Precision validation of MIPAS-Envisat products C. Piccolo and A. Dudhia Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, UK
Abstract. 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).
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.
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 NO2 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.
Citation: Piccolo, C. and Dudhia, A.: Precision validation of MIPAS-Envisat products, Atmos. Chem. Phys., 7, 1915-1923, doi:10.5194/acp-7-1915-2007, 2007.