Error and Technique in Fluorescent dye Tracing

The appropriate approach to dye tracing in karst areas depends upon the objective and context of the trace. Dye tracing in karst areas is undertaken to address geographical, hydrogeological and contaminant problems at particular spatial and temporal resolution in the context of prior knowledge, available resources, social and legal expectations and environmental constraints. The value of a trace is improved if the objective can be formalized into a rational hypothesis and where the signal is demonstrably distinct from error. This requires sampling and analysis as much to define error as to detect the signal. The tolerable error depends on the dye trace objective and context, and scales with the sophistication of both, becoming increasingly critical and challenging as higher level interpretations are made. The appropriate technique for a particular trace therefore depends not only on the problem and context, but also upon the necessity of defining and correcting errors. Simpler problems such as establishment of underground connections can often be usefully tackled with simple techniques. Variable background fluorescence is a particularly difficult systematic error in dye tracing that can be reduced by supplementary sampling and control. This approach is illustrated for fluorescence spectra and in situ filter fluorometry. To extract a signal from spectra a statistical correction has been developed allowing compositional and concentration corrections to highlight anomalous samples. Supplementary sampling is required to provide the background statistics necessary for such an approach. The strong spectral coherence of background allows concurrent green fluorescence measurements to define variable background fluorescence during a red dye trace. The relationship between red and green fluorescence in un-dyed samples can be used to model background behavior in the presence of the red dye.