The spectrum of scattered sunlight from an object like an asteroid is subject to a combination of Doppler shifts due to the radial motion of the object relative to both the Sun and the observer on Earth.

This small shift can readily be seen in the high resolution spectrum of Vesta taken in twilight, where the spectrum of the asteroid can be directly compared with that of the sky background. The sky background provides a stable reference allowing the shift to be measured to an accuracy greater than the stability of the spectrograph might normally allow.  The shift is too small to measure from a single line however with any precision. The noise in the spectrum for example limits the accuracy to which the line position can be determined. 

By cross correlating the entire asteroid and sky spectra however the shift can be measured with higher precision, a technique which is tolerant of low signal to noise ratio, as done here using ISIS software

 (A similar technique was used to measure the velocity of comet C/2020/F3 (NEOWISE) where an additional measurement of the sodium emission from the comet allowed the two components of the velocity to be separated)