penetrometer vehicle. 



When the vehicle and the sound source are assembled, the Expendable 

 Doppler Penetrometer is a 365-pound, 10-foot-long, 3-1 /2-inch-diameter 

 package (see Figure 1). The penetrometer attains a free-fall terminal 

 velocity of about 80 feet per second and should penetrate up to 30 feet 

 into soft seafloor soils. Less penetration is expected in firm soils 

 and sands. While it is falling, it emits a 12,500-Hertz sound held to 

 an accuracy of plus or minus one part in 100,000. It is this sound that 

 is received with shipboard equipment as a Doppler- shifted signal that 

 becomes the data from the penetrometer. 



THEORY OF OPERATION 



The Doppler principle can be stated as 



f = f —i (D 



v + v 



where 



f ' = frequency received 



f = frequency transmitted 



v = velocity of sound 



v = velocity of source (penetrometer) 



This principle is used by the Expendable Doppler Penetrometer to generate 

 an analog of the kinematics of its motion. The depth sounder-receiver, 

 with which most Navy ships are equipped, may be used in the listen mode 

 to receive the signal from the penetrometer. At the expected terminal 

 velocity of the penetrometer (about 80 feet per second) and its prototype 

 operation frequency of 12,500 Hertz, a sound at 12,304 Hertz will be 

 received by the depth sounder- receiver. This is a frequency shift of 

 196 Hertz or 1.63% from the 12,500-Hertz signal of the penetrometer 

 (assuming the velocity of sound in seawater is 4,800 feet per second). 

 In the range of penetrometer velocities of to 100 feet per second it 

 can be shown that the frequency shift is nearly linear at 2.45 Hertz 

 for each f oot-per-second of velocity. The changes in the received 

 frequency are then a linear frequency analog of the kinematics of the 

 penetrometer. This frequency analog may be recorded and processed as is 

 any frequency-modulated telemetry signal. 



