"Key party responsible for gathering information and conducting research. This is the person who is responsible for making the measurements and securing the quality of the data. In general, there should be exactly one PrincipalInvestigator associated with every measurement and (a possibly different person) associated with a station. The PrincipalInvestigator may delegate responsibilities, for example to technicians or postdoctoral researchers, and yet remain PrincipalInvestigator as the person overseeing the measurements and data distribution."(xsd:string)