These product profiles are produced using Simpson Weather Associatesí Lidar Simulation Model (funded, in part, by NASA) with a Nature Run produced by the European Center for Medium range Weather Forecasts (ECMWF). Clouds, wind and relative humidity are obtained directly from the Nature Run. Optical properties of the clouds, variance of the winds on sub-grid scales and the global distribution of aerosols are derived/prescribed in manners described at SWA's Lidar Simulation Model homepage.
Subvisual cirrus, elevated desert-dust layers, and aerosols resulting from biomass burning or significant volcanic activity, while acting to enhance the performance of the coherent lidar, have not been included in the simulations. Cloud porosity, which may permit 20-25 % more shots to reach the lower troposphere then we have simulated, has not been invoked.
In all concept scenarios, an eight-point step stare scan has been assumed. The number of shots accumulated at each staring azimuth are noted in the figures. In real operations, a bi-view scan could be selectively employed to improve the threshold sensitivity by a factor ranging from 1.5 to 2, depending upon the orbit and scan geometry. While it has become conventional to use the "beta (50)" as a reference for comparing DWL concepts, the simulated data products here have used a higher standard of usefulness, i.e. beta(90). This means that 90% of the estimates resulting from the shot accumulation will be correct to within the accuracy of locating the peak in the frequency spectrum (~. 5 to 1.5m/s).
The data product quality is expressed in terms of the percentage difference between the DWL wind estimate for a 200 km X 200 km grid cell and the "true" average wind for that same area based upon the ECMWF Nature Run. Thus, representativeness of the data is included in the velocity errors. Expressing error as a percent allows one to judge the usefulness of the data in a fashion that is similar to how Global Circulation Models view the value of the data.
This format for expressing the coverage and accuracy of data products from a space-based DWL was developed by Simpson Weather Associates, Inc.. Any published use of this format should properly reference SWA.
COHERENT DWL POINT DESIGNS Shuttle Freeflyer NPOESS/WP NPOESS/OP NPOESS/LO Current Wind Observations
Jem 0.5 J Background Atm.
Jem 0.5 J Enhanced Atm.
Jem 2.0 J Background Atm.
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Jem 2.0 J Enhanced Atm.
|This page managed by S. A. Wood||Last modified: 03/20/2003|