The Narrow-Field-of-View Zenith Radiometer (NFOV) is a ground-based radiometer that looks straight up. As implied by the name, the field of view of the instrument is narrow, thus permitting the measurement of the downwelling zenith radiance.
The instrument outputs a time series of 1-sec observations of the zenith spectral radiance measured at a wavelength of 869 nm. Data from the instrument have many uses; for example, the internal structure of clouds can be characterized by examining a time series of the radiance data.