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.

The launch of the Suomi NPP satellite in October 2011 marked the beginning of significantly improved nighttime visible imaging with the VIIRS Day Night Band, the successor to the OLS nighttime visible channel. The Day Night Band’s higher spatial resolution and greater sensitivity are providing opportunities for new products and applications. Future JPSS polar orbiters will have this same imaging capability.

Coverage: Nighttime only

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

  • Polar-orbiting satellites:
    • DMSP OLS:
      Nighttime Vis (red and green); longwave IR (blue)
    • VIIRS:
      Day Night Band Vis (red and green); I5 (11.45 µm) or M15 (10.763 µm) IR (blue)
  • Geostationary satellites: A nighttime Vis channel is currently not available on GEO satellites

Color scheme: With sufficient moonlight

  • Low (warm) clouds and snow cover are yellow
  • High (cold) clouds are blue
  • Thick, high (cold) 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; it also shows city lights and fires, and occasionally shows lightning from thunderstorms with high lightning flash rates.

Limitations:

  • Features, such as low clouds and snow cover, are only illuminated when there is sufficient moonlight
  • The quality of the legacy DMSP OLS sensor is poor, but significant improvements have come online with the VIIRS imager on board Suomi NPP; VIIRS is also planned for future NOAA JPSS polar orbiters

Data links:

More information:

References:

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.

Hillger, D. H., T. Kopp, T. Lee, D. Lindsey, C. Seaman, S. Miller, J. Solbrig, S. Kidder, S. Bachmeier, T. Jasmin, and T. Rink, in press: First-light imagery from Suomi NPP VIIRS. Bull. Amer. Meteor. Soc.

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 alone. 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 alone.

Exercise:

Match the three RGB scenes with the lunar conditions under which they were imaged. Review the lunar conditions, then choose the condition in each selection box that matches the RGB image. Remember that in the nighttime Vis RGB, low clouds and snow cover are yellow; high clouds are blue; thick, high clouds are white; and cities and fires are yellow.

Lunar conditions: The moon in the new moon phase The moon in the First Quarter phase The moon in the Waxing Gibbous phase

a) Vis nighttime RGB showing features illuminated with a first-quarter moon
The correct answer is New Moon.
b) Vis nighttime RGB showing features illuminated with a three-quarters moon
The correct answer is Waxing Gibbous.
c) Vis nighttime RGB showing features illuminated with a half moon
The correct answer is First Quarter.

RGB (a) illustrates no-moon (new moon) conditions. There is insufficient illumination to see the low clouds in bright yellow; only high clouds can be detected by the infrared channel (seen in blue). RGB (b) illustrates gibbous moon conditions (greater than half but not a full moon); there is robust enough illumination to view low clouds. RGB (c) illustrates first-quarter moon conditions. There is barely enough illumination to see low clouds; the pale yellow on the left side of the image gives just a hint of their presence.