Statistical and computational uncertainties in atmospheric profiles from radio occultation: Mariner 10 at Venus |
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| Authors: | Belinda Lipa G Leonard Tyler |
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| Institution: | Center for Radar Astronomy, Standford University, Standford, California 94305, USA |
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| Abstract: | Radio occultation studies of planetary atmospheres and ionospheres are based on measurements of the frequency and amplitude of the received radio signal. These measurements have random errors due to noise in the receiving system and linearly mapped into atmospheric profiles to give uncertainties can be estimated from the data and linearly mapped into atmospheric profiles to give uncertainties in temperature, T, pressure, p, and absorption profiles. For Mariner 10 occultation immersion at Venus, the standard deviations of T and p due to receiver noise are less than 2° K and 2 mbar over the range of radii from 6087 to 6140 km, based on our reduction from analog, “ open-loop” data. The temperature has a systematic error due to boundary uncertainty, estimated to be 50°K at 6140 km, that decays rapidly with depth; below 6117 km, it is less than 0.5°K. For the attenuation profile, systematic errors incurred during our calculations are more important than statistical errors. We estimate an upper bound to the uncertainty which is 32% at the peak value of absorption, which is about 0.01 db/km and occurs at a radius of 6096 km. A calculation of the 95% confidence limits for T profiles indicates that the local deviations are statistically significant to about 1°K or less. We have also analyzed “closed-loop” data to give temperature profiles which deviate from the open-loop results by less than 0.2°K below 6110 km but by as much as 2°K in the upper atmosphere. For the same occultation and the same boundary conditions, our closed-loop T-p profile is within 2°K of that of P. D. Nicholson and D. O. Muhleman but differs from those derived by A. J. Kliore by as much as 10°K. We cannot account for deviations as large as the latter by minor differences in trajectory information or computational methods. |
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