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Earth Science and Applications from Space 25 3D-Winds Three-Dimensional Tropospheric Winds Launch: 2016â2020 Mission size: Large Orbit: LEO, SSO Agency: NASA Estimated cost: $650 million (Stage I demonstration) Areas of interest: Water, Weather Instruments: Doppler lidar Benefits: More accurate, longer-term weather forecasts Improved storm track prediction and evacuation planning Improved planting and harvesting schedules and outlooks Although weather forecasts have improved steadily over recent decades, the prediction models on which those forecasts are based are limited by a lack of wind measurements over many parts of the globe. Large uncertainties remain in three-dimensional wind data over the oceans, the Southern Hemisphere, and polar and tropical regions. Improved three-dimensional wind data throughout the troposphere (the lowest 8 to 16 kilo- meters of the atmosphere) would yield concrete benefits, including better day-to-day weather forecasts as well as improved forecasts of hurricane track and intensity, El NiÃ±o and La NiÃ±a, and the transport of air pollutants. 3D-Winds will measure the tropospheric wind fields using two complementary Doppler wind lidars: one in the near-infrared range, well suited for measuring winds in the presence of dust, pollution, or other airborne particles, and the other in the ultraviolet range, detecting molecular- scale Doppler shifts in order to measure winds in air that is relatively pristine. Together, the system will be able to collect wind data across most tropospheric and stratospheric conditions. Given the complexity of the hybrid system proposed for 3D-Winds, the committee rec- ommends an early research program to address high-risk components, followed by design, construction, and testing of a pro- totype, which could be demonstrated in low Earth orbit as early as 2016.