WP 3: Cross comparison

Leaders: V. Catoire, M. Dorf

Cross-comparison/validation will be addressed on each payload on species relevant for dynamics (blue colour in the Table below) and chemistry (green).The cross-comparison and cross-validation will focus on a direct comparison of simultaneously monitored species by different instruments on the same payload. The goal is to evaluate the absolute accuracy of the measurements by comparing the results of the different techniques.
All instruments onboard the MIPAS and LPMA gondolas perform remote sensing measurements, whereas the instruments mounted on the TWIN and SPIRALE payloads perform in-situ observations. This facilitates cross-comparison especially also for the remote sensing instruments, since most of them even use the same viewing geometry, i.e. MIPAS/TELIS and LPMA/DOAS.
Nevertheless, there are essential differences in the individual techniques that give rise to systematic uncertainties and discrepancies: different spectroscopic approaches, which might also result in different light-paths for the observations, differences in the altitude and time resolution, instrumental characterisation and calibration issues (e.g. calibration standards), different retrieval approaches and profile inversion techniques.
A direct comparison of results obtained with different techniques will greatly help to identify some of the systematic uncertainties and further improve the reliability of balloon-borne observations. Table 1 summarizes the chemical species included in the cross-comparison/validation.
The CO2 and CH4 measurements from the picoSDLA instrument operated on TWIN, and the CH4 and CO measurements of OFCEAS on SPIRALE are very recent and a comparison with measurements of the other instruments onboard the TWIN and SPIRALE payloads will be used for their validation. Since instruments on both payloads perform in-situ measurements, biases due to geophysical hypotheses for vertical profile retrievals will be avoided. Table below lists the techniques used for the cross-comparisons. It can be seen that very various methods and spectroscopic windows will be employed, which will give confidence in the results obtained.

Payload MIPAS TWIN LPMA SPIRALE
Instruments MIPAS, TELIS, DOAS, miniDOAS BONBON, HALOX-B, picoSDLA LPMA, DOAS, miniDOAS SPIRALE, OFCEAS
Dynamics N2O cross comparison
H2O cross comparison
CO cross comparison cross comparison
CH4 cross comparison cross comparison
CO2 cross comparison cross comparison
Ozone O3 cross comparison cross comparison
Chemistry ClO cross comparison
BrO cross comparison
NO2 cross comparison
HNO3 cross comparison cross comparison
HOCl cross comparison
List of species involved in the cross-comparisons on each payload

Species Instrument Measurement
technics 		Wavelength
or
wavenumber range
N2O MIPAS FTIR limb emission 1100 - 1330 cm-1
TELIS sub-mm/far-IR
limb emission 		16.75 cm-1
CO2 BONBON GC-MS chemical method
picoSDLA IR laser absorption 3729.712 cm-1
CH4 BONBON GC-MS chemical method
picoSDLA IR laser absorption 3085.8 - 3085.9 cm-1
SPIRALE IR laser absorption 1260.811 cm-1
OFCEAS IR laser absorption 4300.366 cm-1
CO MIPAS FTIR limb emission 2050 - 2210 cm-1
TELIS sub-mm/far-IR
limb emission 		61.42 cm-1
SPIRALE IR laser absorption 2123.699 cm-1
OFCEAS IR laser absorption 4300.700 cm-1
H2O
&
isotopic fractionation 		MIPAS FTIR limb emission 800 - 1700 cm-1
TELIS sub-mm/far-IR
limb emission 		16.2 - 16.4 cm-1
60.5 - 60.7 cm-1
61.3 - 61.7 cm-1
O3 DOAS UV/vis 560 - 615 cm-1
LPMA FTIR 779 - 781 cm-1
3040 - 3041 cm-1
O3
&
isotopic fractionation 		DOAS UV/vis 560 - 615 cm-1
MIPAS FTIR limb emission 700 - 1150 cm-1
TELIS sub-mm/far-IR
limb emission 		16 - 22 cm-1
60 cm-1
NO2 DOAS UV/vis 430 - 485 cm-1
MIPAS FTIR limb emission 1590 - 1650 cm-1
TELIS sub-mm/far-IR
limb emission 		17.54 cm-1
DOAS UV/vis 430 - 485 cm-1
LPMA FTIR 2914 - 2915 cm-1
HNO3 MIPAS FTIR limb emission 860 - 890 cm-1
and other bands
TELIS sub-mm/far-IR
limb emission 		16 - 22 cm-1
HOCl MIPAS FTIR limb emission 1210 - 1270 cm-1
TELIS sub-mm/far-IR
limb emission 		20.44 cm-1
60 cm-1
ClO MIPAS FTIR limb emission 810 - 870 cm-1
TELIS sub-mm/far-IR
limb emission 		16.72 cm-1
BrO DOAS UV/vis 340 - 360 cm-1
TELIS sub-mm/far-IR
limb emission 		17.51 cm-1
List of species and corresponding instruments used for the cross-comparison.
For spectroscopic measurements, the wavelength range is given.

Link to the description of the other workpackages.