A series of small, lightweight, autonomous spectrometer systems has been designed in Tartu Observatory. They are used for obtaining top-of-canopy spectral reflectance measurements for vegetation remote sensing, validation of radiative transfer models, and reflectance-based vicarious calibration of satellite and airborne sensors. The spectrometer systems are based on miniature spectrometer modules by Carl Zeiss Jena GmbH. The radiometric properties of the modules have been characterized based on laboratory measurements and appropriate data correction methods have been developed. The UAVSpec series spectrometer systems have been in operational use for several years and have been proven to be valuable tools for airborne, as well as on-ground and laboratory measurements. They are suitable for being carried by an unmanned aerial vehicle, which could make the measurement truly autonomous and independent of any service provider.