357
Airborne Water Vapor Differential Absorption Lidar
data on hurricane forecasts for each of these storm forecasts compared to the control
runs. These impacts are clearly noted in the analysis and in the medium-range forecasts. In general, the inclusion of the LASE moisture data reduced the track error by
100 km on 3-day forecasts.
The intensity forecasts and the issue of sensitivity to LASE data sets are addressed
from an examination of the maximum wind in the isotach fields at the 850-hPa surface in the storm vicinity for these experiments. The right panel of Figure 14.13
illustrates the intensity errors at 12-h intervals for both of the storms. The intensity
error was calculated as the difference between the experiment and the corresponding observed intensity. It can be seen that the initial errors are large in both of
the experiments and they amplified more with the time integration; however, these
errors are slightly reduced in the LASE experiments compared to the CTRL. On the
average, the skill from the LASE experiment is consistently higher compared to the
CTRL run, and a 20–25% improvement was obtained in the reduction of intensity
errors.
14.3.3 aiRBoRne h 2 o dial aRound 940 nM
Unlike the transmitter designed to operate near 730 nm and 820 nm (corresponding
to the weak 4ν vibrational absorption band of water vapor), the transmitter that
works in the 940-nm spectral region uses the one order of magnitude stronger 3ν
vibrational absorption band for its measurements. The 940-nm transmitters have the
advantage of a much higher measurement sensitivity in regions of low water vapor
content in the upper troposphere and lower stratosphere.
Laser emission in the 940-nm region can be obtained by means of the Ti:Sa laser,
optical parametric oscillator (OPO), and LD pumped solid-state laser. With the
focus on high-quality water vapor measurements in the upper troposphere and lower
stratosphere, an airborne water vapor DIAL system operating in the 940-nm region
has been developed at the German Aerospace Centre (DLR; Ehret et al. 2000). This
system uses an OPO with high peak and average power that fulfills all spectral
requirements for water vapor measurements. This DIAL system has been aboard the
DLR research aircraft Falcon 20E since 1999 in the Mesoscale Alpine Program field
campaign (Bougeault et al. 2001).
14.3.3.1 General Description
The schematic setup of the airborne DLR H 2 O DIAL system mounted in the meteoDIAL system mounted in the meteoDIAL system mounted in the meteosystem mounted in the meteosystem mounted in the meteomounted in the meteomounted
meteorological research aircraft Falcon 20E is shown in Figure 14.14. The key element of
this instrument is the transmitter, which is based on an injection-seeded, narrowband OPO. At 925 nm, the output energy of the OPO is about 18 mJ per pulse,
which degrades to 12 mJ for operation at 935 nm. The high-wavelength flexibility
of the OPO allows an easy selection of proper water vapor absorption lines around
935 nm to be most sensitive for mixing ratio measurements in the upper troposphere
over a large dynamic range. Uncertainties in the water vapor retrieval stem from
both systematic and statistical errors. The systemic error is estimated to be about
5%. The statistical error of this DIAL measurement is controlled by horizontal and
vertical data smoothing. Atmospheric backscatter and depolarization is measured
Airborne Water Vapor Differential Absorption Lidar
data on hurricane forecasts for each of these storm forecasts compared to the control
runs. These impacts are clearly noted in the analysis and in the medium-range forecasts. In general, the inclusion of the LASE moisture data reduced the track error by
100 km on 3-day forecasts.
The intensity forecasts and the issue of sensitivity to LASE data sets are addressed
from an examination of the maximum wind in the isotach fields at the 850-hPa surface in the storm vicinity for these experiments. The right panel of Figure 14.13
illustrates the intensity errors at 12-h intervals for both of the storms. The intensity
error was calculated as the difference between the experiment and the corresponding observed intensity. It can be seen that the initial errors are large in both of
the experiments and they amplified more with the time integration; however, these
errors are slightly reduced in the LASE experiments compared to the CTRL. On the
average, the skill from the LASE experiment is consistently higher compared to the
CTRL run, and a 20–25% improvement was obtained in the reduction of intensity
errors.
14.3.3 aiRBoRne h 2 o dial aRound 940 nM
Unlike the transmitter designed to operate near 730 nm and 820 nm (corresponding
to the weak 4ν vibrational absorption band of water vapor), the transmitter that
works in the 940-nm spectral region uses the one order of magnitude stronger 3ν
vibrational absorption band for its measurements. The 940-nm transmitters have the
advantage of a much higher measurement sensitivity in regions of low water vapor
content in the upper troposphere and lower stratosphere.
Laser emission in the 940-nm region can be obtained by means of the Ti:Sa laser,
optical parametric oscillator (OPO), and LD pumped solid-state laser. With the
focus on high-quality water vapor measurements in the upper troposphere and lower
stratosphere, an airborne water vapor DIAL system operating in the 940-nm region
has been developed at the German Aerospace Centre (DLR; Ehret et al. 2000). This
system uses an OPO with high peak and average power that fulfills all spectral
requirements for water vapor measurements. This DIAL system has been aboard the
DLR research aircraft Falcon 20E since 1999 in the Mesoscale Alpine Program field
campaign (Bougeault et al. 2001).
14.3.3.1 General Description
The schematic setup of the airborne DLR H 2 O DIAL system mounted in the meteoDIAL system mounted in the meteoDIAL system mounted in the meteosystem mounted in the meteosystem mounted in the meteomounted in the meteomounted
meteorological research aircraft Falcon 20E is shown in Figure 14.14. The key element of
this instrument is the transmitter, which is based on an injection-seeded, narrowband OPO. At 925 nm, the output energy of the OPO is about 18 mJ per pulse,
which degrades to 12 mJ for operation at 935 nm. The high-wavelength flexibility
of the OPO allows an easy selection of proper water vapor absorption lines around
935 nm to be most sensitive for mixing ratio measurements in the upper troposphere
over a large dynamic range. Uncertainties in the water vapor retrieval stem from
both systematic and statistical errors. The systemic error is estimated to be about
5%. The statistical error of this DIAL measurement is controlled by horizontal and
vertical data smoothing. Atmospheric backscatter and depolarization is measured