BACKGROUND

Communications between an aircraft or satellite and submarines or other submerged devices is very difficult. Several techniques exist for closing this link, but all have limitations. For example, a combined acoustic signal and radar technique has been proposed. This method uses radar to measure acoustic disturbances on the surface caused by acoustic signals.

SUMMARY OF INVENTION

Aspects and embodiments provide improved systems and methods for establishing communications links between an underwater object and an airborne or space-based platform based on a combined acoustic and optical approach that uses water surface tension to convert between the two communications mediums.

According to one embodiment, an acoustic to optical communications method comprises emitting a modulated acoustic signal from an underwater object submerged in a body of water towards a surface of the body of water, with an active optical transceiver, optically measuring surface deformations at the surface of the body of water produced by the modulated acoustic signal, the surface deformations being representative of a modulation of the modulated acoustic signal, and recovering information encoded on the acoustic signal by the modulation based on the measurements of the surface deformations.

In one example, the modulation of the modulated acoustic signal is phase modulation and measuring the surface deformations includes detecting at least one of constructive and destructive interference patterns at the surface of the body of water.

In another example, the modulation of the modulated acoustic signal is amplitude modulation and measuring the surface deformations includes optically measuring a change in water surface height relative to a reference. In one example, measuring the surface deformations further includes measuring a rate of change of the water surface height.

The method may further comprise performing additional water surface measurements to produce surface condition data to characterize communications channel noise at a given time. In one example, performing the additional water surface measurements occurs between instances of measuring the surface deformations representative of the modulation of the modulated acoustic signal.

According to another embodiment, a method of acoustic to optical communications comprises performing active optical measurements of modulation-based surface deformations at a surface of a body of water using an active optical receiver to produce modulation data, the modulation-based surface deformations being representative of a modulation of a modulated acoustic signal originating beneath the surface of the body of water, between instances of performing the active optical measurements of the modulation-based surface deformations, optically measuring surface conditions of the body of water to produce channel information, and based on the modulation data and the channel information, recovering data encoded in the modulation of the modulated acoustic signal.

In one example, performing the active optical measurements of the modulation-based surface deformations includes detecting at least one of constructive and destructive interference patterns at the surface of the body of water. In another example, recovering the data encoded in the modulation of the modulated acoustic signal includes detecting phase changes indicative of phase modulation of the modulated acoustic signal based on the detected interference patterns.

In one example, performing the active optical measurements of the modulation-based surface deformations includes measuring a rate of change of a height of the surface.

In another example, performing the active optical measurements of the modulation-based surface deformations includes measuring a height of the surface relative to a reference. In one example, recovering the data includes detecting amplitude modulation of the modulated acoustic signal based on changes in the height.

According to another embodiment, an active optical receiver configured for acoustic to optical communications comprises a LiDAR transmitter configured to produce an optical probe signal for measuring modulation-based surface deformations of a surface of a body of water representative of a modulation of a modulated acoustic signal originating beneath the surface of the body of water, a LiDAR receiver configured to receive reflections of the optical probe signal from the body of water and to output first measurement data based on the reflections of the optical probe signal, the first measurement data being representative of the modulation of the modulated acoustic signal, an interpreter module configured to recover binary symbols from the first measurement data, and a message reconstruction module configured to convert the binary symbols into a message structure having one of a first message class and a second message class, the first message class being a data message and containing information corresponding to data encoded in the modulation of the modulated acoustic signal.

In one example, the LiDAR transmitter is further configured to produce an optical channel measurement signal for measuring surface conditions of the body of water, and the LiDAR receiver is further configured to receive reflections of the optical channel measurement signal from the body of water and to output second measurement data based on the reflections of the optical channel measurement signal, the second measurement data being representative of the surface conditions of the body of water. The active optical receiver may further comprise a surface correction module configured to receive the second measurement data and to provide surface condition information to the interpreter module. In one example, the interpreter module is configured to use the surface condition information to recover the binary symbols from the first measurement data. In another example, the interpreter module is configured to recover the binary symbols from the first measurement data and the second measurement data, and the message reconstruction module is configured to convert the binary symbols recovered from the first measurement data into the message structure having the first message class and to convert the binary symbols recovered from the second measurement data into the message structure having the second message class.

In one example, the optical receiver further comprises a data storage module configured to store the information corresponding to the data encoded in the modulation of the modulated acoustic signal.

In another example, the LiDAR receiver includes an optical resonator. In one example, the optical resonator is a Fabry-Perot etalon.

Still other aspects, embodiments, and advantages of these exemplary aspects and embodiments are discussed in detail below. Embodiments disclosed herein may be combined with other embodiments in any manner consistent with at least one of the principles disclosed herein, and references to “an embodiment,” “some embodiments,” “an alternate embodiment,” “various embodiments,” “one embodiment” or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one embodiment. The appearances of such terms herein are not necessarily all referring to the same embodiment.

