Martin Satre born May 1851 in Norway

This is probably not enough information, but I've hit the wall so seeking assistance ... Martin Satre (Satra, Sathre, Sather, Setre) (Suspect possibly Sættre, Sætre, Sæther in Norway) Emigrated to North Dakota in 1883, possibly with wife. Wife's name may be Birta Velten, born in Norway (not sure abt this) Children: Mike, Annie, Olaf, Almer, so those names may be in family. Exhausted all efforts in Digitalarkivet, think I may need a course ... anyone know if there is such a thing? Any pointers or clues would be greatly appreciated ... Carra Johnson Callies