S - U
SAGE II
Scientific Objectives: Since October 1984, the SAGE II instrument has been flying aboard the Earth Radiation Budget Satellite (ERBS) collecting data that are being processed and archived at NASA LaRC to produce four Level 2 data products: aerosol extinction profiles at 1020, 525, 453, and 385 nanometers, and ozone, water vapor, and nitrogen dioxide mixing ratio profiles. These products are nearly global in coverage, with data spanning from 80 degrees North to 80 degrees South latitudes. The accuracy of these data was verified by extensive validation efforts and the data sets are now archived and available for general scientific use. These data may be of use to investigators who are interested in spatial and temporal variations of ozone, aerosols, water vapor, and nitrogen dioxide caused by seasonal and short-term meteorological variations, atmospheric chemistry and microphysics, and transient phenomena, such as volcanic eruptions. These data may also be of some benefit for those who perform upper tropospheric studies of aerosols or who perform climatology studies of cirrus clouds. SAM II, SAGE I, and SAGE II have provided data sets that are now available for use and provide a span of aerosol data from late 1978 up through the present time. Project Description: The SAGE II instrument is a seven-channel Sun photometer using 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 with an image of the Sun formed at the focal plane. The instrument's instantaneous field-of-view, defined by an aperture in the focal plane, is a 1/2 X 2-1/2 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. The SAGE II experiment is ongoing. The Langley DAAC continues to archive these data. Data Used and Produced: The SAGE II science and engineering data, along with spacecraft time, position, and housekeeping data, are stored aboard the spacecraft and downlinked to NASA GSFC through a ground station. GSFC then forwards these data to LaRC for processing and scientific analysis. GSFC also sends spacecraft and solar ephemeris data to LaRC. These data are the input to the inversion process which is explained in the next section. At the completion of the data processing, four Level 2 SAGE II products are produced: aerosol extinction profiles, ozone concentration profiles, water vapor profiles, and nitrogen dioxide profiles. The SAGE2_AERO_PRF data set contains over ten years of aerosol extinction profiles data. Each granule consists of one month of data. These data are in Hierarchical Data Format (HDF). The data coverage begins October 1984 and continues to present. Data are stored in parameter format. Each measurement event consists of 44 parameters. The SAGE2_AERO_PRF_ASC data set contains over ten years of aerosol extinction profiles data. Each granule consists of one month of data. These data are in ASCII format. The data coverage begins October 1984 and continues to present. Data are stored in parameter format. Each measurement event consists of 44 parameters. The SAGE2_AERO_PRF_NAT data set contains over ten years of aerosol extinction profiles data. Each granule consists of one month of data. These data are in SAGE II's native binary format. The data coverage begins October 1984 and continues to present. Data are stored in parameter format. Each measurement event consists of 44 parameters. The SAGE2_CLOUD data set contains over ten years of cloud occurrence data at a given location. These granules consist of three months of data (seasonal data). The data coverage begins December 1984 and extends through November 1990. Data are stored in Hierarchical Data Format (HDF). The SAGE2_H2O_PRF data set contains five years of water vapor profiles data. Each granule consist of one month of data. These data are in Hierarchical Data Format (HDF). The data coverage begins January 1986 and extends through May 1991. The SAGE2_NO2_PRF data set contains over nine years of nitrogen dioxide concentration profiles data. Each granule consists of one month of data. These data are in Hierarchical Data Format (HDF). The data coverage begins October 1984 and continues to the present. Data are stored in parameter format. Each measurement event consists of 34 parameters. The SAGE2_NO2_PRF_ASC data set contains over nine years of nitrogen dioxide concentration profiles data. Each granule consists of one month of data. These data are in ASCII format. The data coverage begins October 1984 and continues to the present. Data are stored in parameter format. Each measurement event consists of 34 parameters. The SAGE2_NO2_PRF_NAT data set contains over nine years of nitrogen dioxide concentration profiles data. Each granule consists of one month of data. These data are in SAGE II's native binary format. The data coverage begins October 1984 and continues to the present. Data are stored in parameter format. Each measurement event consists of 34 parameters. The SAGE2_O3_PRF_ASC data set contains over nine years of ozone concentration profiles data. Each granule consists of one month of data. These data are in ASCII format. The data coverage begins October 1984 and continues to the present. Data are stored in parameter format. Each measurement event consists of 33 parameters. The SAGE2_O3_PRF_NAT data set contains over nine years of ozone concentration profiles data. Each granule consists of one month of data. These data are in SAGE II's native binary format. The data coverage begins October 1984 and continues to the present. Data are stored in parameter format. Each measurement event consists of 33 parameters. The SAGE2_O3_MONTHLY data set contains six years of ozone mixing ratio monthly data. Each granule consists of one month of data. These data are in Hierarchical Data Format (HDF). The data coverage begins January 1985 and extends through December 1990. Data are stored in parameter format. Each measurement event consists of 5 parameters. The SAGE2_CD_ROM contains seven years of data and contour color maps. The maps are of monthly mean aersols, ozone, water vapor, and nitrogen dioxide measurements. The CD-ROM contains data from January 1985 and extends through December 1993. These data are in Hierarchical Data Format (HDF). Project Archive Contact: Langley DAAC User Services Office Mail Stop 157D 2 South Wright Street NASA Langley Research Center Hampton, VA 23681-2199 USA Phone: (757) 864-8656 FAX: (757) 864-8807 INTERNET > larc@eos.nasa.gov WWW Home Page: "http://eosweb.larc.nasa.gov/" Project Manager Contact: M. Patrick McCormick Physics Department Hampton University Hampton, VA 23668 USA Phone: (757) 728-6867 FAX: (757) 864-6910 INTERNET > mmc@hamptonu.edu Michael W. Rowland SAIC Mail Stop 475 Hampton, VA 23681-0001 USA Phone: (757) 864-2691 FAX: (757) 864-2671 INTERNET > M.W.ROWLAND@LaRC.NASA.GOV References: The following list of references is provided as a starting point for someone wishing to learn more about the SAGE II instrument, inversion method, validation studies and recent scientific studies. Chu, W. P. and M. P. McCormick, "Inversion of Stratospheric Aerosol and Gaseous Constituents from Spacecraft Solar Extinction Data in the 0.38 - 1.0 Micron Wavelength Region," Applied Optics 18:1404-1413, 1979b. Chu, W. P., M. P. McCormick, J. Lenoble, C. Brognoiz, and P. Pruvost, "SAGE II Inversion Algorithm," J. Geophys. Res. 94:8339, 1989. Mauldin, L. E., N. H. Zaun, M. P. McCormick, J. J. Guy, and W. R. Vaughn, "Stratospheric Aerosol and Gas Experiment II Instrument: A Functional Description," Optical Engineering 24:307, 1985. Russell, P. B., and M. P. McCormick, "SAGE II Aerosol Data Validation and Initial Data Use: An Introduction and Overview," J. Geophys. Res. 94:8335. 1989. Russell, P. B., M. P. McCormick, T. J. Swissler,"Validation of Aerosol Measurements by the Satellite Sensors SAM II and SAGE," Adv. Space Res., 2, #5, 1983. Russell, P. B., M. P. McCormick, T. J. Swissler, L. R. McMaster, J. M. Rosen, D. J. Hofmann, "Satellite and Correlative Measurements of the Stratospheric Aerosol III: Comparison of Measurements by SAM II, SAGE, Dustsondes, Filters, Impactors and Lidar," J. Atmos. Sci., 41, 11, 1984. Yue, G. K., M. P. McCormick, W. P. Chu, "A Comparative Study of Aerosol Extinction Measurements Made by the SAM II and SAGE Satellite Experiments," J. Geophys. Res., 89, 1984. Yue, G. K., M. P. McCormick, W. P. Chu, "Comparative Studies of Aerosol Extinction Measurements Made by the SAM II and SAGE II Satellite Experiments," J. Geophys. Res., 94, 1984.