A huge plastic balloon floated high in the skies over
The onboard instrument was an experimental spectrometer designed to collect and measure visible and infrared wavelengths of light ranging from 350 to 2,300 nanometers. Simpler, lighter and less expensive than conventional counterparts, the spectrometer was tested to determine how accurately it can measure the relative energy of light emitted by the Sun and subsequently reflected or scattered by the Earth and Moon.
The flight was launched from the Columbia Scientific Balloon Facility in
Researchers at NIST's
For nearly a decade, NIST Boulder researchers have been using carbon nanotubes, the darkest material on Earth, to make coatings for laser power detectors.* Nanotubes efficiently absorb nearly all light across a broad span of wavelengths, a useful feature for reducing internal scatter in the balloon imager. NIST also has facilities for, and expertise in, pairing nanotubes with micromachined silicon chips.**
For the balloon spectrometer, known as HySICS (HyperSpectral Imager for Climate Science), NIST made two types of custom chips that were stacked together in a sandwich. In the middle were aperture chips, coated with aluminum to block light transmission through the silicon, with small rectangular openings etched into the chip to allow light into the instrument.
A precision spectrometer must ensure that it only gathers light coming directly from its target, so the two outer layers of the sandwich were masking chips--larger openings etched at an angle and coated with tall, thin carbon nanotubes. These VANTAs ("vertically aligned nanotube arrays") act as superefficient sponges to absorb scattered or stray light across the entire spectral range of the Sun.
While the balloon was in flight, the spectrometer scanned the slit across the Sun to measure solar irradiance. Spectral filters were calibrated by scanning the slit across the Moon and making measurements with and without filters in the beam path. The spectrometer also imaged light emitted from the Earth using the Sun as a reference light source.
NIST's experimental slit was made as part of the
*See the 2010 NIST Tech Beat article, "Extreme Darkness: Carbon Nanotube Forest Covers NIST's
**See the 2013 NIST Tech Beat article, "NIST's 'Nanotubes on a Chip' May Simplify Optical Power Measurements," at www.nist.gov/public_affairs/tech-beat/tb20130124.cfm#radiometer.
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