Scientific Objectives and methodology
ACCRID is a very useful tool for modeling of planetary atmospheres which aims to be enhanced with new experimental results (finer spectral resolution, wider spectral coverage), in order to adapt to the aux precision and accuracy of current and future space missions such as IASI-NG, Forum, 3MI, etc.
Accurate modeling of the effect of particles on the different atmospheric processes requires information about its chemical/mineralogical composition, concentration, size distribution (SD), or height and thickness of the aerosol plume or cloud.
These information can be obtained using different active or passive remote sensing techniques.
However, regardless of the measurement method or spectral range used, it is essential to have a thorough knowledge of their optical properties. Indeed, the extinction of radiation produced by particles depends mainly on the particles size distribution, and complex refractive indices m(nu)=n(nu)+ik(nu), where nu denotes spectral wavenumber. The predominant part of the uncertainty in modeling the effect of aerosols and clouds on atmospheric radiative transfer arises from the lack of knowledge of these parameters, which requires assumptions to be made about them leading to uncertainties in remote sensing and radiative forcing estimates.
Thus, like quantification by remote sensing of the gas phase which requires knowledge of optical reference parameters obtained in the laboratory (center of a transition, intensity or broadening parameters), the chemical and/or microphysical characterization of particles requires a perfect knowledge of their optical properties, in particular the complex index of refraction. The optical constants of solid or liquid particles were usually obtained from two different methods:
(1) using KBr pellet sample, (2) exploiting reflectance spectra and dispersion theory of solid crystal coupled with emissivity spectra and Fresnel’s law. Furthermore, it is now accepted that the optical constants obtained from these techniques are not suitable for aerosols on the one hand because the use of bulk material underestimates the scattering effect and on the other hand because the use of pellets modifies the size, the shape and the vibrational modes.
The primary goal of ACCRID is therefore to provide as much data as possible and therefore contains a mixture of calculated and experimental sources from the literature in order to best cover the diversity of atmospheric particles, however in order to use the most accurate parameters possible, it is recommended when it is possible to choose optical data for which the mention “suspended particles” is indicated in the “sample form” part of the metadata.
What ACCRID can do:
- Select a type of particle (aerosol or cloud), then view the imaginary and/or real parts of the indices in wavelength or wave number.
- Zoom or extend the spectral range with the mouse or by specifying the "range" values.
- Interpolate data by defining the step.
- Download either the raw data or exactly what is displayed on the graph.
- Select data to perform some calculations such as absorption, scattering, extinction coefficients or Single Scattering Albedo (SSA)
- Select the shape, and choose the scattering theory (e.g. Rayleigh, Mie, T-matrix, etc.)
- Use monomodal or bimodal size distribution, and specify the concentration, the average diameter and the standard deviation.
- View and/or download the results
- Easy to share your data selection and options with explicit URLs
What ACCRID can’t (yet) do:
- Mixing of different types of particles
- Phase function calculation
- Calculation for particle size greater than 20 µm (in diameter)
