Measurement of aerosol optical depth and sub-visual cloud detection using the optical depth sensor (ODS)
نویسندگان
چکیده
A small and sophisticated optical depth sensor (ODS) has been designed to work in the atmosphere of Mars. The instrument measures alternatively the diffuse radiation from the sky and the attenuated direct radiation from the Sun on the surface. The principal goals of ODS are to retrieve the daily mean aerosol optical depth (AOD) and to detect very high and optically thin clouds, crucial parameters in understanding the Martian meteorology and climatology. The detection of clouds is undertaken at twilight, allowing the detection and characterization of clouds with opacities below 0.03 (sub-visual clouds). In addition, ODS is capable to retrieve the aerosol optical depth during nighttime from moonlight measurements. Recently, ODS has been selected at the METEO meteorological station on board the ExoMars 2018 Lander. In order to study the performance of ODS under Mars-like conditions as well as to evaluate the retrieval algorithms for terrestrial measurements, ODS was deployed in Ouagadougou (Africa) between November 2004 and October 2005, a Sahelian region characterized by its high dust aerosol load and the frequent occurrence of Saharan dust storms. The daily average AOD values retrieved by ODS were compared with those provided by a CIMEL sunphotometer of the AERONET (Aerosol Robotic NETwork) network localized at the same location. Results represent a good agreement between both ground-based instruments, with a correlation coefficient of 0.77 for the whole data set and 0.94 considering only the cloud-free days. From the whole data set, a total of 71 subvisual cirrus (SVC) were detected at twilight with opacities as thin as 1.10 and with a maximum of occurrence at altitudes between 14 and 20 km. Although further optimizations and comparisons of ODS terrestrial measurements are required, results indicate the potential of these measurements to retrieve the AOD and detect sub-visual clouds.
منابع مشابه
Interactive comment on “Measurement of aerosol optical depth and sub-visual cloud detection using the optical depth sensor (ODS)” by D. Toledo et al
Reviewer #1: Synopsis: This paper provides a description of a rather innovative instrument to estimate aerosol optical depth. Readers are first reminded that this Optical Depth Sensor (ODS), was originally designed to fly on a mission to Mars. Thus, the instrument must be robust (preferably no moving parts), and must be able to account for changing calibration, such as when dust collects on win...
متن کاملInteractive comment on “Measurement of aerosol optical depth and sub-visual cloud detection using the optical depth sensor (ODS)” by D. Toledo et al
Author’s response: This is a reasonable suggestion. We have changed the lines 15-18 in page 9620 by: "For testing the reliability of calculations, first the radiance simulated by SHDOM code was compared against the DISORT plane-parallel radiative transfer code and using different values of the number of streams. These comparisons were carried out for a total opacity of 0.5, a single scattering ...
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