The existence of a living painter named Richard Jansen makes researching Richard H. Jansen (on the web) a bit difficult. Richard H. Jansen was, of course, a post office muralist. Like many of the postoffice muralists, Jansen seems to have at spent time in the midwest and had ties to Wisconsin. You can see a photo of Jansen, along with other WPA artists, and some of their work here. You can also see examples of his work on the website for the United States Army Art Collection.
Jansen created three post office muralists: Threshing Wheat (Sauk Centre, Minnesota), Threshing Grain (Lincolnton, North Carolina), and Dairy Farming (Reedsburg, Wisconsin).