![]() ![]() Three stages of gain allow the DNB to span the dynamic range of radiances encountered during the daytime, twilight, and nighttime with measured radiometric uncertainties of 3.5%, 7.8%, and 11.0%, respectively. The DNB has a measured spectral response of 505–890 nm (full width at half maximum, with nominal band-center wavelength of 705 nm) and features several advances to the heritage OLS, including full calibration and improved spatial (0.74 km vs. Included on VIIRS is a next-generation low-light sensor, the Day/Night Band (DNB). Suomi NPP carries the Visible/Infrared Imager/Radiometer Suite (VIIRS), an optical spectrum (22 bands spanning ∼0.4–13 μm) sensor providing imagery at high spatial resolution (0.375–1.6 km, band dependent) across a 3,000-km-wide swath. Suomi, considered widely as the “father of satellite meteorology,” NPP provides risk reduction for the Joint Polar Satellite System (JPSS) series of National Oceanic and Atmospheric Administration (NOAA) operational meteorological satellites and continuity to the National Aeronautics and Space Administration (NASA) Earth Observing System (EOS) Terra and Aqua climate research satellites ( 9). The Suomi National Polar-orbiting Partnership (NPP) satellite ( ) was launched on October 28, 2011, and placed into an 834-km altitude sun-synchronous orbit with local equatorial crossing times of ∼1:30 PM and 1:30 AM. The OLS was designed to amplify visible light and detect clouds under twilight and moonlight (e.g., signals down to ∼10 −8 W⋅cm −2⋅sr −1⋅μm −1) illumination conditions ( 4) but soon revealed many additional capabilities based on signals from both natural and anthropogenic sources ( 5 – 8). Low-light imaging capabilities have existed on the Operational Linescan System (OLS) on the Defense Meteorological Satellite Program (DMSP) constellation since the late 1960s. At visible and near infrared wavelengths (e.g., 0.4–1.1 μm), the combined illumination from these sources yields down-welling radiances at Earth’s surface in the range ∼10 −11 to 10 −9 W⋅cm −2⋅sr −1⋅μm −1 ( 3), or approximately 1 billion times fainter than sunlight. The other sources produce a complex global distribution of nighttime diffuse sky brightness that varies considerably across space, time, and spectrum. Auroras, although a relatively strong source, are ephemeral and confined to high latitudes. The primary sources are the polar aurora, airglow, integrated starlight (including the Milky Way), and zodiacal light ( 1 – 3). ![]() The sky on a dark, moonless night is, in fact, immersed within a sea of visible-spectrum light that the dark-adjusted human eye can only begin to discern. ![]() The ability to leverage diffuse illumination sources for nocturnal environmental sensing applications extends the advantages of visible-light information to moonless nights. Examples collected during new moon reveal not only meteorological and surface features, but also the direct emission of airglow structures in the mesosphere, including expansive regions of diffuse glow and wave patterns forced by tropospheric convection. Here we show that the Day/Night Band (DNB) low-light visible sensor on the recently launched Suomi National Polar-orbiting Partnership (NPP) satellite has the unique ability to image cloud and surface features by way of reflected airglow, starlight, and zodiacal light illumination. ![]() A few sensors can take advantage of moonlight, but the inconsistent availability of the lunar source limits measurement utility. Most environmental satellite radiometers use solar reflectance information when it is available during the day but must resort at night to emission signals from infrared bands, which offer poor sensitivity to low-level clouds and surface features. ![]()
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