Airglow intensity variations in the 90 km altitude range are generally interpreted as the optical signature of gravity waves propagating through the airglow layer. In contrast, modulations of the 630 nm emission in the F region are subject to atmospheric wave propagation and ionospheric electrodynamics, which makes it difficult to determine the dominating process. Spacecraft-based imaging of the 630 nm airglow could produce global data of airglow modulations greatly needed for the understanding of thermospheric dynamics. Observations of the thick 630 nm airglow layer between 200 and 300 km altitude are used to demonstrate the ability to tomographically retrieve the modulated volume emission rates from limb observations from a spacecraft. An algebraic reconstruction technique is used to obtain vertical and horizontal distributions with average errors of 20%. Its effectiveness is demonstrated by simulations with numerical data. Forward limb observations in the 630 nm range strongly reduce the angular range and limit the measurement scale to 300 km. These results are obtained without any assumptions about the original distribution other than nonnegativity. The overall computational effort would allow the analysis of a large number of observations as provided by global survey experiments. ¿ 2001 American Geophysical Union