Bering Sea Ice Extent and Temperature
The following three images of the Bering Sea from 24 April 2001 illustrate the usefulness of MODIS data and sea ice products for monitoring sea ice conditions.
Figure 1 was derived from Level-1B calibrated visible-band radiances (Bands 1, 4, and 3), available from the MODIS Characterization Support Team (MCST): Level 1B Product Information and Status Web site. Although sea ice is clearly seen in the middle portion of the image, sea ice typically is not easily distinguished from cloud cover. MODIS sea ice products alleviate this confusion with an algorithm that identifies sea ice on the basis of reflectance characteristics in the visible and near infrared wavelengths, and also estimates Ice Surface Temperature (IST).
Figure 1. Visible Image of Bering Sea, 24 April 2001
Figure 2 is a sea ice extent image derived from the MODIS/Terra Sea Ice Extent L2 Swath 1km, Version 4 data set, available from NSIDC. Sea ice extent was determined from reflectance criteria, based on a Normalized Difference Snow Index (NDSI) algorithm adapted for sea ice. The NDSI detects high reflectance of sea ice at visible wavelengths, and low reflectance at infrared wavelengths. Sea ice is clearly distinguished from cloud cover in this image. Source file used to create this image: MOD29.A2001114.2305.003.2001239004123.hdf.
Figure 2. Sea Ice Extent in the Bering Sea, 24 April 2001
Figure 3 shows IST, derived from the MODIS/Terra Sea Ice Extent L2 Swath 1km, Version 4 data set. Sea ice is identified as any pixel with a surface temperature less than or equal to the freezing point of sea water (271.5 K). Source file used to create this image: MOD29.A2001114.2305.003.2001239004123.hdf.
Figure 3. Sea Ice Surface Temperature in the Bering Sea,