Celebrating 35 years of sea ice satellite data

Image of Arctic sea ice derived from SMMR data This image is derived from the Scanning Multichannel Microwave Radiometer (SMMR), and shows Arctic Ocean sea ice extent in August 1985. Purple and red show greater ice coverage, while greens and blues indicate less ice. The black circle over the pole indicates no data—SMMR took observations very close to, but not directly over, the pole. Image credit: NSIDC

Polar scientists are celebrating an anniversary of sorts. Thirty-five years ago, sea ice research took a great leap forward. On October 26, 1978, the Scanning Multichannel Microwave Radiometer (SMMR) beamed its first data records back down to Earth. The instrument, pronounced simmer, was capable of mapping global sea ice concentration and extent, giving scientists a more comprehensive look at Arctic and Antarctic sea ice. Thanks to SMMR and its successor remote sensing instruments, scientists now have a long and detailed record of sea ice that helps them understand how sea ice works, and how it is changing.

Fine-tuning the view

Researchers had employed remote sensing to monitor sea ice since the mid 1960s. Microwave radiometers can see through clouds, providing an uninterrupted view of ocean, land, and ice below the overcast conditions that often prevail at the poles. So scientists hoped that the instruments would be able to accurately distinguish between ice and water. But they soon discovered that SMMR, launched aboard the Nimbus-7 satellite, could distinguish between first-year ice and multiyear ice. This distinction is particularly important in the Arctic, which maintains a portion of its sea ice pack from year to year, unlike Antarctica.

In contrast to previous instruments, SMMR was multichannel, which allowed it to better resolve ambiguities in the data. For instance, features that might look similar in one channel may look different in another channel. These distinctions allowed researchers to fine tune their knowledge of the sea ice pack. They could also begin pairing this time series with other observations to see how other phenomena affected both first-year and multiyear ice.

Data image showing Arctic sea ice extent in August 2013 Captured 28 years after the image above, this image shows Arctic sea ice extent in August 2013. Data is from the Sea Ice Index, a time series that relies on a variety of sensors, including the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) instrument. Image credit: NSIDC

Tracking the time series

Satellite observations have given scientists a direct and consistent source of data year-round from even the most inhospitable polar regions. The Nimbus-7 SMMR operated for only nine years, but it set the pattern for a series of multichannel satellite instruments that continue to capture a record of conditions from decade to decade. Scientists can now monitor concentration and extent, observe when ice forms and melts each year, discern how young or old ice is, and see where winds and ocean currents push it. While there may be no cake or ice cream to celebrate, SMMR’s birthday reminds us how much knowledge we now have about Earth’s polar climates.

Related Icelights posts
Arctic sea ice before satellites

SMMR data at NSIDC
Sea Ice Index at NSIDC

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