We have designed, built, and calibrated a transfer radiometer for the VNIR region of the optical spectrum. The instrument is based on a "trap" detector configuration of large-area silicon detectors. The spectral bandpass of the nine bands between about 410 and 1050 nm is set by interference filters. This paper presents the design, characterization, and calibration of the radiometer.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.