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An acoustic Doppler current profiler ( ADCP ) is a hydroacoustic current meter similar to a sonar , used to measure water current velocities over a depth range using the Doppler effect of sound waves scattered back from particles within the water column .
 Doppler
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Doppler