Current Status

In support of the GEWEX Continental Scale International Project (GCIP) and GEWEX Americas Prediction Project (GAPP), NOAA/NESDIS has been producing in real time, shortwave Surface Radiation Budget (SRB) parameters since January 1996, using GOES-8 satellite observations. The estimates are being made on an hourly basis for 0.5 degree targets for an area bounded by 70-125 W longitude and 25-50 N latitude. This product became operational in July 2000.

Example of surface downward flux estimated at 18:19 UTC on 1 Dec 1997.
(Click here for an enlarged version.)

The NOAA/NESDIS product in a graphical format can be viewed at:

http://orbit-net.nesdis.noaa.gov/goes/gcip

At the NOAA/NESDIS site, graphical information is kept for the latest few days of operation. At the university of Maryland web site, several SRB parameters from the NOAA/NESDIS product are provided almost in real time as well as validation results. For information on data that are currently provided go to Data Access.

Methodology

A modified version of the GEWEX SRB algorithm (Version 1.1), developed at the University of Maryland, has been used. The model is driven with GOES - 8 satellite data, as preprocessed at NOAA/NESDIS, and auxiliary information on the state of the atmosphere, as available from the NCEP Eta model. Information on the NCEP Eta model can be found at:

http://www.emc.ncep.noaa.gov:/mmb/gcip.html

The implementation of the model requires satellite data preprocessing and cloud screening, which are being performed at NESDIS under the direction of Dr. J. D. Tarpley. Additional information required for implementing the model is related to the state of the atmosphere and the surface. Such information is extracted in real time from the NCEP regional forecast model under the direction of Dr. K. Mitchell and appended to the data stream. These include snow cover and precipitable water.

Developmental activity, in preparation for the operational implementation at NOAA, included the development of angular corrections as appropriate for the filter functions of GOES-8 . The visible channel on the GOES-8 satellite is a narrowband channel. A study was undertaken to obtain angularly dependent relationships between the broadband reflectance and the narrowband reflectance, as observed from the visible channel of GOES-8 (0.52- 0.72 um). Effects of surface properties, aerosols, clouds and sun-viewing geometry are taken into account. The relationships were developed based on simulations of filtered visible channel reflectance of GOES-8 and unfiltered broadband reflectance. An angularly dependent atmospheric radiation model (LOWTRAN 7) was used for simulations. Results are calculated for a wide range of relative azimuth angles and satellite zenith angles, in conjunction with various surface types, such as ocean, vegetated land, desert, and snow. Several cloud types, such as stratus, altostratus, stratocumulus and cirrus, are also included in the simulations. Conditions with different loading of aerosols are simulated separately, to analyze aerosol sensitivity of the relationships. Experiments are in progress on the need to perform operationally angularly dependent transformations. In the current version of the SRB model as implemented by NESDIS, only one transformation, based on the ensemble of simulations, is in use.

Details about the algorithm can be found in Pinker and Laszlo (1992).

Parameters produced at NOAA/NESDIS

Four types of data are produced: Satellite based information used to drive the model Auxiliary input data model Eta model products relevant for hydrologic modeling Independently derived satellite products (Click here for a complete list of parameters).

Activities in progress at the University of Maryland