SRB in the context of GCIP/GAPP objectives

The main objectives of GCIP are:

determination of the time/space variability of the hydrological and energy budget over continental scales;
development and validation of macro- scale hydrological models;
development and validation of information retrieval schemes;
incorporation of existing and future satellite observations;
and providing capability to translate the effects of future climate change into impacts on water resources.

The main objectives of GAPP are:

develop and demonstrate a capability to make reliable monthly to seasonal predictions of precipitation and land-surface hydrologic variables through improved understanding and representation of land surface and related hydrometeorological and boundary layer processes in climate prediction models;

interpret and transfer the results of improved seasonal predictions for the optimal management of water resources;

The objective will be achived, "if improvements are made in the understanding of land surface, precipitation , radiation and hydrologic processes over a continental domains at space and time resolutions appropriate for future climate and related hydrologic models" (GAPP Science Plan and Implementation Strategy, 2001).

Of particular interest is the need to link radiative and hydrological processes. Satellites provide the most realistic approach for obtaining radiative fluxes on scales of interest in climate studies. NOAA/NESDIS is supporting the GEWEX Continental-Scale Project (GCIP) and GEWEX Americas Prediction Project (GAPP) activities by developing new operational products from satellite observations. Shortwave radiative fluxes at the surface and at the top of the atmosphere are part of this product. They include both upwelling and downwelling shortwave fluxes, total and diffuse, as well as spectral fluxes (e.g., the photosynthetically active radiation (PAR), cloud amount and surface skin temperature. Implementation of these products required development of a new configuration of satellites data stream, and outputs from mesoscale numerical weather prediction models. A brief summary of steps taken to reach this stage will follow.

Surface downward flux
(Example of estimated surface downward flux (W/m**2), October 1, 1998)


SRB implementation activity

In the framework of a NOAA/NESDIS activity entitled: "Geostationary Satellite Products for GEWEX Continental-Scale Project (GCIP)" directed by Dr. J. D. Tarpley from the NESDIS Satellite Research Laboratory, and supported by the NOAA Climate and Global Change Research Program, an insolation algorithm developed at the University of Maryland (Pinker and Laszlo, 1992) has been transferred to NOAA/NESDIS for implementation with GOES-8 (Menzel and Purdom, 1994). Changes in the algorithm to meet the specifications of new sensors on board GOES-8, were implemented at the University of Maryland. Developmental activity, in preparation for operational implementation at NOAA, included the development of angular corrections as appropriate for the filter functions of GOES-8 (Zhou et al., 1996). A new interface between the 'raw' satellite observations and the inputs required for the insolation model, were prepared at NOAA/NESDIS. The insolation algorithm has been implemented on an hourly basis, for 0.5 degree targets for an area bounded by 70-125 W longitude and 25-50 N latitude belts. For each target, at appropriate forecast times, selected data from the NCEP regional forecast ETA model (Black, 1994) have been delivered to the satellite data stream, to serve as inputs to the insolation model. They include snow cover and precipitable water. The assumption has been that the input data as available from the ETA model will lead to improvements in the satellite estimates of the surface and top of the atmosphere radiative fluxes. In turn, the derived radiative fluxes can help to diagnose the NCEP forecast model as to its ability to predict correctly radiative fluxes. The evaluation of this new configuration included comparisons of the operational version of the model with an off-line version, as well as evaluation against ground truth, as available from independent projects, such as the Surface Radiation Monitoring Network (SURFRAD) and other available networks.


Current status

NOAA/NESDIS is producing operationally shortwave (SW) surface and top of the atmosphere radiation budget parameters, in support of the GEWEX Continental Scale International Project (GCIP) (Leese,1994; 1997). The implementation activity by NOAA is described in Tarpley et al. (1996). The model is driven with GOES-8 satellite data as preprocessed at NOAA/NESDIS, and with auxiliary information on the state of the atmosphere and the surface, as available from the NOAA/NCEP ETA model, and from the Air Force snow analysis. Information on wind speed, temperature, specific humidity at three levels at 50 mb intervals, starting from the surface up, is also saved. At the University of Maryland, the model can be run in an off-line mode, with the same input data as used at NESDIS, and the NOAA/NESDIS model outputs is stored. This allows to evaluate the performance of the operational version of the model; to test possible improvements; and to evaluate results against ground truth. About 20 stations are available from the Illinois State Water Survey (Hollinger et al., 1994); about twenty one stations are available from the Arizona Meteorological Network (AZMET) (Brown, 1989); and four stations from the Surface Radiation (SURFRAD) network (Hicks et al., 1995). These include stations in Bondville, Ill., Fort Peck, Montana,Goodwin Creek, Missouri, and Table Mountain, Colorado. Several locations have multiple sites. For instance, at Bondville, Ill, both the Illinois State Water Survey and SURFRAD have independent stations.


Calibration issues

There is no visible calibration source on board the satellite (Weinreb, 1997). The infrared channel is calibrated in flight by taking data when the instrument is viewing space and an on board calibration black body. The visible data are normalized. This is a process of scaling the data in each visible channel to compensate for differences in gain among the channels. Quality monitoring, generation of visible normalization tables, and the archiving of calibration data is done later off line at NOAA/NESDIS after the transmitted data are received. It is planned that over the lifetime of each instrument, its calibration trends will be monitored and improvements will be made. According to current plans, a relative calibration, based on terrestrial targets, will be performed routinely to correct for long term drift. As documented in "GOES-I-M Product Assurance Plan", the NESDIS Physics Branch will assume responsibility for the calibration. A calibration data base containing daily GOES- I-M observations of approximately 50 terrestrial targets will be compiled. The relative calibration technique that is currently in use for the AVHRR Pathfinder Project will be applied.

Home Project Background Data Access Validation The Gallery Known Problems Contacts Links References Updates Faq