Lidar déjà vu: John Goldsmith returns to a highlight of his career
By Patti Koning
When John Goldsmith (8131) looks back on his 30-year career at Sandia, he’s incredibly proud of his work on a Raman lidar (light detection and ranging) system that has been deployed and operating continuously at the Atmospheric Radiation Measurement (ARM) program’s Oklahoma site for the past 15 years. This year, he’s had the chance to recreate that project.
BEEN THERE, DONE THAT — John Goldsmith aligning the optics in the Oklahoma Raman lidar in 1996 (left) and the Darwin, Australia, Raman lidar in 2010 (right).
“The Raman lidar system was one of the most satisfying projects of my career,” he says. “Nothing else I’ve worked on has had this kind of lasting impact on something as important as climate change. So the chance to build a second system was really exciting.”
Raman lidar is an active, laser remote-sensing instrument used to measure atmospheric water vapor, a measurement important in studying climate change, as well as temperature, clouds, and aerosol particles. The instrument identifies water vapor by pulsing laser light for billionths of a second, then recording the light scattered back, some of it slightly shifted in wavelength by the molecules of water and nitrogen in the atmosphere.
The raw data is analyzed by automated value-added procedures (VAPs) developed by the ARM program and then made available to scientists across the globe. By comparing the ratio of the water vapor signal to the nitrogen signal, the software is able to strip away variables that would otherwise make the data difficult to interpret.
This data is critical to creating accurate general circulation models for climate study. “Climate scientists need good atmospheric data to initialize and validate these complex computer codes,” John says. “The amount of water vapor in the atmosphere and its distribution in terms of space and time is crucial. Much of the dynamics of climate is related to interactions with water in the form of vapor and clouds.”
Lidar system launched
The original Raman lidar system was launched in 1995, early in Sandia’s involvement in DOE’s ARM program, and was expected to operate for 10 years. The system is entering its 16th year of operation, running over 90 percent of the time with very little operator attention. In fact, John says, the most significant maintenance task is cleaning the window.
With the success of the original system, there has been significant interest in updating and expanding the capabilities of the Tropical Western Pacific ARM Climate Research User Facility (ACRF) in Darwin, Australia. Recently, the DOE Office of Science allocated funds to Sandia for the capital upgrade of ACRF data collection sites in Oklahoma and Alaska. Sandia also was asked to add Raman lidar to the suite of instruments at the Darwin site (Lab News, Aug. 28, 2009).
John describes the system as a “laser lab in a box,” housed in a standard shipping container with a window at the top for the laser beam to exit and a telescope and associated optics to measure backscatter radiation. The new system is essentially a carbon copy of the current Oklahoma system, including the many upgrades and improvements that were made over the past 16 years.
“When I was told we needed to get this instrument built and operational in Darwin by the end of this year, I knew it would be a challenge,” says John. Fortunately, he was able to work with many of the same players that contributed to the original Raman lidar system.
Sixteen years ago, Orca Photonics Systems Inc., a small company in Redmond, Wash., built the shipping container laboratory. “The company is still there, even the same guys who built the original container,” John says. “They are scientists and they know lidar. They understood exactly what I needed, sometimes better than I did.”
For the Darwin system, Orca separated the equipment into two shipping enclosures, one for the lidar and the other for the utilities. The new laser came from the same company, Continuum of Santa Clara, Calif., that supplied the Oklahoma system. For the electronics, John went to Berlin-based Licel GmbH, which he used for an upgrade of the Oklahoma system about eight years ago.
He also credits Lupe Martinez (8514) and others in the project engineering and facilities departments with keeping the project on track. “They’ve done a tremendous job supporting this project from start to finish,” he says. “Getting the right kind of power to run the system while it was here on site was tricky, since Australia runs on 415 volts/50 hertz.”
Australia presented a few other challenges. In Oklahoma, the sun is always to the south and thus never directly overhead. Darwin is located in Australia’s Northern Territory and sits north of the Tropic of Capricorn, so at certain times of the year the sun is directly overhead.
“If the telescope points directly at the sun, the collected sunlight will do a great deal of damage,” says John. “We had to develop a protection system to ensure that the telescope is always covered unless actively opened.” A sliding hatch covers the window on top of the container and a second shade is gravity loaded so that it will close automatically if power is lost.
In terms of risks, John says he’s most worried about the laser arriving safely in Darwin. It left on Sept. 13 on what he describes as “the slow boat to Australia” and will arrive in mid-November. “If you’ve been to a port and seen shipping containers, you know it’s not done in the gentlest fashion,” he explains. “So we put a lot of thought into packing the system to withstanding bumps and bangs.”
When the system arrives in Darwin, John plans to be the first one to open the container. If all the equipment makes it safely, he’ll only have to worry about the saltwater (estuarine) crocodiles commonplace at Kakadu National Park, about 100 miles from Darwin. Not coincidentally, that’s where the Crocodile Dundee movies were filmed.