New Calorimeter Techniques

This chapter is dedicated to calorimeter techniques that have been developed since the first edition of this monograph was published (2000). The Dual Readout Method (DREAM) aims to combine the advantages of compensation (linearity, excellent hadron resolution, Gaussian line shape) with a certain amount of design flexibility. This method, based on simultaneous detection of scintillation and Cherenkov light produyced in the shower development, eliminates some of the disadvantages of compensating devices, and in particular the dependence on efficient neutron detection of the latter. The Particle Flow Analysis method aims to combine the information provided by a good tracking system with that provided by a fine-grained calorimeter system to obtain excellent performance for the detection of jets. The results achieved with both methods, and the challenges faced in practice, are described in detail.

Line Shapes

Line shapes describe how absorption and emission are spectrally distributed around the line positions formed by rotational, vibrational, and electronic transitions. Line shapes arise from the different processes that spectrally broaden the absorption and emission of radiation. Optical thickness and equivalent width are shown to be fundamentally related to line shape. The fundamental line shape functions for atmospheres including the Gaussian line shape due to molecular motion and the Lorentzian line shape from lifetime broadening, including collision (pressure) broadening are described. Their convolution, the Voigt line shape, which is important in some atmospheric conditions is also described. The standard HITRAN database of spectroscopic parameters of molecules for use in calculation of radiative transfer in planetary atmospheres, from radiofrequencies to the near ultraviolet, is introduced.

Improved retrieval of global tropospheric formaldehyde columns from GOME-2/MetOp-A addressing noise reduction and instrumental degradation issues

We present a new dataset of formaldehyde vertical columns retrieved from observations of GOME-2 on board the EUMETSAT MetOp-A platform between 2007 and 2011. The new retrieval scheme, which has been optimised for GOME-2, includes a two-step fitting procedure that strongly reduces the impact of spectral interferences between H2CO and BrO, and a modified DOAS approach that better handles ozone absorption effects at moderately low sun elevations. Owing to these new features, the noise in the H2CO slant columns is reduced by up to 40% in comparison to baseline retrieval settings used operationally. Also, the previously reported underestimation of the H2CO columns in tropical and mid-latitude regions has been largely eliminated, improving the agreement with coincident SCIAMACHY observations. To compensate for the drift of the GOME-2 slit function and to mitigate the instrumental degradation effects on H2CO retrievals, an asymmetric Gaussian line-shape is fitted during the irradiance calibration. Additionally, external parameters used in the tropospheric air mass factor computation (surface reflectances, cloud parameters and a priori profile shapes of H2CO) have been updated using most recent databases. Similar updates were also applied to the historical datasets of GOME and SCIAMACHY, leading to the generation of a consistent multi-mission H2CO data record covering the time period from 1997 until 2011. Comparing the resulting time series of monthly averaged H2CO vertical columns in 12 large regions worldwide, the correlation coefficient between SCIAMACHY and GOME-2 columns is generally higher than 0.8 in the overlap period, and linear regression slopes differ by less than 10% from unity in most of the regions. In comparison to SCIAMACHY, the largely improved spatial sampling of GOME-2 allows for a better characterisation of formaldehyde distribution at the regional scale and/or at shorter timescales, leading to a better identification of the emission sources of non-methane volatile organic compounds.

Improved retrieval of global tropospheric formaldehyde columns from GOME-2/MetOp-A addressing noise reduction and instrumental degradation issues

We present a new data set of formaldehyde vertical columns retrieved from observations of GOME-2 onboard of the EUMETSAT MetOp-A platform between 2007 and 2011. The new retrieval scheme, which has been optimised for GOME-2, includes a two-step fitting procedure that strongly reduces the impact of spectral interferences between H2CO and BrO, and a modified DOAS approach that better handles ozone absorption effects at moderately low sun elevations. Owing to these new features, the noise in the H2CO slant columns is reduced by up to 40% in comparison to baseline retrieval settings used operationally. Also, the previously reported underestimation of the H2CO columns in tropical and mid-latitudes regions has been largely eliminated, improving the agreement with coincident SCIAMACHY observations. To compensate for the drift of the GOME-2 slit function and to mitigate the instrumental degradation effects on H2CO retrievals, an asymmetric Gaussian line shape is fitted during the irradiance calibration. Additionally, external parameters used in the tropospheric air mass factor computation (surface reflectances, cloud parameters and a priori profile shapes of H2CO) have been updated using most recent data bases. Similar updates were also applied to the historical data sets of GOME and SCIAMACHY leading to the generation of a consistent multi-mission H2CO data record covering the time period from 1997 until 2011. Comparing the resulting time series of monthly averaged H2CO vertical columns in 12 large regions worldwide, the correlation coefficient between SCIAMACHY and GOME-2 columns is generally higher than 0.8 in the overlap period, and linear regression slopes differ by less than 10% from unity in most of the regions. In comparison to SCIAMACHY, the largely improved spatial sampling of GOME-2 allows for a better characterisation of formaldehyde distribution at the regional scale and/or at shorter timescales, leading to a better identification of the emission sources of non-methane volatile organic compounds.

Photoautoionization structure in the halogen systems Br2, I2, BrCl, ICl, and IBr

The photoabsorption ion-yield spectra of the titled molecules have been recorded in the threshold ionization region between the two spin-orbit components of the ground states of the molecular ions. All ion-yield spectra display rather simple autoionization structure superimposed on a smoothly rising continuum in the ionization energy region. The structure was analyzed in terms of autoionizing Rydberg states and their vibrational profiles simulated using Rydberg–Klein–Rees (RKR) derived potential energy curves and calculated Franck–Condon factors using Gaussian line-shape functions. All of the structure observed is attributed to spin-orbit autoionization. There seems to be a propensity for autoionization of sσ Rydberg states in all of the interhalogen molecules studied.

An Attempt to Incorporate the Gaussian Line Shape in the Study of Spectroscopic Limiting Line Intensity

We approach the problem of detection limits in particle or photon counting spectroscopies by looking at both the intensity and the shape of the spectral line instead of looking only at the background under the line. We develop a method by which, for a given experimental situation in which the background height and FWHM are known, and at a given statistical precision, we obtain a uniquely defined limiting line intensity.

Solution of an Infinite Set of Green-Function Equations for a Trapped Electron

A Gaussian line shape is obtained for absorption of light by a single trapped electron, interacting linearly with the lattice vibrations, by solving an infinite set of double-time Green-function equations valid to lowest order in the adiabatic approximation. It is assumed that the phonons do not mix different electronic states. The result is the same as that obtained by applying the strong-coupling approximation to the exact Fourier-transformed expression, and can be extended to the case of a more general Hamiltonian.