Lebanese American University


NASA scientist explains the role of satellites in tracking climate change

During her Beirut-campus lecture, Dr. Diane Evans, Director for Earth Science at NASA's Jet Propulsion Lab in California, explains how satellites are being used to monitor climate change.

Evans reveals areas of Antarctica and Greenland that are being lost due to global warming, during her Byblos-campus lecture.

January 26, 2010—

“We don’t know the ultimate fate of the planet,” said Dr. Diane Evans, Director for Earth Science at NASA’s Jet Propulsion Lab in California, “but things are going to get more dramatic.”

Evans, who has worked at the lab for over two decades, warned of the urgency to combat climate change as she revealed NASA data illustrating the severity of shrinking icecaps and rising sea levels in a lecture entitled “The Critical Role of Satellites in Understanding the Environment,” offered twice at LAU on January 21 — in Beirut in the morning and Byblos in the afternoon.

“Islands will be underwater, coastlines will be eroded,” she warned. “So there is a lot of concern about sea levels rising, but the other element of why we care about fresh water coming into the ocean is because it affects the whole ocean circulation which regulates the temperature of the planet.”

Rising sea levels can be attributed to two reasons: thermal expansion as a result of increasing water temperature, and added water mass from melting icebergs.

“But the big question is how do we tell the difference?” Evans said, as she explained that information revealing changes to the Earth’s climate and physical land and water masses are being carefully monitored by NASA satellites through three different remote sensing techniques: satellite altimetry, gravity recovery and climate experiment (GRACE), and interferometric synthetic aperture radar (InSAR).

Using satellite altimetry, satellites beam radar signals to the surface of the ocean and measure the distance between the satellites and the ocean surface over different periods to calculate the rise in sea level.

The next step, Evans explained, is to use GRACE, a system involving two satellites that chase each other around the orbit and communicate through a radar link. As the first satellite reaches an area of higher gravity, it speeds up relative to the other satellite before the second satellite reaches that point and catches up.

Through the gravity measurement the satellites pick up, NASA is able to build and constantly update new gravity models for Earth, which are revealing the loss of ice mass in Antarctica and Greenland. After recording the amount of melted ice from the poles, the final step is to simply subtract the figure from the total rise in sea level to calculate thermal expansion.

When it comes to measuring land mass changes, or to see how ice is physically being lost to the ocean, Evans explained how InSAR, a satellite-imaging tool, comes in handy. The system sends signals between antennas on the Earth and space to capture the precise distance between a specific area and the satellite. When the satellite passes through the same location, it measures the change in distance and reveals the deformation of the Earth’s surface.

Information gathered through satellites using these different techniques are helping build models to predict what changes are likely to occur in the future.

In response to a question over how technology may help the planet reverse the damages caused by climate change, Evans said the best option is for us to use available technology to reduce CO2 emissions.

Available technologies include hybrid cars and energy-efficient appliances.

“Certainly technology is the key to reducing our dependency on fossil fuel and needing to cut down forests,” she said. “That’s where I think technology immediately can have a huge benefit.”

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