Nighttime Visible

Table describing some of the most widely used RGB products, with a sample image for the nighttime visible RGB

Description: The Defense Meteorological Satellite Program (DMSP) has long had a nighttime visible observing capability with its Operational Linescan System (OLS) sensor. OLS has made it possible to see nighttime features such as fires, lights, and the aurora. Low clouds and snow cover can also be detected when there’s sufficient moonlight. These capabilities will be greatly improved with the VIIRS imager.

Coverage: Nighttime only

Channels: Since the OLS has only two channels (visible and infrared), the RGB is created using these channels at night. The channels and color scheme are the same as the GOES daytime product. Interpretation is also the same if there is moonlight: low clouds are yellow, high clouds are blue.

Color scheme: With sufficient moonlight:

  • Low clouds and snow cover are yellow
  • High clouds are blue
  • Thick, high clouds are white
  • Cities and fires are yellow

Advantages: Unlike nighttime longwave IR images, this product makes it possible to view features, such as low clouds and snow cover, at night and also shows city lights and fires.

Limitations:

  • Features, such as low clouds and snow cover, are only illuminated when there is sufficient moonlight
  • The quality of the current DMSP OLS sensor is poor (but significant improvements are expected with the VIIRS imager)

Link: NRL NexSat website, http://www.nrlmry.navy.mil/NEXSAT.html

Reference: Lee, T.E., S.D. Miller, F.J. Turk, C. Schueler, R. Julian, S. Deyo, P. Dills, and S. Wang, 2006: The NPOESS VIIRS Day/Night Visible Sensor. Bull. Amer. Meteor. Soc., 87, 191-199.

Example:

DMSP/OLS 11.0 um IR window 19 Sept 2002 0250 UTC showing Tropical Storm Iselle

As this image of Tropical Storm Iselle shows, it’s hard to see low clouds at night with longwave infrared imagery. High clouds are in red. But where is the low-level center, a feature that’s critical to identify when locating tropical storms?

DMSP/OLS Nighttime VIS RGB  19 Sept 02 0250 UTC 19 Sept 2002 0250 UTC showing Tropical Storm Iselle

In the absence of a shortwave infrared channel, the nighttime visible RGB can detect low-cloud features that are illuminated by moonlight. We can now see that the center is far displaced from the one inferred from the infrared image.


Exercise: