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TitleSolar irradiance and effective brightness temperature for SWIR channels of AVHRR/NOAA and GOES imagers
AuthorTrishchenko, AORCID logo
SourceJournal of Atmospheric and Oceanic Technology vol. 23, no. 2, 2006 p. 198-210, Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 2004351
PublisherAmerican Meteorological Society
Mediapaper; on-line; digital
File formatpdf
SubjectsScience and Technology; Nature and Environment; satellite imagery; satellites; remote sensing; optical properties; solar energy; reflectance
Illustrationsformulae; tables; histograms
ProgramReducing Canada's Vulnerability to Climate Change
Released2006 02 01
AbstractSatellite observations in the shortwave infrared (SW IR) part of spectrum between 3.5 µm and 4.0 µm deliver critically important information for many applications. The satellite signal in this spectral band consists of solar reflected radiation and thermal radiation emitted by surface, clouds and atmosphere. Accurate retrievals require precise knowledge of solar constants. The magnitude of solar constants for shortwave infrared channels (3.7 µm -3.9 µm) for the AVHRR/NOAA-7 to NOAA-18 and GOES-8 to GOES-12 is considered in this paper. Four recent models of the solar spectrum (Kurucz, 1998; Gueymard, 2004; ASTM, 2000; Wehrli, 1985) are analyzed to determine uncertainties in the knowledge of solar constants for SW IR channels of listed sensors. Because thermal radiation is frequently converted to effective blackbody temperature for analysis, computations and calibration purpose, it is proposed here to express solar constants in terms of brightness temperature as well. It is shown that solar constants for AVHRR radiometers expressed in terms of blackbody equivalent brightness temperature correspond to the range 355 K -360 K, and vary around 345 K for SW IR channels on GOES imagers. The values of solar constants and brightness temperatures are provided for various models. The relative difference in solar constants computed from different models of solar spectrum is between 0 % and 2.5 %. Differences expressed in terms of brightness temperatures may reach 0.8 K. The results for the ASTM and the Kurucz models agree within 0.1% relative difference. Parameters of linear fits relating effective brightness temperatures and spectral radiance equivalent temperatures are also determined for all sensors. They are required for precise radiance-temperature and temperature-radiance conversion through Planck's functions in the case of finite spectral response of real sensors.

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