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Requirements for the measurements of Earth’s top-of-atmosphere energy budget can be derived on the basis of resolving an imbalance between incoming solar radiation and outgoing Earth radiation, currently estimated to be 0.6 W m-2. Over the past two decades, significant reduction in the uncertainty of solar irradiance has been achieved that is within this climate-quality constraint. The uncertainty in outgoing radiation from Earth, on the other hand, while also reduced over the last two decades, is not yet at a level sufficient to resolve the imbalance. It is anticipated that future measurements of outgoing emitted longwave and reflected shortwave radiance will have uncertainties that are a factor of 5 to 10 lower than current measurements, but still insufficient for resolving an imbalance on the order of 1 W m-2 or less. The focus of this paper is on state-of-the-art SI-traceable absolute radiometry for measuring top-of-atmosphere incoming and outgoing radiation. Advances in detector technology (microbolometers using vertically aligned carbon nanotubes), control (closed-loop electrical substitution) and implementation (from single detectors for solar total and spectral irradiance and rapid scanning of Earth limb-to-limb broad-band radiance to linear arrays for spatially resolved Earth radiance) that are already being implemented in current and for future missions. Features of this radiometry have several goals: lower uncertainty because of substantial reduction to inequivalence and lower noise (demonstrated by modeling and intra-comparisons); room temperature operation; faster and cheaper fabrication; and lower implementation costs because of reduced size, weight, and power. This will provide a path for data continuity and multiple redundant missions dispersed over time. Enhanced long-wavelength sensitivity and spectral uniformity to enhance measurement and imaging of cooler earth features such as clouds and oceans. We have recently undertaken a decadal revalidation of the LASP Total-solar-irradiance Radiometer Facility (TRF), and established a replacement room temperature standard known as Not Another Cryogenic Radiometer (NACR). The results of this extensive measurement campaign bridge the past TRF radiometer comparison against the NIST primary standard (POWR – Primary Optical Watt Radiometer) of 2008 to the present radiometric assessment of NACR and serves as a basis for validating upcoming missions including the Compact Total Irradiance Monitor mission (CTIM), the Black Array of Broadband Absolute Radiometers (BABAR), Libera, and others. NACR is a very portable primary standard, designed for irradiance measurements at solar power levels of 1361 W m-2. It is capable of being directly compared to other solar viewing instrumentation deployed in the field.
Topic : Theme 1: Earth Energy Balance.
Reference : T1-C5
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