Abstract
Abstract. Synergistic exploitation of redundant and complementary information from independent observations of the same target remains a major issue in atmospheric remote sounding and increasing attention is devoted to investigate optimized or innovative methods for the combination of two or more measured data sets. This paper focuses on the synergy between middle infrared and millimeter-wave limb sounding measurements of atmospheric composition and temperature and reports the results of a study conducted as part of the preparatory activities of the PREMIER (Process Exploration through Measurements of Infrared and millimeter-wave Emitted Radiation) mission candidate to the Core Missions of the European Space Agency (ESA) Earth Explorer 7. The activity was based on data acquired by the MIPAS-STR (Michelson Interferometer for Passive Atmospheric Sounding – STRatospheric aircraft) and MARSCHALS (Millimetre-wave Airborne Receivers for Spectroscopic CHaracterisation in Atmospheric Limb Sounding) instruments on-board the high-altitude research aircraft M-55 Geophysica during the flight of the PremierEx (PREMIER Experiment) campaign on 10 March 2010 from Kiruna, Sweden, for observation of the Arctic upper troposphere and lower stratosphere. The cloud coverage observed along the flight provided representative test cases to evaluate the synergy in three different scenarios: low clouds in the first part, no clouds in the central part and high tropospheric clouds at the end. The calculation of synergistic profiles of four atmospheric targets (i.e., O3, HNO3, H2O and temperature) was performed using a posteriori combination of individual retrieved profiles, i.e., Level 2 (L2) data rather than simultaneous inversion of observed radiances, i.e., Level 1 (L1) data. An innovative method of data fusion, based on the Measurement Space Solution (MSS) was applied along with the standard approach of inversion of MARSCHALS spectral radiances using MIPAS-STR retrieval products as a priori information (L1 + L2 method). A quantitative estimate and cross-check of the results of MSS data fusion and (L1 + L2) method was achieved based on a specific set of quantifiers including the total retrieval error, the number of degrees of freedom, the relative information distribution and the synergy factor.
Highlights
The growing number and increasing capabilities of Earth Observation missions from space provides a huge amount of remotely sensed data about the state of the atmosphere and of the ocean and land surface, such as those obtained by newgeneration hyper- and ultraspectral sounders (Smith et al, 2009) like the Atmospheric Infrared Sounder (AIRS), the Infrared Atmospheric Sounding Interferometer (IASI) and the Cross-track Infrared Sounder (CrIS), or those expected from the joint EU/European Space Agency program Copernicus (Aschbacher et al, 2012)
As part of the preparatory activities of PREMIER, a series of engineering and scientific flights with the high-altitude research aircraft M-55 Geophysica was conducted at midlatitudes and high latitudes carrying an infrared and a mmwave limb sounder on board, to demonstrate the measurement concepts proposed for the investigation of chemical, dynamical and radiative processes occurring in the upper troposphere and lower stratosphere (UTLS)
For a correct interpretation of the plots discussed hereafter, we recall that – as already pointed out in Sect. 2.1.1 – MARSCHALS observation strategy was based on acquisition of single limb scans with sequential spectral coverage in band B, band C and band D and with different performance depending on the target species
Summary
The growing number and increasing capabilities of Earth Observation missions from space provides a huge amount of remotely sensed data about the state of the atmosphere and of the ocean and land surface, such as those obtained by newgeneration hyper- and ultraspectral sounders (Smith et al, 2009) like the Atmospheric Infrared Sounder (AIRS), the Infrared Atmospheric Sounding Interferometer (IASI) and the Cross-track Infrared Sounder (CrIS), or those expected from the joint EU/European Space Agency program Copernicus (Aschbacher et al, 2012). The proposed PREMIER spaceborne mission was aimed at investigating processes responsible for interactions between atmospheric composition and climate at the critical heights of the UTLS by carrying a scientific payload composed of an imaging limb sounding Fourier transform spectrometer in the middle infrared (IRLS, InfraRed Limb Sounder) and a millimeter-wave (mm-wave) limb sounder (STEAMR, Stratosphere-Troposphere Exchange And climate Monitor Radiometer). In this perspective, we report on the lesson learned in a dedicated study, focusing on the investigation of the potential synergy between infrared and mm-wave limb measurements acquired by two airborne precursors of the STEAMR and IRLS remote sounders proposed for PREMIER.
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