Observations, Ray-tracing, and Data Assimilation in Aerosol Assessment
Steve Albers
CIRA Noon in NCWCP Conference Center
Abstract:
By tracing rays from natural (Sun, Moon, and other astronomical
objects) and artificial (city) light sources and assessing how they are
affected by the atmosphere, aerosols, and land / ocean surface,
full-color visually realistic images of the environment can be created
based on 3D Numerical Weather Prediction (NWP) analyses or model
forecasts. Simulated Weather IMagery (SWIM) can be compared with
observed images (camera or other photometric measurements) to (1)
validate existing ray tracing and NWP analyses / forecast algorithms,
or (2) assimilate observed images affected by atmospheric, aerosol, and
surface variables into numerical analyses (NWP Data Assimilation, DA).
As for (1), in clear daytime skies, radiance patterns depend on the
aerosol optical depth (AOD, see Fig. 1) and size distributions. The
appearance of the sky during twilight, on the other hand, is most
sensitive to the presence of stratospheric aerosols. Other
relationships and observation platforms will be discussed in the
presentation.
Since aerosols affect both simulated and observed weather images, we
will use DA techniques to synthesize all aerosol related observational
information into analysis states expanded by aerosol related “control”
variables. AOD, scale height, single scattering albedo, and other
aerosol parameters that are currently manually prescribed using a
subjective estimation of visibility will be variationally estimated as
2- or 3D control variables, influenced by aerosol related observations
(e.g., camera, photometer, LIDAR, AERONET, aerosonde, satellite) and a
“first guess” forecast from an aerosol resolving numerical model such
as GSD’s WRF- or FIM-Chem.