The project “Building Infrastructure for the validation of satellite derived atmospheric pa-rameters” with the acronym “Phaethon” aimed at developing a low-cost ground based sys-tem for the retrieval of column densities of various atmospheric gases, based on a proto-type system that was developed for aerosol optical depth and solar radiation measurements. This system was upgraded by modifying its optical characteristics to fulfill the require-ments for atmospheric gas retrievals with the Differential Optical Absorption Spectroscopy (DOAS) technique. As a DOAS instrument, Phaethon records spectra of solar radiation (radiance or direct irradiance) that have been modified by absorption and scattering from atmospheric constituents. These spectra are compared with a reference spectrum that has undergone much weaker absorption. Differences in wavelength-dependent absorption fea-tures of these spectra from a reference spectrum that has undergone weaker absorption ap-pear as a characteristic differential spectrum of proportional magnitude. This “differential” spectrum is analyzed by least-squares fits of cross sections, after the removal of slowly-varying spectral features by spectral smoothing to derive differential slant column densities (DSCD) of the absorbers.
The project comprised three major phases:
1. The upgrade of the original Phaethon system both in terms of hardware and software
2. The validation of the system by comparison to a state of the art MAX-DOAS system
3. A pilot application of the system for the validation of corresponding satellite products