Comparison Between CERES/Aqua and POLDER/PARASOL Shortwave Fluxes

Abstract:

Radiative Budget, essential to the monitoring of climate change, can be investigated with ERB-dedicated instruments like the NASA Clouds and the Earth Radiant Energy System (CERES) (Wielicki, 1996). However, non-dedicated instruments, such as POLDER-3/PARASOL, measuring narrowband radiances, can also be used advantageously to obtain shortwave albedos and fluxes (Buriez et al, 2007; Viollier et al, 2002). We present here a comparison between the shortwave fluxes and albedos derived from POLDER-3 radiances and those obtained from the ERB-dedicated instrument CERES flying aboard Aqua.

Monthly means of shortwave fluxes computed from the measurements of the two instruments are first set side by side and show a good agreement between the values in the all-sky case. However, the values from POLDER-3 display a drift which corresponds to the lowering of the orbit of the PARASOL satellite and the modification of its overpass time. In clear-sky only situations, greater differences between POLDER and CERES shortwave fluxes are observed, especially over land regions. A second comparison is presented, between instantaneous collocated shortwave albedos in the period of near-instantaneous observations between POLDER-3 and CERES/Aqua. The values of albedo are quite similar but the drift is present with a greater slope. This tends to show that the POLDER algorithm leading to the monthly means moderates the increase of shortwave albedo values due to the change of Solar Zenith Angle at the time of observation of POLDER-3.