On Sunday August 7, 2011, NASA’s DC-8 aircraft took off from the Dryden Aircraft Operations Facility in Palmdale, California for an eight-hour flight along the west coast of North America.  The flight was part of a series of flights testing laser instruments that may be selected to fly on a future satellite mission to measure atmospheric carbon dioxide. For more information about the ASCENDS II campaign, please see this recent article: “NASA’s DC-8 Flying Lab Validates Laser Instruments”  

NASA DC-8flight track (in red).  The DC-8took off from the NASA Dryden Aircraft Operations Facility in Palmdale, Calif.,flew north through the Cascade Mountains and into southern British Columbia, Canadaduring an eight-hour flight on Sunday August 7, 2011.

The pilots, crew, and scientists met at 6:30AM inside the hangar at the NASA Dryden Aircraft Operations Facility.  After the flight briefing, we boarded the DC-8 and took off at 8AM, heading north from Palmdale.  One of the goals of this flight was to test the performance of the instruments over a wide variety of terrains, including vegetated surfaces and surfaces covered with snow and ice.   In order to find snow in August, we flew to the northern Cascade Mountains in Washington State and British Columbia, Canada.   

Crew andscientists prepare for takeoff inside the NASA DC-8 on Sunday August 7, 2011 (Imagecredit: E. Schaller)

After takeoff, we traversed the California Central Valley to test the performance of the instruments over vegetated terrain.  We continued north through California over the Cascade Mountain Range, flying through Oregon, Washington, and Southern British Columbia, Canada.  Along the way, we saw many famous peaks of North America including Mt. Shasta, Mt. St. Helens, Mt. Rainier, and Mt. Baker. 

Mt. Bakerin northern Washington State seen from the NASA DC-8 (Image credit: E.Schaller)

We then crossed into Canadian airspace and continued northwest, flying over numerous glaciers and snowfields.   All of the instruments were performing well, which afforded many of the scientists and crew the opportunity to step away from their computers and consoles and look out the windows at the beautiful scenery passing by below us.

DC-8flight track through Canada

A glacier in British Columbia, Canada near 51.4N 125.8W (Image credit: E. Schaller)

Another goal of the mission was to directly sample carbon dioxide in the atmosphere to compare with the remote carbon dioxide values measured by the laser systems.  We flew in slow ascending and descending spiral patterns while directly measuring carbon dioxide as we increased or decreased in altitude.  Once we re-entered Washington State after flying over the Canadian glaciers, mountains, and snowfields, we flew in a descending spiral pattern, decreasing in altitude from ~20,000 ft down to ~2000 feet.  We then flew a planned missed-approach over a small airport near Forks, Washington (Quillayute Airport).  After the missed-approach, we climbed back up to 12,000 ft, flew to another small airport near Toldeo, Washington (Ed Carlson Memorial Field), and flew another missed-approach.  

Flight track in Washington State showing the spiral patterns near Forks, WA and Toledo, WA 

Following the second missed-approach, we flew another spiral pattern, this time steadily increasing in altitude until we reached 31,000 ft.  This last spiral pattern allowed everyone onboard to see Mt. Rainier, Mt. Adams, and Mt. St. Helens multiple times.

Mt. StHelens seen from the NASA DC-8 during the ascending spiral pattern (Imagecredit: E. Schaller)

Finally, we flew south back to Palmdale along nearly the same track as we had flown north in the morning.  Though we almost landed twice, we did not actually touch the ground until we returned to Palmdale eight hours and 3500 miles later (roughly the distance between New York and London.)

Though a bit tired from the 8-hour flight, all onboard were very excited with the quality and abundance of data that was collected.

Broadband Lidar Instrument Team Concludes Successful Test Flights on the NASA DC-8

How do instruments end up on satellites orbiting the Earth? 

For many of them, long before they are ever launched into space, they are tested from NASA airplanes. One of the objectives of the NASA Airborne Science Program is to test new instruments in space-like environments. Testing future satellite instruments from airplanes is the next best thing to actually testing them in space.

The NASA DC-8 at the Dryden Aircraft Operations Facility in Palmdale, CA (Credit: E. Schaller)

Over the past three weeks, a team from the Goddard Space Flight Center led by Bill Heaps has been testing an instrument on the NASA DC-8 that they hope will fly on the ASCENDS satellite mission. ASCENDS (Active Sensing of Carbon dioxide Emissions over Nights Days and Seasons) is an upcoming NASA satellite expected to be launched in 2018-2020. The goal of ASCENDS is to measure the sources, distribution, and variations in carbon dioxide gas to a very high precision all over the Earth. Mapping carbon dioxide is important for understanding the global carbon cycle and for modeling global climate change.

Bill Heaps tests the Broadband Lidar instrument inside the NASA DC-8 (Image Credit:  E. Georgieva)

How do you measure carbon dioxide from space? Carbon dioxide makes up a very small fraction of the gas in Earth’s atmosphere. In addition, the majority of the carbon dioxide variability occurs in the first hundred feet above the surface of the Earth. In order to measure the abundance of carbon dioxide from a satellite, any instrument must therefore look through Earth’s entire atmosphere in order to detect the variations in carbon dioxide occurring near the surface.

Heaps’ instrument, a broadband Lidar, uses an infrared laser beam aimed at the surface of the Earth.  As the laser passes through the atmosphere and bounces off of the ground, carbon dioxide molecules in the atmosphere absorb some of the light from the laser.  Measuring the amount of absorption that occurs as the instrument passes over different locations on the Earth will allow the team to build global carbon dioxide maps.

Typical Lidar systems have lasers that emit light at very specific colors (wavelengths). The broadband laser used in Heaps’ instrument emits light with a broader range of wavelengths. The carbon dioxide molecule absorbs light at a several different infrared wavelengths. A broadband Lidar, therefore, has the advantage of being able to detect carbon dioxide absorption in multiple wavelength bands with one laser. The wavelength control requirements are also less strict than for a more conventional narrowband laser, which may make the system easier to implement on a satellite.

The Goddard team worked for over two weeks to install and test their instrument on the DC-8 on the ground at the NASA Dryden Aircraft Operations Facility in Palmdale, California. 

Broadband Lidar Instrument team members (Wen Huang and Elena Georgieva) test the performance of their laser inside the DC-8 at the NASA Dryden Aircraft Operations Facility (Image Credit:  W. Heaps)

This week, the team flew with their instrument on two, four-hour flights on the DC-8. During the flights, they tested the instrument performance at variety of altitudes and over different types of surfaces (deserts, agricultural fields, mountainous terrain, the ocean, and the flat waters of Lake Tahoe). The team was very pleased with the performance of the instrument. “The system definitely measured CO2 on both flights even transmitting a very small amount of laser power. I believe the broadband technique has excellent potential to be scaled up for measurements from space,” Heaps said.

DC-8 flight track (in red) from Wednesday May 4, 2011.  During the four-hour flight, the Broadband Lidar Instrument was tested at variety of altitudes and over a variety of different surface terrains.

This July, several instrument teams all vying to be chosen to fly on ASCENDS will test their instruments side by side on the DC-8. With data from the test flights of the Broadband Lidar Instrument in hand, Heaps’ team will return to Goddard to make refinements and improvements in the hope that their instrument will be chosen to fly on the ASCENDS satellite mission.

Funding for the Goddard Broadband Lidar was provided by the NASA Earth Science Technology Office Instrument Incubator program.