I. INTRODUCTION 



As part of the inshore survey of Penobscot Bay In the summer and early fall 

 of 1959, many grab samples, cores, and Sonoprobe records of excellent quality 

 were obtained. This report attempts to utilize the bottom and subbottom data, 

 oceanographic information, and historical data to arrive at an overall picture of 

 past and present sedimentation in Penobscot Bay. Particular emphasis is placed 

 upon the use and evaluation of the Sonoprobe as a tool for obtaining geological 

 data . 



II. THE SONOPROBE 



A. General 



The Sonoprobe, manufactured by Scientific Service Laboratories, Is an 

 Instrument for measuring the depth of water and the depth and thickness of sedi- 

 mentary beds beneath the sea bottom by acoustic means. The parameter measured 

 Is the time lapse between the outgoing signal and the reflected signal . Signals 

 ore pulsed at a rate of 12/sec. The reflections are recorded on chart paper which 

 Is drawn through a recorder. As the survey ship passes over the bottom, a contin- 

 uous trace of bottom and subbottom reflections Is recorded . 



B. Instrument Operation 



The Sonoprobe consists of two hull mounted transducers; the transmitting 

 transducer and the hydrophone, and four deck units; the Pulser, the Control - 

 Display Unit, the Recorder, and the Precision 60-cycle Power Unit (Plate I). 



The pulser drives the transmitter at frequencies of 3, 4.5, or 6 kc . The 

 pulse duration Is 0.3 millisecond. At the Instant of discharge, voltages up to 

 1000 volts and currents to 1000 amperes are attained. 



These high Intensity pulses of acoustic energy are transmitted into the water 

 from the magnetostrlctlve transducer mounted in the hull of the survey ship. The 

 energy is peaked In the downward direction and forms a cone with approximately 

 a 30** angle. Part of the signal is reflected at the water bottomland part pene- 

 trates the bottom material where It Is absorbed or reflected by acoustic disconti- 

 nuities In the subbottom sediments. The hull mounted hydrophone receives the 

 ""energy of the reflected signals and converts It Into electrical energy. 



Signals from the hydrophone are applied to the Control -Display Unit where 

 they are filtered, amplified, displayed, and passed on to the recorder. The 

 filters are variable and serve to eliminate ship's noise and other extraneous signals, 



