Abstract: Methods and systems are provided for investigating an image set of geophysical data distributed over a first N-dimensional volume where N?2. A subvolume that encloses a known feature of interest within a target set of geophysical data distributed over a second N-dimensional volume is selected. A cross-correlation is calculated between the data distributed within the subvolume and corresponding data distributed in the first N-dimensional volume about multiple positions.

Abstract: Methods and systems are provided for acquiring seismic data. An ambient electromagnetic signal having a known time dependence is transmitted for propagation within a survey area. The ambient electromagnetic signal is received at distinct geographic locations with independently operating data acquisition units positioned at the distinct locations. Data representing acoustic signals received from the Earth at the distinct geographic locations are collected with the data acquisition units. The collected acoustic signals for the distinct geographic locations are synchronized by correlating the known time dependence of the propagated electromagnetic signal with time dependencies of the collected acoustic signals.

Abstract: A self-contained data acquisition unit is provided for acquiring seismic data. The unit has a microprocessor and an antenna adapted to receive an electromagnetic signal. A decoder is connected with the microprocessor and adapted to convert received electromagnetic signals to dual-tone multiple-frequency (“DTMF”) digits. A geophone interface is provided with a geophone for collecting acoustic data incident on the geophone. A memory is connected with the geophone interface for storing a representation of the collected acoustic data and for storing a representation of a reference electromagnetic signal to be used in synchronizing acoustic data collected by other data acquisition units. A battery power source is connected with the microprocessor.

Abstract: Apparatus and methods are provided for simultaneously retrieving data from multiple data acquisition units and for recharging such data acquisition units. The data offload and charging unit comprises a frame that defines stations for holding the data acquisition units and a host computer. A combined power and communications port at each such station is adapted to interface with one of the data acquisition units such that power may flow from the data offload and charger unit to that data acquisition unit and data may flow from that data acquisition unit to the host computer substantially simultaneously. Communications links are provided between the host computer and each combined power and communications port.

Abstract: Methods and systems are provided for acquiring seismic data. Data are collected representing acoustic signals received from the Earth at distinct geographic locations. Data representing an ambient signal at the distinct geographic locations are also collected. For each of the geographic locations, a known time dependence of the ambient signal is correlated with a time dependence of the collected acoustic-signal data to define time-correlated acoustic signal data. The collected acoustic-signal data for the distinct geographic locations are synchronized from the time-correlated acoustic-signal data.

Abstract: Methods and systems are provided for investigating an image set of geophysical data distributed over a first N-dimensional volume where N?2. A subvolume that encloses a known feature of interest within a target set of geophysical data distributed over a second N-dimensional volume is selected. A cross-correlation is calculated between the data distributed within the subvolume and corresponding data distributed in the first N-dimensional volume about multiple positions.

Abstract: A method used for controlling vibrator ground force output from a seismic vibrator and reducing potential damage to nearby structures. The method may be applied to any type of seismic vibrator for controlling the amount of vibrator force output applied to a ground subsurface. The subject method controls the vibrator force output as a function of frequency to form a force variable sweep. Low frequency waves are harmful to structures. The force variable sweep reduces the percentage of harmful low frequency waves while imparting a great deal of energy. The method steps include first selecting and constructing a frequency dependent force function from either a hyperbolic tangent function mathematical equation or a simple step function mathematical equation. Second, implementing a seismic vibrator frequency control instrument with the selected frequency dependent force function. Third, applying the force function to either a seismic upsweep or a seismic downsweep.