Global wind measurements are a critical component of weather prediction, but have been inferred from other measurementssuch as temperature and atmospheric pressurerather than accurately measured themselves. The new technology will measure wavelength changes from an infrared laser fired into the atmosphere from an orbiting satellite, and those measurements will indicate wind speed, direction, and vertical profile. The acronym stands for Space Readiness Coherent Lidar Experiment and is expected to fly in 2001. This first global wind measurement from space is made possible by a major breakthrough in laser technology in 1997 by SPIE member Upendra N. Singh and researchers at the Remote Sensing Technology Branch of NASA's Langley Research Center. Singh and his crew developed the power oscillator needed for the project.
Coherent lidar uses a special form of optical detection that preserves backscattered photons.
The phase of light contains information about the mean frequency, frequency spectrum, and polarization of the photons. The detector responds to the square of the total optical field illuminating it, thereby producing the cross-product of the backscattered and LO optical fields. The product contains both sum and frequency terms. The desired information is contained in the portion of the detector's output current that oscillates at the frequency difference between the LO and backscattered light. For the laser to be used as a coherent lidar transmitter, the beam quality has to be near-diffraction limited and the linewidth should be no more than a few MHz, nearly transform limited.