Tuesday, 4 June 2002
Development of Correction Factors to Derive a Global Radiation Budget from Triana Data
The Triana mission provides a unique approach to monitoring the Earth's radiation budget. Triana will be the first Earth-observing platform in the Lagrange position (L1) and will always view the sunlit side of the planet. This view eliminates the need for temporal corrections to derive the daytime global radiation budget. However, it does not view the dark side of the globe. The Triana satellite carries the Scripps-NISTAR (National Institute of Standards and Technology Absolute Radiometer), which will measure global broadband shortwave (SW) and longwave (LW) radiances every few minutes. The measured radiances must be converted to fluxes to obtain the radiation budget. A small sunlit sliver of the Earth’s disc will not be in the Triana view because of its Lissajous orbit about the L1 position. Global correction factors are needed to account for the anisotropy of the radiances and the unviewed part of the planet. These global correction factors depend on the diurnal and seasonal cycles as well as orbit position. With the aid of reliable correction factors, Triana should provide the most accurate global radiation budget to date complementing higher resolution measurements like higher resolution data from the Clouds and the Earth’s Radiant Energy System Project. To derive these factors, it is necessary to realistically simulate the viewed scenes. The Triana radiometer data are simulated using Earth Radiation Budget Experiment (ERBE) data for the 1985-1989 time period. Instantaneous regional ERBE broadband fluxes are interpolated regionally and temporally with enhancements based on 3-hourly International Satellite Cloud Climatology Project (ISCCP) geostationary and Advanced Very High Resolution Radiometer (AVHRR) narrowband radiances. The narrowband radiances are converted to broadband fluxes and then normalized to the ERBE data. The interpolation yields hourly global GMT (synoptic) SW and LW radiances that are converted to fluxes using state-of-the art anisotropic models. These regional radiances are then integrated to produce the single global radiance for any Triana position. Correction factors are computed and evaluated diurnally, seasonally, and interannually. The factors are parameterized using Fourier analysis and cloud information based on the narrowband data. The Triana satellite has the Scripps-EPIC (Earth Polychromatic Imaging Camera) for deriving cloud properties. An error analysis of the global correction factors is presented.