Ralf Kohlhaas is Head of the OptX section at SRON, the Netherlands Institute for Space Research, where he oversees optical design, performance and calibration engineering, as well as the management of optical research activities. In this interview, Ralf explores the role of passive optical instruments—such as spectrometers and radiometers—in monitoring Earth’s land and atmosphere, highlighting their applications in agriculture, climate science, and future innovations in instrument design.