![[Side-view configuration of the airborne UV DIAL system on the DC-8 aircraft.]](/img/TP_Bro1.jpg)
Characteristics of the Airborne UV DIAL System
The
airborne UV DIAL (Differential Absorption Lidar) system consists of two
frequency-doubled ND:YAG lasers that are used to pump two high efficiency dye
lasers which are frequency-doubled into the UV to produce the DIAL on-line (289
nm) and off-line (300 nm) wavelengths. The
residual 1064-nm beams from the frequency-doubling process of the Nd:YAG lasers
are transmitted along with the residual visible beams from the
frequency-doubling process of the dye lasers.
In total there are four wavelengths (288, 300, 600, and 1064 nm)
transmitted simultaneously into the atmosphere below and above the aircraft for
lidar backscatter measurements. The
DIAL on and off wavelengths are produced in sequential laser pulses with a time
separation of 300 ms. This close
spacing ensures that the same atmospheric scattering volume is sampled at both
wavelengths during the DIAL measurement. The
four laser beams are transmitted collinearly with the receiver telescope through
40-cm diameter fused silica windows in the top and bottom of the aircraft.
The receiver system consists of two 35-cm diameter Cassegrain telescopes
(one pointed in the zenith and the other in the nadir) with optics to direct the
received signals through narrowband optical filters and onto detectors.
The detectors include gateable photomultiplier tubes for the UV and
600-nm returns, and avalanche photodiodes (APD) for the 1064-nm returns.
Four different detectors can be accommodated simultaneously in each
direction. The transmitter and
receiver characteristics for the UV DIAL system are summarized in Table 1, and
Figure 1 shows a block diagram of the system.
The measurement capabilities of the airborne UV DIAL system are given in
Table 2.
Pump lasers (2)
Continuum PL-9030
Pulse
separation, ms
300
Pulse energy
at 532, mJ
800
Pulse length,
ns
6
Repetition
rate, Hz
30
Transmitted
laser energy at 1064 nm, mJ
400
Dye lasers (2 Lasers)
Continuum ND-6000
Dye laser output energy, fundamental, each laser,
mJ
220
Doubled fundamental (UV laser energy), each laser, mJ
30 on /off
UV laser linewidth, pm
<4
Transmitted UV laser energy, each direction, mJ
15 on & off
Transmitted fundamental energy, each
direction, mJ
50
Receiver:
Wavelength Regions
289-300 nm
578-600 nm 1064 nm
Efficiency
to detector,3 %
31
40
31
Detector
quantum efficiency, %
21 (PMT)
8 (PMT)
40 (APD)
Total
receiver efficiency, %
6.5
3.2
12.4
Receiver field-of-view (selectable), mrad <1.5 ≤1.5 ≤1.5
Physical p
Total weight (lbs)
3825
Dimensions of lasers and laser support structure (L x W x H)
234” x 40” x 43”
(telescope included in length, but not height)
Power requirements (kW)
30
1
Near 600 nm; 2 Near 300 nm;
3Includes
filter transmission for daytime operation.
Table 2. Ozone and aerosol measurement parameters for airborne UV DIAL
system.
Vertical resolution
Ozone vertical averaging interval: 300 m
Horizontal resolution
Aerosol horizontal averaging interval:
2 seconds or
approximately 470 m
Ozone horizontal averaging interval:
300 s or approximately 70 km
Measurement accuracy and precision
Aerosols:
Accuracy and precision:
1%
Ozone:
Accuracy: 10% or 2 ppbv, whichever is larger
Precision: better than 5% or
1 ppbv, whichever is larger
Measurement range
Aerosols: Near surface to 750 m below aircraft and 750 m above aircraft to
10-15 km above aircraft