UARS CLAES LEVEL 3A DATA SETS

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GES DISC DAAC Data Guide:
UARS CLAES Level 3A Data Sets Document

The Cryogenic Limb Array Etalon Spectrometer (CLAES) is one of 10 instruments aboard the Upper Atmosphere Research Satellite (UARS). The CLAES instrument measured the altitude profiles of temperature and a series of minor and trace gases important in stratospheric ozone chemistry. Measured gas species include ozone, water vapor, methane, members of the nitrogen and chlorine families, and two chlorofluorocarbons. CLAES also obtained aerosol extinction coefficients at several infrared wavelengths. These data capture the vertical distributions of important ozone-layer gases in the stratosphere and their variation with time of day, season, latitude, and longitude. Currently, CLAES version 8 level 3AL and 3AT data products from 21 October 1991 to 05 May 1993 are available from the Goddard Space Flight Center (GSFC) Distributed Active Archive Center (DAAC). However, the species CFC-12, CH₄, H₂O, and NO are not available in version 8, but are available as version 7 data products.

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 3AL DAILY LATITUDE ORDERED DATA

UARS CLAES LEVEL 3AT DAILY TIME ORDERED DATA

Data Set Introduction:

There are two CLAES level 3A data products archived at the DAAC:

Level 3AL: CLAES level 3AL data are daily latitude- and time-ordered data interpolated to intervals of 4 degrees latitude at the intersection of the tangent track of the instruments line of sight (LOS). Each record consists of a single array of data of one parameter for a specific time. Level 3AL data records are written to UARS defined standard latitudes, which range from -88 to +88 degrees in 4 degree intervals.
Level 3AT: CLAES level 3AT data are daily time-ordered data, arranged at time intervals of 65.536 seconds, or about 495 km intervals along the LOS tangent track. The reference time at which level 3AT data are arranged is common across all UARS level 3AT files. Each data record contains time, latitude, longitude, solar zenith angle, local time, and an array of data, as well as an array of quality (standard deviation) values. Data file structures for these file types are found in the Standard Formatted Data Units (SFDU) documents listed in the References section below.

Objective:

To produce a 19-month global database showing the vertical distributions of important ozone-layer gases in the stratosphere and their variation with time of day, season, latitude, and longitude.

Summary of Parameters:

The CLAES version 8 level 3A data are a subset of the UARS data set. The main objective of the CLAES experiment is to measure the altitude profiles of temperature and a series of minor and trace gases important to stratospheric ozone chemistry. Gases include ozone (O₃), water vapor (H₂O), methane (CH₄), chlorofluorocarbon 11 (CFCl₃), chlorofluorocarbon 12 (CF₂Cl₂), chlorine nitrate (ClONO₂), hydrogen chloride (HCl), nitric oxide (NO), nitrogen dioxide (NO₂), nitrous oxide (N₂O), dinitrogen pentoxide (N₂O₅), and nitric acid (HNO₃). Aerosol extinction coefficients are also measured at several infrared wavelengths.

NOTE: HCl data are not included in the version 7 or 8 CLAES data sets.

Discussion:

The CLAES Level 3AL and 3AT data files are written in the Standard Data Format Units (SFDU) format. 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:

All UARS level 3AL and 3AT files use the same formats to allow for intercomparisons of atmospheric profiles between the different instruments. Other UARS instruments which measure chemical species include the Microwave Limb Sounder (MLS), the Halogen Occultation Experiment (HALOE), and the Improved Stratospheric and Mesospheric Sounder (ISAMS).

2. Investigators:

Principal Investigator:

Name:: Aidan E. Roche
Address:: Lockheed Palo Alto Research Laboratory; B/255, O/91-20; 3251 Hanover Street; Palo Alto, CA 94304
Telephone Numbers:: Phone: (415) 424-2109
Electronic Mail Address:: roche@claes.space.lockheed.com

Title of Investigation:

Cryogenic Limb Array Etalon Spectrometer

Contact Information:

Principal Scientist:

Name:: John B. Kumer
Address:: Lockheed Palo Alto Research Laboratory; B/255, O/91-20; 3251 Hanover Street; Palo Alto, CA 94304
Telephone Numbers:: Phone: (415) 424-2327
Electronic Mail Address:: kumer@claes.space.lockheed.com

RAC System Manager/Delivery Representative:

Name:: Gary A. Ely
Address:: Lockheed Palo Alto Research Laboratory; B/255, O/91-20; 3251 Hanover Street; Palo Alto, CA 94304
Telephone Numbers:: Phone: (415) 424-2361
Electronic Mail Address:: ely@claes.space.lockheed.com

3. Theory of Measurements:

CLAES infers the amounts of gases in the stratosphere from the measurement of the unique infrared emission features associated with each gas. To separate the often very weak signatures of "trace" gases such as CFCs from the intense atmospheric background radiation, requires both high spectral resolution and high sensitivity. This was done by combining a telescope with an infrared spectrometer and solid state detectors, and cryogenically cooling the whole instrument to prevent its own thermal infrared emissions from interfering with the measurement of weak atmospheric signals. The spectrometer had a resolving power of about 4000 and operated over the wavelength range 3.5 to 12.9 microns.

4. Equipment:

Instrument Description:

The CLAES instrument collects infrared radiation through its 6-inch aperture Mersene telescope. Spectroscopy is performed by tilt scanning one of the four solid etalons between one or more of the nine blocking filters. The nine filters are centered at 2843, 1897, 1605, 1257, 925, 879, 843, 792 and 780 cm^-1. The Fabry Perot spectrometer is augmented by a 72 Hz chopper and two refractive lens groups which direct focused infrared radiation to the focal plane array. A solid cryogen cooler keeps the CLAES instrument cooled below 150 Kelvin. CLAES collected scientific data from 01 October 1991 to 05 May 1993.

Collection Environment:

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

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 Project document 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. From 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 (raw) data to level 1, 2, 3A and 3B data. The Goddard DAAC acquires the UARS data from the CDHF.

6. Observations:

Data Notes:

None at this time.

7. Data Description:

Spatial Characteristics:

Spatial Coverage:

Spatial coverage alternates each UARS yaw cycle. This means that CLAES alternately views from 34N to to 80S or 34S to 80N in 36 day periods. The instrument consists of a telescope, a spectrometer, and a linear array of 20 detectors to obtain vertical profiles of species concentrations between 10 and 60 km.

Spatial Coverage Map:

Data coverage for CLAES looking northward on 5/22/1991.

Map showing UARS orbital tracks

Spatial Resolution:

Horizontal resolution is 4 degrees for level 3AL files, and about 495 km along the orbital track for level 3AT files.

Vertical resolution for level 3A files is about 2.5 km between pressure surfaces.

Projection:

Not Applicable.

Grid Description:

All CLAES level 3A data have been referenced to the UARS standard pressure grid. 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,...

Temporal Characteristics:

Temporal Coverage:

Temporal coverage is from 21 October 1992 to 05 May 1993. Below is a list of dates within the above time period for which CLAES data are missing or unavailable:

13-JAN-1992 to 16-JAN-1992
31-JAN-1992
13-FEB-1992 to 17-FEB-1992
04-MAR-1992
08-MAR-1992
22-MAR-1992 to 25-MAR-1992
13-APR-1992
30-APR-1992 to 04-MAY-1992
17-MAY-1992
30-MAY-1992 to 10-JUN-1992
19-JUN-1992
11-JUL-1992 to 16-JUL-1992
18-JUL-1992
29-JUL-1992
11-AUG-1992 to 15-AUG-1992
18-SEP-1992 to 23-SEP-1992
10-OCT-1992
27-OCT-1992 to 31-OCT-1992
13-NOV-1992
27-NOV-1992 to 01-DEC-1992
08-JAN-1993 to 11-JAN-1993
28-JAN-1993
07-FEB-1993 to 11-FEB-1993
17-MAR-1993 to 21-MAR-1993
27-MAR-1993
30-MAR-1993
04-APR-1993
16-APR-1993 to 20-APR-1993
25-APR-1993 to 29-APR-1993

NOTE: The first 3 months of CLAES level 3A data are not available in the version 7 data release.

Temporal Resolution:

The temporal resolution of CLAES level 3A data granules is daily.

Data Characteristics:

Parameters:

There are 22 parameters for CLAES level 3AL and 3AT data products. The parameters are classified according to CLAES subtypes. The measured parameters are listed below with the original CLAES subtype name, DAAC parameter name, and units:

Subtype	DAAC Parameter Name	Units
AERO780	AEROSOLS AT 780 cm^-1	1/km
AERO790	AEROSOLS AT 790 cm^-1	1/km
AERO843	AEROSOLS AT 843 cm^-1	1/km
AERO880	AEROSOLS AT 880 cm^-1	1/km
AERO925	AEROSOLS AT 925 cm^-1	1/km
AERO1257	AEROSOLS AT 1257 cm^-1	1/km
AERO1605	AEROSOLS AT 1605 cm^-1	1/km
AERO1897	AEROSOLS AT 1897 cm^-1	1/km
ALT	ALTITUDE	km
CFCL3	CHLOROFLUOROCARBON 11	mixing ratio
CF2CL2	CHLOROFLUOROCARBON 12	mixing ratio
CH4	METHANE	mixing ratio
CLONO2	CHLORINE NITRATE	mixing ratio
H2O	WATER VAPOR	mixing ratio
HNO3	NITRIC ACID	mixing ratio
NO	NITRIC OXIDE	mixing ratio
NO2	NITROGEN DIOXIDE	mixing ratio
N2O	NITROUS OXIDE	mixing ratio
N2O5	DINITROGEN PENTOXIDE	mixing ratio
O3B8	OZONE AT 780 cm^-1	mixing ratio
O3B9	OZONE AT 790 cm^-1	mixing ratio
TEMP	ATMOSPHERIC TEMPERATURE	K

NOTE:mixing ratio = 10e^-6 parts per million by volume.

8. Data Organization:

Data Granularity:

The granularity of CLAES level 3A data are defined such that there is one granule for each level and parameter subtype (see the Data Description section above) per day, for a total of 22 granules per day. Each CLAES level 3A granule is a multi-file granule consisting of two files:

the binary data file (files ending with PROD, or *PROD extension) which contains the profile data and quality indicators, as well as time, latitude, longitude, solar zenith angle, and local solar time values.
an ASCII metadata file (files ending with META, or *META extension) associated with the data file containing items such as start and stop time, PI assigned quality flag, and record length size of the data file.

The format for granule file names is CLAES_Llll_Sssss_Ddddd .Vvvvv_Ccc_xxxx, where

lll: is the UARS processing level (3AL or 3AT),
ssss: is the subtype or parameter,
dddd: is the UARS acquisition day (0001 = 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.

Average granule size is about 270 kb for CLAES_L3A_DAILY granules, and 390 kb for CLAES_L3AT_DAILY granules. The *META files are small, only about 700 bytes each.

Data Format:

The data are in a native UARS format (SFDU). 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. CLAES data file structures are presented in the Standard Formatted Data Units (SFDU) documents listed in the References section.

9. Data Manipulations:

Formulae:

Derivation Techniques and Algorithms:

CLAES uses a multi-channel, multi-emitter retrieval scheme that includes many elements of the vector-vector procedure described by "Retrieval Atmospheric Temperature and Composition from Remote Measurements of Thermal Radiation", by C.D. Rodgers, Rev. Geophys. and Space Phys. 14, 609-624, 1976.

Data Processing Sequence:

Processing Steps (and Data Sets):

The reader is directed to the CLAES Ground Data Processing Software User Guide, version 6.00, 11 October 1995 for a complete description of the processing overview.

Processing Changes:

The current version 8 data set was produced by the CLAES Batch Data Processing Software (BDPS), version 6.06 and yielded data version 8 (V8). The V8 processing did not target improvement in all CLAES species. Species that were targeted for improvement, and that were significantly improved include N2O5, F11 and the aerosols. These have been transferred to the DAAC. The V8 species O3(B9), ClONO2, HNO3, N2O, NO2 and temperature have also been transferred to the DAAC. These are improved generically by comparison with V7 in that:

The V8 data have been processed for the period 21 October 1991 until 5 May 1993, when the CLAES cryogen was totally expended. The V7 data was processed on just a segment of that period, from 6 January 1992 to 5 May 1993.
An improved calibration approach that corrected for a trend in responsivity near missions end (e.g., see discussion by Roche et al., J. Geophys. Res., Vol. 101, No. D6, 9679 - 9710, 1996) was used in V8 but not in V7.
The embedded error bars in V8 agree better with independent error estimates (e.g., such as the track intersect method as described by Kumer et al., J. Geophys. Res., Vol. 101, No. D6, 9657 - 9678, 1996)

The V8 species CFC-12, CH4, and H2O have not been transferred to the DAAC. These inadvertently regressed in V8. The source of the problems in V8 have been identified and these will be improved over V7, and therefore V8, in our next version, V9. However, at present the highest version on the DAAC for these species is V7. The latter is recommended for use pending their replacement with V9.

10. Errors:

Sources of Error:

The embedded error estimates in V8 have been considerably improved. The goal was to provide embedded error roughly equivalent to the independently derived estimates of precision. In some cases the error is driven by estimated instrument noise rather than radiance residuals in order to achieve this goal. Also, a coding error in the embedded error bars for O3 (B9) as reported by Bailey et al. (J. Geophys. Res., Vol. 101, No. D6, 9621 - 9656, 1996) has been fixed. Finally, a coding error, as is described below, has been introduced that is specific to the aerosol subtype AERO790 in the V8.

Quality Assessment:

Basically, the CLAES multi-emitter multi-channel problem is broken down to the equivalent of a single emitter and single channel problem for each species i by using a linear least squares approach for fitting calculated radiances to the observed data. Next, a method similar to the Newtonian iterative algorithm (equation (99) on page 621 in the paper by Rodgers ( Rev. Geophys. and Space Phys., Vol. 14, 609-624, 1976) is used for retrieval and error estimation for each species. The error is driven by the radiance residuals, and for the multi-emitter multi-channel case this can some times be larger than would be predicted from random instrument noise alone as the result of systematic effects or undetected noise spikes, for example. The result was that in many cases the embedded V7 error estimates were too large on comparison with independently derived estimates of precision as reported in the special UARS Data Validation Issue, J. Geophys. Res., Vol. 101, No. D6, 1996.

Data Validation by Source:

Data are checked by the CLAES science team and assigned quality values. These values appear as the DATA_QUALITY_UARS and DATA_QUALITY_PI fields in the ASCII metadata files. The format for DATA_QUALITY_UARS is a 3 character field of the form "p.q" where:

                VALUE       MEANING
         for p      0       Machine inspected
                    1       Qualitative evaluation
                    2       Intensive analysis
         for q      1       less than 50% good data
                    2       50% - 75% good data
                    3       76% - 98% good data
                    4       better than 98% good data

CLAES does not use the optional DATA_QUALITY_PI field.

Measurement Error for Parameters:

The procedure for error estimation for the CLAES data version V7 is described in appendix A of the paper by Kumer et al. (J. Geophys. Res., Vol. 101, No. D6, 9621 - 9656, 1996). Basically, the CLAES multi-emitter multi-channel problem is broken down to the equivalent of a single emitter and single channel problem for each species i by using a linear least squares approach for fitting calculated radiances to the observed data. Next, a method similar to the Newtonian iterative algorithm (equation (99) on page 621 in the paper by Rodgers ( Rev. Geophys. and Space Phys., Vol. 14, 609-624, 1976) is used for retrieval and error estimation for each species. The error is driven by the radiance residuals, and for the multi-emitter multi-channel case this can some times be larger than would be predicted from random instrument noise alone as the result of systematic effects or undetected noise spikes, for example. The result was that in many cases the embedded V7 error estimates were too large on comparison with independently derived estimates of precision as reported in the special UARS Data Validation Issue, J. Geophys. Res., Vol. 101, No. D6, 1996.

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:

Temperature: When compared to NMC and UKMO analysis CLAES temperatures are generally cold by 2-5 K from 1-100 mb, and are warm above the 1 mb level. They are very cold in the tropics near 10 mb and in the southern polar winter above 10 mb and near thick PSC's.
O3(B9): Tends to be biased high at low altitudes in tropics, possible due to aerosol interference
N2O: Local maxima in the tropics, 40-20 mb, prior to September 1992.
NO2: Biased low by 30-40% vs correlative data. Generally errors increase rapidly below 20 mb. Potentially large errors in polar night winter conditions with large vertical temperature gradients.
HNO3: There may be a problem in the southern hemispheric mid to high latitude data in autumn and early winter for cases where the vmr exceeds ~ 15 ppbv. In these cases the vmr may systematically be too large by more than the 20% value that is given in the summary table.
ClONO2: Errors increase substantially above 6 mb. Tropical (20S-20N) data below 26 km possibly showing interference from Pinatubo aerosol cloud prior to May 1992. Some PSC interference in Antarctic winter.
N2O5: Very good confidence from 10 to 1 mb for the offsets subtracted case. SW is available at CLAES anonymous ftp site to perform the subtraction. The data is also useful at higher and lower altitudes for some regions and times, but user should be VERY careful in assessing what the offset might be, as this has not been done by the CLAES team. The systematic error applies for the offset subtracted case. It varies with region, altitude, and time into the mission.
CFCl3: Likely significant interference from Pinatubo aerosol and polar winter PSCs. Most qualitatively-useful data for summer-fall northern hemisphere-looking periods between July 17 and October 26, 1992, and summer-fall southern hemisphere-looking periods between November 2, 1992 and April 15, 1993.
Aerosol: The 1257 cm-1 V0008 retrieved aerosol absorption coefficients are set near zero for altitudes where the continuum extinction coefficients become < 6.3E-04 km-1; the daytime 1897 cm-1 has significant contribution from solar scattering; there is a 25% to 35% difference between the 790 and 780 cm-1 regions but theory suggests a 3% maximum difference.

Any other Relevant Information about the Study:

None.

12. Application of the Data Set:

Anticipated uses of these data are in the fields of understanding unperturbed atmospheric chemistry and dynamics, tracking global change and long term atmospheric trends, predicting atmospheric response to chemical or energetic perturbations, environmental and agricultural planning, weather forecasting, atmospheric energy input and loss studies, and radiation budgets.

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 CLAES level 3A 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 are examples showing how to run the programs:

   $ READUMP_L3AT_DATA                          (Fortran program)
    PLEASE ENTER META DATA FILE NAME BELOW:
   CLAES_L3AT_SH2O_D0001.V0003_C01_META

or $ readump_l3at_data CLAES_L3AT_SH2O_D0001.V0003_C01_META      (C program)

15. Data Access:

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

    Data Set = UARS

Data Product = CLAES L3AL DAILY LAT ORDERED
           CLAES L3AT DAILY TIME ORDERED

Procedures for Obtaining Data:

The CLAES level 3A 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://wist.echo.nasa.gov/~wist/api/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 level 3AL, 3AT, and 3B data products.

16. Output Products and Availability:

The CLAES level 3A data are available. See the section above on Procedures for Obtaining Data for specific information. For more information on CLAES, please refer to the CLAES Home Page.

17. References:

CLAES level 3AL SFDU Version 8, NURSCL02.

CLAES Change History Document, NURSCL04.

Horne, C., UARS Granule Level File (*META) Description, July 1994.

18. Glossary of Terms:

DATA PRODUCT: A collection of parameters packaged with associated ancillary and labeling data. Uniformly processed and formatted. Typically uniform temporal and spatial resolution. CLAES level 3A data products include CLAES_L3AL_DAILY and CLAES_L3AT_DAILY. The CLAES data product class is divided into data product subclasses according to measured parameters.
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.) CLAES 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:

CDHF	Central Data Handling Facility
CFCl₃	chlorofluorocarbon 11
CF₂Cl₂	chlorofluorocarbon 12
CH₄	methane
ClONO₂	chlorine nitrate
DAAC	Distributed Active Archive Center
DCF	Data Capture Facility
EOS	Earth Observing System
FOV	field of view
GSFC	Goddard Space Flight Center
H₂O	water vapor
HNO₃	nitric acid
HF	hydrogen fluoride
IMS	Information Management System
K	Kelvin
km	kilometer
LOS	line of sight
m	meter
mb	millibar
CLAES	Cryogenic Limb Array Etalon Spectrometer
NASA	National Aeronautics and Space Administration
NO	nitric oxide
NO₂	nitrogen dioxide
N₂O	nitrous oxide
N₂O₅	dinitrogen pentoxide
O₃	ozone
PI	Principal Investigator
ppmv	parts per million by volume
RAC	Remote Analysis Computer
SFDU	Standard Formatted Data Units
TDRSS	Tracking and Data Relay Satellite System
UARS	Upper Atmosphere Research Satellite
USO	User Services Office