Merging Two Data Sets of Hemispheric Sunspot Numbers

First results on merging two data sets of hemispheric sunspot numbers - from the Kanzelhohe Solar Observatory and the Skalnate Pleso Observatory - for the time span 1977-1978 are presented. A total coverage of 86% was reached for the merged data set. In order to have a homogeneous time series, the daily sunspot numbers for the full disk from both observing stations were normalized to the international relative sunspot number of the day. The derived hemispheric sunspot numbers from Kanzelhohe and Skalnate Pleso Observatory compared for 290 common observing show very high correlations (r>=0.95), and the estimated data noise yields significant differences only for small values of sunspot numbers. These outcomes demonstrate the high potential of the applied merging procedure, and are the basis for an ongoing project to derive hemispheric sunspot numbers back to the year 1945 using sunspot drawings from Kanzelhohe and Skalnate Pleso Observatory.