SAGE II (Stratospheric Aerosol and Gas Experiment II) was launched aboard the Earth Radiation Budget Satellite (ERBS) in October 1984. During each sunrise and sunset encountered by the orbiting spacecraft, the instrument used the solar occultation technique to measure stratospheric aerosols, ozone, nitrogen dioxide, and water vapor.

SAGE II continued the SAGE measurements of stratospheric ozone from 1984-2005. This long-term, stable data set has proven invaluable in determining trends in ozone.

Data from SAGE II, in conjunction with data from sister instruments SAM II and SAGE I, can be used to estimate long-term constituent trends and identify responses to episodic events such as volcanic eruptions.

The data SAGE II collected was integral to confirming human-driven changes to ozone, and thus contributed to the 1987 Montreal Protocol that banned certain harmful chemicals. SAGE II also saw that ozone stopped decreasing in response to this action.

Major results from SAGE II include illustrations of the stratospheric impact of the 1991 Mount Pinatubo eruption, identification of a negative global trend in lower stratospheric ozone during the 1980s, and quantitative verification of the positive water vapor feedback in current climate models.

The platform for SAGE II is the Earth Radiation Budget Satellite (ERBS).
Nominal orbit parameters for ERBS are:

  • Launch Date: October 5, 1984
  • Planned Duration: 2 years
  • Actual Duration: powered off on August 26, 2005
  • Orbit: non-sun synchronous, circular at 650 km
  • Inclination: 57 degrees
  • Nodal Period: 96.8 minutes

The SAGE II instrument was a seven-channel Sun photometer that used a Cassegrainian-configured telescope, holographic grating and seven silicon photodiodes, some with interference filters, to define the seven spectral channel bandpasses. Solar radiation is reflected off a pitch mirror into the telescope, forming an image of the sun at the focal plane. The instrument’s instantaneous field-of-view, defined by an aperture in the focal plane, is a 0.5-by-2.5 arc-minute slit that produces a vertical resolution at the tangent point on the Earth’s horizon of about 0.5 kilometers. Radiation passing through the aperture is transferred to the spectrometer section of the instrument containing the holographic grating and seven separate detector systems. The holographic grating disperses the incoming radiation into the various spectral regions centered at the 1020, 940, 600, 525, 453, 448, and 385 nanometer wavelengths. Slits on the Rowland circle of the grating define the spectral bandpass of the seven spectral channels. The spectrometer system is inside the azimuth gimbal to allow the instrument to be pointed at the Sun without image rotation. The azimuth gimbal can be rotated over 370 degrees so that measurements can be made at any azimuth angle.

The operation of the instrument during each sunrise and sunset measurement is totally automatic. Prior to each sunrise or sunset encounter, the instrument is rotated in azimuth to its predicted solar acquisition position. When the Sun’s intensity reaches a level of one percent of maximum in the Sun sensor, the instrument adjusts its azimuth position to lock onto the radiometric center of the Sun to within +/-45 arc-seconds and then begins acquisition of the Sun by rotating its pitch mirror in a predetermined direction depending on whether it is a sunrise or a sunset. When the Sun is acquired, the pitch mirror rotates back and forth across the Sun at a rate of about 15 arc-minutes per second. The radiometric channel data are sampled at a rate of 64 samples per second per channel, digitized to 12-bit resolution, and recorded for later transmission back to Earth.

SAGE II Instrument

Spatial / Temporal Coverage

  • Spatial Coverage: 80N to 80S, 180E to 180W
  • Spatial Resolution: .5km Altitude
  • Temporal Coverage: 10/24/1984 – 8/31/2005, no data available for August-October 2000
  • Temporal Resolution: Sunrise/Sunset Events

Data Products

  • Ozone
  • Aerosol Extinction Profiles
  • Nitrogen Dioxide
  • Water Vapor
  • Derived Aerosol Properties

SAGE II stratospheric aerosol extinction coefficient for 1998-2003.

SAGE II Science Team Members:

Derek M. Cunnold, Massachusetts Institute of Technology

Georgio Fiocco, Inst. Di Fisica dell’Atmosfera

Gerald W. Grams, Georgia Institute of Technology

M. Hilrono, Kyushu University, Japan

Ronald M. Nagatani, NOAA, National Met. Center

Jennifer le Noble, Universite de Lille, France

M Pat McCormick, Hampton University (Previously NASA Langley Research Center)

David G. Murcray, University of Denver

Theodore J. Pepin, University of Wyoming

David H. Rind, Goddard Institute for Space Studies

Phillip B. Russell, SRI International Science

After nearly 21 years, the SAGE II Instrument on the ERBS platform was powered off on August 22, 2005.

NASA’s retired Earth Radiation Budget Satellite (ERBS) reentered Earth’s atmosphere at 11:04 p.m. EST on Sunday, January 8, 2023 after almost four decades in space.
Retired NASA Earth Radiation Budget Satellite Reenters Atmosphere

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SAGE II on ERBS in 1984 before launch.