An apparatus hydromechanically decouples a hydrophone arrangement disposed n a water medium from the effects of current, wind and surface wave action. A first float carrying a transmitter-antenna assembly extends through the water-air interface and is tethered to an auxiliary float which buoyantly supports the hydrophone arrangement. A line, hundreds or thousands of feet long, is suspended by the auxiliary float and terminates in a sonobuoy tube at a predetermined depth. From the tube the hydrophone arrangement and a high pressure float are pulled out by a weighted nose portion. After the hydrophone arrangement, high pressure float and a length of line are pulled from the tube, a weak link between the hydrophone arrangement and nose portion snaps allowing the weighted nose to sink. The high pressure float has sufficient buoyancy to support the hydrophone arrangement and a portion of the length of line causing it to assume a cantenary configuration. The combination of the tether, the entrained mass of the tube and the cantenary hydromechanically decouples the hydrophone arrangement from the effects of current, wind, and surface wave action acting on the other components of the sonobuoy.

BACKGROUND OF THE INVENTION 
Sonobuoys and related seismic sensing devices have been in use for some 
time to sense acoustic phenomena of interest. A common design suspends a 
hydrophone from a spar buoy like float which also supports a 
transmitter-antenna combination. Signals representative of impinging 
acoustic energy on the hydrophone are transmitted to a distant monitoring 
station for appropriate data processing. This design provided acceptable 
performance in the audiofrequency range under calm conditions. An example 
of this type of conventional system is disclosed in the U.S. Pat. No. 
3,982,222 entitled "Deep Hydrophone String" and issued on Sept. 21, 1976 
to Robert J. Urich. Although this design calls for the lower end of the 
array being achored, fluctuations from the buoyant member will induce 
accelerations and pressure variations at the individual hydrophone 
elements creating what might be an unacceptable signal-to-noise ratio. The 
objectionable noise is the result of mechanical disturbances being 
transmitted to the hydrophone elements which, in turn, create 
representative spurious signals to be amplified. The objected-to 
disturbances are largely the product of the buoyant member's reacting to 
the effects of current, wind and surface wave action. These disturbances 
cannot be anticipated to allow their being compensated for in a 
sophisticated data processing technique, since they are extremely 
variable. For example, with the wind, waves and current all going the same 
way a certain pattern of mechanical disturbances is created. However, when 
the current is perpendicular or at some angle to the direction of the 
waves and the wind is from still another direction, a rigidly suspended 
hydrophone element will produce totally dissimilar spurious signals. 
The self-propelled array system disclosed in U.S. Pat. No. 4,004,265 issued 
to Thomas E. Woodruff, et al on Jan. 18, 1977 seeks to avoid the 
generation of spurious signals due to the interaction of a transmitter 
float. Their plan is to sink the array and anchor it on the bottom while 
relying on other means for deploying it in a more or less horizontal 
plane. However, certain places in the ocean are much too deep for such a 
buoying scheme or tactical expediency may dictate that a float supported 
array is the better choice. 
The subsurface system of U.S. Pat. No. 3,818,523 issued to Steven L. 
Stillman, Jr. on June 25, 1974 is another noteworthy attempt to provide 
for increased reliability. This moored system actually takes advantage of 
the ocean's currents to submerge or refloat the sonobuoy package. In one 
modification a portion of his tethering cable is made buoyant. This must 
necessarily reduce the transmission of hydromechanical disturbances to the 
hydrophone elements although it appears that the purpose of such a 
modification is to get the cable off the ocean's floor. 
Thus, from the foregoing it is apparent that there currently exists in the 
state of the art a continuing need for an unmoored hydrophone arrangement 
which hydromechanically decouples a suspended hydrophone arrangement from 
the effects of current, wind and surface wave action. 
SUMMARY OF THE INVENTION 
The present invention is directed to providing an apparatus for 
hydromechanically decoupling a hydrophone arrangement disposed in a water 
medium from the effects of current, wind and surface wave action. A 
transmitter-antenna assembly carried on a float extends through the 
water-air interface for transmitting signals representative of impinging 
acoustic energy on the hydrophone. An auxiliary float is configured to lie 
at and below the water-air interface for buoyantly supporting the 
hydrophone arrangement and is tethered to the transmitter-antenna float. A 
long line is connected to the auxiliary float and the hydrophone 
arrangement for suspending the hydrophone arrangement well below the 
water-air interface. A sonobuoy tube, originally containing all the 
elements of the apparatus is carried on the line near the hydrophone 
arrangement for damping mechanical disturbances. A high pressure float 
having a buoyancy for supporting the hydrophone and a portion of the line, 
forms a cantenary in the line after a weighted nose portion has pulled it 
from the cannister and separated from it. 
OBJECTS OF THE INVENTION 
It is an object of the invention to provide an improved sonobuoy. 
Another object of the invention is to provide an apparatus by which the 
sensor elements of a sonobuoy are decoupled from the influences of 
current, wind and surface wave action. 
Still another object is to provide a sonobuoy arrangement contained within 
a sonobuoy tube prior to deployment. 
Yet another object is to provide a sonobuoy having a transmitting-antenna 
float extending through the water-air interface being tethered to an 
auxiliary float disposed at and below the water-air interface to aid in 
the hydromechanical decoupling of a hydrophone arrangement. 
A further object is to provide a sonobuoy arrangement which positions the 
sonobuoy tube near the hydrophone arrangement to aid in the damping of 
mechanical disturbances. 
Still another object is to provide a sonobuoy system that locates the 
sensor elements deep within the ocean suspended by a high pressure float 
supported cantenary. 
Yet still another object of the invention is to provide a sonobuoy 
arrangement that combines tethered, separated floats, the entrained mass 
of a water filled tube near the hydrophones and a cantenary support for 
hydromechanically decoupling a hydrophone arrangement from the effects of 
current, wind and surface wave action. 
These and other objects of the invention will become more readily apparent 
from the ensuing specification when taken with the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1 of the drawings, a sonobuoy 10 is shown during an 
initial stage of deployment as it penetrates the water-air interface. A 
weighted nose portion 11 is shaped to penetrate the water and at the 
opposite end of a sonobuoy tube 12, fluted surfaces tend to act as vanes 
to maintain a proper orientation. 
As the sonobuoy continues sinking, a transmitter-antenna float 13 is 
released from the aft end of the sonobuoy. A light stiff wire antenna 13a 
has a minimum drag in high winds and serves to relay data to a remote 
station. A variety of transmitters and antennas are well established in 
the art and a routineer could choose from them to practice this invention. 
An auxiliary float 14 also is deployed from the sonobuoy and pulls a 
suspension line 15 from within the sonobuoy tube. Between float 13 and 
float 14, approximately 150 feet of coiled line 16 tethers them together. 
The tether line is held coiled by a mild adhesive which releases coils as 
the floats are separated by wind, waves, etc. 
Since the antenna float extends through the water-air interface to enable 
the transmission of signals representative of impinging acoustic energy, 
the tether line functions to block the transmission of mechanical 
disturbances from the rest of the elements of the sonobuoy. These 
disturbances are caused as the transmitter-antenna float responds to wind, 
surface currents and surface waves. Wind, in particular, will rock the 
transmitter-antenna float violently and heaving waves bob it about. 
While the transmitter-antenna float is designed to extend through the 
water-air interface, the auxiliary float is sized to provide buoyant 
support for the rest of the elements of the sonobuoy and to come to the 
surface only in the wave trough. That is to say, it has only a few ounces 
of positive buoyancy so that it will ride below and at the water-air 
interface. This lends stability to the remainder of the sonobuoy elements, 
as will be elaborated on below. Giving both of the floats a streamlined 
configuration further helps reduce their reaction to the unstabilizing 
effects of high sea states, winds and currents. 
The suspension line 15 can be any length, one tested had a length of over 
one thousand feet. Looking to FIG. 3, at the 1,000 feet level downward 
travel of the sonobuoy is arrested and it is suspended. A traverse wall 
12a is provided with several small openings, not shown, to allow trapped 
air to escape. The wall does, however, give the tube a damping capability. 
This capability is largely attributed to a large water mass entrained by 
the wall within the sonobuoy tube. 
When downward motion of sonobuoy tube 12 is arrested, the weighted nose 
portion falls out or is otherwise suitably released. In so doing, it pulls 
out a section of weighted line 17, and a high pressure float 18, coupled 
via a line 19 to a hydrophone arrangement 20. High pressure floats are 
commonplace in the state of the art and hydrophone arrangements, be they 
single elements or arrays of elements, are well known. 
A weak link 21 couples the hydrophone arrangement to the weighted nose 
portion so that when elements 17 through 20 have been fully withdrawn and 
extended, the weighted nose portion draws the weak link taut, and snaps it 
allowing the weighted nose portion to sink by itself. This being done, the 
buoyancy of the high pressure float is of such a magnitude as to support 
the hydrophone arrangement and a portion, preferably about one-half, of 
the weighted line 17 to form the line into a cantenary with the hydrophone 
arrangement being supported by the high pressure float, see FIG. 4. 
In FIG. 4, a modification of the auxiliary float is shown. A number of 
small floats 14a are disposed along the length of line 16 for the same 
purpose as float 14. There are a number of floats 14a in a short length to 
provide the vertical support for the remainder of the sonobuoy elements 
with the spacing between adjacent floats 14a becoming greater and greater 
as antenna float 13 is approached. This arrangement of the small floats 
helps keep them below or at the trough of the waves to reduce the problems 
associated with heave, wind, etc. 
The embodiment of FIG. 4 depicts the sonobuoy in a condition where the wind 
is from left to right and, therefore, antenna float 13 appears to be 
drifting to the right. Current is from right to left so that the cantenary 
of line 17 suspends the hydrophone arrangement to the left of the sonobuoy 
tube. This being the case, the length of tether line 16, the mass of the 
entrained water in sonobuoy tube 12 and the cantenary of line 17 reduce to 
a minimum the mechanical influences of the hydrophone arrangement. In 
particular, the cantenary has a resonant frequency that is a small 
fraction of the higher wave frequencies so that residual surface motions 
are severely damped and become insignificant as a self noise source. The 
use of the entrained water mass in the sonobuoy tube near the almost 
neutrally buoyant hydrophone arrangement, inhibits acceleration due to 
surface heave and strumming before these influences can possibly reach the 
hydrophone arrangement. Finally, line 16 prevents the transmission of any 
heaving or rocking motions from the transmitter-antenna float from 
reaching the hydrophone arrangement. 
At this point it may be well to mention that metallic or fiber optic 
conductors of electromagnetic energy are contained within the lines 16, 17 
and 19. Also discussion regarding necessary power sources, preamplifier 
stages, etc. have been dispensed with to avoid belaboring the obvious. 
Obviously, many modifications and variations of the present invention are 
possible in the light of the above teachings, and, it is therefore 
understood that the invention may be practiced otherwise than as 
specifically described.