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Stratospheric Aerosol Measurement II (SAM II)
Langley DAAC Project Guide

Summary:

The Stratospheric Aerosol Measurement II (SAM II) experiment flew aboard the Nimbus-7 spacecraft and provided vertical profiles of aerosol extinction in both the Arctic and Antarctic polar regions. The SAM II data coverage began on October 29, 1978 and extended through December 18, 1993 until SAM II was no longer able to acquire the Sun. The data coverage for the Arctic region extends through January 7, 1991, and contains data gaps beginning in 1988 that increase in size each year. The data coverage for the Antarctic region is continuous through December 18, 1993 except for a time period from mid-January 1993 through October 1993. The data gaps for both the Arctic and Antarctic regions are due to an orbit degradation associated with the Nimbus-7 spacecraft.

Table of Contents:

  1. Project/Campaign Overview
  2. Data Availability
  3. Data Access
  4. Principal Investigator Information
  5. Submitting Investigator Information
  6. References
  7. Glossary and Acronyms
  8. Document Information

1. Project/Campaign Overview:

Name of Project/Campaign:

Stratospheric Aerosol Measurement II, SAM II

Project/Campaign Introduction:

See Summary

Project/Campaign Mission Objectives:

The SAM II instrument, aboard the Earth-orbiting Nimbus-7 spacecraft, was designed to measure solar irradiance attenuated by aerosol particles in the Arctic and Antarctic stratosphere. The scientific objective of the SAM II experiment was to develop a stratospheric aerosol data base for the polar regions by measuring and mapping vertical profiles of the atmospheric extinction due to aerosols. This data base allows for studies of aerosol changes due to seasonal and short-term meteorological variations, atmospheric chemistry, cloud microphysics, volcanic activity and other perturbations. The results obtained are useful in a number of applications, particularly the evaluation of any potential climatic effect caused by stratospheric aerosols.

Discipline(s):

The measurement technique is solar occultation. The spectrometer is activated to take solar irradiance measurements during the periods when the line-of-sight from the SAM II instrument to the Sun has tangent altitudes between sea level and 150 km. It is self-calibrating in that an exoatmospheric measurement is made before a sunset or after a sunrise measurement. Attenuation of sunlight by a species is measured and processed to produce profile data.

Geographic Region(s):

All the points obtained during one day in a given region will be at very nearly the same latitude, but as time progresses, the latitude of the measurements will slowly change with the season by one to two degrees each week. The latitude range for SAM II varies with season. The latitude of the measurements for years 1978 through 1987 gradually moves from the lowest latitude, 64 degrees, at the solstices to the highest latitude, 83 degrees, at the equinoxes. After 1987, the Antarctic coverage gradually moved equatorward and by 1992, the latitude of measurements moved from the lowest latitude, 53.1 degrees at the solstices to the highest latitude, 69.2 degrees at the equinoxes. In the Arctic region, the latitude of measurements by 1991 gradually moved from the lowest latitude, 64 degrees a the solstices to the highest latitude, 86.2 degrees at the equinoxes. The longitude interval for consecutive sunrises or consecutive sunsets is about 26 degrees.

Detailed Project/Campaign Description:

The SAM II instrument is a single-channel Sun photometer employing a cassegrainian telescope and interference filter to define the spectral passband. Solar radiation is reflected off a scan mirror into the telescope with an image of the Sun formed at the slot plate. The instrument's instantaneous field of view, defined by the aperture on the slot plate, is a 30-arc-second circle which produces a vertical resolution on the horizon of approximately 0.5 km. Radiation passing through the aperture is collected with a field lens, passes through an interference filter, and is measured by a silicon photodiode detector. The spectral passband, defined by the interference filter, has a 0.038 micron bandwidth centered at a wavelength of 1.0 micron.

The entire optical and detector system is contained in the azimuth gimbal to allow the instrument to be pointed at the Sun. Prior to spacecraft sunrise or sunset, the instrument is moved (i.e., pointed to the predicted solar acquisition angle). When the Sun enters the instrument field of view, the instrument locks onto the radiometric center of the Sun within +- arc minute in azimuth and then acquires the Sun in elevation by rotating the scan mirror.

As the Sun sets or rises relative to the Earth's horizon, the elevation mirror scans vertically across the solar disk at a nominal rate of 15 arc minutes per second. The radiometric data are then sampled at a rate of 50 samples per second, digitized to 10-bit resolution, and recorded for later transmission back to Earth for data reduction.

The SAM II instrument uses the Sun as a constant irradiance source (thus is self-calibrating before each sunset or after each sunrise) and measures the radiation that passes through the Earth's atmosphere during a sunrise or sunset.

The photometer assembly scans the Sun at a nominal rate of 15 arc minutes per second. The photometric data are sampled at a rate of 50 samples-per-second and digitized to 10-bit resolution.

The SAM II instrument, along with a number of other sensors, is mounted on the Earth-orbiting spacecraft. The orbital characteristics of this spacecraft determine the frequency and geographic locations of the SAM II measurements. The mode of operation of the SAM II instrument is such that it takes data during each sunrise and sunset encountered. The spacecraft has an orbital period of 104 minutes, which means that it circles the Earth nearly 14 times per day. There is a measurement opportunity for the SAM II each time that the spacecraft enters into or emerges from the Earth's shadow. Consequently, the instrument takes data during approximately 14 sunrises and 14 sunsets each Earth day. The spacecraft was placed in a high-noon, Sun-synchronous orbit; that is, the spacecraft crossed the Equator during each orbit at local noon. In general terms, this means that the orbital plane of the spacecraft was fixed with respect to the Sun, and thus all sunsets occur in the Arctic region and all sunrises occur in the Antarctic region.

In the course of a single day, measurements of the stratospheric aerosol are obtained at 14 points spaced 26 degrees apart in longitude in the Arctic region and similarly for the Antarctic region. All the point obtained during 1 day in a given region are at very nearly the same latitude, but as time progresses, the latitudes of the measurements slowly change with the season by 1 to 2 degrees each week, gradually sweeping out the area from approximately 64.0 to 83.0 degrees. The lowest latitude coverage occurs at the solstices whereas the highest latitudes are measured at the equinoxes.

In the course of 1 week, therefore, the instrument makes about 98 measurements in each region, all in a band of latitude of approximately 1.0 degree. Theses measurements give a fairly spatially dense set of data points. When the locations of all the measurements obtained in one week are plotted on a geographic set of axes, one finds that the separation between points is only about 4.0 degrees in longitude. In a 6-month period of time, the total number of observations is on the order of 5000.

However, due to an orbit degradation associated with the spacecraft, there has been a change and disruption in the collection of SAM II data beginning in 1987. During the period of time from 1987 through 1993, orbital precession caused the spacecraft to cross the equator earlier than the planned high-noon crossing. This gradually moved the Antarctic coverage equatorward. Initially the Antarctic latitudinal coverage extended from the lowest latitude, 64.5 degrees at the solstices, to the highest latitude, 81.0 degrees at the equinoxes. By 1992 the Antarctic coverage gradually shifted to extend from 53.1 degrees at the solstices, to 69.2 degrees at the equinoxes. In the Arctic region the initial latitudinal coverage extended from the lowest latitude, 64.1 degrees at the solstices, to the highest latitude, 83.0 degrees at the equinoxes. Gradually by 1991 the highest Arctic latitudinal coverage extended to 86.2 at the equinoxes.

The orbital precession also affected the spacecraft orientation and prevented the SAM II instrument from acquiring the Sun for certain periods of time. In the Arctic region many sunset events were lost because an S-band antenna blocked SAM II's view to the Sun. Sunset events were lost for the following periods of time: mid-June through mid-August 1988; mid-March through mid-September 1989; mid-January through September 1990; and from January 7, 1991, through December 1993. In the Antacritc region the SAM II instrument was not able to acquire the Sun for the period of time from mid-January through October 1993. The final 2 months of SAM II data for the Antarctic region were collected during November and December 1993.

2. Data Availability:

Data Type(s):

Atmospheric transmittance data at one wavelength are obtained during solar occultation at each satellite sunrise and sunset. Solar irradiance measurements are made at 1.0 micron. Each record contains eight parameters: vertical profiles of extinction km-1, extinction km-1 uncertainty, extinction ratio, extinction ratio uncertainty, NMC temperature, temperature uncertainty, and pressure as a function of altitude.

Input/Output Media:

The data are available by FTP.
Data are also available on cd-rom.

Proprietary Status:

All data are available to the public.

3. Data Access:

Data Center Location:

Langley DAAC User and Data Services Office
NASA Langley Research Center
Mail Stop 157D
Hampton, Virginia 23681-2199
USA
Telephone: (757) 864-8656
FAX: (757) 864-8807
E-mail: larc-asdc-uds@lists.nasa.gov

Contact Information:

Kathleen A. Powell
Aerosol Research Branch
Mail Stop 475
Atmospheric Sciences Division
NASA Langley Research Center
Hampton, Virginia 23681
USA
Telephone: (757) 864-2688
FAX: (757) 864-2671
E-mail: kathleen.a.powell@nasa.gov

Associated Costs:

There is no fee for retrieving this data.

4. Principal Investigator Information:

Dr. M. P. McCormick, Experiment Scientist and Experiment Team Leader
NASA Langley Research Center

5. Submitting Investigator Information:

Dr. M. P. McCormick, Experiment Scientist and Experiment Team Leader
NASA Langley Research Center

6. References:

  1. Albritton, D. L., et al., Scientific Assessment of Stratospheric Ozone: 1989, WMO Global Ozone Research and Monitoring Project Report No. 20, 1990.
  2. 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, Appl. Opt., 18, no. 9, 1404-1413, May 1, 1979.
  3. Chu, W. P., M. T. Osborn, and L. R. McMaster, SAM II Data Users' Guide, NASA RP-1200, July 1988.
  4. Hamill, P. and L. R. McMaster, Polar Stratospheric Clouds - Their Role in Atmospheric Processes, NASA CP-2318, 1984.
  5. Hamill, P., O. B. Toon, and R. P. Turco, Characteristics of Polar Stratospheric Clouds During the Formation of the Antarctic Ozone Hole, Geophys. Res. Lett., 13, no. 12, Nov. Suppl., 1288-1291, 1986.
  6. Hamill, P., O. B. Toon, and R. P. Turco, Aerosol Nucleation in the Winter Arctic and Antarctic Stratospheres, Geophys. Res. Lett., 17, 417-420, 1990.
  7. Hamill, P. and O. B. Toon, Denitrification of the Polar Winter Stratosphere: Implications of SAM II Cloud Formation Temperatures, Geophys. Res. Lett., 17, 441-444, 1990.
  8. Hofmann, D. J. and J. M. Rosen, On the Temporal Variation of Stratospheric Aerosol Size and Mass During the First 18 Months Following the 1982 Eruptions of El Chichon, J. Geophys. Res., 89, no. D3, 4883-4890, June 20, 1984.
  9. Kent, G. S. and M. P. McCormick, SAGE and SAM II Measurements of Global Stratospheric Aerosol Optical Depth and Mass Loading, J. Geophys. Res., 89, no. D4, 5303-5314, June 30, 1984.
  10. Kent, G. S., C. R. Trepte, U. O. Farrukh, and M. P. McCormick, Variation in the Stratospheric Aerosol Associated With the North Cyclonic Polar Vortex as Measured by the SAM II Satellite Sensor, J. Atmos. Sci., 42, no. 14, 1536-1551, July 15, 1985.
  11. Kent, G. S., P. -H. Wang, U. O. Farrukh, and G. K. Yue, Validation of SAM II and SAGE Satellite, Final Report NASA CR-178256, April 1987.
  12. Kent, G. S., U. O. Farrukh, P. -H. Wang, and A. Deepak, SAGE I and SAM II Measurements of 1.0 micron Aerosol Extinction in the Free Troposphere, J. Appl. Meteorol., 27, 269-279, March 1988.
  13. Madrid, C. R., The Nimbus 7 Users' Guide, NASA Goddard Space Flight Center, NASA TM-79969, August 1978.
  14. McCormick, M. P., P. Hamill, T. J. Pepin, W. P. Chu, T. J. Swissler, and L. R. McMaster, Satellite Studies of the Stratospheric Aerosol, Bull. American Meteorol. Soc., 60, no. 9, 1038-1046, September 1979.
  15. McCormick, M. P., W. P. Chu, L. R. McMaster, G. W. Grams, B. M. Herman, T. J. Pepin, P. B. Russell, T. J. Swissler, SAM II Aerosol Profile Measurements, Poker Flat, Alaska, July 16-19, 1979 Geophys. Res. Lett., 8, no. 1, 3-4, January 1981.
  16. McCormick, M. P., W. P. Chu, G. W. Grams, P. Hamill, B. M. Herman, L. R. McMaster, T. J. Pepin, P. B. Russell, H. M. Steele, and T. J. Swissler, High Altitude Stratospheric Aerosols Measured by the SAM II Satellite System in 1978 and 1979, Science, 214, no. 4518, 328-331, October 16, 1981.
  17. McCormick, M. P., H. M. Steele, P. Hamill, W. P. Chu, and T. J. Swissler, Polar Stratospheric Cloud Sightings by SAM II, J. Atmos. Sci., 39, no. 6, 1387-1397, June 1982.
  18. McCormick, M. P., C. R. Trepte, and G. S. Kent, Spatial Changes in the Stratospheric Aerosol Associated With the North Polar Vortex, Geophys. Res. Lett., 10, no. 10, 941-944, October 1983.
  19. McCormick, M. P., P. Hamill, and U. O. Farrukh, Characteristics of Polar Stratospheric Clouds as Observed by SAM II, SAGE, and Lidar, J. Meteorol. Soc. Japan, 63, no. 2, 267-276, April 1985.
  20. McCormick, M. P. and J. C. Larsen, Antarctic Springtime Measurements of Ozone, Nitrogen Dioxide, and Aerosol Extinction by SAM II, SAGE, and SAGE II, Geophys. Res. Lett., 13, no. 12, Nov. Suppl., 1280-1283, 1986.
  21. McCormick, M. P. and C. R. Trepte, SAM II Measurements of Antarctic PSC's and Aerosols, Geophys. Res. Lett., 13, no. 12, Nov. Suppl., 1276-1279, 1986.
  22. McCormick, M. P. and C. R. Trepte Polar Stratospheric Optical Depth Observed Between 1978 and 1985, J. Geophys. Res., 92, no. D4, 4297-4306, April 30, 1987.
  23. McCormick, M. P., C. R. Trepte, and M. C. Pitts, Persistence of Polar Stratospheric Clouds in the Southern Polar Region, J. Geophys. Res., 94, no. D9, 11241-11251, August 20, 1989.
  24. McCormick, M. P., P. -H. Wang, and M. C. Pitts, Background Stratospheric Aerosol and Polar Stratospheric Cloud Reference Models, Advances in Space Research, 13, no. 1, 7-29, 1993.
  25. McCormick, M. P., P. -H. Wang, and L. R. Poole, Chapter 8: Stratospheric Aerosols and Clouds, pp. 205-222, Aerosol-Cloud-Climate Interactions. Edited by Peter V. Hobbs, Copyright by Academic Press, Inc., Harcourt Brace & Company, 1993.
  26. McMaster, L. R., Stratospheric Aerosol and Gas Experiment (SAGE II), Sixth Conference on Atmospheric Radiation, American Meteorological Soc., J46-J48, 1986.
  27. Osborn, M. T. and C. R. Trepte, SAM II and SAGE Data Management and Processing, NASA CR-178244, February 1987.
  28. Osborn, M. T., M. C. Pitts, K. A. Powell, and M. P. McCormick, SAM II Aerosol Measurements During the 1989 AASE, Geophys. Res. Lett., 17, 397-400, 1990.
  29. Osborn, M. T., L. R. Poole, and P. -H. Wang, SAM II and Lidar Aerosol Profile Comparisons During AASE, Geophys. Res. Lett., 17, 401-404, 1990.
  30. Pepin, T. J. and M. P. McCormick, Stratospheric Aerosol Measurement Experiment MA-007, Apollo-Soyuz Test Project - Preliminary Science Report, NASA TMX-58173, 1976.
  31. Pitts, M. C., L. R. Poole, and M. P. McCormick, Climatology of Polar Stratospheric Clouds Determined from SAM II Observations, Digest of Topical Meeting on Optical Remote Sensing of the Atmosphere, 1990, (Optical Society of America, Washington D. C., 1990), 4, 206-209.
  32. Pitts, M. C. and L. W. Thomason, The Impact of the Eruptions of Mount Pinatubo and Cerro Hudson on Antarctic Aerosol Levels During the 1991 Austral Spring, Geophys. Res. Lett., 20, no. 22, 2451-2454, November 19, 1993.
  33. Poole, L. R. and M. P. McCormick, Polar Stratospheric Clouds and the Antarctic Ozone Hole, J. Geophys. Res., 93, no. D7, 8423-8430, July 20, 1988.
  34. Poole, L. R., S. Solomon, M. P. McCormick, and M. C. Pitts, The Interannual Variability of Polar Stratospheric Clouds and Related Parameters in Antarctica During September and October, Geophys. Res. Lett., 16, 1157-1160, 1989.
  35. Poole, L. R. and M. C. Pitts, Polar Stratospheric Cloud Climatology Based on SAM II Observations from 1978-1989, in press, J. Geophys. Res., 1994.
  36. Pueschel, R. F., K. G. Snetsinger, P. Hamill, J. K. Goodman, and M. P. McCormick, Nitric Acid in Polar Stratospheric Clouds: Similar Temperature of Nitric Acid Condensation and Cloud Formation, Geophys. Res. Lett., 17, 429-432, 1990.
  37. Russell, P. B., M. P. McCormick, L. R. McMaster, T. J. Pepin, W. P. Chu, and T. J. Swissler, SAM II Ground-Truth-Plan Correlative Measurements for the Stratospheric Aerosol Measurement-II (SAM II) Sensor on the Nimbus G Satellite, NASA TM-78747, 1978.
  38. Russell, P. B., M. P. McCormick, T. J. Swissler, W. P. Chu, J. M. Livingston, W. H. Fuller, Jr., J. M. Rosen, D. J. Hofmann, L. R. McMaster, D. C. Woods, and T. J. Pepin, Satellite and Correlative Measurements of the Stratospheric Aerosol II: Comparison of Measurements Made by SAM II, Dustsondes and an Airborne Lidar, J. Atmos. Sci., 38, no. 6, 1295-1312, June 1981.
  39. Russell, P. B., T. J. Swissler, M. P. McCormick, W. P. Chu, J. M. Livingston, and T. J. Pepin, Satellite and Correlative Measurements of the Stratospheric Aerosol I: An Optical Model for Data Conversions, J. Atmos. Sci., 38, no. 6, 1279-1294, June 1981.
  40. Russell, P. B., M. P. McCormick, T. J. Swissler, J. M. Rosen, D. J. Hofmann, and L. R. McMaster, Satellite Correlative Measurements of the Stratospheric Aerosol III: Comparison of Measurements by SAM II, SAGE, Dustsondes, Filters, Impactors and Lidar, J. Atmos. Sci., 41, no. 11, 1791-1800, June 1, 1984.
  41. Russell, James M., III, Middle Atmosphere Program - Handbook for MAP, Volume 22, Univ. of Illinois, NASA CR-180128, September 1986.
  42. Steele, H. M., P. Hamill, M. P. McCormick, and T. J. Swissler, The Formation of Polar Stratospheric Clouds, J. Atmos. Sci., 40, no. 8, 2055-2067, August 1983.
  43. Turco, R. P., O. B. Toon, and P. Hamill, Heterogeneous Physiochemistry of the Polar Ozone Hole, J. Geophys. Res., 94, no. D14, 16493-16510, November 30, 1989.
  44. Twomey, S., Introduction to the Mathematics of Inversion in Remote Sensing and Indirect Measurements, Elsevier Scientific Publ. Co., 1977.
  45. Wang P. -H. and M. P. McCormick, Behavior of Zonal Mean Aerosol Extinction Ratio and Its Relationship With Zonal Mean Temperature During the Winter 1978-1979 Stratospheric Warming, J. Geophys. Res., 90, no. D1, 2360-2364, February 20, 1985.
  46. Wang, P. -H. and M. P. McCormick, Variations in Stratospheric Aerosol Optical Depth During the Northern Warmings, J. Geophys. Res., 90, no. D6, 10597-10606, October 20, 1985.
  47. Watterson, I. G. and A. F. Tuck, A Comparison of the Longitudinal Distributions of Polar Stratospheric Clouds and Temperatures for the 1987 Antarctic Spring, J. Geophys. Res., 94, no. D14, 16511-16525, November 30, 1989.
  48. Yue, G. K., M. P. McCormick, and W. P. Chu, A Comparative Study of Aerosol Extinction Measurements Made by the SAM II and SAGE Satellite Experiments, J. Geophys. Res., 89, no. D4, 5321-5327, June 30, 1984.
SAM II Measurements of the Polar Stratospheric Aerosol:

7. Glossary and Acronyms:

EOSDIS Acronyms (PDF).

CDC - Control Data Corporation
DAAC - Distributed Active Archive Center
DBMS - Database Management System
EOSDIS - Earth Observing System Data and Information System
ERB - Earth Radiation Budget
GSFC - Goddard Space Flight Center
GUI - Graphical User Interface
IMS - Information Management System
LaRC - Langley Research Center
MET - Meteorological
NASA - National Aeronautics and Space Administration
NMC - National Meteorological Center
NOAA - National Oceanic and Atmospheric Administration
PSC - Polar Stratospheric Cloud
SAGE - Stratospheric Aerosol and Gas Experiment
SAGE I - Stratospheric Aerosol and Gas Experiment I
SAGE II - Stratospheric Aerosol and Gas Experiment II
SAM II - Stratospheric Aerosol Measurement II
UDS - User and Data Service
URL - Uniform Resource Locator

8. Document Information:


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