Cloud Over Snow

Table describing some of the most widely used RGB products, with a sample image for the cloud over snow RGB

Description: This RGB distinguishes clouds from snow cover, something that’s hard to do in most visible images. Therefore, the product is mostly useful in winter and over mountain ranges.

Coverage: Daytime only

Channels: MODIS 0.06-µm, 1.38-µm, 1.6-µm, 10.8-µm, 2.2-μm

Color scheme:

  • Snow cover is bluish white
  • Clouds are yellow
  • Cloud-free land is green

Advantages:

  • Simplifies interpretation during winter and over mountainous terrain
  • Avoids the ambiguity between snow cover and clouds on visible and true color images

Limitations:

  • Sometimes features do not appear in the expected colors; snow cover can look like cloud and vice versa
  • Old snow cover can look like cloud-free land
  • The product works best for fresh snow that’s less than a few days old

Reference: Satellite-Based Imagery Techniques for Daytime Cloud/Snow Delineation from MODIS Steven D. Miller, Thomas F. Lee, and Robert L. Fennimore Journal of Applied Meteorology
Volume 44, Issue 7 (July 2005) pp. 987–997.

Example:

Terra MODIS True color RGB over the Great Lakes Region (U.S), 03 December 2007

In this true color product, we cannot differentiate between snow cover and cloud. It’s particularly difficult to distinguish lake-effect cloud from snow on the ground.

Terra MODIS Cloud Over Snow RGB over the Great Lakes Region (U.S), 03 December 2007

With bluish-white snow cover and yellow clouds, this RGB minimizes the ambiguity.


Exercise:

MODIS VIS image, 4 April 2007