Recent advancements in the development of passive millimeter and sub-millimeter wave heterodyne techniques for ground-based, air-borne, and space-borne observations of key parameters in Earth's ...middle atmosphere have triggered the development of adequate data analysis methods and models.
This paper provides a detailed description of the versatile forward- and inversion-model for the millimeter- and sub-millimeter wavelength range, MOLIERE (v5) (Microwave Observation LIne Estimation and REtrieval, version 5). Present applications of the model include data analysis for ground-based and space-borne heterodyne instruments such as the sub-millimeter radiometer (SMR) on board the
Odin satellite as well as definition studies for future limb sensors dedicated to Earth observation and Mars exploration.
The physical and mathematical basics of the forward- and retrieval-model parts are presented. The main emphasis is then put on the description of the numerical implementation of the algorithms for radiative transfer and weighting function computations as well as on the employed method for modeling atmospheric refraction.
This paper describes the capabilities of a nadir thermal infrared (TIR) sensor proposed for deployment onboard a geostationary platform to monitor ozone (O3 ) and carbon monoxide (CO) for air quality ...(AQ) purposes. To assess the capabilities of this sensor we perform idealized retrieval studies considering typical atmospheric profiles of O3 and CO over Europe with different instrument configuration (signal to noise ratio, SNR, and spectral sampling interval, SSI) using the KOPRA forward model and the KOPRA-fit retrieval scheme. We then select a configuration, referred to as GEO-TIR, optimized for providing information in the lowermost troposphere (LmT; 0-3 km in height). For the GEO-TIR configuration we obtain ~1.5 degrees of freedom for O3 and ~2 for CO at altitudes between 0 and 15 km. The error budget of GEO-TIR, calculated using the principal contributions to the error (namely, temperature, measurement error, smoothing error) shows that information in the LmT can be achieved by GEO-TIR. We also retrieve analogous profiles from another geostationary infrared instrument with SNR and SSI similar to the Meteosat Third Generation Infrared Sounder (MTG-IRS) which is dedicated to numerical weather prediction, referred to as GEO-TIR2. We quantify the added value of GEO-TIR over GEO-TIR2 for a realistic atmosphere, simulated using the chemistry transport model MOCAGE (MOdèle de Chimie Atmospherique à Grande Echelle). Results show that GEO-TIR is able to capture well the spatial and temporal variability in the LmT for both O3 and CO. These results also provide evidence of the significant added value in the LmT of GEO-TIR compared to GEO-TIR2 by showing GEO-TIR is closer to MOCAGE than GEO-TIR2 for various statistical parameters (correlation, bias, standard deviation).
We present a new compact and automated ground- based microwave mobile radiometer dedicated to the study of middle atmospheric water vapor, which is convenient for measurement, intercomparison, and ...validation campaigns, particularly in remote places. The instrument detects the 6 16 -5 23 H 2 O transition line at 22.235 GHz by means of balanced beam-switching observation of the atmosphere. Tipping curves are performed to estimate the tropospheric opacity. The sky is used as a cold load for calibration, minimizing the use of liquid nitrogen. The main technical issues are caused by the small horn antenna (a beamwidth of ~12deg) inducing large bias when using pencil- beam approximation for the calculation of elevation-dependent parameters. Numerical methods have been developed to include this effect in the data calibration process. Preliminary vertical profiles are retrieved with the Microwave Odin Line Estimation and REtrieval radiative transfer and inversion tool from 25 to 55 km with a vertical resolution of 10-20 km increasing with height, for an integration time of ~12 h and a measurement error of ~15% (~0.8 ppmv). Preliminary comparisons with the spaceborne instrument Aura/Microwave Limb Sounder show a good agreement (~5%) in the 35-55-km altitude range, whereas a negative bias is detected below (up to -30% at 25 km).
This paper presents the intercomparison of O3, HNO3, ClO, N2O and CO profiles measured by the two spaceborne microwave instruments MLS (Microwave Limb Sounder) and SMR (Submillimetre Radiometer) on ...board the Aura and Odin satellites, respectively. We compared version 1.5 level 2 data from MLS with level 2 data produced by the French data processor version 222 and 225 and by the Swedish data processor version 2.0 for several days in September 2004 and in March 2005. For the five gases studied, an overall good agreement is found between both instruments. Most of the observed discrepancies between SMR and MLS are consistent with results from other intercomparison studies involving MLS or SMR. O3 profiles retrieved from the SMR 501.8 GHz band are noisier than MLS profiles but mean biases between both instruments do not exceed 10%. SMR HNO3 profiles are biased low relative to MLS's by ∼30% above the profile peak. In the lower stratosphere, MLS ClO profiles are biased low by up to 0.3 ppbv relative to coincident SMR profiles, except in the Southern Hemisphere polar vortex in the presence of chlorine activation. N2O profiles from both instruments are in very good agreement with mean biases not exceeding 15%. Finally, the intercomparison between SMR and MLS CO profiles has shown a good agreement from the middle stratosphere to the middle mesosphere in spite of strong oscillations in the MLS profiles. In the upper mesosphere, MLS CO concentrations are biased high relative to SMR while negative values in the MLS retrievals are responsible for a negative bias in the tropics around 30 hPa.
Water vapour plays an important role for the chemistry and dynamics of the atmosphere. It is a strong greenhouse gas in the troposphere and contributes to cooling in the stratosphere. As the main ...source of chemically active
HO
x
radicals, it is linked to many photo-chemical cycles controlling the composition of the middle atmosphere.
In order to improve our knowledge of the amount and variability of water in the middle atmosphere, the Sub-Millimetre Radiometer (SMR) on board the Odin satellite, launched in February 2001, observes several thermal emission lines of water vapour in the 486–581
GHz spectral range from the Earth's limb. Bands centred at 488.9 and 490.4
GHz are used to study water vapour and its isotopes, on the basis of four observation days per month. Vertical profiles of
H
2
O
16
,
H
2
O
18
, and HDO are retrieved between roughly 20 and 70
km in the stratosphere and mesosphere. A strong water vapour line at 556.9
GHz is simultaneously measured in a second band, providing information in the mesosphere and lower thermosphere between about 40 and 100
km. Measurements of
H
2
O
17
at 552.0
GHz in monthly intervals complete the picture of middle atmospheric water vapour provided by Odin/SMR.
The measurements of the isotope HDO in the 20–70
km altitude range allow to study the isotopic ratio of deuterium in stratospheric water vapour
(
D
/
H
)
, potentially supplying information on the origin of stratospheric water vapour: transport of tropospheric air through the tropical tropopause layer (TTL) versus in situ chemical production such as from methane oxidation. The unique measurements of the molecules
H
2
O
18
and
H
2
O
17
containing heavy isotopes of oxygen may provide a crucial test for our understanding of the complex chemical reaction mechanisms controlling the exchange of oxygen between water vapour and ozone.
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