Atmospheric Chemistry and Physics
www.atmos-chem-phys.net
1680-7316
1680-7324
7
8
2007
10.5194/acp-7-1915-2007
http://www.atmos-chem-phys.net/7/1915/2007/
http://www.atmos-chem-phys.net/7/1915/2007/acp-7-1915-2007.html
http://www.atmos-chem-phys.net/7/1915/2007/acp-7-1915-2007.pdf
1915
1923
2007-04-17
Precision validation of MIPAS-Envisat products
C. Piccolo
piccolo@atm.ox.ac.uk
A. Dudhia
Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, UK
This paper discusses the variation and validation of the precision,
or estimated random error, associated
with the ESA Level 2 products from the Michelson
Interferometer for Passive Atmospheric Sounding (MIPAS).
<br><br>
This quantity represents the propagation of the radiometric noise from
the spectra through the retrieval process into the
Level 2 profile values.
The noise itself varies with time, steadily rising between ice
decontamination events, but
the Level 2 precision has a greater variation due to the atmospheric
temperature which controls the total radiance received. Hence, for all
species, the precision varies latitudinally/seasonally with
temperature, with a small superimposed temporal structure determined by
the degree of ice contamination on the detectors.
<br><br>
The precision validation involves comparing two MIPAS retrievals at the
intersections of ascending/descending orbits. For 5 days per month of
full resolution MIPAS operation, the standard deviation of the
matching profile pairs is computed and compared with the precision
given in the MIPAS Level 2 data, except for NO<sub>2</sub> since it has a large
diurnal variation between ascending/descending intersections.
Even taking into account the propagation of
the pressure-temperature retrieval errors into the VMR retrieval, the
standard deviation of the matching pairs is usually a factor 1–2
larger than the precision. This is thought to be due to effects such as
horizontal inhomogeneity of the atmosphere and instability of the retrieval.
ESA, SP-1229: ESA ENVISAT-MIPAS: an instrument for atmospheric chemistry and climate research, European Space Agency, ESTEC, Noordwijck, The Netherlands, 2000.
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Raspollini, P. and Ridolfi, M.: Mapping of temperature and line-of-sight errors in constituent retrievals for MIPAS/ENVISAT measurements, Atmos. Environ., 34, 5329–5336, 2000.
Raspollini, P., Belotti, C., Burgess, A., et al.: MIPAS level 2 operational analysis, Atmos. Chem. Phys., 6, 5605–5630, 2006.
Ridolfi, M., Carli, B., Carlotti, M., et al.: Optimised forward model and retrieval scheme for MIPAS near-real-time data processing, Appl. Opt., 39(8), 1323–1340, 2000.