Atmospheric and surface retrievals in the infrared
and shortwave using the HT-FRTC code
Stephan Havemann, Jean-Claude Thelen, Anthony J Baran,
We have developed a new algorithm for the simultaneous retrieval of the atmospheric profiles (temperature, humidity, ozone and
aerosols, clouds) and the surface reflectance/emissivity from infrared and shortwave hyperspectral radiances measured by
air/space-borne, hyperspectral imagers such as ARIES, IASI, CrIs, Hyperion EO-1 or AVIRIS.
The new scheme, proposed here, consists of a fast radiative transfer code, the HT-FRTC code which is based on empirical
orthogonal functions (EOFs), and a 1D-Var retrieval scheme. The inclusion of an 'exact' scattering code based on spherical
harmonics, allows for an accurate treatment of Rayleigh scattering and scattering by aerosols, water droplets and ice-crystals,
thus making it possible to retrieve cloud and aerosol optical properties. An important point to notice here is that the surface
reflectance/emissivity profiles are retrieved in principal component space and not in physical space, thus enabling us to retrieve
all the channels for a given instrument without difficulties.
Moreover, as the HT-FRTC code is sensor-independent only one training set is required for a given wavelength interval. For
Example retrievals for ARIES, IASI, AIRS and CrIs can be done without needing to retrain the HT-FRTC code.
3. IASI 1d-Var Cirrus Cloud Retrievals
1. Surface Emissivity Retrievals over the Oklahoma ARM Site
Aircraft Heading
MODIS Image 1114Z
SW
Temperature Retrievals from
1700 radiance measurements
Humidity Retrievals from
1700 radiance measurements
NE
SW
NE
1700 Retrieved surface emissivity profiles.
Night-Time flight B284 of
JAIVEx Campaign
Lidar Return on-board BAe146
2. Surface Reflectance Retrievals over Beijing
BAe146 Flight Track
Aerosol
Beijing
19/05/01
Clear sky
Temperature, humidity and aerosol profile retrieved from centroid
of cluster 1. Aerosol used: Aged organic carbon
Clear – Sky Retrieval (19/05/01)
Aerosol Retrieval (19/05/01)
Full
Scattering
False Colour Image of
Hyperion EO 1 Scene in
absence of aerosol.
Chou
Scaling
Beijing
03/05/01
Cloud
Scattering
Chou
IWC (mg/m3)
19.8±3.5
13.8±2.8
Top (hPa)
303.7±6.1
304.6±8.4
Fraction
0.54±0.05
0.65±0.08
Temperature, humidity and aerosol profile retrieved from centroid
of cluster 1. Aerosol used: Aged organic carbon
Clear – Sky Retrieval (19/05/01)
Aerosol Retrieval (03/05/01)
False Colour Image of
Hyperion EO 1 Scene in
the presence of aerosol.
Retrieval performed using ‘Aged Organic Carbon’.
Chou scaling cannot be used for cirrus property retrievals (underpredicting ice water content (by
30-50%). The measured values for the IWC and cloud fraction were 20 mg/m3 and 0.55%
respecyively
Met Office FitzRoy Road, Exeter, Devon, EX1 3PB United Kingdom
Tel: 01392 884438 Fax: 01392 885681
Email: jean-claude.thelen@metoffice.gov.uk
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