We review here the history of satellite missions and their measurements of the earth radiation budget from the beginning of the space age until the present time. The survey emphasizes the early struggle to develop instrument systems to monitor reflected shortwave and emitted long-wave exitances from the earth and the problems associated with the interpretation of these observations from space. In some instances, valuable data sets were developed from satellite measurements whose instruments were not specifically designed for earth radiation budget observations. The effort of understanding the earth radiation budget has been the work of many people from different countries of the world, an effort of proud accomplishment. INTRODUCTION Satellite measurements of the radiative exchange between the planet earth and its space environment represent one of the fundamental observations for studying the driving mechanisms of terrestrial weather and climate. The history of earth radiation budget (ERB) measurements closely parallels the overall space effort within the United States and other countries of the world. The first observations of weather from space in the late 1940s were taken from cameras that viewed the earth from suborbital rockets. Composite pictures from altitudes of 160 km showed the organization of extensive cloud patterns. The launch of Sputnik 1 on October 4, 1957, caused the rapid development of satellite experiments in the United States which included plans for meteorological spacecraft. Sixteen months later, the headlines of the New York Times (Figure 1) announced the successful launching of the Explorer 6 satellite from a Vanguard 2 rocket on February 17, 1959. Explorer 6 ushered in the era of satellite meteorology and provided the first observations of the ERB. The planning phase for meteorological satellite systems started in the early 1950s with the 1951 classified document by Greenfield and Kellogg [see Greenfield and Kellogg, 1960]. This effort created a growing interest and excitement within the meteorological community that had access to classified information. When the subject area was declassified in 1954, papers began appearing in the open literature. Some of the contributions of note were the works of Wexler [1954], Widger and Touart [1957], Singer [1957], Greenfield and Kellogg [1959], and Widger [1961]. Suomi [1957] proposed the first experimental satellite dedicated to the measurement of the ERB. The momentum Of this planning effort resulted in an explosion of satellite launches in the 1960s. Paper number 5R0785. 8755-1209/86/005R-0785515.00 nology. In the early 1960s, satellites were launched in prograde, drifting orbits with relatively small payloads [Sternberg and Stroud, 1960]. The attitudes of spacecraft were stabilized by spinning the satellites before release from the last rocket stage. This means of attitude control limited observations to about half the orbital period for radiometers which utilized spacecraft spin to scan the earth. As the orbit precessed in its plane, the radiom...

Studies of the earth's radiation budget now form a major part of climate research using measurements made from earth-orbiting and geostationary satellites. However, there has been considerable interest in this topic well before the development of space observing systems. In this paper we provide the historical perspective to radiation of budget studies and describe the early studies from the beginning of this century until the 1960s. 5, 2, 27-43, 1950.

The Earth radiation budget data obtained from the Nimbus 7 Earth Radiation Budget (ERB) and the Earth Radiation Budget Experiment (ERBE) spacecraft missions are compared for several overlapping months during the period November 1984 to January 1986. The Nimbus 7 ERB data set starts in November 1978 and extends through October 1987 (9 years). The ERBE data set starts in November 1984 with the ERBS satellite, which was supplemented by the NOAA 9 in January 1985 and the NOAA 10 in September 1986. Data from both the ERBS and the NOAA 9 are presently being released to the scientific community. The principal aim of the ERBE project is to obtain improved measurements of the diurnal variations in the Earth radiation budget in order to derive accurate radiation budget products. On the Nimbus 7 ERB, only the wide field of view sensors have been active since July 1980. During the comparison period, both the ERBS and NOAA 9 had active wide field of view, medium field of view, and narrow field of view (scanner) sensors. Top of the atmosphere, colocated wide field of view (WFOV) measurements are compared to estimate relative biases. Then all the time‐ and space‐averaged products are compared. Each WFOV instrument has a shortwave and a total spectral channel. The outgoing longwave radiation is taken as the difference between the total and shortwave readings. The Nimbus 7 WFOV shortwave sensor reads about 2.5% higher than the ERBS sensor, while the Nimbus 7 total channel reads about 1% below the ERBS channel near midnight and about 1% above it near noon. A comparative study of the time‐ and space‐averaged data products for April, July, and October 1985 and January 1986 shows that the Nimbus 7 ERB global averages agree in the mean with the combined ERBS/NOAA 9 scanner values to within 0.16% in the outgoing longwave radiation and 0.03% in the albedo. The agreement of the combined ERBS/NOAA 9 WFOV products to the ERBS/NOAA 9 scanner products is 0.17% in the outgoing longwave radiation and 3.55% in the albedo. Certain fortuitous approximations in the time‐ and space‐averaging algorithms appear to have helped the agreement in the final mean Nimbus 7 and ERBE products. Monthly and regional differences are somewhat larger than for the 4‐month mean global values.

The Earth Radiation Budget Satellite (ERBS) and the NOAA-9 spacecraft solar monitors were used to measure the total solar irradiance during the period October 1984 to December 1989. Decreasing trends in the irradiance measurements were observed as sunspot activity decreased to minimum levels in 1986; after 1986, increasing trends were observed as sunspot activity increased. The magnitude of the irradiance variability was found to be approximately 0,1% between sunspot minimum and maximum (late 1989). When compared with the 1984 to 1989 indices of solar magnetic activity, the irradiance trends appear to be in phase with the 11-year sunspot cycle. Both irradiance series yielded 1 365 Wm-2 as the mean value of the solar irradiance, normalized to the mean Earth/Sun distance. The monitors are electrical substitution, active-cavity radiometers with estimated measurement precisions and accuracies of less than 0,02% and 0,2%, respectively.

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