searching for Clemetsen

I'm searching for information on my 3xgreat grandparents who emigrated from Norway to Wisconsin and then Minnesota in the mid 1800's. Osten Clemetsen and Gunhild Palmesdr were married in Buskerud in 1847 and emigrated with 2 children, Kari(b. 1947) and Nels (B. 1848). Their next child was born in Minnesota in 1854 (Christen). They must have travelled between 1849 and 1853. Any further info would be welcome (emigration records, etc.)