1. What is the purpose of this site?

    Over 30 years ago scientists first realized that man-made CFCs being released into the atmosphere could destroy large amounts of ozone in the stratosphere through a previously unrecognized catalytic reaction.

    In 1975 Congress directed NASA "to provide for an understanding of and to maintain the chemical and physical integrity of the Earth's upper atmosphere."

    Here we provide the results and data related to these ongoing studies.

  2. Is there a list of acronyms?

    Yes!

    ATBD

           Algorithm Theoretical Basis Document

    BUV

           Backscattered UltraViolet

    DOAS

           Differential Optical Absorbtion Spectroscopy

    DU

           Dobson Unit

    EP

           Earth Probe instrument

    ESDT

           Earth Science Data Type

    GOME

           Global Ozone Monitoring Experiment

    GOME-2

           Global Ozone Monitoring Experiment-2

    HDF

           Hierarchical Data Format

    HDF-EOS

           Hierarchical Data Format - Earth Observing System

    IDL

           Interactive Data Language

    KNMI

           Koninklijk Nederlands Meteorologisch Instituut
    (Royal Netherlands Meteorological Institute)

    M3

           Meteor 3 instrument

    MODIS

           MODerate resolution Imaging Spectroradiometer

    N7

           Nimbus 7 instrument

    NASA

           National Aeronautics and Space Administration

    NOAA

           National Oceanic and Atmospheric Administration

    OMI

           Ozone Monitoring Instrument

    OMPS

           Ozone Mapping and Profiler Suite

    OMSAO

           OMI/Smithsonian Astrophysical Observatory

    OSST

           OMI Science Support Team

    PGE

           Product Generation Executive/Executable

    SBUV

           Solar Backscatter UltraViolet instrument

    TOMS

           Total Ozone Mapping Spectrometer

    UV

           UltraViolet

  3. What is meant by Level 1, Level 2, Level 3, etc. products?

    Here is a NASA page that describes this well.

  4. What is OMI?

    OMI is a nadir-viewing near-UV/Visible CCD spectrometer aboard NASA's Earth Observing System's (EOS) Aura satellite. Aura flies in formation about 15 minutes behind Aqua, both of which orbit the earth in a polar Sun-synchronous pattern. Aura was launched on July 15, 2004, and OMI has collected data since August 9, 2004.

    OMI measurements cover a spectral region of 264-504 nm (nanometers) with a spectral resolution between 0.42 nm and 0.63 nm and a nominal ground footprint of 13 x 24 km2 at nadir. Essentially complete global coverage is achieved in one day. The significantly improved spatial resolution of OMI measurements as well as the vastly increased number of wavelengths observed, as compared to TOMS, GOME and SCIAMACHY, sets a new standard for trace gas and air quality monitoring from space. The OMI observations provide the following capabilities and features:

    • A mapping of ozone columns at 13 km x 24 km and profiles at 13 km x 48 km (a continuation of TOMS and GOME ozone column data records and the ozone profile records of SBUV and GOME)
    • A measurement of key air quality components: NO2, SO2, BrO, HCHO, and aerosol (a continuation of GOME measurements)
    • The ability to distinguish between aerosol types, such as smoke, dust and sulfates
    • The ability to measure aerosol absorption capacity in terms of aerosol absorption optical depth or single scattering albedo
    • A measurement of cloud pressure and coverage
    • A mapping of the global distribution and trends in UV-B radiation
    • A combination of processing algorithms including TOMS Version 8, DOAS (Differential Optical Absorption Spectroscopy), Hyperspectral BUV retrievals and forward modeling to extract the various OMI data products
    • Near real-time measurements of ozone and other trace gases

    The OMI is a contribution of NIVR (Netherlands Institute for Air and Space Development) of Delft, in collaboration with FMI (Finnish Meteorological Institute), Helsinki, Finland, to the EOS Aura mission. The Dutch industrial efforts focused on the optical bench design and assembly, thermal design and project management. The detector modules and the readout and control electronics were provided by Finnish industrial partners.

    For more details on the OMI instrument and project, see the OMI web site, the OMI Project Guide, and the OMI instrument overview. For details on OMI results, see the OMI publications web site.

    OMI multimedia information
  5. What is the OMI swath?

    The instantaneous swath of any imaging instrument, including OMI, is the width of the region that is actually observed across the track of the instrument at any time during any particular overflight. The global measurement mode is the default mode, sampling the complete swath of 2600 km for the complete wavelength range. The ground pixel size at nadir position in the global mode is 13 x 24 km2 (along-track x cross-track) for the UV-2 and VIS channels, and 13 x 48 km2 for the UV-1 channel.

    The spatial zoom-in mode has a nadir ground pixel size of 13 x 12 km2, but the swath width has a minimum of 725 km. The spatial zoom-in mode is used one day each 32 days, always above the same geo-locations. In the spectral range of 264-311 nm, the pixel size in the cross-track direction is twice as large (that is, a nadir ground pixel size of 13 x 24 km2). The swath is symmetric with respect to the sub-satellite track. The spatial zoomin mode results in two products:

    • A Zoom Radiance product consisting of all the zoom data.
    • A Global Radiance product in which the zoom data are effectively degraded to match the resolution of images produced in the global mode but only cover half the normal mode radiance.

    The spectral zoom-in mode has a nadir ground pixel size of 13 x 12 km2 and a full swath of 2600 km. It has a limited spectral coverage of 307-432 nm to cover the most important scientific products. This mode was tested during the pre-launch period and run a few times between early August and early October 2004, during Launch and Early Operations (LEO). Because this mode has not been used since that time, it is not addressed in this document.

  6. What is OMI's orbit?

    The Aura satellite orbits at an altitude of 705 km in a sun-synchronous polar orbit with an exact 16-day repeat cycle and with a local equator crossing time of 13.45 (1:45 P.M.) on the ascending node. The orbital inclination is 98.1 degrees, providing latitudinal coverage from 82° N to 82° S.

  7. What is OMI's ground path?

    Every 233 orbits, the EOS-Aura orbital repeat cycle, the spacecraft covers the exact same ground track. By describing the ground coverage for each orbit in the orbital repeat cycle, the ground coverage of a science data product can be described in terms of a reference to one of these pre-defined paths, rather than using bounding boxes or polygons. This method for describing the ground coverage of a science data product in metadata is called NOSE, Nominal Orbit Spatial Extent. The NOSE metadata can be used for geo-spatial searches. To refine these searches, each ground track is split up in blocks. Each science data product then only needs to refer to the paths and blocks covered by the product in order to allow for geo-spatial searches. The definition of the NOSE paths and blocks needs to be included in the search system.

    For OMI, 466 NOSE paths are defined. Paths 1 .. 233 specify the ground coverage of nominal global measurements for each orbit in the orbital repeat cycle, paths 234 .. 466 specify the ground coverage of spatial zoom-in measurements. The paths are split up in blocks: each block covers about two minutes of measurement time.

  8. What is the data coverage for OMI?

    The OMI instrument has daily global coverage of data. More information on data coverage is available in the summary page.

  9. Where can I find detailed information about the contents of OMI data products?

    See the OMI Data User Guide and OMI Data Products and Data Access Information. The theory behind the algorithms used to process OMI data is in the Algorithm Theoretical Basis Documents (ATBD).

  10. What is meant by "Collection"?

    As OMI continues to reprocess the data products, Collections of scientifically consistent sets of data product versions become available. Collections may contain multiple format, production, and ESDT Versions. The current collection version is collection 3.

  11. What is OMI's file naming convention?

    The file names used for OMI products all contain two date/time stamps: the data date and the production date. The data date is the start time for the OMI granule or orbit measurement data in the file. The processing date/time indicates when the file for the given product was created. Here is an example of an aerosol product Level 2 file name.

    OMI-Aura_L2-OMAERO_2008m0830t1828-o21953_v003-2008m0831t021052.he5

    OMI = Instrument Name
    Aura = Satellite Name
    L2 = Level
    OMBRO = Product Name
    2008m0830t1828 = Data Date
    o21953 = Orbit Number
    v003 = Collection Number
    2008m0831t021052 = Production Date
    he5 = Extension

    OMI data set file naming convention description can be found in OMI Level 2 Aerosol Data Product Specification.

  12. What is the quality of the OMI data products?

    Intensive assessment of OMI product data quality is an ongoing activity. Users can refer to the Quality Assessment Document for more information.

  13. Where can I obtain OMI imagery?

    OMI SO2 imagery can be obtained from SO2 group's web site, which includes daily images. OMI O3, NO2, UV Index and other images are available from Tropospheric Emission Monitoring Internet Service (TEMIS).

  14. How do I obtain OMI information and data?

    OMI data is availabe from Goddard Earth Sciences Data and Information Center (DISC) site. Follow the steps below to order the data you need.

    • Go to Goddard Earth Sciences Data and Information Center (DISC) site
    • You will see all the data products listed (Level 1, Level 2 and Level 3). Click on the product you need. For example you need OMAERUV Level 2 data. Then click on OMAERUV
    • You will arrive in Data Access Page. Click on "WHOM - search & download OMAERUV data"
    • Then select the "Year" you want the data product for. You will also have other selection options. For example: you want data for 2007. Then click on 2007.
    • Then you can choose the months and days by selecting them
    • You will then get instructions on what to do to get the data files. For example:
      1. Download the "FTP script for full size granules" provided after the table of granules below.
      2. On SGI or Linux machines, run: ftp -p -n aurapar2u.ecs.nasa.gov < script
      3. Or on SunOS, Windows/DOS, or Mac platforms, run: ftp -n aurapar2u.ecs.nasa.gov < script
    • You will also have options to select granules, select parameters and do spatial subsetting. Choose your selections and the click on "Submit SUBSET Request".
    • You will then get instructions for single and multiple file download. For example for multiple download you will get instructions such as:
      1. Download the FTP_script: order_xxx....txt
      2. On SGI or Linux machine, run: ftp -p -n aurapar2u.ecs.nasa.gov < order_16498.txt
      3. On DOS, SunOS or Windows/Mac platforms, run: ftp -n aurapar2u.ecs.nasa.gov < order_16498.txt
    • Follow the instructions and you get your data.
  15. How are OMI science data products generated?

    OMI data products are grouped into three processing levels. Level 1 processing provides corrected (or calibrated) instrument data. These data are processed and calibrated to remove many of the instrument effects. The resulting products thus contain minimal instrument or spacecraft artifacts and are most suitable for subsequent scientific derivations. Level 2 processing provides retrieval of derived scientific quantities, such as atmospheric aerosol and cloud measurements. Level 3 processing produces global grids of various parameter elements from the Level 2 products. These global grids are produced daily.

  16. What OMI products are currently available?

    Public release information for OMI Level 1, and 2 products is available at KNMI website. Information about Level 3 globally gridded products is available at Goddard Giovanni site.

  17. How do I decide which OMI product files to order?

    Chapter 3, OMI Data Products, of the OMI Data User's Guide may be helpful in determining which data products to order.

  18. What OMI Level 1 products are available?

    See the DISC web site OMI Level 1 Products for a complete list of data products The main products are OMI geolocated earth radiances and OMI solar irradiances.

  19. What OMI Level 2 products are available?

    Level 2 products can be divided into products in 3 different categories. They are: Ozone Clouds, Aerosols, and Surface UV Irradiance * Trace Gases

    A complete list of Level 2 products is available at the DISC web site.

  20. What types of OMI Level 3 products are available?

    OMI Level 3 products are produced for some Level-2 standard products. Each Level-2 product file contains data from a single orbit. For each Level-2 product there will be 14 files per day. OMI Level-3 daily global products are produced by averaging data over small equal angle grids (0.25 deg x 0.25 deg), (0.5 deg x 0.5 deg) or (1 deg x 1 deg) covering the whole globe. Each grid also contains the corresponding statistical parameters (number of pixels, minimum, maximum, and standard deviation).

  21. What tools are available to work with OMI data products?

    The OMI data products are in HDF-EOS format. The Aura Tools site lists available tools for reading and working with OMI data. Tools are also available from KNMI's site.

  22. What is OMPS?

    OMPS is the Ozone Mapping and Profiler Suite.

  23. What OMPS Level 1 products are available?

    Take a look at the OMPS data portal on this site: http://ozoneaq.gsfc.nasa.gov/data/omps

  24. Is there a description of the SBUV Version 8 Algorithm?

    V8 Algorithm Description

    The Solar Backscatter Ultraviolet instruments, SBUV on Nimbus 7 and SBUV/2s on NOAA-9, -11, -14, -16 and -17, are nadir-viewing instruments that infer total column ozone and the ozone vertical profile by measuring sunlight scattered from the atmosphere in the ultraviolet spectrum. Heath et al. (1975) describes the SBUV flown on Nimbus-7. Frederick et al. (1986), and Hilsenrath et al. (1995) describe the follow-on SBUV/2 instruments flown on the NOAA series of spacecraft.

    The instruments are all of similar design: nadir-viewing double-grating monochromators of the Ebert-Fastie type. The instruments step through 12 wavelengths in sequence over 24 seconds, while viewing the Earth in the fixed nadir direction with an instantaneous field of view (IFOV) on the ground of approximately 180 km by 180 km. To account for the change in the scene-reflectivity due to the motion of the satellite during the course of a scan, a separate co-aligned filter photometer (centered at 343 nm on SBUV; 380 nm on SBUV/2) makes 12 measurements concurrent with the 12 monochromator measurements. Each sequence of measurements is separated by 8 seconds from the next, producing a complete set every 32 seconds on the daylight portions of an orbit.

    The instruments are flown in polar orbits to obtain global coverage. Since the SBUV ozone measurements rely on backscattered solar radiation, data are only taken on the dayside of each orbit. There are about 14 orbits per day with 26 degrees of separation at the equator. Unfortunately, the early NOAA polar orbiting satellites are not sun-synchronous. For example the NOAA-11 equator crossing times drifted from 1:30 pm (measurements at 30 degrees solar zenith angle at the equator) at the beginning of 1989 to 5:00 pm by the end of 1995 (measurements at 70 degrees solar zenith angle). As the orbit drifts, the terminator crossing location moves to lower latitudes and coverage decreases.

    Ozone profiles and total column amounts are derived from the ratio of the observed backscattered spectral radiance to the incoming solar spectral irradiance. This ratio is referred to as the backscattered albedo. The only difference in the optical components between the radiance and irradiance observations is the instrument diffuser used to make the solar irradiance measurement; the remaining optical components are identical. Therefore, a change in the diffuser reflectivity will result in an apparent trend in ozone. This is the key calibration component for the SBUV(/2) series. See Hilsenrath et al. (1995) for a longer discussion.

    The spectral resolutions for SBUV(/2) monochromators are all approximately 1.1 nm, full-width at half-maximum (FWHM) with triangular bandpasses. The bandwidths of the photometers are approximately 3 nm FWHM. The wavelength channels used for Nimbus 7 SBUV were: 256, 273, 283, 288, 292, 298, 302, 306, 312, 318, 331, and 340 nm. The wavelengths for NOAA-9 and the other NOAA SBUV/2 instruments were very similar except that the shortest channel was moved from 256 nm to 252 nm in order to avoid emission in the nitric oxide gamma band that contaminated the SBUV Channel 1 measurement. Data from the 256 and 252 nm channels are not used in this Version 8 processing for any of the instruments.

    Version 8 SBUV(/2) Ozone Profile Retrieval Algorithm (V8A)

    The Version 8 SBUV(/2) ozone profile retrieval algorithm combines backscattered ultraviolet measurements and a priori _ profile information in a maximum likelihood retrieval. See _Rodgers (1990) for an analysis of this class of retrievals. It improves on the Version 6 SBUV(/2) algorithm described in Bhartia et al. (1996). Among the improvements are the following:

    1. The V8A has a new set of a priori _profiles varying by month and latitude, leading to better estimates in the troposphere (where SBUV/2 lacks retrieval information) and allowing simplified comparisons of SBUV/2 results to other measurement systems (in particular, to Umkehr ground-based ozone profile retrievals which use the same _a priori data set).
    2. The V8A has a true separation of the a priori and first guess. This simplifies averaging kernel analysis. Examples and further information are provided below.
    3. The V8A has improved multiple scattering and cloud and reflectivity modeling. These corrections are updated as the algorithm iterates toward a solution.
    4. Some errors present in the V6A will be reduced. These include the elimination of errors on the order of 0.5% by improved fidelity in the bandpass modeling.
    5. The V8A incorporates several ad hoc Version 6 algorithm improvements directly. These include better modeling of the effects of the gravity gradient, better representation of atmospheric temperature influences on ozone absorption, and better corrections for wavelength grating position errors.
    6. The algorithm uses improved terrain height information and gives profiles relative to a climatological surface pressure.
    7. The V8A is also designed to allow the use of more accurate external and climatological data and allow simpler adjustments for changes in wavelength selection.
    8. Finally, the V8A is designed for expansion to perform retrievals for hyperspectral instruments, such as the Ozone Monitoring Instrument (OMI), the Global Ozone Monitoring Experiment (GOME-2) and the Nadir Profiler in the Ozone Mapping and Profiler Suite (OMPS).

    The atmospheric ozone absorption decreases by several orders of magnitude over the 252 to 340 nm wavelength range. The V8A uses a variable number of backscattered ultraviolet measurements depending on the solar zenith angle (SZA) of the observations to maintain its sensitivity to ozone changes in the lower atmosphere. For small SZAs (the sun high in the sky), only six wavelengths are used in the retrievals. They are at 273 nm, 283 nm, 288 nm, 292 nm, 298 nm, and 302 nm. As the SZA increases the 306 nm, then the 313 nm and finally the 318 nm channels are added to the retrieval.

    Version 8 Algorithm A Priori Profiles

    The a priori profile database is provided in a data file (climat.txt). The profile data set gives the climatological averages for 18 10-degree latitude bands and 12 months. These profiles can be used to determine the information used in a specific retrieval by interpolating in latitude and day with the apriori FORTRAN code. The lowest layer from the _a priori _program will differ from that used in the retrieval if the surface pressure is not 1 atmosphere. Another data file (terrain.txt) and the terrpres FORTRAN code are provided to generate the surface pressure for a given latitude and longitude.

    The a priori covariance is constructed as follows: the diagonal elements correspond to 50% variance and the non-diagonal covariance elements fall off with a correlation length of twelve fine layers (approximately two Umkehr layers). The measurement covariance is diagonal and corresponds to radiance errors of 1% in each channel.

    The profile database was created from 15 years (1988 to 2002) of ozonesonde measurements and SAGE (Version 6.1) and/or UARS-MLS (Version 5) data. Over 23,400 sondes from 1988 to 2002 were used in producing this climatology. Data was "filtered", i.e., obvious bad data points were removed. Data from balloons that burst below 250 hPa were discarded. Data from bouncing balloons were sorted by pressure. Note: No total ozone correction factors (TOMS or Dobson) filtering were used. The stations were weighted equally for each band so that we do not introduce any additional longitudinal biases (e.g., Resolute and Nyalesund have equal weights in December even though Nyalesund has three times as many sondes as Resolute for that month). The SAGE data was also "screened" to remove anomalous retrievals. Average profiles from ozonesondes and SAGE are merged over a 4-km range with the sonde weight decreasing from 80 to 60 to 40 to 20% and the SAGE weight increasing correspondingly.

    Averaging Kernel Plots for Nimbus 7

    This section gives some sample averaging kernel plots to help describe the V8A retrieval capabilities. The averaging kernels give the theoretical responses in the retrieval layer amounts to changes in the true atmospheric profiles.

    Fig. 1 shows Averaging Kernels (AKs) (for fractional changes in ozone) at the 15 pressure levels where the ozone mixing ratios are provided on this DVD. The short horizontal lines on the right side of the graph show the pressure levels and point to the corresponding AK. The horizontal and AK lines – styles correspond. In general, the (fractional) variation in the mixing ratio reported by SBUV at a given pressure level is a weighted average of the (fractional) variation of the mixing ratio at surrounding altitudes, relative to the a priori profile. Since the SBUV V8 a priori profiles have no inter-annual variation, the AKs also show how the algorithm would smooth a long-term trend in ozone mixing ratio. Note, however, that individual SBUV profiles usually have structures that are finer than those implied by the AKs; these structures come from the assumed a priori profile, rather than from the measurements themselves. This figure shows typical AKs at the equator. The AKs show best resolution of ~6 km near 3 hPa, degrading to ~10 km at 1 and 20 hPa. Outside this range the retrieved profiles have little information. For example, the (fractional) variation in ozone mixing ratio seen at 0.5 hPa actually represents the (fractional) variation from the region around 1 hPa, and the variation around 50 hPa represents the variation from around 30 hPa.

    Fig. 2 shows typical AKs for March at 40N latitude. At this latitude the 50 hPa AK does capture some of the atmospheric variation, albeit with a resolution of ~11 km. In general, the upper AKs get progressively better as the solar zenith angle increases, and the lower AKs become better as the ozone density peak drops in altitude.

    Fig. 3 shows typical AKs for March at 80N latitude. One can see the improvement in AKs for the upper portions of the profile, especially the 0.5, 0.7, 1, and 1.5 hPa AKs, in capturing the atmospheric variation more accurately than in Figs. 2 and 1, with better resolution of ~6 km at 0.7 hPa.

    References

    Bhartia, P.K., S. Taylor, R.D. McPeters, and C. Wellemeyer, Application of the Langley plot method to the calibration of the solar backscatter ultraviolet instrument on the Nimbus 7 satellite, J. Geophys. Res., 100, 2997-3004, 1995.

    Bhartia, P.K., R.D. McPeters, C.L. Mateer, L.E. Flynn, and C.G. Wellemeyer, Algorithm for the estimation of vertical profiles from the backscattered ultraviolet technique, J. Geophys. Res., 101, 18,793-18,806, 1996.

    Frederick, J.E, R. P. Cebula, and D. F. Heath, Instrument characterization for the detection of long-term changes in stratospheric ozone: An analysis of the SBUV/2 radiometer, J. Atmos. Oceanic Technol., 3, 472-480, 1986.

    Gleason, J.F, R.D. McPeters, Correction to the Nimbus 7 solar backscatter ultraviolet data in the "nonsync" period (February 1987 to June 1990), J. Geophys. Res., 100, 16,873-16,877, 1995.

    Heath, D. F., A. J. Krueger, H. R. Roeder, B. D. Henderson, The solar backscatter ultraviolet and total ozone mapping spectrometer (SBUV/TOMS) for Nimbus G, Optical Engineering, 14, 323-331, 1975.

    Heath, D.F., Z. Wei, W.K. Fowler, and V.W. Nelson, Comparison of Spectral Radiance Calibrations of SSBUV-2 Satellite Ozone Monitoring Instruments using Integrating Sphere and Flat-Plate Diffuser Technique, Metrologia, 30, 259-264, 1993.

    Hilsenrath, E., R.P. Cebula, M.T. Deland, K. Laamann, S. Taylor, C. Wellemeyer, and P.K. Bhartia, Calibration of the NOAA-11 Solar Backscatter Ultraviolet (SBUV/2) Ozone Data Set from 1989 to 1993 using In-Flight Calibration Data and SSBUV, J. Geophys. Res., 100, 1351-1366, 1995.

    Rodgers, C. D., The Characterization and Error Analysis of Profiles Retrieved from Remote Sounding Measurements, J. Geophys. Res., 95, 5587-5595, 1990.

  25. Is there a description of the SBUV Version 8 profile data?

    Version 8.0 SBUV Profile Data Readme

    Introduction

    This web site contains a complete time series record of atmospheric ozone profiles from November 1978 to December 2003 derived from satellite Solar Backscattered Ultraviolet (SBUV) measurements. Data from the SBUV instrument on the Nimbus-7 satellite and the SBUV/2 instruments on NOAA-11, NOAA-16 and NOAA-9 satellites are selected to give a complete time series using the highest quality data available. As discussed further in V8 Data Documentation and indicated by the Error Codes and the Residue Quality Control (Residue QC) parameters in the data files, the overall data quality varies with instrument and time. Parts of Nimbus-7, NOAA-11 and NOAA-16 have the best quality. The data from the NOAA-9 SBUV/2 instrument are considered to be of poorer quality, and are included only to complete gaps in time not covered by the other instruments. The Noaa09_post92 directory contains data covering the period when there are no NOAA-11 data. The Noaa09_pre89 directory contains data covering the Nimbus-7 out-of-synchronization period. Some overlap of instrument measurements is provided. See V8 Data Documentation for guidelines to select the best quality data and some discussion of instrument problems that affect data quality. Links to the latest information on the data provided on this DVD can be found at: NOAA SBUV/2 V8 DVD Link

    Description of Data

    In the V8DATA directory, there are subdirectories for each instrument. These have subdirectories for each year containing the daily data files in ASCII format. A sample ASCII file shows the beginning of a daily file with eight lines of header and the subsequent first three 3-line data records. As briefly described in the header, each data record starts with 11 parameters relative to the profile, followed by ozone amounts in Dobson Units for 13 layers and finally the ozone concentrations in PPMV units at 15 pressure levels. A brief description of the first eleven parameters is as follows:

    • Year : The four digit Common Era year Day_of_Year : The day of the year with January 1st equal to 1 GMT_seconds : The Greenwich Mean Time at the start of the measurement Latitude : The Latitude (Degrees North) of the measurement Longitude : The Longitude (Degrees East) of the measurement Solar_Zenith : The Solar Zenith Angle (Degrees) of the measurement Total_Ozone : The total column ozone in Dobson Units from the ground up Reflectivity : Effective reflectivity from the ground and/or clouds. Aerosol_Index : Significant quantities indicate the presence of aerosols. Quality_Residue : Average of the absolute final residues (See V8 Data Documentation). Error_Flag : Three digit error code (See V8 Data Documentation).

    Note: a daily file may contain part of an orbit of data from the following day, and some of the data for the start of a day may only appear in the preceding day's file.

    These files can be accessed through the SBUV Ozone Profile page or by modifying one of the sample IDL or FORTRAN 90 programs to read in a day's data.


    Documentation Files

    1. V8 Algorithm Description
    2. V8 Data Quality
    3. V8 Validation Results

    Acknowledgments

    The reprocessed SBUV/2 data were made available with support from the NOAA Climate and Global Change Program, Atmospheric Chemistry Element and the NOAA National Environmental Satellite Data and Information Services, Product Systems Development and Implementation Program. Support for SSAI contributors was provided under NASA contracts NAS5-00220 and NAS5-01008.

  26. What is the Earth Probe TOMS Data Coverage?

    Summary of Level 2 Data Coverage
    
    EP/TOMS was launched into a 500 km sun synchronous orbit on
    July 2, 1996.  The first EP/TOMS Earth scan data were taken
    during orbit 216 on July 16, 1996.  Normal science operations
    began during orbit 339 on July 24, 1996.  Orbits prior to 7903
    (December 4, 1997) were at the initial 500 km altitude.  Orbits
    after 8037 (December 13, 1997) were at 740 km altitude after an
    orbit boosting maneuver.
    
    No Earth scan science data (and therefore no Level 2 data) were
    acquired for the orbits listed in Table 1. Seventy-two (72) of
    these orbits were before the start of normal operations.
    
    Table 2 lists orbits that have incomplete data coverage.
    Nine (9) of these orbits were prior to normal operations.
    
    Table 3 lists orbits that have some fixed scene view ("stare mode")
    data that interrupts the usual continuous daytime Earth scan data.
    Each affected orbit has a minimum 3 minute Level 2 data gap.
    
    ----------------------------------------------------------------
                             Table 1
               EP/TOMS Orbits with No Level 2 Data
    ----------------------------------------------------------------
    Jul 17-19, 1996: 220, 228, 233-263
    Jul 22-24, 1996: 300-338     (Prior to Normal Operations)
    Nov    28, 1996: 2258
    Nov 16-19, 1997: 7640-7675   (Attitude Anomaly)
    Dec  4-13, 1997: 7903-8037   (Orbit Boost)
    Nov 17-18, 1998: 12935-12951 (Leonid Meteors)
    Dec    13, 1998
     -Jan   2, 1999: 13311-13610 (Spacecraft Anomaly)
    Nov 17-18, 1999: 18209-18225 (Leonid Meteors)
    May    14, 2000: 20798       (Operations Error)
    Nov 17-19, 2001: 28783-28802 (Leonid Meteors)
    Aug  2-12, 2002: 32516-32663 (Spacecraft Anomaly)
    Nov 18-19, 2002: 34085-34100 (Leonid Meteors)
    May 15-22, 2003: 36657-36767 (Spacecraft Anomaly)
    
    ---------------------------------------------------------------
                             Table 2
              EP/TOMS Orbits with Partial Level 2 Data
              (percent available shown in parenthesis)
    ---------------------------------------------------------------
    Jul 16, 1996: 216 (84%), 219 (61%)
    Jul 17, 1996: 221 (40%), 227 (61%), 229 (40%), 232 (29%)
    Jul 19, 1996: 264 (39%)
    Jul 22, 1996: 299 (12%)
    Jul 24, 1996: 339 (40%)  (all before normal operations)
    Oct  9, 1996: 1505 (64%), 1506 (80%)
    Nov 28, 1996: 2257 (38%), 2259 (62%)
    Dec 31, 1996: 2773 (77%)
    Mar  9, 1997: 3794 (65%)
    Nov 16, 1997: 7639 (41%)
    Nov 19, 1997: 7676 (60%)
    Dec  4, 1997: 7902 (38%)
    Dec 13, 1997: 8038 (67%)
    Apr 14, 1998: 9807 (82%)
    May  1, 1998: 10045 (75%)
    May 12, 1998: 10212 (96%), 10213-10216 (38% each)
    May 13, 1998: 10217-10223 (38% each), 10224 (40%)
    May 24, 1998: 10376 (61%), 10377 (39%)
    Nov 17, 1998: 12934 (40%)
    Nov 18, 1998: 12952 (61%)
    Dec 13, 1998: 13310 (37%)
    Jan  3, 1999: 13610 (63%)
    Nov 17, 1999: 18208 (39%)
    Nov 18, 1999: 18226 (62%)
    Feb  5, 2000: 19365 (68%)
    May 14, 2000: 20797 (59%), 20799 (52%)
    Apr  9, 2001: 25572 (57%)
    Nov 17, 2001: 28782 (13%)
    Nov 19, 2001: 28803 (49%)
    Dec 31, 2001: 29423 (38%)
    Jan  1, 2002: 29424 (65%)
    Aug  2, 2002: 32515 (59%)
    Aug 12, 2002: 32664 (77%)
    Nov 18, 2002: 34084 (65%)
    Nov 19, 2002: 34101 (63%)
    Dec 31, 2002: 34712 (69%)
    May 15, 2003: 36656 ( 8%)
    May 22, 2003: 36768 (41%)
    
    ----------------------------------------------------------------
                             Table 3
        EP/TOMS Orbits with Fixed Scene ("stare mode") Data
    ----------------------------------------------------------------
    Apr  1, 1997: 4152
    Apr  2, 1997: 4167
    Apr  6, 1997: 4228, 4230
    Apr 11, 1997: 4306
    Apr 15, 1997: 4367
    Apr 16, 1997: 4382
    Apr 20, 1997: 4443
    Apr 21, 1997: 4458
    Apr 25, 1997: 4519
    Apr 30, 1997: 4595
    May  4, 1997: 4656
    May  5, 1997: 4671
    May  8, 1997: 4717
    May  9, 1997: 4732
    May 10, 1997: 4747
    May 13, 1997: 4793
    May 14, 1997: 4808
    May 18, 1997: 4869
    May 19, 1997: 4884
    May 23, 1997: 4945
    May 27, 1997: 5006
    May 28, 1997: 5021
    Jun  1, 1997: 5082
    Jun  2, 1997: 5097
    Jun  5, 1997: 5143
    Jun  6, 1997: 5158
    Jun  7, 1997: 5173
    Jun 10, 1997: 5219
    Jun 11, 1997: 5233, 5234
    Jun 12, 1997: 5240, 5250
    Jun 14, 1997: 5277, 5280
    Jun 15, 1997: 5295
    Jun 16, 1997: 5309, 5310
    Jun 17, 1997: 5316, 5326
    Jun 19, 1997: 5353, 5356
    Jun 20, 1997: 5371
    Jun 21, 1997: 5386
    Jun 24, 1997: 5432
    Jun 25, 1997: 5446, 5447
    Jun 28, 1997: 5493
    Jun 29, 1997: 5508
    
    Last updated July 16, 2003
    
  27. Is there a TOMS data quality assessment?

    Until late in its life, EP/TOMS data were of high quality, consistent with nominal uncertainties.

    Frequently asked questions regarding the Earth Probe TOMS near real-time data:

  28. What are the TOMS uncertainties?

    The nominal uncertainties in the Earth Probe TOMS near real-time data products are summarized in the tables below:

    Uncertainty in Earth Probe TOMS Ozone

    Uncertainty in:

    Nominal

    Solar Zenith Angle > 80

    Absolute Value

    3%

    4%

    Precision

    2%

    5%

    Long-term Mean

    1%

    1%

    Uncertainty in Earth Probe TOMS Reflectivity and Aerosol Index

    Uncertainty in:

    Reflectivity at Low Reflectivity

    Reflectivity at High Reflectivity

    Aerosol Index
    (331 nm Residue)

    Absolute Value

    0.008

    0.015

    0.30

    Precision

    0.002

    0.003

    0.15

    Long-term Mean

    0.005

    0.01

    0.1


    The effective Lambertian equivalent surface reflectivity and the aerosol index are not physical quantities. Because of this, no algorithmic error sources have been included. Nominal instrument calibration errors of 1.5% at 360 nm and 0.75% at 331 nm relative to 360 nm have been assumed. Evidence of uncorrected diffuser degradation drives the errors in long-term mean for the reflectivity and aerosol index, but there is no significant effect on derived ozone.

    More information on error sources is found in the EP TOMS Data Products User's Guide.

  29. What is a Dobson Unit?

    A dobson unit is the most basic measure used in ozone research. The unit is named after G.M.B. Dobson, one of the first scientists to investigate atmospheric ozone (~1920 - 1960). He designed the 'Dobson Spectrometer' - the standard instrument used to measure ozone from the ground. The Dobson spectrometer measures the intensity of solar UV radiation at four wavelengths, two of which are absorbed by ozone and two of which are not.

    [Image illustrating what an ozone column is]

     

    The illustration above shows a column of air, 10 deg x 5 deg, over Labrador, Canada. The amount of ozone in this column (i.e. covering the 10 x 5 deg area) is conveniently measured in Dobson Units.

    If all the ozone in this column were to be compressed to stp (0 deg C and 1 atmosphere pressure) and spread out evenly over the area, it would form a slab approximately 3mm thick.

    1 Dobson Unit (DU) is defined to be 0.01 mm thickness at stp; the ozone layer over Labrador then is ~300 DU.


    NOTE: This page, including the copyrighted graphic, is based on a page developed by Owen Garrett for the Centre for Atmospheric Science at Cambridge University, UK. The center has kindly given us permission to reproduce it. (Take their excellent Multimedia Ozone Hole Tour!)

  30. How did the most recent EP/TOMS data compare with historical values?

    How do the 2005 ozone data (plus) compare with the 2004 data (solid) and with the entire Nimbus 7 TOMS climatology (shaded)? (10K/graph). The white curve shown on each of the plots is the climatological mean.

    Select to learn more about this image. Select to learn more about this image.

    Select to learn more about this image. Select to learn more about this image.

  31. What geophysical events affected EP/TOMS data quality?

    Solar eclipses occurred on February 16 and August 11 of 1999. When the Sun is obscured or partly obscured, the calibration of the TOMS measurement is compromised. For this reason, data covering the region of the eclipses are excluded from the Level-2 (orbital) and Level-3 (map) data products.

    Elevated values of Aerosol Index (AI) starting July 23, 1999 in North America are associated with Canadian Forest Fires. This may cause small underestimation of total column ozone amount in the vicinity of these fires. This map also shows dust emanating from Northern Africa and smoke from biomass burning in Southern Africa. The impact of dust and smoke on ozone derived from EP/TOMS measurements is described in Section 6.1 of the TOMS Data User's Guide.

    The eruption of Soufriere Hills Volcano on Monserat (lat, Lon) on July 21, 1999 caused a slight elevation in the Aerosol Index (AI) reported on the EP/TOMS Level-2 data product (not readily apparent in Level-3). The effect is small and does not lead to any data rejection from the Level-3 product, nor to any significant error in the total column ozone amounts.

    During spring, some data were being rejected by the EP/TOMS algorithm in the vicinity of the North Pole. This was the result of air masses of very high total ozone amounts but with unusually low ozone concentration in the upper stratosphere. This situation was more prevalent in spring of 1999 than in previous years. This might possibly be associated with the two stratospheric warmings that occurred this Spring. Missing data in the TOMS Level-3 map products near the North Pole on April 25, for example, are the result of this type of data rejection. The white hole in the map is where the missing data is.

    For more details on the TOMS profile mixing scheme, please refer to the algorithm section of the TOMS data User's Guide.

    The eruption of Shishaldin (54.76 N, 163.97 W) on April 19. 1999 produced an ash cloud visible in the TOMS aerosol index (AI) over the Alaskan peninsula. Some of the TOMS ozone retrievals in this region are rejected for contamination due to the sulfur dioxide cloud produced by the eruption.

  32. Does EP/TOMS have missing data or data taken in an alternate instrument mode?

    The tables below indicate data that are permanently missing from the Level-2 EP/TOMS data record. Some filling can occur in the Level-3 product due to overlapping data from adjacent orbits. Also, additional gaps may occur in the Level-3 data resulting from bad retrievals due to desert dust or smoke from forest fires as described in the EP/TOMS Data Products User's Guide.

    EP/TOMS Orbits with no Derived Products

    Month

    Days

    Year

    Orbit Numbers

    Comment

    July

    17-19

    1996

    220, 228, 233-263

     

    July

    22-24

    1996

    300-338 (all before normal operations)

     

    November

    28

    1996

    2258

     

    November

    16-19

    1997

    7640-7675

     Instrument in "safehold"

    December

    4-13

    1997

    7903-8037

     Orbit altitude being raised

    November

    17-18

    1998

    12935-12951 (Leonid meteors)

     Instrument in "safehold"

    December-January

    13-2

    1998-1999

    13311-13609 (s/c anomaly)

     Orbit altitude being raised

     

    EP/TOMS Orbits with Partial Coverage

    Date

    Year

    Orbit (% Available)

    July 16

    1996

    216 (84%), 219 (61%)

    July 17

    1996

    221 (40%), 227 (61%), 229 (40%), 232 (29%)

    July 19

    1996

    264 (39%)

    July 21

    1996

    295 (60%)

    July 22

    1996

    299 (12%)

    July 24

    1996

    339 (40%)

    October 9

    1996

    1505 (64%), 1506 (80%)

    November 28

    1996

    2257 (38%), 2259 (62%)

    December 31

    1996

    2773 (77%)

    March 9

    1997

    3794 (65%)

    November 16

    1997

    7639 (41%)

    November 19

    1997

    7676 (60%)

    December 4

    1997

    7902 (38%)

    December 13

    1997

    8038 (67%)

    April 14

    1998

    9807 (82%)

    May 1

    1998

    10045 (72%)

    May 12

    1998

    10212 (96%), 10213-10216 (38% each)

    May 13

    1998

    10217-10223 (38% each), 10224 (40%)

    May 19

    1998

    10312 (99%)

    May 20

    1998

    10327 (98%)

    May 24

    1998

    10376 (61%), 10377 (39%)

    June 14

    1998

    10675 (99%)

    July 21

    1998

    11220 (99%)

    August 23

    1998

    11692 (99%)

    September 24

    1998

    12155 (99%)

    October 15

    1998

    12459 (99%)

    October 29

    1998

    12663 (99%)

    October 31

    1998

    12737 (99%)

    November 5

    1998

    12760 (98%)

    November 6

    1998

    12780 (97%)

    November 17

    1998

    12934 (40%)

    November 18

    1998

    12952 (61%)

    November 25

    1998

    13051 (99%)

    December 1

    1998

    13144 (99%)

    December 8

    1998

    13237 (99%)

    December 10

    1998

    13279 (99%)

    December 13

    1998

    13310 (37%)

    January 3

    1999

    13610 (63%), 13617 (99%)

    January 11

    1999

    13738 (99%)

    March 2

    1999

    14454 (99%), 14455 (99%)

  33. Briefly discuss EP/TOMS instrument calibration

    As discussed in the User's Guide, the EP/TOMS working diffuser is deployed every week to make solar measurements. The EP/TOMS reference diffuser is deployed only every 10 weeks, So the working to reference ratio indicates degradation of the working diffuser, which is critical to the long-term calibration of EP/TOMS. Every time a working diffuser measurement is made, the near real-time calibration of EP/TOMS is extrapolated for another week to permit continuous processing of the data. The following graphics are used to monitor the quality of this calibration system. The upper plot in both graphics pertains to the single 360 nm channel and affects the calibration of the derived reflectivity. The middle plot pertains to the 331 nm / 360 nm ratio, which affects the aerosol index. The bottom plot pertains to the A-triplet of channels, which corresponds to ozone errors.

    Select to learn more about this image.

    Select to learn more about this image.
    The working diffuser degradation relative to reference (5K) The degree to which extrapolated calibration tracks actual solar measurements (4K)

  34. What effect did spacecraft attitude anomalies have on EP/TOMS data?

    The EP/TOMS spacecraft has experienced a number of attitude anomalies listed in the table below. These anomalies are short lived and tend to affect only the extreme off-nadir scans. The ozone errors are typically 1 D.U. or less though they may become larger during extreme events.

    Orbit Number per Devia- tion

    Universal Time Interval

    Maximum Attitude Error during Interval (deg)

    Spacecraft Position (Geodetic; deg)

    Year

    Day

    hh:mm:ss

    hh:mm:ss

    Roll

    Pitch

    Yaw

    Latitude

    Longitude

    337

    1996

    206

    18:36:48

    19:07:27

    -0.70

    -0.95

    0.70

    28.5

    -121.9

    611

    1996

    224

    18:08:12

    18:09:29

    -0.55

    0.31

    -0.88

    32.3

    -108.0

    693

    1996

    230

    03:33:06

    03:33:10

    -0.18

    0.056

    -0.26

    17.9

    113.4

    723

    1996

    232

    02:55:39

    02:56:04

    0.17

    0.064

    0.32

    21.1

    122.2

    754

    1996

    234

    03:54:11

    03:54:16

    0.19

    0.076

    0.34

    27.3

    106.7

    800

    1996

    237

    04:31:39

    04:33:54

    -0.40

    0.19

    -0.83

    36.3

    95.1

    981

    1996

    249

    02:11:07

    02:13:02

    0.57

    0.26

    1.2

    14.5

    133.9

    1300

    1996

    270

    01:51:17

    01:51:38

    0.22

    0.089

    0.41

    25.9

    137.6

    1863

    1996

    307

    02:32:12

    02:34:23

    0.54

    0.21

    1.2

    27.0

    126.8

    1893

    1996

    309

    01:53:23

    01:55:14

    -0.34

    0.13

    -0.74

    26.3

    136.7

    2196

    1996

    329

    00:07:38

    00:14:40

    -0.52

    0.23

    -1.5

    42.6

    158.7

    2351

    1996

    339

    04:45:17

    04:45:33

    0.19

    0.080

    0.36

    14.8

    95.9

    2438

    1996

    344

    23:34:49

    23:35:50

    0.47

    0.24

    0.85

    3.5

    174.9

    2473

    1996

    347

    05:17:16

    05:20:20

    0.58

    0.30

    1.3

    23.4

    86.0

    2577

    1996

    354

    01:25:23

    01:28:28

    -0.52

    0.24

    -1.3

    22.7

    144.1

    3003

    1997

    016

    01:43:30

    01:45:21

    0.52

    0.24

    1.1

    23.1

    139.9

    4150

    1997

    091

    11:32:56

    11:34:46

    0.28

    0.12

    0.62

    24.6

    -7.6

    4484

    1997

    113

    10:25:54

    10:32:15

    0.43

    0.19

    1.3

    34.2

    6.5

    4583

    1997

    119

    22:37:39

    22:40:19

    -0.47

    0.21

    -1.0

    24.1

    -173.8

    4629

    1997

    122

    23:09:39

    23:18:27

    -0.52

    0.32

    -1.5

    40.1

    173.7

    4703

    1997

    127

    19:54:53

    19:55:01

    0.18

    0.081

    0.34

    11.5

    -130.7

    4816

    1997

    135

    06:10:19

    06:14:29

    0.37

    0.23

    1.6

    29.5

    71.8

    4910

    1997

    141

    10:27:05

    10:29:49

    0.50

    0.28

    1.4

    25.0

    8.7

    5007

    1997

    147

    19:27:17

    19:30:42

    0.50

    0.24

    1.0

    25.3

    -126.5

    5017

    1997

    148

    11:15:55

    11:16:19

    0.21

    0.11

    0.51

    23.3

    -2.6

    5132

    1997

    156

    00:38:08

    00:41:16

    0.47

    0.21

    1.3

    28.2

    155.4

    5333

    1997

    169

    05:42:38

    05:42:46

    0.27

    0.11

    0.44

    24.9

    80.6

    5524

    1997

    181

    18:55:13

    18:57:08

    0.62

    0.33

    1.4

    23.5

    -117.8

    5607

    1997

    187

    05:52:41

    05:53:54

    0.31

    0.27

    0.61

    31.6

    76.7

    5614

    1997

    187

    16:53:30

    16:54:23

    -0.39

    0.25

    -0.51

    23.5

    -87.1

    5774

    1997

    198

    05:14:43

    05:16:22

    0.28

    0.18

    0.67

    27.9

    86.7

    5848

    1997

    203

    01:58:19

    02:00:18

    -0.54

    0.26

    -1.1

    33.9

    134.7

    5934

    1997

    208

    17:33:46

    17:33:58

    0.17

    0.12

    0.33

    17.3

    -96.0

    6208

    1997

    226

    17:41:22

    17:43:50

    0.39

    0.39

    0.77

    26.9

    -99.9

    6241

    1997

    228

    21:41:25

    21:45:02

    -0.60

    0.29

    -1.3

    21.6

    -159.4

    6367

    1997

    237

    04:28:07

    04:32:37

    -0.52

    0.29

    -1.4

    41.6

    95.1

    6565

    1997

    250

    04:38:31

    04:40:10

    -0.51

    0.22

    -0.83

    17.8

    97.4

    6593

    1997

    252

    00:50:57

    00:53:08

    0.56

    0.29

    1.2

    30.6

    152.2

    6620

    1997

    253

    19:25:04

    19:26:06

    -0.30

    0.22

    -0.50

    25.5

    -125.2

    6634

    1997

    254

    17:27:56

    17:29:30

    0.36

    0.17

    0.73

    20.7

    -95.3

    6772

    1997

    263

    19:04:43

    19:05:44

    -0.39

    0.22

    -0.60

    22.0

    -119.6

    6787

    1997

    264

    18:46:50

    18:46:54

    0.16

    0.067

    0.25

    29.3

    -116.0

    7277

    1997

    296

    23:11:50

    23:13:49

    0.37

    0.17

    0.96

    12.0

    179.9

    7805

    1997

    338

    02:52:46

    03:29:22

    -0.81

    -1.2

    -0.84

    3.9

    117.2

    8061

    1997

    348

    17:53:20

    17:55:23

    0.41

    0.17

    0.93

    22.1

    -102.0

    8135

    1997

    353

    20:49:56

    20:51:26

    -0.46

    0.22

    -0.68

    12.6

    -144.5

    8209

    1997

    358

    23:47:25

    23:49:48

    0.59

    0.29

    1.4

    11.0

    171.1

    8237

    1997

    360

    23:57:45

    00:00:33

    0.60

    0.31

    1.6

    7.5

    169.0

    8319

    1998

    001

    16:08:58

    16:09:56

    0.31

    0.15

    0.66

    -16.8

    -69.7

    8322

    1998

    001

    19:36:46

    19:38:57

    -0.33

    0.12

    -0.64

    18.1

    -127.3

    8340

    1998

    003

    01:29:27

    01:33:08

    -0.50

    0.21

    -1.3

    15.4

    144.6

    8444

    1998

    010

    06:24:02

    06:24:06

    -0.21

    0.053

    -0.32

    19.2

    71.3

    8597

    1998

    020

    20:37:42

    20:40:34

    -0.60

    0.31

    -1.4

    20.6

    -143.0

    8618

    1998

    022

    09:02:38

    09:05:09

    0.30

    0.12

    0.60

    -12.1

    35.8

    8709

    1998

    028

    16:18:27

    16:18:35

    0.22

    0.10

    0.40

    -13.0

    -72.4

    8841

    1998

    037

    18:07:23

    18:07:27

    0.14

    0.053

    0.29

    11.6

    -103.3

    8845

    1998

    038

    00:43:03

    00:43:07

    0.16

    0.057

    0.28

    1.2

    159.3

    8916

    1998

    042

    22:44:28

    22:47:32

    -0.40

    0.15

    -0.86

    19.2

    -174.5

    8986

    1998

    047

    19:04:18

    19:06:58

    0.42

    0.20

    1.1

    16.7

    -118.9

    8986

    1998

    047

    19:04:18

    19:06:58

    0.42

    0.20

    1.1

    16.7

    -118.9

    9213

    1998

    063

    12:19:33

    12:24:48

    0.45

    0.21

    1.6

    31.7

    -21.1

    9267

    1998

    067

    07:31:14

    07:31:18

    0.16

    -0.052

    0.30

    -32.1

    62.8

    9835

    1998

    106

    15:29:11

    15:31:26

    0.55

    0.27

    1.3

    -9.6

    -61.1

    9845

    1998

    107

    06:34:57

    06:37:49

    0.51

    0.25

    1.4

    21.5

    67.6

    9877

    1998

    109

    11:48:27

    11:48:47

    0.18

    0.074

    0.43

    23.1

    -10.4

    10173

    1998

    130

    01:12:03

    01:15:03

    0.63

    0.32

    1.5

    0.3

    151.6

    10191

    1998

    131

    05:32:42

    05:36:52

    0.30

    0.14

    1.3

    24.5

    82.4

    10551

    1998

    156

    07:09:16

    07:09:20

    0.16

    0.052

    0.34

    23.2

    59.5

    10582

    1998

    158

    07:21:51

    07:21:59

    0.18

    0.082

    0.31

    26.4

    55.8

    10624

    1998

    161

    05:08:29

    05:10:53

    -0.39

    0.18

    -0.81

    30.9

    87.7

    10661

    1998

    163

    18:35:58

    18:39:19

    0.53

    0.26

    1.2

    29.2

    -114.1

    10798

    1998

    173

    06:16:21

    06:18:57

    -0.57

    0.29

    -1.2

    30.9

    70.7

    10884

    1998

    179

    05:12:32

    05:14:27

    0.51

    0.25

    1.2

    34.1

    86.1

    10943

    1998

    183

    07:17:06

    07:18:36

    0.24

    0.099

    0.55

    39.6

    53.8

    11130

    1998

    196

    05:54:10

    06:00:27

    0.58

    0.32

    1.9

    31.9

    75.1

    11172

    1998

    199

    03:41:01

    03:43:08

    -0.55

    0.26

    -1.1

    13.2

    112.7

    11369

    1998

    212

    19:07:33

    19:07:54

    0.19

    0.082

    0.42

    26.3

    -120.7

    11433

    1998

    217

    05:27:11

    05:30:16

    0.56

    0.32

    1.4

    32.6

    82.5

    11532

    1998

    224

    02:02:53

    02:04:40

    0.38

    0.18

    0.82

    45.6

    130.7

    11576

    1998

    227

    03:02:19

    03:04:54

    0.40

    0.21

    1.1

    23.2

    120.6

    11648

    1998

    232

    02:44:29

    02:47:05

    -0.57

    0.29

    -1.2

    36.5

    122.5

    11907

    1998

    250

    01:06:08

    01:07:50

    0.38

    0.16

    0.83

    30.7

    148.5

    11961

    1998

    253

    18:48:52

    18:50:55

    0.50

    0.29

    1.20

    29.0

    -116.9

    12057

    1998

    260

    10:18:07

    10:20:22

    -0.57

    0.26

    -1.20

    22.9

    11.8

    12067

    1998

    261

    02:57:48

    02:59:14

    -0.31

    0.11

    0.54

    29.7

    120.9

    12299

    1998

    277

    04:28:23

    04:28:27

    0.17

    0.07

    0.29

    27.9

    98.9

    12413

    1998

    285

    01:53:07

    01:54:16

    -0.31

    0.12

    -0.57

    30.8

    136.9

    12920

    1998

    320

    04:13:45

    04:17:55

    -0.59

    0.29

    -1.4

    27.2

    101.7

    13300

    1998

    346

    11:36:26

    11:36:30

    0.11

    0.050

    0.28

    15.3

    -6.0

    14398

    1999

    057

    14:15:18

    14:15:55

    -0.061

    -0.078

    0.32

    -41.2

    -36.4

    14659

    1999

    075

    16:09:40

    16:13:33

    0.69

    0.39

    1.8

    -18.7

    -70.3

    15027

    1999

    101

    02:25:35

    02:25:44

    0.16

    0.093

    0.29

    17.3

    131.1

    15100

    1999

    106

    03:44:42

    03:48:03

    0.48

    0.22

    1.3

    25.2

    109.2

    15187

    1999

    112

    04:22:27

    04:25:15

    0.61

    0.32

    1.5

    26.3

    99.7

    15202

    1999

    113

    05:18:51

    05:21:48

    0.29

    0.30

    0.80

    27.9

    85.3

    15563

    1999

    138

    05:20:40

    05:22:34

    -0.47

    0.20

    -0.88

    22.6

    85.9

    15794

    1999

    154

    05:19:46

    05:22:22

    0.51

    0.28

    1.3

    32.3

    84.1

    16443

    1999

    199

    03:59:54

    04:00:55

    0.29

    0.22

    0.55

    28.4

    105.1

    16444

    1999

    199

    05:42:01

    05:45:26

    -0.64

    0.40

    -1.4

    44.7

    75.2

    16471

    1999

    201

    02:33:05

    02:35:20

    -0.24

    0.12

    -0.47

    37.0

    124.7

    16486

    1999

    202

    03:26:29

    03:30:26

    0.62

    0.34

    1.6

    33.3

    111.8

    16658

    1999

    214

    01:19:35

    01.21.29

    -0.40

    0.18

    -0.81

    32.0

    144.2

    16659

    1999

    214

    03:02:03

    03:03:37

    0.28

    0.13

    0.52

    40.5

    116.8

    16674

    1999

    215

    03:52:59

    03:58:35

    0.60

    0.33

    1.8

    36.9

    103.9

    16718

    1999

    218

    05:03:37

    05:05:07

    -0.54

    0.30

    -0.94

    33.3

    88.0

    16750

    1999

    220

    10:11:56

    10:15:04

    -0.59

    0.30

    -1.2

    29.8

    11.3

    16760

    1999

    221

    02:51:21

    02:55:02

    0.59

    0.37

    1.4

    39.6

    119.1

    16805

    1999

    224

    05:39:27

    05:40:57

    0.40

    0.19

    0.87

    35.0

    78.7

    17159

    1999

    248

    17:58:44

    17:59:25

    -0.26

    0.14

    -0.39

    33.1

    -105.6

    17248

    1999

    254

    23:23:25

    23:24:10

    -0.28

    0.085

    -0.40

    -0.5

    178.7

    17325

    1999

    260

    05:47:32

    05:49:39

    0.53

    0.27

    1.2

    25.0

    78.4

    17389

    1999

    264

    16:11:00

    16:14:04

    -0.63

    0.38

    -1.4

    36.8

    -80.1

    17901

    1999

    300

    02:57:37

    03:01:02

    0.62

    0.36

    1.6

    24.6

    120.5

    18255

    1999

    324

    16:41:45

    16:42:05

    0.14

    -0.054

    0.45

    -20.0

    -78.0

    18421

    1999

    336

    03:02:25

    03:02:33

    0.17

    0.077

    0.27

    19.6

    120.8

    18622

    1999

    350

    00:56:58

    01:00:36

    -0.61

    0.32

    -1.5

    20.9

    151.0

    18695

    1999

    355

    02:14:27

    02:19:26

    0.63

    0.34

    2.1

    26.8

    130.3

    19085

    2000

    017

    02:11:21

    02:12:52

    -0.34

    0.21

    -0.58

    12.6

    134.2

    19215

    2000

    026

    02:12:42

    02:14:16

    -0.28

    0.083

    -0.57

    22.8

    132.2

    19389

    2000

    038

    03:14:17

    03:15:02

    -0.23

    0.12

    -0.37

    10.5

    118.9.0

    19649

    2000

    056

    03:09:35

    03:11:34

    -0.50

    0.22

    -1.1

    14.5

    119.1

    19855

    2000

    070

    09:20:01

    09:22:17

    0.58

    0.30

    1.3

    9.6

    27.1

    20057

    2000

    084

    08:54:31

    08:55:16

    -0.36

    0.18

    -0.39

    12.7

    33.4

    20068

    2000

    085

    03:11:09

    03:15:48

    -0.55

    0.23

    -1.6

    27.6

    115.8

    20385

    2000

    107

    01:43:29

    01:46:38

    -0.54

    0.27

    -1.2

    28.4

    137.8

    20572

    2000

    120

    00:14:29

    00:17:05

    -0.60

    0.29

    -1.3

    14.9

    162.5

    20885

    2000

    141

    16:03:14

    16:07:24

    0.47

    0.24

    1.5

    24.6

    -76.8

    21125

    2000

    158

    06:38:20

    06:41:24

    -0.62

    0.31

    -1.3

    29.7

    63.8

    21500

    2000

    184

    05:20:33

    05:22:15

    -0.43

    0.19

    -0.80

    26.9

    84.0

    21513

    2000

    185

    02:58:09

    02:58:13

    0.15

    0.05

    0.33

    29.7

    119.5

    21600

    2000

    191

    03:24:10

    03:25:24

    -0.38

    0.18

    -0.63

    27.8

    113.0

    21688

    2000

    197

    05:32:35

    05:35:56

    0.42

    0.24

    0.86

    39.1

    78.0

    21701

    2000

    198

    03:06:06

    03:08:29

    -0.60

    0.32

    -1.3

    30.5

    116.7

    21716

    2000

    199

    04:03:03

    04:03:27

    0.20

    0.09

    0.42

    31.8

    102.7

    21845

    2000

    208

    02:13:31

    02:16:23

    -0.56

    0.30

    -1.1

    38.2

    128.0

    21903

    2000

    212

    02:32:49

    02:34:27

    0.53

    0.29

    1.1

    38.6

    123.4

    21991

    2000

    218

    04:38:42

    04:38:59

    -0.23

    0.075

    -0.36

    30.6

    94.0

    22207

    2000

    233

    03:15:07

    03:16:46

    -0.26

    0.12

    -0.55

    33.3

    113.9

    22279

    2000

    238

    02:46:55

    02:47:03

    0.20

    0.077

    0.35

    25.7

    122.8

    22403

    2000

    246

    16:40:53

    16:42:03

    -0.44

    0.27

    -0.71

    36.5

    -88.1

    22424

    2000

    248

    03:29:26

    03:33:15

    -0.59

    0.27

    -1.2

    33.8

    109.7

    22481

    2000

    252

    02:09:41

    02:09:49

    0.17

    0.074

    0.29

    28.8

    131.5

    22517

    2000

    254

    15:18:35

    15:20:22

    -0.58

    0.33

    -1.2

    -25.2

    -57.6

    22700

    2000

    267

    05:42:59

    05:44:42

    0.51

    0.27

    1.0

    29.3

    77.6

    22751

    2000

    270

    18:22:50

    18:22:54

    0.14

    0.062

    0.26

    24.0

    -110.9

    22779

    2000

    272

    16:52:44

    16:54:35

    -0.49

    0.24

    -0.88

    31.9

    -90.4

    22831

    2000

    276

    07:09:47

    07:12:52

    0.39

    0.34

    0.79

    27.9

    55.8

    23015

    2000

    289

    00:39:36

    00:42:07

    -0.43

    0.19

    -0.91

    36.9

    151.6

    23129

    2000

    296

    23:24:52

    23:24:52

    0.14

    -0.051

    0.27

    -1.7

    177.4

    23317

    2000

    309

    21:52:03

    21:54:35

    0.52

    0.25

    1.2

    18.2

    -163.0

    23537

    2000

    325

    03:02:05

    03:04:08

    -0.54

    0.23

    -0.97

    17.7

    119.6

    23563

    2000

    326

    23:45:34

    23:46:48

    0.48

    0.22

    0.83

    -2.6

    172.0

    23610

    2000

    330

    04:12:24

    04:15:32

    -0.58

    0.30

    -1.3

    24.9

    100.5

    23638

    2000

    332

    02:41:46

    02:44:34

    0.27

    0.14

    0.79

    27.5

    122.8

    23652

    2000

    333

    01:52:46

    01:54:28

    -0.38

    0.17

    -0.65

    12.4

    137.8

    23709

    2000

    337

    00:30:04

    00:32:56

    -0.59

    0.31

    -1.3

    19.7

    157.1

    23754

    2000

    340

    03:14:21

    03:14:32

    0.21

    0.083

    0.39

    23.5

    116.0

    23796

    2000

    343

    02:28:06

    02:29:36

    -0.43

    0.17

    -0.75

    -2.6

    131.2

    23825

    2000

    345

    01:00:45

    01:04:26

    0.67

    0.40

    1.9

    22.2

    148.7

    23999

    2000

    357

    01:49:46

    01:50:07

    0.26

    0.084

    0.51

    19.3

    137.8

    24021

    2000

    358

    15:47:57

    15:50:58

    0.60

    0.30

    1.5

    -12.9

    -67.6

    24057

    2000

    361

    02:02:23

    02:05:43

    0.65

    0.34

    1.6

    21.5

    133.5

    24158

    2001

    002

    01:44:10

    01:45:43

    -0.39

    0.17

    -0.76

    32.3

    136.5

    24230

    2001

    007

    01:10:22

    01:11:52

    -0.25

    0.06

    0.50

    22.5

    146.7

    24259

    2001

    009

    01:15:35

    01:18:43

    0.82

    0.35

    1.8

    20.2

    145.4

    24344

    2001

    014

    23:52:06

    23:52:59

    0.26

    0.15

    0.36

    -11.7

    171.6

    24508

    2001

    026

    06:27:46

    06:30:34

    0.54

    0.32

    1.2

    18.0

    67.8

    24513

    2001

    026

    16:17:19

    16:17:23

    0.15

    0.05

    0.30

    -19.1

    -73.3

    24620

    2001

    034

    00:18:57

    00:22:34

    -0.54

    0.25

    -1.3

    21.0

    159.3

    24621

    2001

    034

    01:57:48

    02:01:29

    -0.59

    0.27

    -1.4

    18.4

    135.0

    24707

    2001

    040

    00:41:25

    00:44:17

    0.60

    0.29

    1.3

    19.9

    154.0

    24730

    2001

    041

    16:23:05

    16:23:10

    0.20

    0.053

    0.27

    -18.2

    -75.0

    24743

    2001

    042

    13:50:19

    13:50:23

    -0.052

    -0.064

    0.26

    -43.6

    -31.6

    24743

    2001

    042

    13:50:19

    13:50:23

    -0.052

    -0.064

    0.26

    -43.6

    -31.6

    24750

    2001

    043

    01:34:38

    01:34:42

    -0.14

    0.088

    -0.26

    -16.4

    146.9

    24779

    2001

    045

    00:12:40

    00:12:44

    -0.18

    0.057

    -0.31

    20.3

    161.8

    24987

    2001

    059

    09:19:22

    09:21:29

    -0.33

    0.085

    -0.51

    21.7

    24.3

    25114

    2001

    068

    04:01:38

    04:03:12

    0.52

    0.21

    0.86

    14.8

    105.0

  35. What can you tell me about TOMS Gridded Aerosol Optical Depth Data?

    The TOMS aerosol optical depth record covers the periods from January 1979 to April 1993 (Nimbus7-TOMS observations), and from July 1996 to December 2000 (Earth Probe TOMS measurements).

    The retrieval algorithm [Torres et al, 1998,2002], was applied to observations at 340 and 380 nm by the Nimbus7-TOMS sensor, and to 331 and 360 nm measurements by the Earth Probe instrument. For the sake of continuity, however, the optical depth record is reported at 380 nm for both instruments.

    Data products

    Files of monthly average optical depth on a 1 degree X 1 degree resolution over the oceans and the continents were produced. In addition, files containing the number of days per month used in the calculation of the monthly mean value at each grid point were also created.

    Format

    The data is written in a 360X180 ASCII array, going from 90 to -90 in latitude, and from -180 to 180 in longitude. Effectively, however, no data is available beyond 70 degrees latitude in both hemispheres. Optical depth values have been multiplied by 1000. When no data is available, a fill value of zero (0) is reported.

    Filenames

    The monthly optical depth data files are: nimbus7/data/aot/yYYYY/globe_tau_MMMYY.asc (1979 through 1993) eptoms/data/aot/yYYYY/globe_tau_MMMYY.asc (1996 through 2000)

    where YYYY is four-digit year MMM first three letters of month'name (e.g., jan) YY two digit year.

    The files containing number of days per grid are: nimbus7/data/aot/yYYYY/globe_ndy_MMMYY.asc (1979 through 1993) eptoms/data/aot/yYYYY/globe_ndy_MMMYY.asc (1996 through 2000)

    References

    Torres, O., P.K. Bhartia ,J.R. Herman, A. Sinyuk and B. Holben, A long term record of aerosol optical thickness from TOMS observations and comparison to AERONET measurements, J. Atm. Sci.,59,398-413, 2002

    Torres O., P.K. Bhartia, J.R. Herman and Z. Ahmad, Derivation of aerosol properties from satellite measurements of backscattered ultraviolet radiation. Theoretical Basis, J. Geophys. Res., 103, 17099-17110, 1998


    If these data are downloaded and used in publications, please give proper credit to the NASA/GSFC TOMS group. For more information about the TOMS aerosol optical depth product, contact

    Dr Omar Torres
    Joint Center for Earth Systems Technology
    University of Maryland, Baltimore County

    Mailing address:
    Code 613.3
    NASA Goddard Space Flight Center
    Greenbelt, MD, 20771
    omar.o.torres@nasa.gov

    The Asia-Pacific Data-Research Center hosts some Fortran code that can be used to read these products.