The development and application of optically generated spatial carrier fringes for the quantitative measurement of flowfields and solid surfaces

There are two main approaches to fringe pattern analysis: spatial carrier and temporal carrier. The phase-stepping (PS) method plays a prominent part in the temporal carrier approach. The principal technique of the spatial carrier approach is the discrete Fourier transform (DFT) method. In this thesis, both methods are reviewed and illustrated with examples. The problems associated with these methods are discussed. The effect of weighting function and filtering window on the accuracy of the DFT method is investigated. A review of the minimum spanning tree approach to phase unwrapping is presented. A new fringe evaluation technique has been explored. The technique combines the computational simplicity of the PS method with the singleimage analysis capability of the DFT method. This technique is implemented over two steps. Firstly, a fringe pattern with spatial carrier is subdivided into three component images. Then, the phase is calculated by a three phase step algorithm from these images. A computer simulation has been undertaken to demonstrate the theory and to analyse the systematic errors. Applications in the analysis of the transonic flow-fields are presented. The Fourier Transform Profilometry (FTP) decodes the 3-D shape information from the phase stored in a 2-D image of an object onto which a Ronchi grating is projected. Two different optical geometries used in the FTP have been compared. The phase information can be separated from the image signal by either the phase subtraction method or the spectrum shift method. The result of an experimental comparison between two phase extraction methods is also presented