Climate & the Sun's Radiation
Satellites have been measuring Earth’s energy budget since the NIMBUS missions of the mid-1970s. However, stitching a complete time series together from the collection of sensors that observe different parts of Earth from different angles at different times of day has been challenging. NISTAR (short for National Institute of Standards & Technology Advanced Radiometer) will change all that. The data collected by NISTAR, measured from the vantage point of the L1 orbit, will provide measurements from the whole sunlit face of Earth at once.
“The NISTAR radiometer will measure the reflected and radiated energy from Earth in the important direction back towards the Sun. We have other satellites that measure these quantities at other directions. [But those satellites] have to orbit around Earth, spending only a portion of their orbits in the light,” said Adam Szabo, DSCOVR Project Scientist at NASA's Goddard Space Flight Center. “The advantage of NISTAR is that it observes the whole sunlit face of Earth. Thus we do not have to worry about intercalibrations between different measurements from different platforms.”
How does it work?
What will we learn?
Currently, however, there is a 6.5 w/m2 difference between the estimates derived from direct observations and the estimates that ocean temperature measurements suggest. “Our hope is that using a single well-calibrated instrument to measure the most critical contribution of reflected light [light reflected back towards the sun] will reduce this difference,” said Szabo.
EPIC views of a sunlit Earth
More than just pretty pictures, these images will provide valuable atmospheric data. Combining images from different wavelengths will let scientists measure ozone, aerosol, vegetation cover, dust and volcanic ash, cloud height, and UV radiation estimates at Earth’s surface. “We will be able to follow daily variations,” said Szabo.
The interaction between clouds and aerosols is also a climate issue, since aerosols can change cloud thickness, droplet size, and lifetimes. All these factors affect incoming and outgoing sunlight, which influences the energy balance and therefore, climate.
“Earth does not reflect all wavelengths of light equally. Various gases and particles in our atmosphere are excited by very specific wavelengths of light, absorbing only those photons. Our eye cannot detect these very narrow missing colors,” said Szabo. “For example: one wavelength channel on EPIC corresponds to O3 (ozone) absorption. Differencing the image from this wavelength with a wavelength that’s not sensitive to O3 gives scientists a global map of ozone. Scientists can repeat this same process for reflection of light from the Earth’s surface and atmosphere: green leaf photosynthesis to get a vegetation index, and with SO2 to follow volcanic eruptions.”
DSCOVR started transmitting solar wind data a week after launch, but Szabo says this is for calibration purposes only. “The spacecraft will still be too close to Earth to provide space weather warnings,” he said. The same is true for NISTAR: its data won't be usable until DSCOVR has a full view of Earth, but scientists have already switched the instrument on to begin testing its electronics. The EPIC camera won’t be turned on until the satellite reaches L1 orbit at 115 days. You can expect DSCOVR's first pictures of Earth to appear on the Web sometime in late July or early August.
NOAA's DSCOVR NISTAR Instrument Watches Earth's "Budget." NASA.
NOAA's DSCOVR to Provide "EPIC" Views of Earth. NASA.
Climate and Earth's Energy Budget. NASA Earth Observatory.