Sea ice properties in the Bohai Sea measured by MODIS-Aqua: 1. Satellite algorithm development

Based on the fact that sea ice reflectance drops significantly in the shortwave infrared (SWIR) wavelengths, black pixel assumption is assessed for three SWIR bands for the Moderate Resolution Imaging Spectroradiometer (MODIS)–at 1240, 1640, and 2130 nm—over the sea ice in the Bohai Sea in order to carry out atmospheric correction for deriving sea ice reflectance spectra. For the SWIR 1240 nm band, there is usually a small (but non-negligible) reflectance contribution over sea ice. Although there is a slight sea ice reflectance contribution at the MODIS 1640 nm band over sporadic land-fast or hummock ice, the black pixel assumption is generally valid with the MODIS bands 1640 and 2130 nm in the Bohai Sea. Thus, the SWIR-based atmospheric correction algorithm using MODIS bands at 1640 and 2130 nm can be conducted to derive sea ice optical properties in the region. Based on spectral features of the sea ice reflectance, a regionally optimized ice-detection algorithm is proposed. This regional algorithm shows considerable improvements in detecting sea ice over the Bohai Sea region, compared with a previous MODIS global sea ice detection algorithm. The sea ice coverage as identified in the new algorithm matches very well with the sea ice coverage from both the MODIS true color image and the imagery from the Interactive Multisensor Snow and Ice Mapping System (IMS).

► Black pixel evaluation for the MODIS three SWIR bands over sea ice in the Bohai Sea.
► Remote sensing of the sea ice spectral reflectance in the Bohai Sea using MODIS data.
► Development of the regional sea ice detection algorithm in the Bohai Sea.