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Meteoroids bombard Earth's atmosphere during its orbit around the Sun,depositing a highly varying and significant amount of matter into thethermosphere and mesosphere. The strength of the material source needs to becharacterized and its impact on atmospheric chemistry assessed. In this studyan algorithm for the retrieval of metal atom and ion number densities for atwo-dimensional (latitude, altitude) grid is described and explained. Dayglowemission spectra of the mesosphere and lower thermosphere are used, which areobtained by passive satellite remote sensing with the SCIAMACHY (SCanning Imaging Absorption spectroMeter for AtmosphericCHartographY) instrument on boardEnvisat. The limb scans cover the tangent altitude range from 50 to 150 km.Metal atoms and ions are strong emitters in this region and form sharplypeaked layers with a FWHM (full width at half maximum) of several 10 km in the mesosphere and lowerthermosphere measuring peak altitudes between 90 to 110 km. The emission signalis first separated from the background signal, arising from Rayleigh andRaman scattering of solar radiation by air molecules. A forward radiativetransfer model calculating the slant column density (SCD) from a givenvertical distribution was developed. This nonlinear model is inverted in aniterative procedure to yield the vertical profiles for the emitting species.Several constraints are applied to the solution for numerical stabilityreasons and to get physically reasonable solutions. The algorithm is appliedto SCIAMACHY limb-emission observations for the retrieval of Mg and Mg<sup>+</sup>using emission signatures at 285.2 and 279.6/280.4 nm, respectively. Resultsare presented for these three lines as well as error estimations andsensitivity tests on different constraint strength and different separationapproaches for the background signal

Retrieval algorithm for densities of mesospheric and lower thermospheric metal atom and ion species from satellite-borne limb emission signals