Suomi-NPP, VIIRS, Day-Night Band (DNB): Moon Phases
By Jorel Torres and Erin Dagg
The Suomi-National Polar-Orbiting Partnership (Suomi-NPP) satellite is a prototype for the next generation of Joint Polar-Orbiting Satellite System (JPSS) series of satellites with JPSS-1 scheduled to launch in early 2017. One instrument onboard the Suomi-NPP is the Visible Infrared Imaging Radiometer Suite (VIIRS) http://www.jpss.noaa.gov/viirs.html. It has 22 spectral bands that have a variety of applications, many of which will improve weather, flooding, and storm forecasting capabilities and allow for monitoring of ocean nutrient, aerosols, vegetation health, cloud microphysics and cloud top properties, cloud cover, snow, and fire detection.
One unique band found on VIIRS is the 0.7 µm Day-Night Band (DNB). A concise description of how VIIRS views through the DNB can be found here “Earth at Night – the Black Marble” (http://www.jpss.noaa.gov/pdf/earth_at_night_2012.pdf). Note that the Black Marble image was processed to remove clouds, though for forecasting applications it is necessary to view clouds and their patterns. The illumination of clouds at night is a function of the moon phase and the angle of the moon during subsequent Suomi-NPP overpasses.
Figure 1: DNB imagery identifying clouds, city lights, aurora, and gas flares at 1003 UTC 19 January, 2016.
The animation link below shows VIIRS DNB imagery throughout the latest lunar cycle, from 9 January – 8 February 2016 (new moon to new moon). The approximate moon phase at the time of each image is displayed in the lower-right corner for reference.
Prior to the First Quarter moon phase (between 9-17 January), you will notice that the imagery appears washed out. There is little distinction between individual cities while cloud patterns are hard to discern. Approaching the full moon phase, the imagery appears brighter overall, with noticeable texture differences between cities and clouds. The large synoptic-scale systems moving into and eventually through the contiguous United States (CONUS) appear to have sharper edges and increased contrast with the background (i.e. 23 January, 2016, cyclone depicted along the California coastline).
Another feature that stands out is the elongated bright stream of light across southern Canada. This is the aurora, which is produced when charged particles emitted from the sun, during a solar flare, are able to penetrate the Earth’s magnetic field, colliding and interacting with Earth’s atoms and air molecules.
Throughout the time-lapse there are variable light signatures seen in western North Dakota and in the Gulf of Mexico. These emitted light sources are a product of gas flaring by oil and gas industries and offshore rigs, respectively. The aurora, clouds, gas flares, city lights are identified in Figure 1, above, while the offshore rigs are specified below in Figure 2.
Figure 2: DNB imagery at 1014 UTC 29 January, 2016, showing offshore gas flares in the Gulf of Mexico.
Furthermore, there is an increased saturation of the city lights before the First Quarter and after the Last Quarter moon phase due to the decreased amount of lunar reflection. It is important to note that the gas flares, auroras, lightning and city lights provide their own light source, and often appear brighter in imagery during this time period.
Lightning is also seen by satellite displayed as short streaks of light (Figure 3). The satellite temporal resolution (each scan) is every 1.8 seconds and typical flash events are near ~10 milliseconds. Therefore, the offset timescales between the flash duration (with an influence of light diffusion, i.e., the optical scatter within the cloud) and the satellite temporal resolution produce the streaks of light (Miller et al 2013).
Figure 3: DNB imagery at 1117 UTC 15 January, 2016 showing horizontal streaks of lightning in the Gulf of Mexico.