Systems and methods of optical link communication with seismic data acquisition units are provided. The systems and methods can perform at least portions of seismic data acquisition survey. A plurality of seismic data acquisition units can be deployed on a seabed. An optical communications link can be established between an extraction vehicle and at least one of the seismic data acquisition units. A frequency of the at least one seismic data acquisition unit can be syntonized or synchronized via the optical communications link. The at least one seismic data acquisition unit can be instructed to enter a low power state subsequent to syntonizing the frequency of the at least one seismic data acquisition unit. The seismic data acquisition unit can exit the low power state and acquire seismic data in an operational state.

Systems and methods of performing a seismic survey are provided. The system includes a seismic data acquisition unit having a transmitter window disposed in a first aperture of a lid, and having a receiver window disposed in a second aperture of the lid. A first gasket is positioned between the transmitter window and the first aperture to provide a clearance greater than a threshold to allow the transmitter window to deform. A second gasket is positioned between the receiver window and the second aperture to provide a clearance greater than the threshold to allow the receiver window to deform. At least one of the transmitter window and the receiver window of the seismic data acquisition unit are configured to pass at least one of optical and electromagnetic communications to or from an extraction vehicle via at least one of a transmitter window and a receiver window of the extraction vehicle.

Systems and methods of performing a seismic survey in a marine environment are provided. The system includes a seismic data acquisition unit disposed on a seabed in the marine environment. The seismic data acquisition unit includes a local pressure sensor, an optical transmitter and an optical receiver to determine one or more pressure values. The system includes an extraction vehicle including a reference pressure sensor, an optical transmitter, and an optical receiver to establish an optical communications link with the seismic data acquisition unit, and generate reference pressure data. The system includes at least one of the local pressure sensor and the one or more pressure values calibrated based on the reference pressure data generated by the extraction vehicle.

A system and method for adjusting a clock signal of a seismic data acquisition system. The system includes a data acquisition device having an oscillator that generates a clock signal; a clock adjustment module that receives a time reference signal and the clock signal and outputs an adjusted clock signal; and an analog-to-digital convertor configured to transform analog data into digital data having a sampling rate (F.sub.DATA). A sampling frequency (f.sub.ADC) of the analog-to-digital convertor is selected to be at least twice the sampling rate (F.sub.DATA).

Methods and systems for synchronizing clocks used in underwater devices is described. All clocks have some drift due to frequency accuracy and this disclosure provides a method for periodically synchronizing clocks to an accurate master clock to remove long term drift. A synchronization device can use an accurate clock and hardware to transmit both a sound wave and light pulse at the same point in time. Remote slave clocks can detect the light first, and later the sound, allowing them to calculate the distance the pulse had to travel. The clocks can then synchronize their time to the master clock canceling out any drift. The synchronization device can be packaged in a waterproof housing and can be moved around on a periodic basis between the clock on an underwater robot or any other means.

In some embodiments, an apparatus and a system, as well as a method and an article, may operate to receive a derived clock signal downhole, the derived clock signal being derived from a surface clock signal (associated with a surface clock), such that the frequency of the derived clock signal is less than the frequency of the surface clock signal. Further activity may include measuring the frequency of the derived clock signal in terms of an uncorrected downhole clock frequency (associated with a downhole clock) to provide a measured frequency equivalent, and correcting time measurements made using the downhole clock, based on the measured frequency equivalent, or based on an actual frequency of the downhole clock determined according to the measured frequency equivalent. Additional apparatus, systems, and methods are described.

A wireless seismic data acquisition unit with a wireless receiver providing access to a common remote time reference shared by wireless seismic data acquisition units in a seismic system. The receiver can replicate local version of remote time epoch to which a seismic sensor analog-to-digital converter is synchronized. The receiver can replicate local version of remote common time reference to time stamp local node events. The receiver can be placed in a low power, non-operational state over periods of time during which the unit continues to record seismic data, thus conserving unit battery power. The system corrects the local time clock based on intermittent access to the common remote time reference. The system corrects the local time clock via a voltage controlled oscillator to account for environmentally induced timing errors. The system provides a more stable method of correcting drift in the local time clock.

A system and method for adjusting a clock signal of a seismic data acquisition system. The system includes a data acquisition device having an oscillator that generates a clock signal; a clock adjustment module that receives a time reference signal and the clock signal and outputs an adjusted clock signal; and an analog-to-digital convertor configured to transform analog data into digital data having a sampling rate (F.sub.DATA). A sampling frequency (f.sub.ADC) of the analog-to-digital convertor is selected to be at least twice the sampling rate (F.sub.DATA).

Methods and systems for synchronizing clocks used in underwater devices is described. All clocks have some drift due to frequency accuracy and this disclosure provides a method for periodically synchronizing clocks to an accurate master clock to remove long term drift. A synchronization device can use an accurate clock and hardware to transmit both a sound wave and light pulse at the same point in time. Remote slave clocks can detect the light first, and later the sound, allowing them to calculate the distance the pulse had to travel. The clocks can then synchronize their time to the master clock canceling out any drift. The synchronization device can be packaged in a waterproof housing and can be moved around on a periodic basis between the clock on an underwater robot or any other means.

A system for synchronizing instruments in a drill pipe to detect formation characteristics comprises at least one first transmitter for transmitting a first signal, at least one first receiver for receiving a second signal having information based on the first signal, at least one acoustic transmitter for transmitting an acoustic signal, and at least one acoustic sensor electrically connected to one of the at least one first transmitter and the at least one first receiver, the at least one acoustic sensor for sensing the acoustic signal for synchronizing the at least one first transmitter and the at least one first receiver.