GES DISC DAAC Data Guide:
UARS Level 3B Data Sets Document

Summary:

Upper Atmosphere Research Satellite (UARS) telemetry data are processed at the Goddard Space Flight Center using algorithms and software developed, maintained, and refined by UARS Investigators. Instrument investigators are responsible for processing up to Level 2 (the geophysical data at the "footprint" of the instrument) and Level 3A (the geophysical data interpolated to equal and common spacing along the measurement trajectory). To aid in the analysis and intercomparison of atmospheric data, the UARS Science Team established a requirement to be able to display atmospheric measurements as latitude-longitude contours on selected pressure surfaces using a common algorithm. These data, called Level 3B, are available for the Cryogenic Limb Array Etalon Spectrometer (CLAES), the Improved Stratospheric and Mesospheric Sounder (ISAMS), and the Microwave Limb Sounder (MLS). The UARS level 3B data are available from the Goddard Space Flight Center (GSFC) Distributed Active Archive Center (DAAC).

Table of Contents:

• 1 Data Set Overview
• 2 Investigator(s)
• 3 Theory of Measurements
• 4 Equipment
• 5 Data Acquisition Methods
• 6 Observations
• 7 Data Description
• 8 Data Organization
• 9 Data Manipulations
• 10 Errors
• 11 Notes
• 12 Application of the Dataset
• 13 Future Modification and Plans
• 14 Software
• 15 Data Access
• 16 Output Products and Availability
• 17 References
• 18 Glossary of Terms
• 19 List of Acronyms
• 20 Document Information

1. Data Set Overview

Data Set Identification:

UARS CLAES LEVEL 3B DAILY LATITUDE GRIDDED FOURIER COEFFICIENTS

UARS ISAMS LEVEL 3B DAILY LATITUDE GRIDDED FOURIER COEFFICIENTS

UARS MLS LEVEL 3B DAILY LATITUDE GRIDDED FOURIER COEFFICIENTS

Data Set Introduction:

The Upper Atmosphere Research Satellite (UARS) level 3B data set consists of daily measurements of atmospheric trace gases, temperature, aerosols and wind profiles, represented as sets of Fourier coefficients for each latitude band and pressure level. Associated with each set of coefficients is an error covariance matrix which provides estimates of the uncertainties inherent in the derived coefficients. Results are reported separately for the ascending and descending portions of the orbits.

All UARS level 3B data are derived from the corresponding UARS level 3AL data. The level 3AL data file consists of a collection of profiles of atmospheric data that have been sorted by both latitude and time. The standard latitude values at which level 3AL records are written are from -88.0 degrees to +88.0 degrees latitude in 4.0 degree increments.

The data file structures for this file type is found in the Standard Formatted Data Units (SFDU) documents listed in the References section below.

Objective:

UARS was mandated in 1976 when it became evident that human activities were having a devastating affect on the protective ozone layer, mostly through the use of chlorofluorocarbons (CFCs). The UARS was outfitted with 9 instruments designed to provide the first simultaneous, comprehensive, global coverage of upper atmosphere dynamics (HRDI, WINDII), composition (CLAES, ISAMS, HALOE, MLS), and energy input (PEM, SOLSTICE, SUSIM) data, and began contributing to this effort following its deployment from the space shuttle in September 1991.

Summary of Parameters:

Level 3B data are currently derived by the UARS Central Data Handling Facility (CDHF) for three of the nine UARS instruments for which level 3AL data files exist:

• Cryogenic Limb Array Etalon Spectrometer (CLAES)
• Improved Stratospheric and Mesospheric Sounder (ISAMS)
• Microwave Limb Sounder (MLS)

The three instruments measure chemical composition and temperature. CLAES and ISAMS also measure aerosols. Plans to produce level 3B data for HRDI and WINDII, the two instruments that measure wind fields and temperature of the upper atmosphere have not been implemented to date. No level 3B data are derived for those instruments which measure energy input into the atmosphere (i.e., SOLSTICE, SUSIM, PEM), nor for those make use of solar occultation to determine trace species profiles (i.e., HALOE). All of the above data are archived at the Goddard Distributed Active Archive Center (DAAC).

Discussion:

The Level 3B data files are written in the Standard Data Format Units (SFDU) format. The file structures for the level 3B coefficient and covariance files are similar. Each file consists of three records called SFDU, LABEL, and DATA. SFDU and LABEL records contain descriptive information about the instrument and the data, such as start/stop time of the data, number of records in the file, etc. The DATA record contains the profile data and their standard deviations. Time, latitude longitude, local solar time, and solar zenith angles are provided with each DATA record. Each data file is accompanied by a short ASCII metadata file, which provides descriptive information such as the start and stop time of the data, file record lengths, and the UARS quality flag.

Related Data Sets:

See the Overview section below for information on specific UARS instrument data sets.

2. Investigators:

Gridding Principal Investigator:

Name:

Dr. Carl A. Reber

Addresses:

NASA Goddard Space Flight Center

Mailstop 170.0

Building 8 Room 421

Greenbelt, Maryland 20771

USA

Telephone Numbers:

Voice: +1 301 286-6534

FAX: +1 301 286-1671

Electronic Mail Address:

reber@skip.gsfc.nasa.gov

Title of Investigation:

Contact Information:

Name:

Dr. Frank T Huang

Addresses:

NASA Goddard Space Flight Center

Mailstop 453.3

Greenbelt, Maryland 20771

USA

Telephone Number:

Voice: +1 301 731-9300

Electronic Mail Address:

huang@grid.gsfc.nasa.gov

3. Theory of Measurements:

Consult the level 3A guide documents for each instrument:

• CLAES Theory of Measurements
• ISAMS Theory of Measurements
• MLS Theory of Measurements

4. Equipment:

Instrument Description:

Overview:

All dynamics and composition experiments employ limb-viewing geometry to detect characteristic wavelengths of radiation emitted by atmospheric molecules along a line-of-sight. Intensity of emitted radiation is directly proportional to the gas density. A brief description of each instrument for which level 3B data are available follows.

Cryogenic Limb Array Etalon Spectrometer (CLAES)

Improved Stratospheric and Mesospheric Sounder (ISAMS)

Microwave Limb Sounder (MLS)

Collection Environment:

Satellite.

Platform:

Upper Atmosphere Research Satellite (UARS).

Platform Mission Objectives:

UARS was launched September 12, 1991 with the mission of investigating the chemical and dynamical processes of the Earth's upper atmosphere. See the UARS Platform document for more information.

5. Data Acquisition Methods:

6. Observations:

Data Notes:

There are two types of level 3B coefficients saved on the UARS data system. The first type are the results found from the sequential estimation done forward in time. They are in the form of Fourier coefficients and corresponding covariance matrices representing 12:00 GMT on each day. The second type are the analogous results found by combining the forward and backward estimations, also at 12:00 GMT. The corresponding covariance matrix files are stored in files separate from the coefficient files. Only the combined coefficients are available to users at the Goddard DAAC.

Both the coefficient files and the covariance matrix files contain two sets of results, those representing data from the ascending mode and those representing data from the descending mode. These are also stored in separate level 3B files.

In all, there are eight level 3B files corresponding to each level 3AL file. These consist of coefficient and covariance files, files for ascending and descending mode data, and forward and two sided files.

It should be noted that non-sequential estimates do not generate forward files. For these cases, there are four 3B files for each 3AL file.

7. Data Description:

Spatial Characteristics:

Spatial Coverage:

Spatial coverage alternates each UARS yaw cycle. This means that alternately views from 34N to to 80S or 34S to 80N in 36 day periods. ISAMS also has a telescope that can view both hemispheres. UARS has a near circular orbit at 585 km altitude inclined 57 degrees to the Equator. These orbital parameters, combined with measurement characteristics for most of the atmospheric sensors, yield a measurement pattern that produces near global coverage daily.

Spatial Coverage Map:

Examples of coverage for each instrument are available in the Level 3A Guide documents:

CLAES Coverage Map
ISAMS Coverage Map
MLS Coverage Map

Spatial Resolution:

Level 3B: 4 degrees latitude, varies in longitude.

Vertical resolution is about 2.5 km between pressure levels.

Projection:

Not Applicable.

Grid Description:

The CLAES, ISAMS, and MLS instrument data use pressure referenced data arrays. It should be noted that not all species within a data product will contain all 45 pressure levels. The index of the data array defines the pressure level (in millibars) given by:

        P(i) = 1000 x 10**(-i/6) mb, where i=0,1,2,..... 45

        z(i) = 5*i              for 1 <= i <= 12,
        z(i) = 60  + (i-12)*3   for 13 <= i <= 32,
        z(i) = 120 + (i-32)*5   for 33 <= i <= 88.

Again, not all altitude levels will necessarily be output per file. HRDI will be output to both the pressure and altitude grids.

Temporal Characteristics:

Temporal Coverage:

The temporal coverage of each instrument is shown below. For data coverage available from the Goddard DAAC, please view the data product list within the online Goddard DAAC Information Management System (IMS), or contact the Goddard DAAC User Services Office (see section 6 below). The temporal resolution of these data are daily.

NOTE *: The 183 GHz radiometer on MLS ceased operating in April 1993. Hence, no MLS H2O and O3_183 are available after April 20, 1993.

Temporal Resolution:

The temporal resolution of level 3B data granules is daily.

Data Characteristics:

Parameters:

Level 3B data may not be derived for all measured parameters, as low signal-to-noise ratios may allow only zonal means for some species. In, addition, not all of the level 3B instrument species and wind data will be immediately available through the Goddard DAAC. The data are released to the DAAC in stages pending completion of quality assurance procedures by the UARS Gridding Scientist and the UARS Project Scientists. As of April 1996, the endorsed level 3B products for distribution to the DAAC include the following:

NOTE: vmr = volume mixing ratio = 10E-6 ppmv = parts per million by volume

Users are referred to present and future documents by the individual instrument groups for a current list of measured parameters and altitude ranges.

8. Data Organization:

Data Granularity:

All UARS level 3B scientific instrument data are maintained in files containing data from one instrument and specie/subtype per UARS day. Because the data from the ascending and descending nodes have been treated separately in the level 3B algorithm, there will be a total of four files per day for each specie (i.e., coefficient file ascending node, covariance file ascending node, coefficient file descending node, covariance file descending node). The data have been translated to an IEEE format for sequential access with sequential organization and variable length records.

A data granule is the smallest orderable amount of data, that the Goddard DAAC manages. For the UARS level 3B data, a granule is one instrument, one species, one node per day.

In addition to the binary data file (files ending with PROD, or *PROD extension), an order will be packaged with the following documentation and software:

1. Level 3B SFDU document
2. Level 3B README (this file)
3. Level 3B read routines (see section 4.3)
4. Instrument-specific data quality document (if available)
5. Instrument-specific Whole Data Set SFDU document

The first three items are generic to level 3B data from all UARS instruments, while the last two documents will differ among instruments. Even though the data quality document was written by the UARS PI in reference to the level 3A data, it is included as part of the DAAC's level 3B distribution package since the level 3A data is the primary input to the level 3B processing algorithm.

The naming convention for UARS granule file names distributed by the Goddard DAAC is as follows:

iiii_Lll_Sssss_aa_f_ _Ddddd.Vvvvv_Ccc_xxxx

where:

iiii

is one of the instrument type acronyms, CLAES, ISAMS, or MLS

ll

is the UARS processing level (3B),

ssss

is the subtype or specie,

aa

is the node designator ( AS=ascending, DS=descending),

f

designates a coefficient (C) or covariance (CV) file,

dddd

is the UARS acquisition day (D0001 = 12 September 1991),

vvvv

is the data version number),

cc

is the data version cycle number, and

xxxx

is the file extension (PROD for the binary files, or META for the ASCII metadata files)

For a full description of the naming convention see the "meta_desc.doc" file.

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 DAAC. Data file structures are presented in the Standard Formatted Data Units (SFDU) documents listed in the References section.

9. Data Manipulations:

Formulae:

Level 3B data consist of sets of Fourier coefficients (in longitude), auxiliary information, and the corresponding covariance matrices, representing the measurements at the selected latitudes and altitudes (or pressure levels). A set of coefficients and matrices are produced for each day (corresponding to 12 GMT) for each orbital mode (ascending or descending) for each measured parameter. The coefficients and matrices are calculated using a sequential estimation technique which is run forward and backward in time and then combined. Details on the mathematical formulations can be found in the LEVEL 3B DATA DESCRIPTION DOCUMENT.

Derivation Techniques and Algorithms:

The algorithm used to generate the level 3B data is sequential in nature and is a stationary form of the Kalman filter. At the beginning of each 36 day yaw period, the coefficients and covariance matrices are initialized, and the estimator is run forward in time and separately backward in time for many days; the combined results of the forward and backward estimation, corresponding to 12:00 GMT for each day, are the level 3B product for that day. There are generally 29 or 30 data points per day at a given latitude from the 3AL data used as input. To avoid potential problems due to local solar time effects, the data are initially separated into ascending and descending mode data, and these two sets are treated separately. There are thus 14 or 15 data points for each of the two modes.

For each instrument, parameter, latitude, pressure surface, and ascending or descending mode, the algorithm performs the following operations:

• For each new measurement in a sequence, a set of estimated Fourier coefficients is computed, using as input the set of Fourier coefficients and corresponding covariance matrix obtained from the previous data point, and the uncertainty of the new measurement. (The previous set of coefficients is generally called the a priori coefficients and the previous covariance matrix is referred to as the a priori covariance matrix.)

• The a priori covariance matrix is also updated using a predefined function which determines the filter's memory length and shape.

• This procedure is repeated sequentially for each data point in the set. For the data point which is closest to (but does not exceed) 12:00 GMT of each day, the coefficients and covariance matrix are saved for the next step in the processing.

• Estimates of coefficients are calculated sequentially backward in time, using the same data set.

• The backward and forward estimates near 12:00 GMT are combined and saved. These combined results are obtained by using as weights the forward and backward covariances, and the time differences (from 12:00 GMT) of the nearest data points produced by the forward and backward calculations. It is these combined results that form the Level 3B data set.

Data Processing Sequence:

Processing Changes:

Reprocessing of the data occur about once a year.

Calculations:

Special Corrections/Adjustments:

As one of the primary uses of the level 3B data is display of latitude-longitude contour plots on selected pressure surfaces, it is important to understand the characteristics of these data in terms of latitude and local solar time. Local time of the measurements is a strong function of the latitude of the measurements, with ascending mode data (satellite heading north at the Equator) being 10 to 12 hours out of phase with descending mode data at the Equator. Thus, separating the data into ascending and descending modes provides a rough cut in local time, although data in each mode exhibit large local time variations from high northern to high southern latitudes. Also, at the 57 degree inclination of the UARS orbit, the orbit plane recedes about 20 minutes a day in solar time, so data taken at the same longitude roughly 24 hours later reflect a local time 20 minutes earlier. Thus, a daily global contour plot of these data represents one local time at each latitude (or two local times if the modes are combined), with a 20 minute difference from one end (longitude) to the other. This contrasts with the frequently quoted picture of "synoptic" maps produced from satellite data; a true synoptic data set would represent the atmosphere at one instant in time with all local times represented as a function of longitude.

Calculated Variables:

Examples for calculating the initial set of coefficients and covariance matrices are described in the LEVEL 3B DATA DESCRIPTION DOCUMENT.

10. Errors:

Sources of Error:

Associated with each set of coefficients is an error covariance matrix which provides estimates of the uncertainties inherent in the derived coefficients. Results are reported separately for the ascending and descending portions of the orbits.

Quality Assessment:

Data Validation by Source:

The data set quality is directly related to the level 3AL data quality of individual instruments. The derived quality of the coefficients is reflected in the covariance matrices and related information in level 3B files.

Measurement Error for Parameters:

Variances are included with each data value.

Additional Quality Assessments:

None.

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 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:

It is expected that many users will not regularly use the covariance matrices corresponding to the Fourier coefficients. Because of this, and the fact that the covariance matrices take a significant amount of space, the coefficients and covariance matrices are stored in separate files. Thus, coefficient and covariance files exist for each day (the results correspond to 12 GMT for that day), one set for the ascending mode data, and one for the descending mode data. Within each file, a set of coefficients exists for each 3AL latitude, and each 3AL pressure surface (or altitude in km in the case of wind data).

In addition to the coefficients, the coefficient file contains the following auxiliary information:

• Longitudes of each 3AL data point.
• Standard deviations for each 3AL measurement.
• Average local solar time of the 3AL data for the given day and given latitude. The local solar time changes only by about 20 minutes per day.
• Average solar zenith angle of the 3AL data for the given day and given latitude.
• Number of 3AL data points for the given day and latitude.
• The 3AL data version.

The inclusion of the 3AL and local time information is intended as a convenience to provide for users other information which is useful for further quantitative analysis.

Any other Relevant Information about the Study:

None.

12. Application of the Data Set:

One of the primary uses of the level 3B data is display of latitude-longitude contour plots on selected pressure surfaces.

13. Future Modifications and Plans:

Future reprocessing of the data are possible.

14. Read Software:

Software Description:

Simple read/dump programs are available for reading the level 3B data files. The read programs are available in both Fortran and C languages. These programs simply print the file contents to the screen.

The *META and *PROD files (see the Data Granularity section) must be kept in the same directory, because the programs require the *META file as the input parameter in order to read the *PROD file. The *META file is necessary because it contains file record length information, which is not in the *PROD files.

If you are using the Fortran READ programs you may need to change the OPEN statement. Some machines read 4 byte words, while other machines read 1 byte. If the program isn't working correctly, you should try changing RECL=RECSIZ/4 to RECL=RECSIZ.

Contact science@eosdata.gsfc.nasa.gov for problems with the read/dump software.

Software Access:

To compile the programs, just type:

     f77 FILE_NAME.F -o FILE_NAME       (Fortran programs)

or

     cc file_name.c -o file_name            (C programs)

Below is an example showing how to run the program:

     $ READ_L3B_COEF
      Enter UARS level 3B Coefficient file name :
     MLS_L3B_SO3_205_DS_C_D0320.V0009_C01_PROD
      Do you wish to save result to an ASCII file (y/n) ?
     n

15. Data Access:

Contact Information:

Name:

Help Desk

Addresses:

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:

daacuso@daac.gsfc.nasa.gov

Archive Identification:

The UARS data are archived at the GSFC DAAC, and can be identified by the attributes listed below.

         Data Set = UARS
     Data Product = CLAES L3B DAILY FOURIER COEF
     Data Product = ISAMS L3B DAILY FOURIER COEF
     Data Product = MLS L3B DAILY FOURIER COEF

Procedures for Obtaining Data:

The level 3B data files can be obtained from the Goddard DAAC by several mechanisms. These include the following:

• The DAAC Web-Based Archive Interface provides a means for searching and ordering data. To search the data holdings and place an order, go to the DAAC Home Page located at "/index.shtml", and click on the "Search and Order" icon. Next, pick the "Data Set" link, and from there choose "UARS".

• Earth Observing System Data Gateway (EDG). You can place orders for the UARS data through the Earth Observing System (EOS) Data Gateway. From here you can also order data products from other data centers. The web address for the EDG is "http://eos.gsfc.nasa.gov/imswelcome/".

• DAAC Help Desk. Data can also be obtained by contacting the GSFC DAAC Help Desk listed above.

Data can be ordered electronically (FTP).

Data Archive Status/Plans:

The DAAC currently supports CLAES, ISAMS, and MLS level 3B data products for selected parameters.

16. Output Products and Availability:

The level 3B data are available. See the section above on Procedures for Obtaining Data for specific information. For more information on specific instruments, please refer to the guide document for that instrument:

• UARS CLAES L3A Data Set Document
• UARS ISAMS L3A Data Set Document
• UARS MLS L3A Data Set Document

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.

Kalman, R.E., A New Approach to Linear Filtering Problems, J. Basic Eng., Vol 82D, p. 35 - 45, Mar. 1960.

Haggard, K.V., et. al., 1986, Description of Data on the Nimbus 7 LIMS Map Archive Tape, NASA Technical Paper 2553.

Journal Articles and Study Reports:

Special UARS Section, Journal of Geophysical Research, Vol 98, No D6, p. 10643 - 10814, June 20, 1993.

Evaluation of the UARS Data, "American Geophysical Union", Washington, D.C., 1996.

Goddard DAAC IMS online documentation:

Upper Atmosphere Research Satellite (UARS) Level 3B Data Description Document , NURSGP01.

18. Glossary of Terms:

DATA SET

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.) is a subset of the UARS data set.

GRANULE

A Granule is the smallest aggregation of data which is independently managed.

PARAMETER

A measurable or derived variable represented by the data (e.g. air temperature, snow depth, relative humidity). At the Goddard DAAC, parameters are grouped into a Parameter General category, which is broken down into Parameter Specific.

19. List of Acronyms:

20. Document Information:

Document Revision Date:Fri May 10 11:53:59 EDT 2002

5 May 1998

Document Review Date:

Document ID:

Citation:

Document Curator:

Document URL:

/DATASET_DOCS/uars_l3b_dataset.html

UARS Project

Change History

Version 2.0

Version baselined on addition to the GES Controlled Documents List, May 5, 1998.