Welcome to the Earthdata Forum! Here, the scientific user community and subject matter experts from NASA Distributed Active Archive Centers (DAACs), and other contributors, discuss research needs, data, and data applications.
MODIS is an optical sensor, which has inherent limitations in observing sea ice and snow. Unlike a passive-microwave sensor, which can detect microwave energy through clouds, MODIS cannot observe the surface when cloud cover is present. MODIS products, therefore, have cloud masks built into the data arrays to prevent clouds from being interpreted as ice and snow. These cloud masks are continually improved as limitations are documented. Finally, the visible bands of MODIS are only used during the day, when reflectance is the dominant mechanism for detecting ice and snow. The thermal bands are used during both day and night to measure sea ice surface temperature by emittance.