Retrieval of Geophysical Parameters from GOES

GOES Information

General Satellite Information GSFC-NASA or NOAA-NESDIS
Schedules and Scan Sectors
Current GOES images
GHCC GOES Imager and Sounder Products

Retrieval of Land Surface Temperature and Precipitable Water

The retrieval of land surface temperature (LST) (also known as skin temperature) and total precipitable water (TPW) from GOES measurements is accomplished with an algorithm and the 11 and 12 micrometer channels of either the Imager or the Sounder. The algorithm, know as the Physical Split Window (PSW) technique, is derived from a perturbation form of the radiative transfer equation that is simplified through parameterization to retrieve bulk layer parameters rather than profile information. The physical approach requires a priori information, which includes estimates of temperature and mixing ratio profiles, TPW, and skin temperature. The guess information is used with forward radiative transfer code and GOES spectral response information to calculate channel transmittances and brightness temperatures, which are required for the solution equations.
The retrieval methodology used to obtain LST and TPW varies with the particular application. Often GOES field of views (FOVs) are averaged together over a limited region before the retrieval process to reduce the affect of random noise on the resulting products. Proper screening of the individual FOVs for cloud contamination is crucial for successful retrievals. Our current cloud screening approach uses a one-dimensional spatial variance approach applied to a 3.7 - 11 micrometer difference image (Guillory et. al. 1998) along with single band brightness temperature thresholds. Updates and improvements to this cloud detection are currently being studied (Jedlovec and Laws 2001 - PDF version).

Retrieval of Insolation and Albedo

The amount of solar energy reaching the Earth's surface (insolation) is estimated from the broadband visible channel on GOES. It is desirable to estimate both direct and diffuse radiation (scattering from the atmosphere and clouds). The albedo of the surface is required to accurately compute these components. The surface albedo (for each hour) is calculated using a short term history of GOES visible channel reflectance measurements from cloud-free images (minimum visible value over the history), the solar constant, and an estimate of the water vapor content of the atmosphere. In cloudy regions a historical estimate of the albedo (from cloud-free data) is used. The procedure includes three processes: attenuation of downward flux of solar radiation in cloud-free regions by molecular scattering and absorption by atmospheric water vapor, absorption and scattering of solar radiation by clouds, and the attenuation of solar radiation by the atmosphere below the clouds. Atmospheric absorption is calculated with a parameterized radiative transfer model appropriate for shortwave radiation and is dependent on water vapor (total precipitable water in our case), and satellite and solar viewing geometry. Cloud absorption is parameterized solely on visible reflectance and Rayleigh scattering with a molecular path length.

Last updated on: February 21, 2002