Widess criterion

The criterion of Moe Widess for analysis of vertical resolution (1973) was derived assuming simplified circumstances by convolving a zero-phase wavelet with two isolated reflection coefficients of equal amplitude and opposite sign of a thinning bed.

The study showed that peak/trough separation and composite amplitude of interfering events from a wedge model correlates approximately linearly with bed thickness until a stable composite waveform is obtained approaching a bed thickness of an eigth of the pre-dominant wavelength. The final waveform hereby becomes virtually the derivative of convolving source wavelet itself.

For thicknesses below λ/8, defined as vertical resolution limit by the Widess criterion, seismic amplitude remains the only changing seismic characterisitc making it impossible to destinguish thickness changes from changing reflection coefficients.

In contrast to the Rayleigh criterion, the Widess criterion is based on a reflector model and requires the reflection co-efficients to be isolated.

Effect of a thinning bed on the composite reflection. a)Velocity graph. b) Reflection ray diagram. c) Composite reflection. d) Shape, amplitude and relative timing of the composite reflection as a function of bed thickness. .

See also

• Rayleigh resolution criterion
• Ricker resolution criterion
• Seismic resolution