SMMR and SSM/I-SSMIS and AMSR2

The NSIDC DAAC SMMR, SSM/I, SSMIS, and AMSR2 data collection includes near-global passive microwave data from 1978 to present. The data relate to brightness temperature, sea ice concentration, sea ice age, snow-covered area, snow cover, snow water equivalent, snow melt, sea ice motion, and more.

Historically, these data products have been derived from the Scanning Multichannel Microwave Radiometer (SMMR) instrument on the Nimbus-7 satellite and the Special Sensor Microwave/Imager (SSM/I) and Special Sensor Microwave Imager/Sounder (SSMIS) and instruments on the Defense Meteorological Satellite Program's (DMSP) -F8, -F11, -F13, -F15, -F16, -F17, and -F18 satellites. The use of these instruments began the modern sea ice satellite record, following the Electrically Scanning Microwave Radiometer (ESMR), a single-frequency passive microwave instrument that operated from 1972 to 1977, and using multiple microwave frequencies to observe sea ice concentration and extent. 

With the planned retirement of SSMIS in 2026, data from the JAXA Advanced Microwave Scanning Radiometer 2 (AMSR2) instrument is now being utilized to maintain data coverage continuity with coverage beginning in 2023. While AMSR2 has higher native spatial resolution (smaller sensor footprint) than SSMIS, for this data collection the AMSR2 data have been resampled to match the SSMIS resolution. This allows the AMSR2 data to provide a seamless transition and enables continuation of a consistent data record.

In combination, the data from SMMR, SSM/I, SSMIS, and AMSR2 provides data users with a consistent long-term climatology of polar sea ice, enabling them to track long-term trends of sea ice concentration and extent. This has allowed scientists to better understand cryospheric changes over time since the satellite record began. 

The NSIDC DAAC also hosts complementary data from the Advanced Microwave Scanning Radiometer Unified (AMSR-U) data collection which includes passive microwave data products on sea ice, snow, soil moisture, vegetation water content, and brightness temperature. Data are derived from the Advanced Microwave Scanning Radiometer for the NASA Earth Observing System (AMSR-E) and JAXA’s AMSR2. These AMSR-U products make use of the instrument’s higher native resolution capabilities and thus are not directly compatible with the long-term SMMR-SSM/I-SSMIS-AMSR2 record. As such, the two product suites should not be used inter-changably. 

The NSIDC DAAC distributes the SMMR-SSM/I-SSMIS-AMSR2 product suite as Level-3 products, which range in temporal coverage from October 1978 to present. SMMR data are available from October 1978 through August 1987, when the Nimbus-7 SMMR scanner was shut off. SSM/I and SSMIS data are available from 1987 to present (with a mission end date expected in September 2026), providing more than three decades of continuous measurements. Similarly processed AMSR2 data are currently available from 2023 to present and will extend this record forward, maintaining continuity in the passive microwave time series.These data products are offered in two projections: EASE-Grid and Polar Stereographic.