Direct detection Doppler lidar systems for tropospheric wind speed profiling are considered, concentrating on the spaceflight application. A precisely developed model for the fringe imaging technique is extended to the case of the aerosol signal with a significant Rayleigh background. An analytic model for the Doppler precision of an edge technique analyzer with dual filters, offset in frequency, is developed, also with provision for the Rayleigh background signal. The two models are compared to recent modeling results from McGill at NASA Goddard Space Flight Center, and good agreement found. The less rigorous analytic models developed here offer insights into the design and limitations of fringe imaging and edge detection Doppler analyzers. In particular, a requirement here offer insights into the design and limitations of fringe imaging and edge detection Doppler analyzers. In particular, a requirement for wide wind speed dynamic range implies low sensitivity for he edge detection technique, but not for the fringe imaging technique. The fringe imaging and edge detection techniques are compare for relative precision, for lidar signals of specified amplitude. A detailed conceptual design of a spaceflight Doppler wind lidar system, employing a very large optical collector in order to obtain adequate backscatter signals, shows that the fringe imaging analyzer is a factor 10 superior to the dual-etalon edge detector.