Stratospheric Aerosol and Gas Experiment II (SAGE II) 1. TYPE OF DATA 1.1 Parameter/Measurement 1.2 Unit of Measurement 1.3 Data Source 1.4 Data Set Identification 2. SPATIAL CHARACTERISTICS 2.1 Spatial Coverage 2.2 Spatial Resolution 3. TEMPORAL CHARACTERISTICS 3.1 Temporal Coverage 3.2 Temporal Resolution 4. INSTRUMENT DESCRIPTION 4.1 Mission Objectives 4.2 Key Satellite Flight Parameters 4.3 Principles of Operation 4.4 Instrument Measurement Geometry 5. DATA PROCESSING SEQUENCE 5.1 Processing Steps and Data Sets 5.2 Derivation Techniques/Algorithms 5.3 Special Corrections/Adjustments 5.4 Processing Changes 6. QUALITY ASSESSMENT 6.1 Data Validation by Producer 6.2 Confidence Level/Accuracy Judgment 6.3 Usage Guidance 7. CONTACTS FOR DATA PRODUCTION INFORMATION 8. OUTPUT PRODUCTS AND AVAILABILITY 8.1 Tape Products 8.2 Film Products 8.3 Other Products 9. DATA ACCESS 9.1 Archive Identification 9.2 Procedures for Obtaining Data 9.3 NCDS Status/Plans 10. CONTACTS FOR ARCHIVE/DATA ACCESS INFORMATION 11. REFERENCES 11.1 Satellite/Instrument/Data Processing Documentation 11.2 Journal Articles and Study Reports 11.3 Archive/DBMS Usage Documentation 12. RELATED DATA SETS 13. SUMMARY/SAMPLE 14. NOTES ENDOFTOC 1. TYPE OF DATA 1.1 Parameter/Measurement. Solar irradiance is measured through the Earth's atmosphere during spacecraft sunrise and sunset. These data are used to determine the distribution of aerosols, ozone, water vapor, and nitrogen dioxide in the stratosphere. Measurements are made at the following wavelengths: Channel Wavelength (um) ------- --------------- 1 1.019 2 0.940 3 0.600 4 0.525 5 0.454 6 0.448 7 0.385 1.2 Unit of Measurement. The measurements of solar irradiance are always expressed as a ratio. For this reason, only a relative calibration is made for data reduction. An extinction profile as a function of altitude is also generated for each channel. 1.3 Data Source. Stratospheric Aerosol and Gas Experiment II (SAGE II) carried on the Earth Radiation Budget Satellite (ERBS). 1.4 Data Set Identification. The Meteorological Ephemeris Raw Data Archive Tape (MERDAT) generated from SAGE II contains solar irradiances at seven wavelengths, as well as meteorological and ephemeris data. 2. SPATIAL CHARACTERISTICS 2.1 Spatial Coverage. The latitudinal limits vary with the season. Generally, SAGE II coverage extends from 80 degrees north to 80 degrees south. The sunrise and sunset events are separated by approximately 24 degrees longitude. 2.2 Spatial Resolution. The 1 micrometer wavelength measurement has a vertical resolution of 1 km below 25 km and a resolution of 5 km above 25 km. The vertical resolution of the 0.45 micrometer wavelength channel is 3 km below 25 km. The horizontal resolution is about 250 km for all wavelengths. 3. TEMPORAL CHARACTERISTICS 3.1 Temporal Coverage. SAGE II was launched on October 5, 1984 and is still operating full time. 3.2 Temporal Resolution. The latitudinal region covered by SAGE II varies with each season of the year, thus affecting the coverage cycle. At any one time during the year, full latitudinal range coverage is achieved in approximately 2 1/2 weeks. The entire event cycle covers about 120 degrees of latitude and takes approximately five weeks to complete. 4. INSTRUMENT DESCRIPTION 4.1 Mission Objectives. The mission objectives of the SAGE II are to determine the spatial distribution of stratospheric aerosols, ozone, nitrogen dioxide, and water vapor and to map vertical profiles of each. Specific objectives are: a. To develop a viable satellite-based remote sensing technique for measuring stratospheric aerosols, nitrogen dioxide, ozone, and water vapor. b. To utilize these measurements to study global circulation, transient stratospheric phenomena, and sources and sinks of individual species. c. To investigate aerosol optical properties using data from flight experiments and correlative observations. 4.2 Key Satellite Flight Parameters. Nominal orbit parameters for ERBS are listed below: o Launch Date October 5, 1984 o Planned Duration 1 year o Actual Duration Still operating o Orbit Non-sun synchronous o Normal Altitude 610 km o Inclination 57 degrees o Nodal Period 98 min 4.3 Principles of Operation. SAGE II is a seven-channel solar photometer, with spectral bands centered at 0.385, 0.448, 0.454, 0.525, 0.600, 0.940 and 1.019 micrometers. A holographic diffraction grating is used to obtain the spectral separation required to measure solar radiation. Four channels (0.385, 0.454, 0.600, 1.019) allow the separation of atmospheric extinction along the line-of-sight due to Rayleigh scattering, aerosols, ozone, and nitrogen dioxide. The 0.940 um channel allows concentration profiles of water vapor to be determined. The 0.448 um channel provides an additional channel for nitrogen dioxide detection, and the 0.525 um channel is used for aerosol detection. The SAGE II instrument views a small portion of the sun through the Earth's atmosphere during spacecraft sunrise and sunset. Data are obtained from the attenuation of the sunlight due to scattering and absorption by different atmospheric species. The motion of the spacecraft prior to entering or subsequent to leaving the Earth's shadow provides vertical scanning through the atmosphere. Measurements taken from a tangent-height of 150 km, where there is no attenuation, provide a self-calibration feature for every event. The scan mirror operates at two speeds. When the sun-presence sensor detects a sun intensity of 1% relative to the unattenuated sun, the instrument pulls the sun to within 1 arc-minute of azimuth, and the scan mirror "fast"-scans 3 degrees in elevation until the sun is in view. The mirror then "slow"-scans across the face of the sun at a rate of 15 arc-minutes per second. 4.4 Instrument Measurement Geometry. SAGE II uses the sun as a constant radiant energy source and measures the radiation that reaches the spacecraft after penetrating the Earth's atmosphere during spacecraft sunrise and sunset events. The radiometer vertically scans the solar disk up and down with respect to the Earth's horizon. The nominal scan rate is 15 arc-minutes per second. The radiometric data are sampled at a rate of 64 samples per second per channel and digitized to 12-bit accuracy. Sampling occurs twice per orbit for durations varying from 3 to 10 minutes each. The instrument vertical field-of-view of approximately 0.5 arc-minutes produces a vertical resolution of approximately 1 km at altitudes ranging from cloud tops to 10 km. 5. DATA PROCESSING SEQUENCE 5.1 Processing Steps and Data Sets. Radiance data, along with spacecraft attitude and housekeeping data are stored aboard the satellite and transmitted four times a day to NASA/Goddard Space Flight Center (GSFC) through a ground station or TDRS relay satellite. GSFC then forwards these data to NASA/Langley Research Center (LaRC) for processing and scientific analysis. GSFC also sends spacecraft and solar ephemeris data on a separate tape containing one week of data. Data from three sources are combined at Langley to produce the SAGE II MERDAT data sets. They include: (a) NOAA National Meteorological Center (NMC) temperature and density readings at nineteen different pressure levels in the atmosphere; (b) spacecraft position and velocity vectors as functions of time, and (c) SAGE II raw radiance data in each of the seven spectral bands. Atmospheric parameters are derived from these data, including aerosol, ozone, water vapor, and nitrogen dioxide density. These data are arranged into four-day periods beginning with the first day of every month. 5.2 Derivation Techniques/Algorithms. Raw radiance data are provided on the MERDAT tapes in the form of counts. These data are calibrated relative to the unattenuated solar radiance observed just prior to every sunset or subsequent to every sunrise observed. Extinction profiles are derived from a shell model of the atmosphere with an iterative approach to minimize measurement errors. 5.3 Special Corrections/Adjustments. No special adjustments or corrections are made to the MERDAT data set prior to archiving. However, in order to use this data set to derive parameters, corrections must be made for solar limb darkening, atmospheric refraction, and Rayleigh scattering. Information on this procedure can be found in Item 11.1. 5.4 Processing Changes. No processing changes have been made or are anticipated in the MERDAT production. 6. QUALITY ASSESSMENT 6.1 Data Validation by Producer. A detailed study of the SAGE II data has been made by Kent and Wang, 1985. Comparisons with both SAGE I and SAM II data have shown good agreement. Detailed information on SAGE II data validation can be found in Item 11.1. 6.2 Confidence Level/Accuracy Judgment. The precision of the SAGE II radiance measurements is estimated to be 0.1 percent, although a few anomalies have been found. A slight altitude error was detected in the sunrise data, and contamination from aerosol was found in the water vapor channel. The sources of these anomalies have been identified and corrected. 6.3 Usage Guidance. MERDAT data are regarded as useful only for deriving extinction coefficients and particle densities by an inversion technique, as was done for the data sets mentioned in Item 12. Users must pay special attention to the corrections described in Item 5.3 when deriving atmospheric parameters from the raw data. The current data set has been corrected for the anomalies mentioned in Item 6.2. 7. CONTACTS FOR DATA PRODUCTION INFORMATION 7.1 Senior Scientist Dr. M.P. McCormick Mail Stop 475 NASA Langley Research Center Hampton, Virginia 23665-5225 (804) 864-2669 FTS 928-2669 8. OUTPUT PRODUCTS AND AVAILABILITY 8.1 Tape Products 8.1.1 SAGE II Meteorological, Ephemeris, Raw Archive Date Tape (MERDAT), Level I Medium/Specification: 9-track, 6250-bpi unlabeled computer tape. Format and Content: The tape is generated on a CDC 170 computer. Each SAGE II event contains a header record followed by zero to 100 telemetry records. The header record contains: 12 sets of ephemeris data in one minute increments; the Beta angle (angle of satellite orbit plane and sun-Earth vector); latitude and longitude of sub-tangent point; meteorological data as described below; miscellaneous data and pointers. Each telemetry record contains one 4 second frame of data. There is one end-of-file mark after the last event. The meteorological data include temperature, altitude, and density profiles at 19 different pressure levels in the atmosphere. The pressure levels themselves can be used to derive molecular (Rayleigh) scattering corrections. The ephemeris data include position and velocity vectors. SAGE II telemetry data also consist of solar radiances but are from each of the seven channels for each event. Data Quantity/Rate: SAGE II MERDATs are archived in the form of monthly 2-tape volumes. The first tape contains the first 15 days of events, and the second tape contains day 16 through the end of the month. At the present time, there are 156 tapes in the archive. Status: NSSDC presently has 148 SAGE II MERDAT tapes covering the period from November 1984 through October 1991. Plans/Schedule: Additional deliveries are expected in the near future. 8.2 Film Products. None. 8.3 Other products. 8.3.1 The Greenhouse Effect Detection Experiment (GEDEX) CD-ROM Medium/Specification: CD-ROM in ISO 9660 standard Format and Content: The data on this disk will be stored in a special data-set-independent format, designated the Common Data Format (CDF). CDF was developed as a uniform method of storing and retrieving data on disk. The CDF contains data and descriptions about the data. A standard software package called the "CDF Library" will be included with this CD-ROM allowing a user to create and access these data and descriptions. The CD-ROM will consist of many different data sets related to the study of the Greenhouse Effect, including the Stratospheric Aerosol and Gas Experiment (SAGE II) Profile data sets, and the accompanying NCDS data set documentation. Data Quantity/Rate: 1 CD-ROM disk set. Status: Release date for this product is scheduled for early 1992. Plans/Schedule: Users interested in this product should contact NCDS staff for more details. 9. DATA ACCESS 9.1 Archive Identification. Central Data Services Facility Code 933 National Space Science Data Center Goddard Space Flight Center Greenbelt, Maryland 20771 (301) 286-6695 9.2 Procedures for Obtaining Data. Users may request data by letter, phone, personal visit, or through the NSI DECnet computer network at NSSDC::REQUEST. Data costs are dependent on affiliation and sponsorship of the user program. Data are free to NASA personnel. Communication with the NSSDC Request Coordination Office is advised before ordering. Researchers who reside outside the USA should direct their requests to: World Data Center A for Rockets and Satellites Code 930.2 Goddard Space Flight Center Greenbelt, Maryland 20771 (301) 286-6695 9.3 NCDS Status/Plans. NCDS currently supports SAGE I and SAGE II aerosol, ozone, water vapor and nitrogen dioxide profile data as well as the SAGE NMC meteorological data profiles. (NSSDC supports the Meteorological, Ephemeris Raw Data Archive Tape (MERDAT) generated from SAGE I and SAGE II.) 10. CONTACTS FOR ARCHIVE/DATA ACCESS INFORMATION Request Coordination Office Code 933-Central Data Services Facility National Space Science Data Center Goddard Space Flight Center Greenbelt, Maryland 20771 (301) 286-6695 Goddard DAAC User Support Office NASA/Goddard Space Flight Center Code 935 Greenbelt, Maryland 20771 (301) 286-3209 INTERNET: NCDSUSO@NSSDCA.GSFC.NASA.GOV NSI DECnet: NSSDCA::NCDSUSO 11. REFERENCES 11.1 Satellite/Instrument/Data Processing Documentation a. Chu, W.P. and M.P. McCormick, 1979. "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. b. Kent, G.S., and P.-H. Wang, November 1986. "SAGE II Satellite Data Set Validation." NOAA Contractor Report 178189, Science and Technology Corporation. Hampton, VA. c. McCormick, M.P., P. Hamill, T.J. Pepin, W.P. Chu, T.J. Swissler, and L.R. McMaster, 1979. "Satellite Studies of the Stratospheric Aerosol." Bull. Amer. Meteor. Soc. 60:1038-1046. 11.2 Journal Articles and Study Reports a. Chu, W.P., and M.P. McCormick, 1986. "SAGE Observations of Stratospheric Nitrogen Dioxide." J. Geophys. Res. 91:5465-5476. b. Cunnold, D.M., W.P. Chu, R.A. Barnes, M.P. McCormick, and R.E. Veiga, 1989. "Validation of SAGE II Ozone Measurements." J. Geophys. Res. 94:8447-8460. c. Cunnold, D.M., J.M. Zawodny, W.P. Chu, J.P. Pommereau, F. Goutail, J. Lenoble, M.P. McCormick, R.E. Veiga, D. Murcray, N. Iwagami, K. Shibasaki, P.C. Simon, and W. Peetermans, 1991. "Validation of SAGE II NO2 Measurements." J. Geophys. Res. 96:12,913-12,925 d. Kent, G.S. and M.P. McCormick, 1984. "SAGE I and SAM II Measurements of Global Stratospheric Aerosol Optical Depth and Mass Loading." J. Geophys. Res. 89:5303-5314. e. McCormick, M.P., G.S. Kent, G.L. Yue, and D.M. Cunnold, 1982. "Stratospheric Aerosol Effects from Soufriere, St. Vincent as Measured by the SAGE Satellite System." Science 216:1115- 1118. f. McCormick, M.P., and J.C. Larsen, 1986. "Antarctic Springtime Measurements of Ozone, Nitrogen Dioxide, and Aerosol Extinction by SAM II, SAGE, and SAGE II." Geophys. Res. Letters 13:1280- 1283. g. McCormick, M.P., October 1985. SAGE Aerosol Measurements, Vols I - February 21, 1979 - December 1980. NASA RP 1144. h. McCormick, M.P., January 1986. SAGE Aerosol Measurements, Vol. II - January 1, 1980 - December 31, 1980. NASA RP 1149. i. McMaster, L.R., 1986. "Stratospheric Aerosol and Gas Experiment (SAGE II)." Presented at the 6th Conference on Atmospheric Radiation, Williamsburg, VA, May 13-19, 1986. (Extended Abstracts, pp. J46-J48.) j. Mauldlin III, L.E., N.H. Zaun, M.P. McCormick, J.H. Guy, and W.R. Vaughan, 1985. "Stratospheric Aerosol and Gas Experiment II Instrument: A Functional Description." Opt. Engr. 24:307-312. k. Osborn, M.T., J.M. Rosen, M.P. McCormick, P.-H. Wang, J.M. Livingston, and T.J. Swissler, 1989. "SAGE II Aerosol Correlative Observations: Profile Measurements." J. Geophys. Res. 94:8353-8366. l. Wang, P.-H., M.P. McCormick, T.J. Swissler, and G.Y. Yue, 1986. "A Study of the Stratospheric Aerosol Size Distribution Utilizing Preliminary Data from SAGE II and Correlative Measurements." Presented at the 6th Conference on Atmospheric Radiation, Williamsburg, VA, May 13-19, 1986. (Extended Abstracts, pp. J84-J87.) m. Woodbury, G.E., and M.P. McCormick, 1986. "Zonal and Geophysical Distribution of Cirrus Clouds Determined from SAGE Data." J. Geophys. Res. 91:2775-2785. n. Woodbury, G.E. and M.P. McCormick, 1983. "Global Distribution of Cirrus Clouds Determined from SAGE I Data." Geophysical Research Letters 10:1180-1183. o. Yue, Glenn K., M.P. McCormick, and W.P. Chu, 1984. "A Comparative Studies of Aerosol Extinction Measurements Made by the SAM II and SAGE I Satellite Experiments." J. Geophys. Res. 89:5321-5327. 11.3 Archive/DBMS Usage Documentation a. "AEM-2/SAGE I MERDAT Users Guide." January 1980. NASA/Langley Research Center, Hampton, VA. b. "ERBS/SAGE II MERDAT Users Guide." March 1987. NASA/Langley Research Center, Hampton, VA. 12. RELATED DATA SETS Several related data sets exist online through NCDS as follows: 1) The SAGE I Profile data sets contain derived mixing ratio profiles and number densities for aerosols, ozone, and nitrogen dioxide. These data sets will be available online through NCDS in Common Data Format (CDF). To access these CDFs, specify the following as input within the Data Applications subsystem of the NCDS: NCDS$DATA:SAGEI-PROF_AEROSOLS NCDS$DATA:SAGEI-PROF_NO2 NCDS$DATA:SAGEI-PROF_OZONE 2) The SAGE II Profile data sets contain derived mixing ratio profiles and numbers densities for nitrogen dioxide, aerosols, ozone and water vapor. An additional data set contains the NMC meteorological data profiles. These data sets will be available online by year in Common Data Format (CDF). To access these CDFs, specify the following as input within the Data Applications subsystem of the NCDS: NCDS$DATA:SAGEII-PROF_AEROSOLS NCDS$DATA:SAGEII-PROF_NO2 NCDS$DATA:SAGEII-PROF_OZONE NCDS$DATA:SAGEII-PROF_H20VAPOR NCDS$DATA:SAGEII-PROF_MET-DATA 3) The Nimbus-7 Limb Infrared Monitor of the Stratosphere (LIMS) data sets contain mixing ratio profiles of ozone, nitric acid, water vapor and nitrogen dioxide along with temperature and geopotential height distribution. All profiles are given as a function of pressure. These data sets are available offline through NCDS. To access these data sets, specify the following as input within the Data Applications subsystem of the NCDS. Data sets are converted to Common Data Format (CDF) "on the fly". NCDS$DATA:LIMS-LAMAT_DAY_GRID NCDS$DATA:LIMS-LAMAT_ZONEMEAN 13. SUMMARY/SAMPLE 14. NOTES SAGE I and SAGE II meteorological profile data are provided by the NOAA National Meteorological Center (NMC). The meteorological profile data, combined with spacecraft position and velocity and SAGE I or SAGE II raw radiance data, are needed to map nitrogen dioxide, ozone, aerosol, and water vapor profiles. The meteorological data include temperature, altitude, and density profiles at 19 different pressure levels in the atmosphere. (The pressure levels themselves can be used to derive molecular (Rayleigh) scattering corrections.) In addition, the meteorological data provided by NOAA/NMC contain error estimates for both temperature and density at each of the pressure levels. These meteorological data are included as part of each SAGE I and SAGE II Profile and MERDAT data set. *92/03/12