Global atmospheric observing systems, such as those on NOAA s current Polar-orbitingOperational Environmental Satellites (POES), provide data for Numerical Weather Prediction (NWP) forecasts and the means to monitor and assess the climate. The future National POES System (NPOESS) is scheduled to fly during the 2007-2010 period. The impact of future instruments must be assessed with experiments using simulated observations. These experiments are known as Observing System Simulation Experiments (OSSEs). OSSE will provide a guideline for selection and design of the instrument.

This project is a collaboration among several organizations. Data assimilation will be performed mainly by a technology-neutral organization, the National Centers for Environmental Prediction (NCEP), with collaboration with the NASA/Data Assimilation Office (DAO) and the Naval Research Laboratory (NRL). From the instrument community, Simpson Weather Associates (SWA) and NOAA scientists are participating in the simulation of Doppler Wind Lidar (DWL) observations, and the National Environmental Satellite, Data and Information Service (NESDIS) will simulate both existing and future thermodynamic sounders. NASA/DAO will simulate conventional observations. Through this collaboration, operational data assimilation systems will be ready to handle new data in time for the launch. This process involves the evaluation of the operational load, the development of the data base and data-processing, and a quality control system. All of this development will accelerate the operational use of data from the future instruments. The "nature run" for this project was provided by the European Centre for Medium- Range Weather Forecasts (ECMWF). The representativeness of the nature run was evaluated and found to be suitable to conduct OSSEs after some adjustment. When the data are simulated the identical twin problem considered for valid OSSE. For example, HIRS radiances have been simulated by NOAA/NESDIS. The basic radiative transfer code is RTTOV version 5 which is based on philosophy and uses different spectroscopy than the operational NCEP model, which is based upon OPTRAN (McMillin et al., 1995).

Data impact of existing instruments in real and simulated data are compared for calibration. The impact test showed remarkable similarity on TOVS 1B data and RAOB wind between real and simulated analysis. RAOB temperature may require some adjustment.

For one of the future instruments DWL, the bracketing OSSEs are being performed for various concepts to bound the potential impact. The following technology-neutral observation coverage and measurement error characterizations will be explored.