The Portable Remote Imaging Spectrometer (PRISM) is a pushbroom imaging spectrometer currently under development at the Jet Propulsion Laboratory, intended to address the needs of airborne coastal ocean science research. The distinguishing characteristics of the design are high signal to noise ratio, high uniformity of response, and low polarization sensitivity. The optical design is based on the Dyson spectrometer. We discuss here design refinements that are critical for stray light control and for reducing the polarization sensitivity of the entire instrument to below 2%.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.