MIPAS L2 Error Analyses

Last Updated: 03AUG20 - Spectroscopic Errors updated

*** NOTE *** The SPECDB error has now been redefined - details below.
[Tech Note (25Oct19)] describing mathematical basis of error analyses.

The following table shows the linear error analyses for MIPAS L2 products. These errors have been evaluated for 5 different atmospheric conditions.

DAY
Mid-Latitude day-time (similar to US Standard Atmosphere)
NGT
Mid-Latitude night-time
SUM
Polar Summer day-time
WIN
Polar Winter night-time
EQU
Equatorial day-time

Click on 'Data' for the numerical data that has been plotted. In the plots, the same symbols are used for each error source (explained below) throughout, and listed in the key in the approximate order of significance for that plot. Only the most significant errors are plotted. Click on the atmosphere or species for plots of the atmospheric profiles assumed.

MODE: FR17 (2002-2004, 17 sweeps @ 0.025 cm-1 sampling)
Species DAY NGT WIN SUM EQU
TEM [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
PRE [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
H2O [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
O3 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
HNO3 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
CH4 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
N2O [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
NO2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
CLONO2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F11 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F12 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
N2O5 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
CCL4 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
COF2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F14 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F22 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
HCN [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
C2H2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
C2H6 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
CH3CL [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
CLO [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
COCL2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F113 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F114 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
H2O2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
HDO [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
HOCL [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
OCS [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
SF6 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
MODE: OR27 (2005-2012, 27 sweeps @ 0.0625 cm-1 sampling)
Species DAY NGT WIN SUM EQU
TEM [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
PRE [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
H2O [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
O3 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
HNO3 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
CH4 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
N2O [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
NO2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
CLONO2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F11 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F12 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
N2O5 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
CCL4 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
COF2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F14 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F22 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
HCN [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
C2H2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
C2H6 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
CH3CL [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
CLO [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
COCL2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F113 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F114 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
H2O2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
HDO [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
HOCL [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
OCS [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
SF6 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
MODE: MA (2005-2012, 29 sweeps @ 0.0625 cm-1 sampling)
Species DAY NGT WIN SUM EQU
TEM [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
PRE [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
H2O [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
O3 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
HNO3 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
CH4 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
N2O [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
NO2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
CLONO2 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F11 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
F12 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]
N2O5 [Prof] [MW] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data] [Plot] [Data]

List of errors considered

TOT
Total Error. Root sum square of all SYS and RND components
RND
Random Error. Due to the propagation of instrument noise through the retrieval.
NB: A more accurate assessment of this component is included in the L2 product
NONLTE
Non-LTE error. Due to assumption of local thermodynamic equilibrium when modelling emission in the MIPAS forward model. Based on calculations using vibrational temperatures supplied by M.Lopez-Puertas, IAA, Granada.
SPECDB (updated August 2020)
Spectroscopic database errors. Due to uncertainties in the strength, position and width of infrared emission lines, but only for the target species in each microwindow (CO2 for pT microwindows). For line parameters, each parameter is perturbed by the 1σ uncertainty indicated by the associated error in the HITRAN record (not the HITRAN data itself but the version adapted for MIPAS v4.43), subject to a maximum strength uncertainty error of 3%. For cross-section molecules (eg CFCs) a fixed strength uncertainty of 5% is assumed, which is also intended to include interpolation errors from the tabulated (p,T) datapoints.
GAIN (updated July 2019)
Radiometric Gain Uncertainty. Based on an internal study by A. Kleinert, this is assumed to have a value of 2.5% in band A, 2% bands AB and B, and 1% in bands C and D. It is also assumed to be fully correlated within each band, but uncorrelated between bands.
SPREAD
Uncertainty in width of apodised instrument line shape (AILS). A value of 0.2% has been assumed based on likely variations in apodised instrument line shape from modelled.
SHIFT
Uncertainty in the spectral calibration. The design specification of ±0.001cm-1 has been used, and is consistent with the 1st derivatives signatures in the residual spectra.
CO2MIX
CO2 line-mixing. Due to neglecting line-mixing effects in the retrieval forward model (only affects strong CO2 Q branches in the MIPAS A and D bands)
CTMERR
Uncertainty in gaseous continua. Assumes an uncertainty of ±25% in the modelling of continuum features of H2O (mostly), CO2, O2 and N2.
HIALT
Uncertainty in high-altitude column. Retrieval assumes a fixed-shape of atmospheric profile above the top retrieval level. Effect is calculated assuming `true' profile can deviate by climatological variability.
PT
Propagation of pT retrieval random covariance into VMR retrieval. Note that since July 2019 other errors from the pT retrieval are now propagated and contribute to the various systematic errors (so, for example, there is a component of the Band A gain error from the pT retrieval even for species which are retrieved without using any microwindows in Band A)
[species]
Uncertainties in assumed profiles of contaminant species. For species which are not retrieved this is taken from the climatological 1-sigma variability profiles provided by J Remedios (U.Leicester). For retrieved species it is the optimally-weighted combination of the climatological uncertainty with the retrieval random error, ie smaller than either component.

Use of Systematic Errors

The definition of 'systematic error' here includes everything which is not propagation of the random instrument noise through the retrieval. However, to use these errors in a statistically correct manner for comparisons with other measurements is not straightforward. Each systematic error has its own length/time scale: on shorter scales it contributes to the Bias and on longer scales contributes to the SD of the comparison.

Fortunately, two of the larger systematic errors (PT and SPECDB) can be treated properly:

The pT propagation error (PT) is uncorrelated between any two MIPAS profiles (since it is just the propagation of the random component of the pT retrieval error through the VMR retrieval) so contributes to the SD of any profile comparison

Spectroscopic database errors (SPECDB) are constant but of unknown sign, so will always contribute to the Bias of any comparison, but note that the magnitude of these errors is very uncertain.

Of the other significant errors, the calibration-related errors (GAIN, SHIFT, SPREAD) should, in principle, be uncorrelated between calibration cycles however analysis of the residuals suggests that these errors are almost constant so could be included in the Bias.

The high altitude column (HIALT) and contaminant gas errors ([species]) are likely to be correlated over small areas (1000km) or times (weeks), hence contribute to the Bias for localised comparisons, but as the comparison datasets are extended these errors will contribute more to the SD.

Line mixing errors (CO2MIX) are also contribute towards the Bias but in principle the sign of these errors is known (unlike spectroscopic errors) so this bias could be removed. Non-LTE errors (NONLTE) should also, in principle, contribute a known Bias but these are highly variable (especially diurnally) so care has to be taken to make sure that representative conditions for the comparison are used.