National POES System (NPOESS) is scheduled to fly during the 2007-2010 period. The impact of future instruments need to 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) and repeated by NASA/Data Assimilation Office (DAO). 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 including ACARS and cloud track winds.

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 first "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. Alternative nature run is considered to confirm the results. When the data are simulated, efforts are made to avoid the identical twin problem 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 bias correction.

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. OSSE for other instruments such as atmospheric infrared sounder (AIRS), cross track infrared sounder (CrIS), conically scanning microwave imager/sounder (CMIS), advanced technology microwave sounder (ATMS) are under preparation.

Initial results showed that the impact is very sensitive to the error assignments. In addition to random error large scale error is being tested as well as various representativeness error.