Systematic and random errors in electronic speckle photography

Electronic speckle photography offers a simple and fast technique for measuring in-plane displacement fields in solid and fluid mechanics. Errors from undersampling, illumination divergence, and displacement magnitude have been analyzed and measured. The nature of the systematic error is such that a drift toward the closest integral pixel value is introduced. Because of the finite extent of the sensor area, considerable undersampling is tolerable before systematic errors occur. The random errors are mainly dependent on the effective ƒ-number of the imaging system and speckle decorrelation introduced by object displacement. When sampling at a rate of ~ 70% of the Nyquist frequency, we avoided systematic errors and minimized random errors.