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Ann. Geophys., 19, 71-81, 2001
www.ann-geophys.net/19/71/2001/
© European Geosciences Union 2001
Error analysis for mesospheric temperature profiling by absorptive occultation sensors
M. J. Rieder and G. Kirchengast
Institute for Geophysics, Astrophysics, and Meteorology, University of Graz, Universitätsplatz 5, A-8010 Graz, Austria
Correspondence to: G. Kirchengast, (gottfried.kirchengast@kfunigraz.ac.at)
Abstract. An error analysis for
mesospheric profiles retrieved from absorptive occultation data has been
performed, starting with realistic error assumptions as would apply to intensity
data collected by available high-precision UV photodiode sensors. Propagation of
statistical errors was investigated through the complete retrieval chain from
measured intensity profiles to atmospheric density, pressure, and temperature
profiles. We assumed unbiased errors as the occultation method is essentially
self-calibrating and straight-line propagation of occulted signals as we focus
on heights of 50–100 km, where refractive bending of the sensed radiation is
negligible. Throughout the analysis the errors were characterized at each
retrieval step by their mean profile, their covariance matrix and their
probability density function (pdf). This furnishes, compared to a variance-only
estimation, a much improved insight into the error propagation mechanism. We
applied the procedure to a baseline analysis of the performance of a recently
proposed solar UV occultation sensor (SMAS – Sun Monitor and Atmospheric
Sounder) and provide, using a reasonable exponential atmospheric model as
background, results on error standard deviations and error correlation functions
of density, pressure, and temperature profiles. Two different sensor photodiode
assumptions are discussed, respectively, diamond diodes (DD) with 0.03% and
silicon diodes (SD) with 0.1% (unattenuated intensity) measurement noise at 10
Hz sampling rate. A factor-of-2 margin was applied to these noise values in
order to roughly account for unmodeled cross section uncertainties. Within the
entire height domain (50–100 km) we find temperature to be retrieved to better
than 0.3 K (DD) / 1 K (SD) accuracy, respectively, at 2 km height resolution.
The results indicate that absorptive occultations acquired by a SMAS-type sensor
could provide mesospheric profiles of fundamental variables such as temperature
with unprecedented accuracy and vertical resolution. A major part of the error
analysis also applies to refractive (e.g., Global Navigation Satellite System
based) occultations as well as to any temperature profile retrieval based on air
density or major species density measurements (e.g., from Rayleigh lidar or
falling sphere techniques).
Key words. Atmospheric composition and structure
(pressure, density, and temperature; instruments and techniques) – Radio
science (remote sensing)
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