This photo shows the facility building, which is 541 ft ASL. The building houses the LIDAR control room, a laser/interferometer room, and a utility room. The dome on the roof allows a 300 degree azimuth sweep of the laser beam through the sky. The beam elevation is fixed at 45 deg.
The container in the upper center in this photo holds the 532-nm pulsed laser. The orange plexiglass box contains the post-laser optics that steer the beam through the vertical pipe up to the exit telescope in the dome. A portion of the beam is diverted directly to the interferometer through a fiber optic. This serves as a reference (un-Doppler-shifted) signal.
This telescope assembly holds both the outgoing beam optics and the main (receiving) telescope. The outgoing beam passes through a beam expander, which matches the beam divergence to the field of view of the telescope. The beam, telescope, and dome opening track together as the LIDAR sweeps through the sky.
The computers which control the LIDAR system and monitor, store and analyze the data are in a separate room for reasons of eye safety and to better isolate the laser and interferometer from vibrations and temperature changes.
The laser beam is not intense enough to be visible during daytime operation, but can be seen easily at night in the vicinity of the facility. The scattered light is strong enough to be seen up to altitudes that include the so-called “boundary layer” where aerosols produce a significant return signal. Above that, the signal is not visible to the eye, but can be detected by the LIDAR system.
The GWHI facility was established at the NOAA Mauna Loa Observatory (MLO) on the “big island” of Hawaii in February 2002. This location at 11,141 ft ASL in the middle of the Pacific Ocean was chosen to demonstrate the technology’s ability to make wind measurements in a clean, aerosol-free atmosphere. The tall, isolated Hawaiian Islands make for interesting mountain flows and diurnal effects. The facility is across the valley from the Mauna Kea Observatories, which use the GWHI data for improved weather forecasts.
The GWHI instrument uses a UV (355-nm) light source, which provides an increased molecular return compared to the green (532-nm) light source. UV light is also heavily attenuated by cockpit windows, making this instrument eye safe to pilots. The instrument was designed for remote operations and with a lightweight interferometer to take an additional step toward BalloonWinds and a space-borne instrument.
Because of its isolation from population centers, GWHI is operated remotely from the University of Hawaii (UH), the University of New Hampshire (UNH) and the Michigan Aerospace Corporation (MAC.) The facility is serviced on an as-needed basis by MLO personnel who are stationed on-site.
The GW Hawaii interferometer is a second-generation version, with improved accessibility compared to the original GWNH design. The two black boxes protruding from the side of the interferometer container hold the CCD cameras for the aerosol and molecular channels.
The BalloonWinds phase of the GroundWinds program is designed to more closely match the situation of a space-based LIDAR. BalloonWinds will represent a satellite mission in that it will be down-looking, flying above 99% of the atmosphere. The LIDAR instrument is being designed and built by teams from UNH and MAC (directing Raytheon as a partner and Fibertek as a subcontractor). In addition, the Air Force Research Laboratory (AFRL) at the Kirtland Air Force Base in Albuquerque, New Mexico will provide technical and hardware support for the payload gondola as well as facilities for payload integration and launch. The following table lists the payload teams and their major responsibilities.
The flight plan calls for three balloon launches beginning in the spring of 2006. All launches will be done at Holloman Air Force Base at White Sands, New Mexico. The nominal float altitude is 100,000 feet (30km).
The first two flights are intended to be concept demonstrations. The first flight will demonstrate the electrical, thermal, mechanical, and optical performance of the integrated instrument for nighttime flight conditions. The second flight will demonstrate the ability to operate during the daytime given the additional thermal load and the increased optical background. Instrument modifications based on experience from the initial flights will be made in the 6 months leading up to the final flight, which will experience both day and night conditions. A typical flight timeline going from launch to landing, including about 10 hours at float altitude would last about 14 hours.
A major challenge of the balloon mission is to adapt the LIDAR technology to a balloon-based platform and to support the power and thermal requirements of the instrument in a high-altitude environment. Specifically, the low atmospheric pressure (< 10 mbar) means that critical subsystems must be hermetically sealed and held at a constant (near 1 bar) pressure. The low efficiency of the laser requires substantial battery power to operate over the duration of the mission. Furthermore, the high input power of the laser and, to a lesser extent, the control electronics requires a cooling system, while the need for temperature stability of the interferometer chamber requires heaters. The cooling system uses an ice/water reservoir as a heat sink. Onboard system data acquisition and communication is handled by single-board computers linked via Ethernet. Data is radioed to the ground station in Internet Protocol format.