Lidar Measurements: Atmospheric Constituents ...
241
10.5.3 Near-IR statistical (cw) DAS lidar
Instead of using repetitively-pulsed lasers and deriving the depth information from the r eturnpulse arrival time according to Eq. (10.1), we can also obtain depth profiles from the crosscorrelation function of a statistically modulated continuous-wave laser beam transmitted into
the atmosphere with the observed temporal distribution of the return signal (Takeuchi et al.,
1983). In view of a revival of this technique, tunable multi-wavelength external-cavity diode
lasers (Papen et al., 1994) and also Ar+ /Ti:Ah03-pumped single-frequency HoTm:YLF lasers (Killinger et al., 1994) that are presently being developed may be interesting sources of
radiation.
10.5.4 New components
Of the numerous innovations that occur in optics only a few shall be mentioned here because
in the author's mind they bear the greatest potential for bringing down the size, weight, cost
and operation effort associated with present-day lidars and at the same time improving the
performance of these devices.
Werner et al. (1992) proposed the use of an all-optical amplifier instead of the currently used
electronic devices. Avalanche photodiodes (APDs) of both silicon (Dautel et al., 1993) and
germanium (Tanaka et al., 1994) are likely to soon replace conventional photodetectors. A few
gaps remain to be closed in our understanding of the efficient protection of photomultiplier
tubes by electric (Bristow et al., 1994) and optical switching (Lehmann et al., 1994). Finally
Langford et al. (1994) propose a signal dithering technique suited for extending the effective
range of conventional transient recorders.
What ground-based lidar can measure
Atmospheric constituents
:::: 10- 8 parts by volume
Thin clouds and other aerosols:
geometry
cloud coverage
scattering ratio
multiple/single scattering ratio
lidar ratio
depolarization
effective particle radius
mass density
surface density
Thick clouds:
cloud base
properties @ OD ~ 2
What ground-based lidar cannot measure
Atmospheric constituents
< 10- 8 parts by volume
Thin clouds and other aerosols:
exact shape of particles
full particle size distribution
Thick clouds:
properties beyond OD ~ 2
Table 10.8: Lidar Measurements: Atmospheric Constituents, Clouds, and Ground Reflectance
Summary.
241
10.5.3 Near-IR statistical (cw) DAS lidar
Instead of using repetitively-pulsed lasers and deriving the depth information from the r eturnpulse arrival time according to Eq. (10.1), we can also obtain depth profiles from the crosscorrelation function of a statistically modulated continuous-wave laser beam transmitted into
the atmosphere with the observed temporal distribution of the return signal (Takeuchi et al.,
1983). In view of a revival of this technique, tunable multi-wavelength external-cavity diode
lasers (Papen et al., 1994) and also Ar+ /Ti:Ah03-pumped single-frequency HoTm:YLF lasers (Killinger et al., 1994) that are presently being developed may be interesting sources of
radiation.
10.5.4 New components
Of the numerous innovations that occur in optics only a few shall be mentioned here because
in the author's mind they bear the greatest potential for bringing down the size, weight, cost
and operation effort associated with present-day lidars and at the same time improving the
performance of these devices.
Werner et al. (1992) proposed the use of an all-optical amplifier instead of the currently used
electronic devices. Avalanche photodiodes (APDs) of both silicon (Dautel et al., 1993) and
germanium (Tanaka et al., 1994) are likely to soon replace conventional photodetectors. A few
gaps remain to be closed in our understanding of the efficient protection of photomultiplier
tubes by electric (Bristow et al., 1994) and optical switching (Lehmann et al., 1994). Finally
Langford et al. (1994) propose a signal dithering technique suited for extending the effective
range of conventional transient recorders.
What ground-based lidar can measure
Atmospheric constituents
:::: 10- 8 parts by volume
Thin clouds and other aerosols:
geometry
cloud coverage
scattering ratio
multiple/single scattering ratio
lidar ratio
depolarization
effective particle radius
mass density
surface density
Thick clouds:
cloud base
properties @ OD ~ 2
What ground-based lidar cannot measure
Atmospheric constituents
< 10- 8 parts by volume
Thin clouds and other aerosols:
exact shape of particles
full particle size distribution
Thick clouds:
properties beyond OD ~ 2
Table 10.8: Lidar Measurements: Atmospheric Constituents, Clouds, and Ground Reflectance
Summary.