In early 1938 , he lectured on aerial archaeology at the German Air Ministry ; the Ministry published his lecture as Luftbild und Vorgeschichte .
Crawford was frustrated that the British government did not publish his work with the same enthusiasm .
In early 1938 , he lectured on aerial archaeology at the German Air Ministry ; the Ministry published his lecture as Luftbild und Vorgeschichte , and Crawford was frustrated that the British government did not publish his work with the same enthusiasm .