Abstract
The relative number of sunspots represents the longest evidence describing the level of solar activity. As such, its use goes beyond solar physics, e.g. towards climate research.
The construction of a single representative series is a delicate task that involves a combination of the observations of many observers. We propose a new iterative algorithm that allows construction of a target series of relative sunspot number of a hypothetical stable observer by optimally combining series obtained by many observers.
We show that our methodology provides us with results that are comparable with recent reconstructions of both sunspot number and group number. Furthermore, the methodology accounts for the possible non-solar changes of observers' time series such as gradually changing observing conditions or slow change in the observers' vision.
It also provides us with reconstruction uncertainties. We apply the methodology to a limited sample of observations by the CESLOPOL network and discuss its properties and limitations.