In this paper we present ultraviolet reflectance spectra obtained during two sounding rocket observations of Venus made during September 1988 and March 1991. We describe the sensitivity of the derived reflectance to instrument calibration and show that significant artifacts can appear in the spectrum as a result of using separate instruments to observe both the planetary radiance and the solar irradiance.
We show that surfur dioxide is the primary special absorber in the (190-230 \mathrm{~nm}) region and that the range of altitudes probed by these wavelengths is very sensitive to incidence and emission angles. In a following paper Na et al. (1994, Icarus 112, 389-395) show that sulfur monoxide features are also present in these data. Accurate identification and measurement of additional species require observations in which both the planetary radiance and the solar irradiance are measured with the same instrument.
The instrument used for these observations is uniquely suited for obtaining large phase angle coverage and for studying transient atmospheric events on Venus because it can observe targets within (18^{\circ}) of the Sun while Earth-orbiting instruments are restricted to solar elongation angles (\geq 45^{\circ}). 1994 Academic Preśs, inc.