The Spectrometer Arduino Mega (SpAM) is a prism spectrometer that has been designed and fabricated by the Remote Sensing Group (RSG) at the College of Optical Sciences of the University of Arizona. SpAM is designed to be a low budget, stand alone, solar powered field spectrometer. RSG plans to use SpAM to measure the reflectance of natural surfaces in the field. After the laboratory calibration of SpAM, it will be deployed to the Radiometric Calibration Test Site (RadCaTS) at Railroad Valley, Nevada. A satellite uplink will allow RSG to upload SpAM measurements on a daily basis. SpAM measures and records the spectral composition of a light source or light reflected from a surface. The prism inside of SpAM refracts the input light onto a linear array of 512 silicon detectors. The detector-prism combination produces a spectral resolution of ~2 nm, and the overall spectral range is 433–760 nm. The spectral radiometric measurements produced by SpAM are stored and processed by an Arduino mega micro controller with network capabilities for field applications. SpAM will be used to analyze the spectral reflectance of Railroad Valley dry lake, and its accuracy and performance will be determined by a comparison with filter-based radiometers that have been produced by RSG. This work presents the design and instrumentation of SpAM, and an assessment of its ability to provide radiometric results for satellite calibration and other radiometric measurement applications.