Future performance of ground-based and airborne water-vapor differential absorption lidar. II. Simulations of the precision of a near-infrared, high-power system
When this research was performed, the authors were with the Atmospheric Technology Division, National Center for Atmospheric Research, Boulder, Colorado 80307.
V. Wulfmeyer was also with the Environmental Technology Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado 80303. He (wulfmeye@uni-hohenheim.de) is now with the Institute of Physics, University of Hohenheim, 70599 Stuttgart, Germany.
Volker Wulfmeyer and Craig Walther, "Future performance of ground-based and airborne water-vapor differential absorption lidar. II. Simulations of the precision of a near-infrared, high-power system," Appl. Opt. 40, 5321-5336 (2001)
Taking into account Poisson, background, amplifier, and speckle
noise, we can simulate the precision of water-vapor measurements by
using a 10-W average-power differential absorption lidar (DIAL)
system. This system is currently under development at Hohenheim
University, Germany, and at the American National Center for
Atmospheric Research. For operation in the 940-nm region, a large
set of measurement situations is described, including configurations
that are considered for the first time to the authors’
knowledge. They include ultrahigh-resolution measurements in the
surface layer (resolutions, 1.5 m and 0.1 s) and vertically
pointing measurements (resolutions, 30 m and 1 s) from the
ground to 2 km in the atmospheric boundary layer. Even during
daytime, the DIAL system will have a measurement range from the ground
to the upper troposphere (300 m, 10 min) that can be extended from
a mountain site to the lower stratosphere. From the ground, for the
first time of which the authors are aware, three-dimensional fields of
water vapor in the boundary layer can be investigated within a range of
the order of 15 km and with an averaging time of 10 min. From an
aircraft, measurements of the atmospheric boundary layer (60 m, 1
s) can be performed from a height of 4 km to the ground. At
higher altitudes, up to 18 km, water-vapor profiles can still be
obtained from aircraft height level to the ground. When it is being
flown either in the free troposphere or in the stratosphere, the system
will measure horizontal water-vapor profiles up to 12 km. We are
not aware of another remote-sensing technique that provides,
simultaneously, such high resolution and accuracy.
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Atmospheric parameters for a downward-pointing system
Daytime background Lν (W m-2 nm-1)
0.8
0.4
Atmospheric optical thickness τatm
0.25
0.1
Detector system parameters
Detector gain G
200.0
0.9
Detector quantum efficiency η
0.8
0.9
Detector noise current Idet (A Hz-0.5)
0.4 × 10-12
6.0 × 10-15
For both 945 and 1400 nm, the following
laser parameters are the same: off-line average power, 10 W; pulse
duration Δt, 10–100 ns; transmission of steering optics
las, 0.98, and FWHM of interference filter
ΔλF (nm) 0.2–1.0. The following
atmospheric parameters are the same: nighttime background
Lν, 0.0 W m-2 sr-1
nm-1; surface reflectivity ρ, 0.5. The following
detector system parameters are the same: telescope radius
Rt, 0.5 m on the ground and 0.2 m on an
airplane; field of view, 0.2–0.5 mrad. Transmission of receiver
optics rec, 0.9; detector noise figure
Fdet, 3.0; filter bandwidth of detector system
B, 10.0–50.0 MHz; amplifier noise current
Iamp, 20 × 10–12 A Hz-0.5;
detector quantum efficiency η, 0.8; amplifier gain, 1000–100,000 V
A-1.
Table 2
Parameters for the Simulation of a Horizontally Pointing
or Scanning DIAL System in the ABLa
Variable
Altitude (nm)
940
1400
Atmospheric parameter
Line center of absorption line (cm-1)
10 804.158
7702.545
Ground-state energy E (cm-1)
275.5
222.05
Backscatter coefficient β (m-1 sr-1)
5 × 10-6
4.2 × 10-6
Atmospheric extinction coefficient α (m-1)
10-4
8.3 × 10-5
For both 940 and 1400 nm, the following
laser parameters are the same: pulse duration Δt,
20–100 ns; laser spectral bandwidth
ΔνL, ΔνFT; laser beam radius
RL, 0.4 m; beam divergence excess factor
Fθ, 1; off-line pulse energy
E0 (J) and repetition rate
νL (Hz) are given in Figs. 1–6. The
following atmospheric parameters are the same: absolute humidity
ρ, 8.7 g m-3; water-vapor number density
nH2O, ≈2.9 × 1017
cm-3; line strength of absorption line S,
10-24 cm. The following parameters for data analysis
are also the same: range resolution ΔR, 300 m; average
time T, 10 s; differential optical thickness Δτ, 0.03.
Table 3
Parameters for the Simulation of an Ultrahigh-Resolution
Horizontally Pointing DIAL System in the ABL
Variable
Value at 940 nm
Laser parameters
Off-line pulse energy E
0
(mJ)
10
Repetition rate νL (Hz)
1000
Pulse duration Δt (ns)
10
Laser spectral bandwidth ΔνL
10 × ΔνFT
Laser beam radius RL (m)
0.4
Beam divergence excess factor Fθ
10
Atmospheric parameters
Absolute humidity ρ (g m-3)
8.7
Water vapor number density nH2O (cm-3)
≈2.9 × 1017
Line strength of absorption line S (cm)
2.84 × 10-23
Line center of absorption line
10,304.937
Ground-state energy E (cm-1)
23.784
Backscatter coefficient β (m-1 sr-1)
5 × 10-6
Atmospheric extinction coefficient α (m-1)
10-4
Parameters for data analysis
Range resolution ΔR (m)
1.5
Averaging time T (s)
0.1
Differential optical thickness Δτ
0.0045
Table 4
Parameters for the Simulation of a Vertically Pointing,
High-Resolution DIAL System in the ABL
Atmospheric parameters for a downward-pointing system
Daytime background Lν (W m-2 nm-1)
0.8
0.4
Atmospheric optical thickness τatm
0.25
0.1
Detector system parameters
Detector gain G
200.0
0.9
Detector quantum efficiency η
0.8
0.9
Detector noise current Idet (A Hz-0.5)
0.4 × 10-12
6.0 × 10-15
For both 945 and 1400 nm, the following
laser parameters are the same: off-line average power, 10 W; pulse
duration Δt, 10–100 ns; transmission of steering optics
las, 0.98, and FWHM of interference filter
ΔλF (nm) 0.2–1.0. The following
atmospheric parameters are the same: nighttime background
Lν, 0.0 W m-2 sr-1
nm-1; surface reflectivity ρ, 0.5. The following
detector system parameters are the same: telescope radius
Rt, 0.5 m on the ground and 0.2 m on an
airplane; field of view, 0.2–0.5 mrad. Transmission of receiver
optics rec, 0.9; detector noise figure
Fdet, 3.0; filter bandwidth of detector system
B, 10.0–50.0 MHz; amplifier noise current
Iamp, 20 × 10–12 A Hz-0.5;
detector quantum efficiency η, 0.8; amplifier gain, 1000–100,000 V
A-1.
Table 2
Parameters for the Simulation of a Horizontally Pointing
or Scanning DIAL System in the ABLa
Variable
Altitude (nm)
940
1400
Atmospheric parameter
Line center of absorption line (cm-1)
10 804.158
7702.545
Ground-state energy E (cm-1)
275.5
222.05
Backscatter coefficient β (m-1 sr-1)
5 × 10-6
4.2 × 10-6
Atmospheric extinction coefficient α (m-1)
10-4
8.3 × 10-5
For both 940 and 1400 nm, the following
laser parameters are the same: pulse duration Δt,
20–100 ns; laser spectral bandwidth
ΔνL, ΔνFT; laser beam radius
RL, 0.4 m; beam divergence excess factor
Fθ, 1; off-line pulse energy
E0 (J) and repetition rate
νL (Hz) are given in Figs. 1–6. The
following atmospheric parameters are the same: absolute humidity
ρ, 8.7 g m-3; water-vapor number density
nH2O, ≈2.9 × 1017
cm-3; line strength of absorption line S,
10-24 cm. The following parameters for data analysis
are also the same: range resolution ΔR, 300 m; average
time T, 10 s; differential optical thickness Δτ, 0.03.
Table 3
Parameters for the Simulation of an Ultrahigh-Resolution
Horizontally Pointing DIAL System in the ABL
Variable
Value at 940 nm
Laser parameters
Off-line pulse energy E
0
(mJ)
10
Repetition rate νL (Hz)
1000
Pulse duration Δt (ns)
10
Laser spectral bandwidth ΔνL
10 × ΔνFT
Laser beam radius RL (m)
0.4
Beam divergence excess factor Fθ
10
Atmospheric parameters
Absolute humidity ρ (g m-3)
8.7
Water vapor number density nH2O (cm-3)
≈2.9 × 1017
Line strength of absorption line S (cm)
2.84 × 10-23
Line center of absorption line
10,304.937
Ground-state energy E (cm-1)
23.784
Backscatter coefficient β (m-1 sr-1)
5 × 10-6
Atmospheric extinction coefficient α (m-1)
10-4
Parameters for data analysis
Range resolution ΔR (m)
1.5
Averaging time T (s)
0.1
Differential optical thickness Δτ
0.0045
Table 4
Parameters for the Simulation of a Vertically Pointing,
High-Resolution DIAL System in the ABL
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