From the Field

July 14, 2004

Click for Flash and HTML versions of "Desert Dispatches."

Take a group of strangers, put them in a harsh environment, and give them a challenging mission to accomplish -- scientists who do field research have much more experience with this than reality television producers ever will.

JPL scientists have covered the globe from Antarctica to the Arctic Circle in their quest for knowledge about planet Earth and worlds beyond our own. Recently, JPL's Mark Helmlinger and four British students from Oxford University headed off into the Nevada desert to rendezvous with NASA's Earth-orbiting Terra satellite. Helmlinger will be filing regular field reports along the way, reporting on both the professional and personal challenges they'll confront.

The purpose of their expedition is to help ensure that the measurements made by one of Terra's instruments, the Multi-angle Imaging Spectro-Radiometer, are as accurate as possible. The spectroradiometer measures sunlight reflected off Earth's surface and from particles in the atmosphere, such as haze layers, dust, and clouds. Scientists use these measurements in a variety of different ways, but one of the most important is to study climate.

Calibrating an instrument like the Multi-angle Imaging SpectroRadiometer would be fairly simple if it were sitting in a laboratory. But since it is orbiting 700 kilometers (435 miles) above Earth's surface, the process is a bit more complicated.

As part of the instrument calibration team, Helmlinger and his four summer helpers will make precise measurements on the ground of sunlight coming down and reflecting back up, while at the same time, directly above them, the Multi-angle Imaging SpectroRadiometer makes its own measurements from space. Also at the same time, NASA's ER-2 aircraft will make similar observations of the identical target from its vantage point in the stratosphere with an airborne version of the spectroradiometer. Once all the data are collected and compared, they'll be used to calibrate the spaceborne instrument.

The Challenge

For their efforts to succeed, the calibration team will need several of what they call "golden days," those in which everything falls into place. "We have to have clear weather over the target, no haze and no clouds," says Helmlinger. "It also needs to be calm at the airfield, because the airplane can't take off or land in a cross-wind. We need to have airspace clearance, which can be an issue because of where our targets are located. All the instruments, both airborne and on the ground, must be working as well. That's a lot that needs to go right."

The calibration exercises are planned for two different locations, Railroad Valley and Black Rock Desert. Both are large, dry lakebeds in Nevada about 480 kilometers (300 miles) apart. "They make big, bright calibration targets," says Helmlinger. Both sites are remote, and the local environment can be challenging. Helmlinger and his student assistants, whom he likes to call "Hellwinger's Irregulars," will be making the trip in a recreational vehicle crammed with a mountain of equipment. It will also serve as their home for the six weeks or so that they'll be spending in the desert. "Sometimes the journey itself is an adventure," says Helmlinger.

Helmlinger and the Irregulars have a limited number of opportunities to get the data they need. If they miss one, they'll have to wait five to seven days for the satellite to come back to the same spot and try again. "That's why two dry lakebed, or playa, targets on two different orbits have been chosen," explains Helmlinger, "to increase the chances of success." If all goes well, they may finish everything up in a few weeks; if not, they could be out in the desert for much longer.

The reward for all this effort is a better understanding of Earth's surface, atmosphere and climate. The "ground truth" data collected by the field experiments help researchers make the most of the Multi-angle Imaging SpectroRadiometer. It will also be used to help calibrate several other Earth-observing instruments, including JPL's Atmospheric Infrared Sounder flying on NASA's Aqua satellite.

The calibration team's first attempt for a "golden day" was June 22, meaning Helmlinger and the Irregulars were in place in Railroad Valley with everything set up and ready to go by dawn. It's a long way from Pasadena and Oxford to the Nevada desert and from space to the desert floor. A lot can happen in between.

Stay tuned.

Media contact: Alan Buis (818) 354-0474
Written by: Rosemary Sullivant

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