The Wyoming Cloud Lidar (WCL) is an airborne observational system that provides high-resolution cloud and aerosol structures. There are two WCL systems available, an up-pointing lidar (zenith, WCL-I) at a wavelength of 355 nm and a down-pointing lidar (nadir, WCL-II) at 351 nm, which can be deployed separately or together. WCL is primarily used on the King Air, but has also been used on the NSF/NCAR C-130 and NPS Twin Otter.
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WCL is used in operations where it is desired to describe weather events such as clouds, precipitation, and aerosol, and to provide specific information of these targets. Data ProductsQuicklooks and preliminary processed L0 data is made available within 24 hours during deployment. Standard processed data made available after quality control includes:
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An Ultra Pulsed Nd:YAG Laser from the Big Sky Laser Technologies Inc. providing a
20 Hz 16 mJ output at 355 nm is used for the WCL-I. Operating at 355 nm not only makes
it easy to achieve eye-safe operation, it also provides a stronger molecular backscattering
signal than a lidar operating at 532 or 1064 nm with the same laser energy. This is
important for calibrating backscattering coefficients. The laser beam is expanded
5 times to a diameter of 15 mm before emittance into the atmosphere, making the system
eye-safe beyond a distance of ~65 m. To improve lidar linear depolarization measurements,
a 1/2 λ wave plate is placed after the beam expander and coupled with a cubic polarization
beam splitter in the receiver path.
The receiver in the WCL-I is based on a 75mm refractive lens with a 12.5mm collimated
beam that enters into the cubic polarization beam splitter. The field of view is controlled
by a pinhole located at the focal plane of the receiving lens. The PMT packages include
narrow band filters (0.3 nm), a focus lens, and a compact PMT. To provide the ruggedness
and stability needed for the WCL to operate in a turbulent environment, the receiver
is designed to share the same optical bench with the transmitter. The PMT's gain can
easily be adjusted with bias control voltage. Signals from the PMTs are sent to the
LICEL data acquisition system. The data system has a combined A/D and photon counting
capability. To provide high-resolution spatial measurements, only strong signals digitized
by A/D at 40 MHz are saved at single shot or averaging of number of shots. Thus, the
WCL can provide measurements at ~4.5 m horizontal and 3.75 m vertical resolution from
the UWKA, for an average cruise speed of ~90 m/s.
| Zenith (up-pointing) WCL-I | Nadir (down-pointing) WCL-II | |
| Transmit Laser Wavelength | 355 nm | 351 nm |
| Pulse Energy | 16 mj | 200 μj |
| Pulse Length | 6 ns | 30 ns |
| Pulse Repetition Frequency (PRF) | 20 Hz | 1 KHz |
| Laser Beam Divergence | 1 mrad | 0.3 mrad |
| Polarization (pol) Radiated | Linear | Linear |
| Receiver Diameter | 75 mm | 108 mm |
| Receiver Field of View | 2 mrad | 1 mrad |
| Receiving Channels | 2 | 4 |
| Polarization Received | H&V | H&V |
| Detector | PMT | PMT |
| Range Resolution | 3.75 m and up | 1.5 m and up |
| Temporal Resolution | 0.05 s and up | 0.01 s and up |
| Data Acquisition System | LICEL | GAGE |
The area around the flight level where the laser beam enters into the field of view
(FOV) of the receiving telescope progressively is the "overlap zone", which is about
100 m in length, depending on the transmitted laser beam divergence, the FOV of the
receiving telescope and the angle between the axes of the laser beam and telescope.
The processed data are already corrected for this by using calculated overlap factors.
However the correction may not be completely accurate for all of the profiles due
to the drift in the laser beam's direction.
Also, the near-range signals can saturate when the aircraft is flying through dense
clouds. In this situation, the clouds cannot be fully penetrated by the lidar, and
the signals can be dramatically attenuated with increasing distance.
Owen Cruikshank | ocruiksh@uwyo.edu | (307) 766-3245
University of Wyoming - Flight Center, 2007: The University of Wyoming Cloud Lidar (WCL). University of Wyoming, College of Engineering, Department of Atmospheric Science, doi:10.15786/M25W9D.
WCL-I and WCL-II were developed within the University of Wyoming's Department of Atmospheric Science. Major funding for the acquisition, development and research use of the WCL has been derived from the NSF, ONR, NASA and UW.
The zenith-pointing WCL-I was developed in 2007 and has been successfully deployed
and tested on the UWKA during the Wyoming Airborne Integrated Cloud Observations Experiment
(WAICO) in 2008 and 2009, and on the NSF/NCAR C-130 during the Ice Clouds Experiment-Layer Clouds (ICE-L)
in 2007. Since then, it has been regularly deployed in in many projects aboard both aircraft.
The nadir-pointing WCL-II was developed in 2008 and successfully tested during the
WAICO09 experiments.
In 2011, the WCL-II was upgraded by adding two new receiving channels which can enlarge
the dynamic range of the receiving signals.