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Fringe-pattern analysis using a spatial phase-stepping method with automatic phase unwrapping

Presents a new method of fringe-pattern analysis by spatial phase stepping (SPS). The SPS method combines the computational simplicity of phase stepping with the single-image analysis capability of the Fourier transform method. The technique works by subdividing a linearized fringe pattern into three component images, from which the phase is calculated by a three-phase step algorithm. A computer simulation has been undertaken to demonstrate the theory and to enable an analysis of systematic errors. In addition, an experimental transonic flow field is solved by SPS and a comparison is made with results derived using the Fourier transform method. The experiment also demonstrates the use of the minimum spanning tree phase-unwrapping strategy to create a continuous map of the whole transonic flow field.