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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS2019

A Relationship Between Blue and Near‐IR Global Spectral Reflectance and the Response of Global Average Reflectance to Change in Cloud Cover Observed From EPIC

We performed a detailed analysis of Earth Polychromatic Imaging Camera (EPIC) spectral data. We found that the vector composed of blue and near-infrared (NIR) reflectance follows a counterclockwise closed-loop trajectory from 0 to 24 UTC as Earth rotates. This non-linear relationship was not observed by any other satellites due to limited spatial or temporal coverage of either low earth orbit (LEO) or geostationary (GEO) satellites. We found that clouds play an important role in determining the non-linear relationship in addition to the well-known cloud free land-ocean reflectance contrast in the two bands. The non-linear relationship is the result of three factors: (1) a much larger cloud free land-ocean contrast in the NIR band compared to the blue band; (2) significantly larger difference between cloudy-land and cloudy-ocean reflectance in theNIR band compared to the blue band; (3) the periodic variation of fractions of clear land, clear ocean, cloudy land, and cloudy ocean in the sunlit hemisphere as Earth rotates. We found that the green vegetation contributes significantly to the NIR global average reflectance when the South and North Americas appear and disappear in the EPIC's field-of-view. The blue and NIR relationship can be useful for exoplanet research. Clouds impose a strong impact on global spectral reflectance and the reflectance response to a change in cloud cover depends on whether the change is over land or over the ocean. On average, an increase of 0.1 in cloud coverage will lead to a 7%increase in spectrally integrated global average reflectance.

EPIC↗
NASA NTRS2019

NIRCam: The JWST Near-IR Camera and Slitless Spectrograph

NIRCam is the primary near-infrared camera for JWST. It is well-suited for a wide variety of star formation and other scientific studies and will also be used for aligning the JWST primary mirror segments and telescope. NIRCam will provide high sensitivity, high spatial resolution images in a variety of filters over the 0.6 - 5 μm wavelength region including coronagraphic modes and slitless spectroscopic capabilities. NIRCam consists of two identical optical modules that have adjacent 2.2' x 2.2' fields of view on the sky. Each module is composed of two channels that observe the same field at short (< 2.4 μm) or long (> 2.4 μm) wavelengths simultaneously, with optimized spatial sampling in each channel. NIRCam optical elements include narrow (R = 100), medium (R = 10), and wide (R <= 4) filters, coronagraphic imaging spot and bar masks, and grisms that provide wide-field or time-series slitless spectroscopy. These major NIRCam features will be introduced, and some applications to galactic star formation will be briefly presented.

Greene, Thomas↗