Method for deriving water bottom reflectivity in dual sensor seismic surveys

A method to combine the pressure and velocity signals to eliminate first-order peg-leg multiples while retaining the first reflection off the ocean bottom comprising the steps of:

• (a) determining the value for ocean bottom reflectivity;
• (b) summing the velocity and the pressure signals to provide a trace containing only up-going energy;
• (c) transforming the up-going energy trace from the time domain to the frequency domain;
• (d) calculating the inverse Backus operator (1+RZ).sup.2 where R is the water bottom reflectivity determined in step (a) and Z is the two-way travel time of the seismic signal in the water-layer in Z-domain representation;
• (e) multiplying the frequency domain representation of the up-going energy trace with the inverse Backus filter;
• and
• (f) inverse transforming the filtered trace from the frequency domain to the time domain.

An improved method for determining water bottom reflectivity R in dual sensor seismic surveys, comprising the steps of:

• (a) sensing pressure and velocity using a hydrophone and a geophone in close proximity;
• (b) applying a time window to the pressure and velocity signals;
• (c) summing the time windowed pressure signal and time windowed velocity signal to provide a trace containing only up-going energy;
• (d) calculating the inverse Backus operator (1+RZ).sup.2 where R is the water bottom reflectivity and Z is the two-way travel time of the seismic signal in the water-layer in Z-domain representation;
• (e) multiplying the up-going signal with the inverse Backus operator;
• (f) squaring the amplitudes of the resulting signal;
• (g) measuring the power contained in the signal by summing the squared amplitudes of the signal;
• (h) repeating steps (d)-(g) using different values for the water bottom reflectivity;
• (i) selecting the value for water bottom reflectivity which produces the signal with the lowest power.