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GES DISC DAAC Data Guide:UARS SOLSTICE Level 3BS Data Set Document

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The Solar-Stellar Irradiance Comparison Experiment (SOLSTICE) is one of 10 instruments aboard the Upper Atmosphere Research Satellite (UARS). Its primary objective is the daily measurement of solar UV spectral irradiance. Data collection began 03 October 1991 and has continued, with a few interruptions, to the present. SOLSTICE data have been processed to levels 1, 2, 3AS and 3BS. Currently, SOLSTICE level 3BS version 9 data products are available from the Goddard Space Flight Center (GSFC) Distributed Active Archive Center (DAAC).

Table of Contents:

1. Data Set Overview:

Data Set Identification:


Data Set Introduction:

The SOLSTICE level 3BS data represent a subset of the UARS dataset. SOLSTICE measures solar ultraviolet spectral irradiance at wavelengths between 119 nm and 420 nm to produce 1 nm resolved gridded irradiances. SOLSTICE also reports the intensities of 7 solar lines.


The objective of the UARS SOLSTICE is to measure the full-disk Solar UV irradiance and determine solar variability on three basic time scales:


  1. short-term variations spanning time periods of minutes to hours (exemplified by solar flares),
  2. intermediate-term variations lasting days to weeks (characterized by the solar rotation and the development of active regions),
  3. long-term variations (associated with the 11-year sunspot cycle or the 22-year magnetic field cycle).

The instrument was designed to have a high relative accuracy and precision and to follow the short and intermediate-term variations at and below the one-percent level.

Summary of Parameters:

Solar UV Spectral Irradiance


The SOLSTICE Level 3BS data include gridded irradiances representing 1 nm integrations over the whole spectral range and their formal errors derived from the data along with the values of 7 solar lines for each mission day. Each file consists of three records called SFDU, LABEL, and DATA. SFDU and LABEL records contain descriptive information about the instrument and the data. The DATA record contains the gridded irradiances and their errors followed by parameter names (seven solar line intensities and errors) and parameter values.

Related Data Sets:

The UARS SUSIM level 3BS gridded irradiance data has the same format and units except that the wavelength regions are slightly different. While there may be some similarity in the parameters and solar indices, the SUSIM versions of these, in general, have different definitions and units.

2. Investigator(s):

Investigator(s) Name and Title:

Dr. Gary J. Rottman
Laboratory for Atmospheric and Space Physics
University of Colorado
1234 Innovation Dr.
Boulder, CO 80303-7814
Telephone Numbers:
Voice: (303) 492-8324
Fax: (303) 492-6444
Electronic Mail Address:

Title of Investigation:

Solar-Stellar Irradiance Comparison Experiment

Contacts for Scientific Aspects of the Data:

Barry Knapp
Laboratory for Atmospheric and Space Physics
University of Colorado
1234 Innovation Dr.
Boulder, CO 80303-7814
Telephone Numbers:
Voice: (303) 492-8970
Fax: (303) 492-6444
Electronic Mail Address:

3. Theory of Measurements:

The general data gathering technique performed by the SOLSTICE Instrument is described in detail in the "Solar-Stellar Irradiance Comparison Experiment" article listed in the referece section 17.1 below.

4. Equipment:

Sensor/Instrument Description:


The UARS SOLSTICE instument is a three-channel ultraviolet spectrometer that measures the magnitude of the solar spectral irradiance in the wavelength range 118 to 425 nm. The instrument design permits observations of both the sun and of bright blue stars using the same optical path. Entrance and exit slit sizes along with different integration periods are used to accomodate the several orders of magnitude difference between the brightness of the sun and the stars.

The UARS SOLSTICE is mounted on a two-axis pointing platform which can track the sun and stars with an accuracy of 1.5 arc minutes. SOLSTICE is pointed toward the Sun during the daylight portion of each orbit, and toward stars during most of the nighttime portion of the orbit. One or more full spectral scans of the sun at the instrument resolution is completed each orbit. Stellar observations, requiring much longer integration times, are made at a few selected wavelengths throughout the SOLSTICE spectral range, with typically one or two stars at one or two wavelengths being observed each orbit.

Collection Environment:

Satellite data are collected from a near-circular Earth orbit of about 585 km altitude and 57 degree inclination.


Upper Atmosphere Research Satellite (UARS).

Source/Platform Mission Objectives:

UARS was launched in September 1991 with the mission of investigating the chemistry, dynamics, and energy inputs of the Earth's upper atmosphere. See the UARS Project and UARS Platform documents for more information.

5. Data Acquisition Methods:

Data are telemetered from UARS through the Tracking and Data Relay Satellite System (TDRSS) to the Data Capture Facility (DCF) at NASA GSFC. There the data are given an initial quality check, and are then forwarded to the UARS Central Data Handling Facility (CDHF). The instrument PI teams are connected to the CDHF through remote analysis computers (RACs), where they have developed software to convert the raw data to higher level processed data. The CDHF uses the production software to convert the level 0 data to level 1, 2, 3AS, and 3BS data. The Goddard DAAC acquires the UARS data from the CDHF.

6. Observations:

Data Notes:

The user is referred to the SOLSTICE SFDU metadata documents for any problems with the data. Further questions may answered by contacting the SOLSTICE team at the addresses listed above.

7. Data Description:

Spatial Characteristics:

Spectral Coverage:

119 nm to 420 nm.

Spectral Resolution:

The resolution is that of a 1 nm "boxcar" convolved with the completely resolved full-disk solar spectrum.

Grid Description:

All SOLSTICE Level 3BS data are gridded every nm on the half nm.

Temporal Characteristics:

Temporal Coverage:

Temporal coverage is from 3 October 1991 to the present. The GSFC DAAC currently has the first 5 years of SOLSTICE level 3BS data (up to 31 December 1996). Listed below are the dates within the above period for which SOLSTICE data is missing or unavailable:
          03-JUN-1992 to 10-JUL-1992
          14-JUL-1992 to 17-JUL-1992
          05-AUG-1993 to 08-AUG-1993
          18-SEP-1993 to 21-SEP-1993
          30-MAR-1995 to 05-APR-1995
          18-APR-1995 to 20-APR-1995
          16-MAY-1995 to 23-MAY-1995
          30-JUN-1995 to 02-JUL-1995
          30-JUL-1995 to 31-JUL-1995
          15-OCT-1995 to 18-OCT-1995
          03-FEB-1996 to 11-FEB-1996
          08-MAY-1996 to 09-MAY-1996
          22-JUL-1996 to 28-JUL-1996

Temporal Resolution:


Data Characteristics:


The main parameter is the gridded solar irradiances at 1 nm resolution from 119.5 to 420.5 nm. There are also parameters related to the data and seven solar indices. These include:
  1. Mean Solar Distance (MSD).
  2. H I Lyman alpha (hydrogen @ 121.6 nm) line intensity and error
  3. O I (oxygen @ 130.4 nm) line intensity and error
  4. C IV (carbon @ 154.8 nm) line intensity and error
  5. C I (carbon @ 156.1 nm) line intensity and error
  6. C I (carbon @ 165.6 nm) line intensity and error
  7. Mg II (magnesium @ 280.0 nm) core-wing ratio intensity and error
  8. Ca II (calcium @ 393.3 nm) core-wing ratio intensity and error
  9. Carrington longitude
  10. Carrington latitude

Variable Description/Definition:

The level 3BS solar spectral irradiances are an array of solar fluxes, corrected for instrument degradation. The additional solar parameters are described below:

The emission lines, H I Lyman alpha, O I, C IV, C I (156.1 nm) and C I (165.6 nm), are integrated intenities above the continuum. The Mg II and Ca II, are core to wing ratios of the integrated intensities of the line doublet divided by the mean (instantaneous) intensity of the continuum outside the self-absorbing regions. The MSD is the distance from the satellite to the sun at 1200 GMT on the day of the measurement. The Carrington latitude and longitude corresond to the heliographic latitude and longitude of the sub-earth point on the sun at 1200 GMT.

Unit of Measurement:

The solar spectral irradiance is expressed in units of watt/m3. The units of measurement for the solar parameters and lines are:
  1. UARS Mean Solar Distance (MSD) in Astronomical Units (AU).
  2. The H I, O I, C IV, and C I emission line intensity and error in [W/m3]nm
  3. Mg II, and Ca II core-to-wing ratio and error in nm.
  4. Carington latitude and longitude in degrees.

Data Range:

All values are postive real numbers.

8. Data Organization:

Data Granularity:

SOLSTICE Level 3BS granules are produced daily. Each granule is a multi-file granule consisting of two files:


  1. The binary data file (files ending with PROD, or *PROD extension) which contains the gridded irradiance data, and quality, as well as observation time, the mean solar distance, 7 solar lines and errors and Carrington latitude and longitude.


  2. An ASCII metadata file (files ending with META, or *META extension) associated with the data file containing items such as the PI assigned quality flag and record length size of the data file.

The format for granule file names is SOLSTICE_L3BS_Ddddd.Vvvvv _Ccc_xxxx, where dddd is the UARS day (0001 = 12 September 1991), vvvv is the data version number, and cc is the data version cycle number. The file extension xxxx is either PROD for the binary data files, or META for the ASCII metadata files.

The average size for a SOLSTICE Level 3BS granule is about 13 kB. The *META files are small, only about 700 bytes each.

Data Format:

The data are in a native UARS format. The files were originally created on a VAX/VMS system at the UARS CDHF, and now exist as UNIX stream files at the Goddard DAAC. SOLSTICE data file structures are presented in the Standard Formatted Data Units (SFDU) documents listed in the References section.

9. Data Manipulations:


Derivation Techniques and Algorithms:

Segemented, wavelength-dependent exponential detector degradation functions are computed (using coefficients from a calibration file) for the given day at each wavelength and applied to the irradiance and integrated irradiance data. No degradation correction is made to reported core/wing ratios.

Data Processing Sequence:

Processing Steps:

UARS/SOLSTICE Level 3B Processing for a given day uses as input the corresponding SOLSTICE Level 3A file, and a table (calibration file) of instrument degradation function coefficients which have been determined by analysis of SOLSTICE'S observations of selected bright blue stars whose irradiances in the 115-425 nm spectral range are assumed to be constant with time. The time-degradation function (which varies with wavelength) is applied to the Level 3A irradiance spectrum and the integrated irradiance of the selected spectral emission features (but not to the core/wing ratios), to produce the Level 3B product.

Processing Changes:

Version 9 data differ from version 8 in the use of improved (longer time coverage) degradation coefficients, and additional (Level 2) second-order calibrations (e.g., voltage, temperature, and PMT "turn-on" effects. Reprocessing of the data occur about once or twice a year.


Special Corrections/Adjustments:


Calculated Variables:

The data record of SOLSTICE level 3BS product contains the 1 nm resolution irradiances and associated qualities for wavelengths between 119.5 nm to 420.5 nm, starting wavelength, and solar parameters. There are five solar line intensities and their errors, two core-to-wing ratios and their errors, the mean solar distance at noon GMT, and the Carrington latitude and longitude at noon GMT.

Graphs and Plots:

Sample SOLSTICE level 3BS spectrum:
solstice sample

10. Errors:

Quality Assessment:

Data Validation by Source:

The standard error is calculated for each irradiance using the counting statistics and the calibration errors. The typical uncertainty of the relative irradiance is less than 1 percent for solar measurements. Not reported is the 2-4 percent uncertainty in the absolute knowledge of the irradiances related to the pre-flight photometric calibrations.

Also, the SOLSTICE Level 3 products are carefully filtered to remove data which may be questionable due to larger than normal pointing uncertainty, contamination by the South Atlantic Anomaly or atmospheric absorption, or which are significantly outside the range of values expected over a solar cycle or observed over the last several orbits.

Measurement Error for Parameters:

Precision information is placed in the form of a measurement standard deviation into the "data quality" field corresponding to each 1nm gridded irradiance. The solar line intensities and core-to-wing ratios also include standard deviations.

Additional Quality Assessments:


Data Verification by Data Center:

Data files are checked to ensure that they are properly transferred and translated from their original VAX/VMS format at the UARS CDHF to the DAAC's UNIX format. No additional data checks are performed by the DAAC.

11. Notes:

Limitations of the Data:

The data files exist as UNIX stream files at the DAAC. Binary data are big-endian IEEE formatted. The binary data files should be read on 32 bit machines running UNIX operating systems. This is especially important for fields which are IEEE floating point values, such as the profile data and quality values. If you are going to use a non 32-bit and/or non-UNIX machine, then you will need to write your own conversion routines to read the data files. File record length information is only listed in the ASCII metadata files (*META extension) which accompany the data and parameter files.

Known Problems with the Data:

None at this time.

Usage Guidance:

SOLSTICE Level 3 solar data may be used for any investigation that does not need a spectral resolution finer than 1 nm, or time resolution less than one day. SOLSTICE Level 3BS data may be used for studies of either short-term (e.g. 27-day) or long-term (e.g. 11-year) solar variability at the level of a few percent.

Any Other Relevant Information about the Study:


13. Future Modifications and Plans:


The SOLSTICE instrument continues to acquire data. Future reprocessing of the data are anticipated.



14. Read Software:

Software Description:

Simple read/dump programs are available for reading the WINDII level 3A data files. The read programs are available in C and IDL languages.

Software Access:

To get the software use the links below:

15. Data Access:

Contacts Information:

Help Desk
NASA Goddard Space Flight Center
Code 610.2
Greenbelt, MD 20771
Telephone Numbers:
Phone: 1-301-614-5224
FAX: 1-301-614-5268
Electronic Mail Address:


Archive Identification:

The UARS WINDII data are archived at the GES DISC under the UARS Project.

Procedures for Obtaining Data:

The SOLSTICE level 3 data files can be obtained from the GES DISC by several mechanisms. These include the following:


Data Archive Status/Plans:

The GES DISC currently supports SOLSTICE level 3BS data products.

16. Output Products and Availability:

The SOLSTICE level 3BS data are available. See the section above on Procedures for Obtaining Data for specific information.

17. References:

Satellite/Instrument/Data Processing Documentation:
  • Reber, C. A., C. E. Trevathan, R. J. McNeal, and M. R. Luther, The Upper Atmosphere Research Satellite (UARS) Mission, J. Geophys. Res. 98, D6, 10643-10647, 1993.
  • Rottman, G. J. and Woods, T. N., "In-Flight Calibration of Solar Irradiance Measurements by Direct Comparison with Stellar Observations", SPIE Proceedings, 924, 136-143, 1988.
  • Rottman, G. J., Woods, T. N., and Sparn, T. P., "Solar-Stellar Irradiance Comparison Experiment 1. 1. Instrument Design and Operation", J. Geophys. Res. 98 (1993), 10667-10677,
  • Woods, T. N., Rottman, G. J., and Ucker, G. J., "Solar-Stellar Irradiance Comparison Experiment 1. 2. Instrument Calibrations", J. Geophys. Res. 98 (1993), 10679-10694.
  • Rottman, G. J. and T. N. Woods, "UARS Solar Stellar Irradiance Comparison Experiment (SOLSTICE)", SPIE Proceedings, 2266, 317-329, 1994.


Journal Articles and Study Reports:
  • Woods, T. N., D. K. Prinz, J. London, G. J. Rottman, P. C. Crane, R. P. Cebula, E. Hilsenrath, G. E. Brueckner, M. D. Andrews, O. R. White, M. E. VanHoosier, L. E. Floyd, L. C. Herring, B. G. Knapp, C. K. Pankratz, and P. A. Reiser, "Validation of the UARS Solar Ultraviolet Irradiances: Comparison with the ATLAS1 and 2 Measurements", J. Geophys. Res., 101, 9541-9569, 1996.


Goddard DAAC IMS online documentation:

18. Glossary of Terms:

A collection of parameters packaged with associated ancillary and labeling data. Uniformly processed and formatted. Typically uniform temporal and spatial resolution.
A logically meaningful grouping or collection of similar or related data. Data having mostly similar characteristics (source or class of source, processing level and algorithms, etc.).
A Granule is the smallest aggregation of data which is independently managed.

19. List of Acronyms:

CDHF Central Data Handling Facility
DAAC Distributed Active Archive Center
DCF Data Capture Facility
EOS Earth Observing System
FOV Field of View
GSFC Goddard Space Flight Center
IMS Information Management System
km kilometer
m meter
MSD mean solar distance
mW milliwatts
NASA National Aeronautics and Space Administration
nm nanometer
PI Principal Investigator
RAC Remote Analysis Computer
SFDU Standard Formatted Data Units
SOLSTICE Solar-Stellar Irradiance Comparison Experiment
SSPP Solar Stellar Pointing Platform
SUSIM Solar Ultraviolet Spectral Irradiance Monitor
TDRSS Tracking and Data Relay Satellite System
UARS Upper Atmosphere Research Satellite

20. Document Information:

Document Revision Date:Fri May 10 11:54:18 EDT 2002

17 Jul 1997

Document Review Date:

17 Jul 1997

Document ID:


Document Curator:


Document URL:

UARS buttonUARS Project

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