An internationally collaborative effort for Full Observing System Simulation Experiments (Full-OSSEs), called Joint OSSE, has been developed for last few years. Full OSSEs allow the quantitative assessment of the analysis and forecast impact if a calibration is performed. Although a large initial investment is required for a full OSSE, using a full OSSE is the most reliable strategy today to assess the quantitative impact from prospective observing systems. Full OSSEs are labor intensive project which made only possible through extensive international collaboltation.

In a Full OSSE, all major observations used for the DAS have to be simulated as a control observation in addition to the observations to be tested by OSSEs. Using the control observations, the calibration of an OSSE verifies the simulated data impact by comparing it to a real data impact. Simulation of control observations and OSSE calibration are the most significant initial investments for a full OSSE before it can be used to evaluate data impact of future instruments, and this most fundamental work is not easy to be funded. NCEP and NESDIS have volunteered to simulate control observations. Calibrations of OSSE systems using the NCEP global data assimilation system are being conducted at ESRL and NCEP.

Simulated data and a data base for alternative simulations are being prepared and being made available through the NASA/GSFC/NCCS portal, where the Nature Run is also available. The simulation software is also provided through the Joint OSSE web site. The calibration and simulation effort at NOAA is coordinated with work being done at NASA/GSFC/GMAO.

Providing Nature Run, truth for OSSE, must be produced by the state of the art forecast model. The first Joint OSSE Nature Run was produced by the European Center for Medium-Range Weather Forecasts (ECMWF). This Nature Run covers a 13 month period at T511 horizontal resolution with 91 vertical levels in 2006. A new Nature Run with higher resolution with improved model is being considered.

Lidar technology is the one of the most focused in near future. Particularly space based Doper Wind Lidar (DWL) will provide three dimensional global wind profile is expected to improve NumericalWeather forecast significantly. Due to the cost of DWL, it has been the most important focus of OSSE for last two decades. With in the Joint OSSE, JCSDA is conducting OSSE to evaluate DWL planned by NASA and ESA. OSSE to evaluate JPSS and DWSS is also in progress at JCSDA.