The Nimbus-7 spacecraft flies in a sun-synchronous, near-polar orbit which provides near-local noon and near-local midnight observations of most of the earth. The satellite was launched in October 1978 and has produced several long-term data sets of potential interest including the Earth Radiation Budget (ERB) observations.
The Nimbus-7 ERB system incorporated a scanner to provide high-resolution radiances and a separate WFOV instrument to provide fluxes at satellite altitude. The experiment is described in detail by Jacobowitz et al. (1984). The scanner operated between November 1978 and June 1980. Because of this short duration, the scanner data have not been included in this archive. The WFOV radiometers are still operating on Nimbus-7 and are capable of measuring the shortwave (0.2-3.8 micrometer) and total longwave (0.2-50 micrometer) outgoing components of the Earth's radiation budget at satellite altitude. Kyle et al. (1984) describe the ERB WFOV calibration adjustments. Observations of ERB WFOV fluxes have been analyzed from November 1978 to October 1987.
The basic spatial resolution of the WFOV measurements is about 1500 km, which provides a smoothed version of the earth's radiation budget. The basic measurement is flux at satellite altitude ( =955 km), which is then inverted to the top-of-the-atmosphere flux by the simplest (RE + h)2/(RE + h0)2 adjustment, where RE is the radius of the earth, h is the satellite altitude and h0 is the altitude at the top of the atmosphere. Deconvolution methods are available, but they amplify the noise.
The accuracy of Nimbus-7 ERB measurements is not as good as with ERBE data because the calibration of the detectors is not as accurate and the analysis scheme is much simpler (Jacobowitz et al. 1989). Also, there has been a systematic degradation of the response of the short-wave flux observations because the transmission of the filter window has decayed over time. This effect has been removed by calculating the trend in the global mean fields and appropriately adjusting the data. Trend detection on the large scale from this instrument, therefore, is not possible. Despite these problems, comparisons of monthly mean fluxes between simultaneous ERBE and Nimbus-7 ERB measurements are very good(Kyle et al. 1990), except for the resolution differences (Campbell et al. 1987). The Nimbus-7 ERB data set may be better than ERBE for estimating the intereannual variability of the monthly mean radiation budget because of its longer time interval and consistent viewpoint.
The Earth Radiation Budget (ERB) data consist of single-level monthly mean fields archived at 4.5o resolution in "TYPEc=CCM1" history tape format. No attempt has been made to place these data on a T42 Gaussian grid because of their coarse resolution.
Only the most widely used fields from Nimbus-7 ERB have been archived for November 1978 through October 1987. Data are not available for April, May and June 1986, and these months have been coded as missing (1.E + 36). Ascending (near local-noon) and descending (near local-midnight) observations are given by "A" and "D". Note that the "day" parameter (ICP "DAYSc") actually refers to monthly means.
Climatologies for each month and field have been produced. The analysis system changed for the Nimbus-7 ERB data in July 1980, so data prior to this time have not been used in the averages. Specifically, data from the last seven years (November 1980 through October 1987) of measurements have been used in the construction of monthly averages. No other attempts have been made to correct for possible biases in the data. The mean fields have the same processor names and units as above, but they are in "TYPEc=SAVTAV" format at 4.5o resolution.
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