The function applies a 13-year weighted low-pass filter, as described by Fritts (1976), on a
data.frame with tree-ring series.
A 13-year weighted low-pass filter, as described by Fritts (1976, p. 270), can be applied to tree-ring series prior to the calculation of event and pointer years using
pointer.norm. According to Cropper (1979), such a filter improves the detection of event and pointer years for complacent series, whereas for sensitive series filtering has little effect.
Note that the resulting time series are truncated by 6 years at both ends inherent to the calculation method.
The function returns a
data.frame with 13-year low-pass filtered index series.
Marieke van der Maaten-Theunissen and Ernst van der Maaten.
Cropper, J.P. (1979) Tree-ring skeleton plotting by computer. Tree-Ring Bulletin 39: 47-59.
Fritts, H.C. (1976) Tree rings and climate. Academic Press Inc. (London) Ltd.
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