Using VIIRS imagery for snow/ice vs cloud discrimination over Alaska, the Arctic Ocean, and the Bering Sea
Suomi NPP VIIRS 0.64 µm visible channel + 1.61 µm near-IR channel images
AWIPS images of 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel and 1.61 µm near-IR channel images (above) demonstrated the value of using the near-IR imagery to help discriminate between snow/ice (which appears darker on the near-IR image) and supercooled water droplet cloud features (which appear as brighter shades of white on the near-IR image) over northern Alaska and the Arctic Ocean on 23 April 2012. Numerous large leads (or cracks) in the Arctic Ocean sea ice are apparent on the visible channel image.
Many of the cloud features over the Arctic Ocean were thin and at a low altitude, so there was not a great deal of thermal contrast seen on the corresponding 11.45 µm IR image (below).
Suomi NPP VIIRS 1.61 µm near-IR channel + 11.45 µm IR channel images
Three days later (on 26 April 2012), a similar comparison of a Suomi NPP VIIRS 0.64 µm visible channel image with the corresponding 1.61 µm near-IR image (below) showed that much of the ice in the Bering Sea was beginning to break up (although a significant amount of land-fast ice remained along the western coastline of Alaska). The near-IR image also helped to highlight other interesting features along the far left edge of the satellite scene: aircraft contrails over Nunivak Island, and a thin trail of wave clouds extending downwind of St. Matthew Island.
Suomi NPP VIIRS 0.64 µm visible channel + 1.61 µm near-IR channel images
GOES-15 0.63 µm visible channel images (click image to play animation)
An animation of 1-km resolution GOES-15 0.63 µm visible channel images (above; click image to play animation) showed the motion of the southern extent of the ice in the Bering Sea on 26 April. On the previous day, the sea ice had retreated northward from Saint George Island (station identifier PAPB), after a record-setting 79 consecutive days with sea ice. Farther to the north, the sea ice would remain at Saint Paul Island (station identifier PASN) into early May, also setting a new record for sea ice duration at that island.
A significant amount of sea ice motion could be seen on the GOES-15 visible images, due to strong surface winds over the southern Bering Sea on that day. In addition, the visible images revealed some interesting wave clouds immediately downwind of the higher terrain of some of the Aleutian Islands.
A better view of the southern extent of ice in the Bering Sea was available using a 1-km resolution NOAA-19 AVHRR false-color Red/Green/Blue (RGB) image (below). As with the GOES-15 images above, Saint Paul Island and Saint George Island are located near the center of the image.
NOAA-19 AVHRR false-color Red/Green/Blue (RGB) image