Satellite Liaison Blog

Following its Provisional Maturity review on 30 March 2023, the NOAA-21 VIIRS Imagery EDR was declared Provisionally Mature effective 0010 UTC the same day. VIIRS SDR was also declared Provisionally mature. During the review, many imagery examples were shown for all 22 NOAA-21 VIIRS bands and resulting RGBs, including comparisons with NOAA-20 and S-NPP, across the globe spanning all times of day, seasons, and a variety of surface and atmospheric situations. The review showed that VIIRS Imagery looks great, compares well with that from NOAA-20 and S-NPP, and is ready to be used operationally. This post will highlight recent VIIRS Imagery examples, including comparisons with that from NOAA-20 and S-NPP.

First, global composites show that NOAA-21 VIIRS imagery is available and of consistent quality across the globe. Shown in Fig 1 are four select global composites, including for bands M5 (Red Visible), M7 (Veggie NIR), M9 (Cirrus SWIF), and M15 (clean window LWIR).

Figure 1: 20 March 2023 NOAA-21 VIIRS EDR M5, M7, M9, M15 Global Composites.

Imagery for all 22 bands over Alaska during the day (Fig 2), and 8 bands at night (Fig 3), reveal no issues for typical scenes over Alaska, where VIIRS imagery is used extensively, and considered a NOAA “Key Performance Parameter”.

Tropical Cyclone Herman, northwest of Australia, provided a uniform, cold, highly reflective scene in which to compare all of the NOAA-21 VIIRS bands (Fig 4).

The desert surface of Africa provided a uniform and hot scene to evaluate the Imagery (Fig 5).

Users often view VIIRS imagery in the form of multispectral imagery products, specifically RGBs. Further, RGBs provide an opportunity to evaluate multiple bands at once. Therefore, numerous, widely used RGBs have been evaluated and compared across the three VIIRS. The following examples are short sequences of the three VIIRS in order of granule time over the respective locations: NOAA-20 (~25-minutes) NOAA-21 (~25 minutes) S-NPP. To start, a VIIRS Dust RGB that combines bands M14, M15, and M16 is shown over Africa (Fig 6).

Figure 6: 21 March 2023 NOAA-20, NOAA-21, and S-NPP VIIRS Color Vision Deficiency Dust RGB over Africa. Dust is bright green and yellow.

Another large blowing dust event that recently took place, this time over northeast Asia, is shown in the VIIRS True Color RGB Imagery, which combines bands M5, M4, and M3 (Fig 7).

Figure 7: 22 March 2023 NOAA-20, NOAA-21, and S-NPP VIIRS True Color RGB over East Asia. Dust is varying shades of tan and brown

The VIIRS Snowmelt RGB allows one to assess a snowpack for blowability, areas of melting snow, and for the evaluation of ice cover vs snow cover (Fig 8). This RGB combines VIIRS bands M10, M8, and M5.

Figure 8: 23 March 2023 NOAA-20, NOAA-21, and S-NPP VIIRS Snowmelt RGB over the Midwest US. Fresh snow is light blue, aged/crusty snow and ice is dark blue.

The sequence of three VIIRS provided a very high resolution (375-m) view of convective initiation on March 23 over southern Oklahoma, by combining bands I5, I1, and I3 into the Day Cloud Phase Distinction RGB (Fig 9).

Figure 9: 23 March 2023 NOAA-20, NOAA-21, and S-NPP VIIRS Day Cloud Phase Distinction RGB over southern Oklahoma. Initiating convection is clouds transitioning from shades of blue and green to yellow, orange, and red.

A large and quickly expanding wildfire over Australia provided an opportunity to evaluate a combination of SWIR and MWIR bands in the Fire Temperature RGB (M12, M11, M10) in Figure 10.

Figure 10: 24 March 2023 NOAA-20, NOAA-21, and S-NPP VIIRS Fire Temperature RGB over Australia. Increasing intensity in fire represented by reds to yellows to whites.

Finally, low clouds across southern (Fig 11) and northern (Fig 12) Alaska provides for a comparison of LWIR bands at night in the Nighttime Microphysics RGB (M13, M15, M16).

Figure 11: 25 March 2023 NOAA-20, NOAA-21, and S-NPP VIIRS Nighttime Microphysics RGB over southern Alaska. Low clouds are bright green.

Figure 12: 25 March 2023 NOAA-20, NOAA-21, and S-NPP VIIRS Nighttime Microphysics RGB over southern Alaska. Low clouds are bright green.

Of course, the unique and widely used VIIRS Day Night Band (DNB) Near Constant Contrast (NCC) product has been evaluated extensively, and was improved considerably with calibration updates that went into place early on March 30, resulting in appearance on par with that from NOAA-20 and S-NPP. The NCC provides visible-like imagery of clouds at night, in addition to other features like aurora, lightning flashes, and light from a variety of anthropogenic sources (cities, boats, gas glares, etc). A three VIIRS image sequence of NCC from overnight across southern Alaska and the Gulf of Alaska shows the similarity in NCC across all three VIIRS (Fig 13). The scene includes city lights, clouds, and the aurora borialis.

Figure 13: 25 March 2023 NOAA-20, NOAA-21, and S-NPP VIIRS DNB/NCC product over southern Alaska.

A recent overnight NOAA-21 VIIRS NCC global composite is shown in Fig 14, capturing many storm systems, the lights of cities, the the aurora borialis and aurora australis.

NOAA-21 VIIRS Imagery will be made available to NWS in AWIPS, and publicly via the CIRA Polar Slider and other webpages, over the coming months. NOAA-21 VIIRS Imagery will continue to be monitored and evaluated, with the Fully Validated maturity review currently expected to occur in July.

Bill Line, NOAA/NESDIS/STAR