228
C. Weitkamp
Clearly, the reflection coefficient of the surface would have to be the same for the signal and
reference wavelength, or at least show a spatially independent ratio. It turned out, however,
that, at least in the middle infrared where CO2 lasers represent a convenient source for airborne
measurements, reflexion coefficients vary greatly and constitute the major source of uncertainty
in the method.
Attempts have therefore been made to conversely use reflection properties of the ground for
information about the nature of the soil, rock, or vegetation responsible for the optical echo
from the planet's surface. An in-depth analysis (Schliissel et al., 1994) shows that the intensity of the return signal is determined by no less than 10 ground-related parameters. These
parameters include the single-scattering albedos and scattering phase function parameters of
soil and vegetation and the leaf area index. Even if up to seven of them have only marginal
influence on the magnitude of the reflection coefficient or can be treated in some analytical
or empirical way, not much relevant information can so far be extracted from the measured
backscatter signal except in a very few special cases such as remote prospection of the surface
of the moon for deposits of ilmenite, a titanium mineral rich in oxygen and a candidate for a
supplier of O2 for a permanently-manned lunar station (Melendrez et al., 1994).
10.3 Instruments and Applications - Case Studies
Of the numerous practical implementations of the lidar principle, only a very few will be presented here; the following paragraphs are meant to illustrate the preceding section, rather than
comprehensively cover the subject. Examples are all from the author's laboratory, primarily
because of easy access to the data and the pictorial material, published or unpublished.
10.3.1 Shipborne IR DAS lidar: Hel distribution, transport, degradation, and lifetime in the marine atmosphere
One of the earliest shipborne DAS lidars was used between 1979 and 1982 for the detection
of hydrogen chloride in plumes of incineration ships. These ships were used to destroy large
quantities of toxic, highly chlorinated chemical waste that was otherwise hard to dispose of.
Incineration was measured to be a clean (no Ch, very little NO x ) and very efficient (> 99.98%
destruction efficiency, <10- 14 total dioxins and furanes) process, only the hydrogen chloride to
which the chlorine was converted was considered a potentially harmful emission. With up to
83% of CI contents and a waste throughput of 10 t/h for each incinerator, considerable amounts
of the gas were released into the atmosphere. To investigate the concentration distributions in
the plume, to elucidate degradation processes, to determine the lifetime, to provide basic data
for the application of numerical transport models, to facilitate the choice of incineration sites
and to assess the overall environmental effects of the technique, a lidar system was built and
mounted on a small ocean-going vessel, the R/V TABASIS.
The system (cf. Fig. 10.8) was equipped with only one laser, a pulsed deuterium fluoride laser
that can be made to emit on several lines between 3.5 and 4.0 J.lm. With a minimum pulse-topulse delay of 200 ms and a maximum pulse-pair repetition frequency of 1 Hz, the system did
not meet the requirement of < 1-ms pulse delay; this was one of the reasons for the relatively
poor sensitivity which, however, was fully adequate for measurements in the plumes of the
incineration ships.
Table 10.2 gives the technical data of the lidar. The reference line is sufficiently far from
the center of an HCI absorption line so the absorption cross section is only 0.056 x 10- 24
C. Weitkamp
Clearly, the reflection coefficient of the surface would have to be the same for the signal and
reference wavelength, or at least show a spatially independent ratio. It turned out, however,
that, at least in the middle infrared where CO2 lasers represent a convenient source for airborne
measurements, reflexion coefficients vary greatly and constitute the major source of uncertainty
in the method.
Attempts have therefore been made to conversely use reflection properties of the ground for
information about the nature of the soil, rock, or vegetation responsible for the optical echo
from the planet's surface. An in-depth analysis (Schliissel et al., 1994) shows that the intensity of the return signal is determined by no less than 10 ground-related parameters. These
parameters include the single-scattering albedos and scattering phase function parameters of
soil and vegetation and the leaf area index. Even if up to seven of them have only marginal
influence on the magnitude of the reflection coefficient or can be treated in some analytical
or empirical way, not much relevant information can so far be extracted from the measured
backscatter signal except in a very few special cases such as remote prospection of the surface
of the moon for deposits of ilmenite, a titanium mineral rich in oxygen and a candidate for a
supplier of O2 for a permanently-manned lunar station (Melendrez et al., 1994).
10.3 Instruments and Applications - Case Studies
Of the numerous practical implementations of the lidar principle, only a very few will be presented here; the following paragraphs are meant to illustrate the preceding section, rather than
comprehensively cover the subject. Examples are all from the author's laboratory, primarily
because of easy access to the data and the pictorial material, published or unpublished.
10.3.1 Shipborne IR DAS lidar: Hel distribution, transport, degradation, and lifetime in the marine atmosphere
One of the earliest shipborne DAS lidars was used between 1979 and 1982 for the detection
of hydrogen chloride in plumes of incineration ships. These ships were used to destroy large
quantities of toxic, highly chlorinated chemical waste that was otherwise hard to dispose of.
Incineration was measured to be a clean (no Ch, very little NO x ) and very efficient (> 99.98%
destruction efficiency, <10- 14 total dioxins and furanes) process, only the hydrogen chloride to
which the chlorine was converted was considered a potentially harmful emission. With up to
83% of CI contents and a waste throughput of 10 t/h for each incinerator, considerable amounts
of the gas were released into the atmosphere. To investigate the concentration distributions in
the plume, to elucidate degradation processes, to determine the lifetime, to provide basic data
for the application of numerical transport models, to facilitate the choice of incineration sites
and to assess the overall environmental effects of the technique, a lidar system was built and
mounted on a small ocean-going vessel, the R/V TABASIS.
The system (cf. Fig. 10.8) was equipped with only one laser, a pulsed deuterium fluoride laser
that can be made to emit on several lines between 3.5 and 4.0 J.lm. With a minimum pulse-topulse delay of 200 ms and a maximum pulse-pair repetition frequency of 1 Hz, the system did
not meet the requirement of < 1-ms pulse delay; this was one of the reasons for the relatively
poor sensitivity which, however, was fully adequate for measurements in the plumes of the
incineration ships.
Table 10.2 gives the technical data of the lidar. The reference line is sufficiently far from
the center of an HCI absorption line so the absorption cross section is only 0.056 x 10- 24