The 15-year ERBE data set upgraded

The dedicated Earth Radiation Budget Satellite (ERBS) carried broadband scanning and nonscanning radiometers which began providing radiation budget measurements in November 1984. The nonscanner included wide-field-of-view (WFOV) radiometers and a solar monitor, and operated until October 1999, producing a 15-year data set of reflected shortwave and outgoing longwave radiation fluxes from a single instrument, covering 86% of the Earth's surface. In-flight calibrations maintained a precision of 0.2 W-m-2. This precision and its stability over the 15-year period exceeded the requirements of the project. The data processing system was designed over two decades ago in accordance with the original accuracy requirements. Subsequent scientific investigation have pushed the accuracy limits of the data products, so that the data processing software has been upgraded The data have been reprocessed to produce the Edition 3 data set. A second upgrade is a refinement to the correction of shortwave fluxes to account better for a drift due to degradation of the quartz filter of the shortwave WFOV radiometer. This correction to the shortwave channel removes a drift of 0.2 W-m-2 per year over the 15-year data period. The total channel has demonstrated consistency to 0.1% on the basis of solar calibrations.

The ERBS orbit precessed through all local times over a period of 72 days. The data processing includes algorithms to account for the time of measurement in order to compute the monthly-average fluxes based on the time of measurement for each region. Algorithms for evaluating the error due to irregular time sampling with the diurnal variations taken into account are used for quality assurance of the monthly-mean shortwave and longwave fluxes. Nevertheless, the computed monthly-mean outgoing longwave radiation has an error due to an aliasing of the diurnal cycle and seasonal cycle due to the 72-day precession of the orbit. For the Tropics, this effect was reduced by use of 36-day periods rather than calender months. This data set is available off-line by request.

These improvements have resulted in data products which reveal changes of radiation budget in the Tropics of less than 0.2 W-m-2 and show strong relations between measurements of radiation and that inferred from heat storage in the ocean as computed by ocean altimetry. The data are available at the Langley Atmospheric Sciences Data Centre.