Concerning Baseline Errors in the Form of Acceleration Transients When Recovering Displacements from Strong Motion Records Using the Undecimated Wavelet Transform

This paper discusses the progression of a novel algorithm that uses a wavelet-transform approach. The transform is a generalization of the decimated, dis-crete wavelet transform (DWT) that is the undecimated DWT or stationary wavelet transform (SWT) also known as the undecimated á trous algorithm. It forms the basis for recovering displacements from acceleration time histories. The approach recovers a low-frequency fling that is usually an almost sinusoidal or cosinusoidal pulse responsible for the big ground motions in strong motion events. The algorithm imple-ments a well known and non-linear, denoising scheme and is applied to the low-frequency sub-band and, in particular, succeeds in recovering the acceleration-fling pulse. The progression is that in order to obtain estimates of displacements, the algo-rithmic baseline-correction scheme can now locate an acceleration transient (i.e., a spike), which creates the DC shift in velocity and the linear trend in displacement, and is therefore the baseline error. Once this acceleration transient is corrected for or eliminated, double-time reintegration recovers the velocity-fling pulse and residual displacement. The paper infers that these acceleration transients may be due to ground rotation, embedded in the translational data. The scheme provides for easier integra-tion once the low- and higher-frequency accelerations are extracted.