There are two basic approaches to obtaining satellite radiance measurements used in retrieving vertical atmospheric temperature and constituent profiles: (1) to make the measurements in a number of different spectral intervals (frequency scanning) or (2) to make the measurements at a number of different zenith angles (angle scanning). This paper describes a study of the effect of combining these two approaches into a single sounding system, which is accomplished by viewing a fixed target at several frequencies and at several zenith angles as the satellite moves along its orbital track. If there are M spectral intervals and N angular views, a total of MxN essentially independent measurements are possible. Instrumental and geometric details,and results of a numerical simulation study of this dual scanning approach are presented, along with a discussion on how one can scan across the orbital track at the same time to obtain two-dimensional horizontal coverage.
Henry E. Fleming,
"Satellite Remote Sensing By A Combination Of Angle And Frequency Scanning", Proc. SPIE 0183, Space Optics II, (27 September 1979); doi: 10.1117/12.957404; https://doi.org/10.1117/12.957404