Team Pulls All-Nighters in Hawaii to Calibrate Satellites

A reflective bunch: The team stares into the mirror on the lidar system they use to prepare for the trips to Hawaii. (Photo: Elisa Haber/The Aerospace Corporation)

From a cramped portable trailer near the beach in Hawaii, a team of Aerospace engineers spent three weeks collecting data using sophisticated laser sensors. The data they collected was then used to help calibrate equipment on board the latest Defense Meterological Satellite Program (DMSP) satellite (F-19), launched in April.

The DMSP satellites provide important weather data in support of U.S. armed forces, and in order to collect accurate data, the satellites must be calibrated properly. Aerospace has unique lidar capabilities that make it perfect to aid in this task.

“What we’re trying to do is get the best data from the ground possible to compare to data that’s being collected from sensors on weather satellites and lidar is an integral part of that,” said Andrew Mollner, a senior member of the technical staff. “It has several advantages over other techniques that you could use.”

Lidar, which is similar to radar, involves sending a laser beam into the atmosphere where it bounces off molecules. By analyzing the light that comes back, the scientists can determine atmospheric pressure, temperature, and water vapor.

This data can be compared to the data collected by the satellite, and then the satellite can be calibrated as necessary.

The more common way to calibrate sensors is by using balloons carrying radiosondes, or weather sensors. One of the problems with this is that is takes a long time for the balloon to ascend, during which time it may drift. Also, the balloon pops at a certain height, whereas lidar can be used to collect data at higher altitudes.

The Aerospace team actually uses both lidar and radiosondes to get the best data set.

“You have two completely separate ways of measuring the same thing, and if they agree that gives you a lot of confidence,” Mollner said.

In order to collect the data for DMSP, the team uses a portable trailer which is parked on a Navy base on Kauai, Hawaii. It’s a good spot because it’s near a warm ocean with a lot of water vapor. It’s also at sea level so they can take data in the lower portions of the atmosphere, which is important for weather satellites.

On this particular trip, Mollner was joined by Paul Belden, Petras Karuza, Stephen LaLumondiere, and Michael Williams.

The trailer itself is rather small, and various members of the team spent a lot of time in there during the three-week period. The DMSP satellite would pass by every 12 hours and the team would collect lidar data for an hour before and an hour after. They also launched a balloon each time.

They obtained 18 data collects for the recently launched DMSP satellite (F-19). They also collected data for the previous DMSP satellite (F-18) when it was coincident with F-19 (eight times) to help facilitate cross-calibration.

An artist’s rendition of a DMSP satellite. (Image courtesy U.S. Air Force)

An artist’s rendition of a DMSP satellite. (Image courtesy U.S. Air Force)

Aerospace is also collecting data for a new NASA/NOAA satellite, the Suomi National Polar-orbiting Partnership (NPP), which launched in 2011. Suomi NPP has new sensors that haven’t flown before, and the data-processing algorithms are still being worked on. Aerospace has been providing data to NOAA for three years to help with the algorithm development.

During this recent trip, the team collected data for Suomi NPP 24 times. Suomi NPP passed by every 12 hours, but it is offset from the DMSP satellite by 6 hours. Just to make things more hectic, the team also collected some data for a European satellite as well, which passed by at a different time from either DMSP or Suomi NPP.

“It was a very busy trip,” Mollner said.

Fortunately, the trailer contained a few bunks in case anyone got too worn out.

Despite the crazy schedule, the team was able to collect some good data for the satellites. This data is important to making sure the satellites can perform as desired.

“Your weather forecasting is only as good as the input data to the models, and most of that input data is coming from these weather satellites,” Mollner said.

Mollner and his team are doing their part to make sure that input data is as good as it can be.

—Laura Johnson