Identification and characterization of transient water quality events by Fourier analysis

Abstract

Natural cycles, particularly diurnal and seasonal cycles, dominate most environmental processes. Transients events are significant deviations from these usual variations. Transient events may have a duration from seconds to days and may occur naturally or as a result of man's activity. Events, which occur on occasion, could be considered on the basis of frequency of occurrence, and of duration of occurrence. In general, these events are rare relative to the density of data which are collected. Many data collection programs fail to identify transient events because of insufficient sampling. High-frequency electronic monitoring of water quality produces a record which contains seasonal, diurnal, transient events, and noise. A method of processing large volumes of data using spectral analysis techniques is described. The methodology is based on the separation of frequency components. This allows the examination of natural cycles, noise, and transient events. This technique allows screening of individual and multiple signals to allow confirmation and classification of transient events.