RTTOV - the fast radiative transfer

Atmospheric radiative transfer codes

An Atmospheric radiative transfer model, code or simulator calculates radiative transfer of electromagnetic radiation through a planetary atmosphere, such as the Earth's.- Methods :...

 model for calculations of radiances for satellite infrared or microwave nadir scanning radiometers (see push broom scanner

Push broom scanner

A Push broom scanner is a technology for obtaining satellite images with optical cameras. It is used for passive remote sensing from space. In a push broom sensor, a line of sensors arranged perpendicular to the flight direction of the spacecraft is used. Different areas of the surface are imaged...

).

Given an atmospheric profile of temperature, variable gas concentrations, cloud and surface properties RTTOV calculates radiances

Radiance

Radiance and spectral radiance are radiometric measures that describe the amount of radiation such as light or radiant heat that passes through or is emitted from a particular area, and falls within a given solid angle in a specified direction. They are used to characterize both emission from...

 and brightness temperature

Brightness temperature

Brightness temperature is the temperature a black body in thermal equilibrium with its surroundings would have to be to duplicate the observed intensity of a grey body object at a frequency \nu....

s. The only mandatory input is water vapour. Optionally ozone

Ozone

Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

, carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, nitrous oxide

Nitrous oxide

Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...

, methane

Methane

Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 and carbon monoxide

Carbon monoxide

Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 can be variable with all other constituents assumed
to be constant. The range of temperatures and water vapour concentrations over which the optical
depth computations are valid depends on the training datasets which were used. The spectral range of the RTTOV9.1 model is 3-20 micrometres (500 - 3000 cm-1) in the infrared.

RTTOV contains forward, tangent linear, adjoint and K (full Jacobian matrices) versions of the model; the latter three modules for variational
assimilation or retrieval applications.
One of several applications of RTOV are retrievals of brightness temperature and sea surface temperature

Sea surface temperature

Sea surface temperature is the water temperature close to the oceans surface. The exact meaning of surface varies according to the measurement method used, but it is between and below the sea surface. Air masses in the Earth's atmosphere are highly modified by sea surface temperatures within a...

 from Advanced Very High Resolution Radiometer

Advanced Very High Resolution Radiometer

The Advanced Very High Resolution Radiometer is a space-borne sensor embarked on the National Oceanic and Atmospheric Administration family of polar orbiting platforms . AVHRR instruments measure the reflectance of the Earth in 5 relatively wide spectral bands...

 sensor.

FASTEM

Surface emissivity model which parameterizes surface emissivity. FASTEM2 computes the surface emissivity averaged over all facets representing the surface of the ocean and an effective path correction factor for the down-welling brightness temperature. FASTEM2 is applicable for frequencies between 10 and 220 GHz, for earth incidence angles less than 60 degrees.

See also

• List of atmospheric radiative transfer codes
• Community Radiative Transfer Model
  Community Radiative Transfer Model
  Community Radiative Transfer Model is the fast radiative transfer model for calculations of radiances for satellite infrared or microwave nadir scanning radiometers ....
  
  

External links

• http://research.metoffice.gov.uk/research/interproj/nwpsaf/rtm/ RTTOV homepage
• http://research.metoffice.gov.uk/research/interproj/nwpsaf/rtm/rttov_applications/simulated_imagery.html Example use of RTTOV with the Unified Model
  Unified Model
  The Unified Model is a Numerical Weather Prediction and climate modeling software suite originally developed by the United Kingdom Met Office, and now both used and further developed by many weather-forecasting agencies around the world...
  
  
• http://cimss.ssec.wisc.edu/itwg/groups/rtwg/fastrt.html Exaplanation of tangent linear, adjoint and K radiative transfer models.