Lidar : Range-resolved optical remote sensing of the atmosphere

New York

2005

455 S.

Ill., graph. Darst., Kt.

Monographie

0-387-40075-3

15392

130289

Soon after the laser was invented it became obvious that this new instrument, providing visible and infrared radiation with high intensity density and small divergence, would be a great tool for remote monitoring of atmospheric properties by radar-like methods. The lidar method (li for light instead of ra for radio) it thus practically as old as the laser itself. In the beginning, measurements using light scattering of aerosols and dust particles were at the focus of attention, e.g., for investigating visibility or cloud height. As lasers became more intense, and systems for detecting backscattered light more sensitive. Rayleigh scattering was also studies to allow parameters such as variation of the total air pressure or clear air turbulence to be investigated. Furthermore, Raman scattering allowed limited selective detection of gas constituents of the atmosphere. Increasing sophistication of laser systems made it possible to study trace constituents of the atmosphere; this was the case as soon as frequency-tunable laser systems, either line-tunable or continuously tunable, became available. This made selective absorption and fluorescence accessible for detecting trace constituents with a sensitivity sufficiently high to be useful. Improved methods such as the differential absorption method were also invented and used to monitor trace constituents over large distances. In this way, the stratospheric ozone concentration, for example, could be monitored with good accuracy and also checked by comparison with the results of other methods applied simultaneously. Today lidar ozone measurements are being routinely applied by many laboratories in the world. Not only were laser systems improved in respect to sophistication, they also became more reliable and more efficient, so that finally, long-term routine use was possible and mobile systems, especially advantageous for pollution monitoring, came into use. Systems were also applied in airplanes and satellites, thus tremendously increasing the range of application of lidar methods. Improvement of laser technology was vital in the lidar field. At first, researchers were mainly concerned with keeping the laser of their lidar system working; finally, they were able to concentrate on optimizing the measurement procedure itself and spend the time evaluating their data. Lidar thus went through many ups and downs. Finally, it can be stated that the technology reached the stage where methods became reliable. With a few exceptions, e.g., the white light femtosecond lidar system, the technique described in the present book are in principle already mentioned in previous reviews of the field. However, the experience gained in the last few years with the different methods has been hugely extended by progress in laser techniques, so that finally the enormous potential of lidar was recognized.