350
Multiscale Hydrologic Remote Sensing: Perspectives and Applications
and Hess 1998) suggest that the origin of air masses sampled in these layers were
diverse, that is, the Gulf of Mexico for the ABL, Canada for the thin dry layer, and
the U.S. West Coast for the elevated moist layer. The thin dry layer could be identified unambiguously well to the south of the bore. This layer was no longer observed
to the north of the bore head, possibly due to the enhanced entrainment at the top of
the ABL in connection with turbulent eddies within the bore head.
14.3.2 aiRBoRne h 2 o dial aRound 820 nM
The most widely used laser material for 820-nm lasers is the Ti:Al 2 O 3 (Ti:Sa)
crystal, which has not only favorable lasing properties but also physical properties.
Crystals of Ti:Sa exhibit a broad absorption band located at the blue–green region.
Tens of nanosecond pulses can be directly generated by pumping with Q-switched,
frequency-doubled neodymium (Nd):YAG lasers. The fluorescence peaks of Ti:Sa
at 780 nm, with a 180-nm bandwidth (FWHM). Therefore, the tunable output from
Ti:Sa lasers is highest between 700 and 900 nm. Besides, Ti:Sa has very high therSa lasers is highest between 700 and 900 nm. Besides, Ti:Sa has very high therlasers is highest between 700 and 900 nm. Besides, Ti:Sa has very high therand 900 nm. Besides, Ti:Sa has very high therand 900 nm. Besides, Ti:Sa has very high therBesides, Ti:Sa has very high therTi:Sa has very high therSa has very high therhas very high therhas very high thervery high therhigh therhigh thermal conductivity, exceptional chemical inertness, and mechanical rigidity. One of
the most important applications of Ti:Sa lasers is as a laser transmitter in water vapor
DIAL instruments (Moore 1997; Ertel 2004; Schiller 2009).
The Lidar Atmospheric Sensing Experiment (LASE) Instrument of the National
Aeronautics and Space Administration (NASA) Langley Research Center is the first
fully engineered, autonomous DIAL system for the measurement of water vapor in the
troposphere (aerosol and cloud measurements are included). A double-pulsed Ti:Sa
laser transmitting in the 815-nm absorption band of water vapor is used as a laser
emitter by LASE. This instrument was thoroughly described by Killinger et al. (1983).
14.3.2.1 General Description
Figure 14.8 shows a schematic diagram of LASE, consisting of a laser system,
detector system, signal processor system, and control and data system. LASE was
originally designed and operated from the Q-bay of the high-altitude NASA ER-2
aircraft in 1995. Since 2001, it has been reconfi gured to fl y on the NASA DC-8 airin 1995. Since 2001, it has been reconfi gured to fl y on the NASA DC-8 air. Since 2001, it has been reconfi gured to fl y on the NASA DC-8 airSince 2001, it has been reconfi gured to fl y on the NASA DC-8 airhas been reconfigured to fly on the NASA DC-8 aircraft, where it acquired data simultaneously in the nadir- and zenith-pointing modes
to permit coverage over the troposphere.
As already mentioned, a Ti:Sa-based laser system is used as a transmitter. The
wavelength of the Ti:Sa laser is controlled by injection seeding with a diode laser
(LD) that is frequency locked to a water vapor line using an absorption cell. The
LASE detector system consists of two silicon avalanche photodiodes (APDs) and
three digitizers to cover a large signal dynamic range (10 6 ). The signal processor
system is designed to be relatively insensitive to rapid changes in signal levels. The
LASE data system on the DC-8 enables real-time and postflight analyses onboard
the aircraft. A 275-MHz Alpine w/DEC Alpha CPU with 128-MB-memory 12-GB
data storage is used for data processing and analysis. In the current mode of operation, LASE can be locked to the center of a strong water vapor line and can also be
tuned to any spectral position on the absorption line electronically to choose the suitable absorption cross section for optimum measurements over a large range of water
vapor concentrations in the atmosphere.
Multiscale Hydrologic Remote Sensing: Perspectives and Applications
and Hess 1998) suggest that the origin of air masses sampled in these layers were
diverse, that is, the Gulf of Mexico for the ABL, Canada for the thin dry layer, and
the U.S. West Coast for the elevated moist layer. The thin dry layer could be identified unambiguously well to the south of the bore. This layer was no longer observed
to the north of the bore head, possibly due to the enhanced entrainment at the top of
the ABL in connection with turbulent eddies within the bore head.
14.3.2 aiRBoRne h 2 o dial aRound 820 nM
The most widely used laser material for 820-nm lasers is the Ti:Al 2 O 3 (Ti:Sa)
crystal, which has not only favorable lasing properties but also physical properties.
Crystals of Ti:Sa exhibit a broad absorption band located at the blue–green region.
Tens of nanosecond pulses can be directly generated by pumping with Q-switched,
frequency-doubled neodymium (Nd):YAG lasers. The fluorescence peaks of Ti:Sa
at 780 nm, with a 180-nm bandwidth (FWHM). Therefore, the tunable output from
Ti:Sa lasers is highest between 700 and 900 nm. Besides, Ti:Sa has very high therSa lasers is highest between 700 and 900 nm. Besides, Ti:Sa has very high therlasers is highest between 700 and 900 nm. Besides, Ti:Sa has very high therand 900 nm. Besides, Ti:Sa has very high therand 900 nm. Besides, Ti:Sa has very high therBesides, Ti:Sa has very high therTi:Sa has very high therSa has very high therhas very high therhas very high thervery high therhigh therhigh thermal conductivity, exceptional chemical inertness, and mechanical rigidity. One of
the most important applications of Ti:Sa lasers is as a laser transmitter in water vapor
DIAL instruments (Moore 1997; Ertel 2004; Schiller 2009).
The Lidar Atmospheric Sensing Experiment (LASE) Instrument of the National
Aeronautics and Space Administration (NASA) Langley Research Center is the first
fully engineered, autonomous DIAL system for the measurement of water vapor in the
troposphere (aerosol and cloud measurements are included). A double-pulsed Ti:Sa
laser transmitting in the 815-nm absorption band of water vapor is used as a laser
emitter by LASE. This instrument was thoroughly described by Killinger et al. (1983).
14.3.2.1 General Description
Figure 14.8 shows a schematic diagram of LASE, consisting of a laser system,
detector system, signal processor system, and control and data system. LASE was
originally designed and operated from the Q-bay of the high-altitude NASA ER-2
aircraft in 1995. Since 2001, it has been reconfi gured to fl y on the NASA DC-8 airin 1995. Since 2001, it has been reconfi gured to fl y on the NASA DC-8 air. Since 2001, it has been reconfi gured to fl y on the NASA DC-8 airSince 2001, it has been reconfi gured to fl y on the NASA DC-8 airhas been reconfigured to fly on the NASA DC-8 aircraft, where it acquired data simultaneously in the nadir- and zenith-pointing modes
to permit coverage over the troposphere.
As already mentioned, a Ti:Sa-based laser system is used as a transmitter. The
wavelength of the Ti:Sa laser is controlled by injection seeding with a diode laser
(LD) that is frequency locked to a water vapor line using an absorption cell. The
LASE detector system consists of two silicon avalanche photodiodes (APDs) and
three digitizers to cover a large signal dynamic range (10 6 ). The signal processor
system is designed to be relatively insensitive to rapid changes in signal levels. The
LASE data system on the DC-8 enables real-time and postflight analyses onboard
the aircraft. A 275-MHz Alpine w/DEC Alpha CPU with 128-MB-memory 12-GB
data storage is used for data processing and analysis. In the current mode of operation, LASE can be locked to the center of a strong water vapor line and can also be
tuned to any spectral position on the absorption line electronically to choose the suitable absorption cross section for optimum measurements over a large range of water
vapor concentrations in the atmosphere.