 In 1949 he wrote a dissertation that was titled "Die frühen europäischen Einflüsse auf die Kultur der Bewohner der Tonga-Inseln 1616-1852" (The early European influences on the culture of the inhabitants of the Tonga Islands 1616-1852).After he received his PhD, he worked at sorting and cataloguing exhibits of the Ethnological Museum of Berlin (Museum für Völkerkunde), which were in storage at Celle.In 1951 Koch carried out field studies in Tonga and also visited Samoa, Fiji and New Caledonia.