Stratospheric Aerosol and Gas Experiment II

Project Description
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.