An investigation of various unwrap/reduction methods to quantify phase-shifted holographic interferometry

Abstract

Measurement time is of the essence for most ground test facilities, so measurement techniques capable of measuring planes of data are much more attractive than those which measure only single points. Many techniques already exist which allow for nonintrusive measurements of pressure, temperature and density; several of which are two-dimensional by design. Holography and holographic interferometry are well established techniques; however, for the most part they provide qualitative data. A computer program for achieving quantitative two-dimensional or axis-symmetric density maps using a phase-shifted holographic interferometer is currently being developed. Several phase unwrapping and data reduction methods were investigated in an effort to produce a computer program capable of correctly analyzing a flow field. Several test holographic interferograms of a candle flame and a heat gun, made in a laboratory setting were used to validate various aspects of the software algorithms. A discussion of the algorithms investigated and the determination of which algorithm best analyzes the flowfield structures will be presented.