M Gai

Publications (3)6.1 Total impact

• Source

  Available from: Bianca Maria Dinelli

  Article: MARC: A code for the retrieval of atmospheric parameters from millimeter-wave limb measurements

  B. Carli, G. Bazzini, E. Castelli, C. Cecchi-Pestellini, S. Del Bianco, B.M. Dinelli, M. Gai, L. Magnani, M. Ridolfi, L. Santurri
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  ABSTRACT: A new data analysis software is presented that has been developed for the retrieval of atmospheric minor constituents from limb-sounding observations made in the millimeter and sub-millimeter spectral regions. The code, which is called MARC (Millimetre-wave Atmospheric-Retrieval Code), has been designed to analyze the observations of the MARSCHALS (Millimetre-wave Airborne Receivers for Spectroscopic CHaracterisation in Atmospheric Limb-Sounding) instrument which operates on the M-55 stratospheric aircraft. The main objective of the analysis of MARSCHALS observations will be to assess long-wave measurement capabilities for the study of the upper troposphere and lower stratosphere regions. The key questions will be the accuracy and spatial resolution that can be achieved by long-wave measurements in presence of clouds and horizontal gradients.MARC performs a global-fit multi-target retrieval, in which optimal estimation is used and errors of the forward model parameters are taken into account for the definition of the cost function minimized in the retrieval. With these features it is easy to use the variables of the problem as either forward model constant parameters or retrieved unknowns with minimum impact on the stability of the retrieval. MARC can perform a wide spectral-band analysis of the observations without a selection of the analyzed channels, and the retrieval process provides an error budget of the retrieved unknowns that includes both the forward model errors and the measurement errors. The error budget obtained in this way is smaller than that obtained when accounting a posteriori for the systematic errors. The new combination of the retrieval features makes possible an efficient and optimal exploitation of the information content of the observations.
  Journal of Quantitative Spectroscopy and Radiative Transfer 02/2013; · 3.19 Impact Factor
• Article: Retrieval of minor constituents in a cloudy atmosphere with remote‐sensing millimetre‐wave measurements

  S. Del Bianco, B. Carli, C. Cecchi-Pestellini, B. M. Dinelli, M. Gai, L. Santurri
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  ABSTRACT: The presence of clouds in remote-sensing measurements is often the cause of information loss about the minor atmospheric constituent profiles that are the goal of the measurement. Millimetre- and submillimetre-wave sounding can be used to abate the problems of cloud contamination. A quantitative assessment of this possibility is provided with the systematic simulation of the retrieval of minor atmospheric constituents in the presence of ice cirrus clouds of different density and particle size. The simulations are made for the particular case of the MARSCHALS instrument which is a heterodyne limb-sounding spectrometer that measures the atmospheric thermal emission in the millimetre- and submillimetre-wave regions operating on board a stratospheric aircraft. Four types of measuring conditions are identified: clouds that do not modify the observation, clouds that are adequately described with an atmospheric continuum absorption model, clouds for which an error is introduced when the limited vertical resolution of the sounding does not resolve the sharp discontinuity of the cloud, and clouds which require the modelling of scattering effects for a correct retrieval. When a rigorous modelling of the cloud is performed, the retrieval of minor atmospheric constituent is marginally affected by the presence of the cloud. We find that in the worst case the cloud causes a loss, with respect to clear-sky conditions, of two degrees of freedom from about 90 and of 7% of information content relative to climatological information. Copyright © 2007 Royal Meteorological Society
  Quarterly Journal of the Royal Meteorological Society 11/2007; 133(S2):163 - 170. · 2.91 Impact Factor
• Article: Measurements of the tropical UTLS composition in presence of clouds using millimetre-wave heterodyne spectroscopy : technical note

  E Castelli, B. Carli, S. Del Bianco, M Gai, L Santurri, BP Moyna, M Oldfield, R Siddans, D Gerber, WJ Reburn, BJ Kerridge, C. Keim
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  ABSTRACT: The MARSCHALS (Millimetre-wave Airborne Receiver for Spectroscopic CHaracterisation of Atmospheric Limb-Sounding) project has the general objectives of demonstrating the measurement capabilities of a limb viewing instrument working in the millimetre and sub-millimetre spectral regions (from 294 to 349 GHz) for the study of the Upper Troposphere – Lower Stratosphere (UTLS). MARSCHALS has flown on board the M-55 stratospheric aircraft (Geophysica) in two measurements campaigns. Here we report the results of the analysis of MARSCHALS measurements during the SCOUT-O3 campaign held in Darwin (Australia) in December 2005 obtained with MARC (Millimetrewave Atmospheric-Retrieval Code). MARSCHALS measured vertical distributions of temperature, water vapour, ozone and nitric acid in the altitude range from 10 to 20 km in presence of clouds that obscure measurements in the middle infrared spectroscopic region. The minimum altitude at which the retrieval has been possible is determined by the high water concentration typical of the tropical region rather than the extensive cloud coverage experienced during the flight. Water has been measured from 10 km to flight altitude (18 km) with a 10% accuracy, ozone from 14 km to flight altitude with accuracy ranging from 10% to 60%, while the retrieval of nitric acid has been possible with an accuracy not better than 40% only from 16 km to flight altitude due to the low signal to noise ratio of its emission in the analysed spectral region. The results have been validated using measurement made in a less cloudy region by MIPAS-STR, an infrared limb-viewing instrument on board the M-55, during the same flight.