***(Revised)***

**Atmospheric Products from the Ozone Monitoring Instrument (OMI)**

Suraiya P. Ahmad[^1]^a^, Pieternel F. Levelt^b^, Pawan K. Bhartia^c^,
Ernest Hilsenrath^c^,

Gilbert W. Leppelmeier^d^, and James E. Johnson^a^

^a^Goddard Earth Sciences Data and Information Services Center (GES
DISC), Code 610.2/RSIS NASA Goddard Space Flight Center, Greenbelt, MD
20771, U.S.A.

^b^Royal Netherlands Meteorological Institute (KNMI), De Bilt, The
Netherlands

^c^Atmospheric Chemistry and Dynamics Branch, Code 613.3, NASA Goddard
Space Flight Center, Greenbelt, MD 20771, U.S.A.

^d^Finnish Meteorological Institute (FMI), Helsinki, Finland

***\
***

**Abstract**

Ozone Monitoring Instrument (OMI) is a Dutch-Finnish ozone monitoring
imaging spectrometer that is designed to provide accurate measurements
of total column ozone, ozone profile, surface UV irradiance, aerosols
and cloud characteristics, and the column amounts of trace gases SO~2~,
NO~2~, HCHO, BrO, and OClO at high spatial resolution. The OMI along
with the three other instruments, the Microwave Limb Sounder (MLS), the
High Resolution Dynamics Limb Sounder (HIRDLS), and the Tropospheric
Emission Spectrometer (TES), will be flown on the NASA's Aura mission in
early 2004. The standard atmospheric chemistry and dynamics products
derived from OMI, MLS, and HIRDLS will be archived at the NASA's GES
DISC (TES data products will be archived at NASA Langley Research Center
DISC) and will be freely available to the public. Highlights of OMI data
products, as well as their availability, distribution and data support
are discussed in this paper.

**Keywords**: atmospheric chemistry, ozone, trace gases, NO~2,~ SO~2~,
BrO, HCHO, OClO, clouds, aerosols, UV and visible spectral radiance,
surface UV-B flux, solar irradiance

**1. Introduction**

To continue the long-term study of the trends in ozone and other trace
gases, and to improve the understanding of atmospheric chemical
processes, the Ozone Monitoring Instrument (OMI), a contribution of the
Netherlands agency for aerospace programs (NIVR) in collaboration with
the Finnish Meteorological Institute (FMI) to NASA's Aura mission, will
be flown on the Aura spacecraft. Aura is part of the NASA\'s long-term
Earth Observing System (EOS) mission and is scheduled for launch in
early 2004. The Aura spacecraft will also carry three other instruments:
the Microwave Limb Sounder (MLS), the High Resolution Dynamics Limb
Sounder (HIRDLS), and the Tropospheric Emission Spectrometer (TES).
These four instruments will provide atmospheric radiance measurements at
high spectral and spatial resolution for studying changes in atmospheric
ozone, tropospheric pollutants and other trace gases. The high quality
atmospheric chemistry and dynamics products derived from these sensors
will provide answers^1^ to the three main objectives of the Aura
mission; is the Earth's ozone layer recovering, is air quality changing,
and how is the Earth's climate changing? (*http://aura.gsfc.nasa.gov/*).

The OMI is a nadir sounder and the MLS and HIRDLS are limb sounding
instruments. The TES has both limb sounding and nadir sounding modes.
The OMI will provide measurements in UV and Visible spectral regions and
will

focus on monitoring the ozone layer, ozone depleting trace gases BrO and
OClO, tropospheric pollutants (tropospheric ozone, NO~2~, tropospheric
aerosols, SO~2~, and HCHO), clouds, aerosols, and erythemal surface UV-B
flux. Tropospheric ozone and aerosols are also important for climate
change. The HIRDLS is an infrared limb-scanning radiometer designed to
look through the \"edge\" of Earth\'s atmosphere to study aerosols and
clouds. The MLS is a passive microwave radiometer/spectrometer that will
study ozone depletion and radiation in the Earth\'s troposphere and
stratosphere. The TES is an infrared imaging spectrometer and will
measure global distributions of key atmospheric pollutants in the
troposphere.

The OMI is built by Dutch Space/TNO-TPD in the Netherlands, in
co-operation with Finnish subcontractors VTT and Patria Finavitec. The
Principle Investigator (PI) Institute is KNMI (Royal Netherlands
Meteorological Institute). Dr. Pieternel F. Levelt is the principle
investigator. The co- investigators are Dr. Gilbert W. Leppelmeier (FMI)
and Ernest Hilsenrath (NASA), and US science team leader is Dr. Pawan K.
Bhartia (NASA). An international team consisting of Dutch, US and
Finnish scientists has been established and are assigned with the
responsibilities of developing retrieval algorithms, monitoring
in-flight instrument calibration, operational handling of the
instrument, and conducting the data validation.

The OMI Level-0 to 1B and Level-2 & 3 data processing will occur at NASA
Goddard Space Flight Center and at KNMI in the Netherlands. Overall
responsibility^2^ for the OMI mission lies with the Netherlands Agency
for Aerospace Programs (NIVR) with the participation of FMI (Finnish
Meteorological Institute).

The standard atmospheric chemistry and dynamics products derived from
OMI, MLS, and HIRDLS aboard Aura, and data from future upper atmospheric
research missions, will be archived at the NASA GES DISC. Data from TES
will be archived at NASA Langley Research Center DAAC. These atmospheric
products will provide continuity to the over 30 year long-term ozone
data records obtained from the heritage atmospheric data missions
including Nimbus-4 BUV and Nimbus-7 Solar Backscatter Ultraviolet
Spectrometers (SBUV), a series of Total Ozone Mapping Spectrometer
(TOMS) instruments, and will provide continuity to a suite of important
ozone depleting trace gases available from the Upper Atmospheric
Research Satellite (UARS) instruments, also archived at the NASA GES
DISC and freely available to the public.

This paper gives an overview of the OMI instrument, data processing,
data products, and the data services provided by the NASA GES DISC
Atmospheric Composition Data Support team to the user in the areas of
accessing data products, documentation, browse, and data analysis
software.

**2. Characteristics of THE OMI Instrument**

The OMI instrument will be flown on the Aura spacecraft into a 705 km,
98.2 degree inclination, sun-synchronous polar orbit with an equatorial
crossing at 1:38 pm (in the ascending mode). OMI will observe almost the
same air mass within 15 minutes of the Aqua measurements. OMI has a very
large field of view of 114 degrees for the swath registration (± 57
degrees relative to nadir) perpendicular to the flight direction of the
satellite. In nominal operation^2^, the OMI swath width on the ground is
2600 km. This wide swath width enables OMI to achieve global coverage in
one day (14 orbits).

**2.1 Spectral Sampling**

OMI is a non-scanning wide angle nadir pointing hyper-spectral push
broom imaging spectrograph, to observe solar backscatter radiation in
the visible and ultraviolet spectral region. The Earth will be viewed in
1560 wavelength bands in the spectral region 270 to 500 nm with a
spectral resolution of approximately 0.5 nm (Table 1). The spectral
samplings are grouped into two optical channels, UV & visible (VIS). The
UV channel is split into two sub-channels: UV-1 ranging from 270 to 310
nm, and the UV-2 ranging from 310 to 365 nm for stray-light
considerations. The VIS-channel ranges from 365 to 500 nm (Table 1). Two
2-dimensional CCD detectors are used, one for UV-1 & 2 and other for the
VIS channel. The nominal integration time of the CCD image is 0.4 sec.
To decrease the data rate and increase the signal-noise ratio, onboard
binning and co-adding of subsequent CCD images are performed. The number
of exposures or images that are averaged is specified by the \"binning
factor\", which is set by the instrument operations team^3^.

**2.2 Spatial Sampling**

There are three sampling modes, global, spatial zoom-in, and spectral
zoom-in. In the global (default) mode, the earth measurements are taken
with the nominal co-addition time of 2 sec (i.e. binning factor 8).
Using this co-addition time, for a swath of 2600 km, a nadir pixel size
of 13 x 24 km^2^ is achieved for the VIS and UV-2 channels, and 13 x 48
km^2^ for the UV-1 channel (Table 1). In the zoom-in measurement or high
resolution mode, binning factor 4 is used. The spatial and spectral
zoom-in modes offer the possibility of smaller ground pixels at the
expense of reduced swath width or spectral range. For example, in the
spatial zoom-in mode (13 x 12 km^2^), the swath width for UV-2 & VIS is
reduced to 725 km and in the spectral zoom-in mode the spectral coverage
for UV and VIS region is reduced. Spatial zoom-in mode will be used for
regional studies. A high resolution data mode with no binning are
referred as "small pixel" data and is used for calibration
measurements^3^.

The nadir ground pixel size also increases because of the earth
curvature effects at large viewing angles. The pixel-size in the
swath-direction increases from 13 x 24 km^2^ (exact nadir position) to
approximately 13 x 128 km^2^ at the outermost swath-angle (57 degrees).
The geolocation^2,\ 4^ of the OMI ground pixels is accurate to about one
tenth of the CCD pixel or 1 to 2 km.

Table 1. OMI swath width and nadir pixel size (along x across track) for
different observation Modes

+-------------+--------+---+-----------------+-----------+--------------+
| **          | *      |   | **Nadir ground  | *         | **A          |
| Observation | *Swath |   | pixel size**    | *Spectral | pplication** |
| mode**      | w      |   |                 | range**   |              |
|             | idth** |   |                 |           |              |
+-------------+--------+---+-----------------+-----------+--------------+
| *Global     |        |   |                 |           |              |
| mode*       |        |   |                 |           |              |
+-------------+--------+---+-----------------+-----------+--------------+
| UV-1        | 2600   | 1 |                 | 270 - 310 | Global       |
|             | km     | 3 |                 | nm        | observations |
| UV-2        |        | x |                 |           | of almost    |
|             | 2600   | 4 |                 | 310 - 365 | all OMI      |
| VIS         | km     | 8 |                 | nm        | products     |
|             |        | k |                 |           |              |
|             | 2600   | m |                 | 365 - 500 |              |
|             | km     | ^ |                 | nm        |              |
|             |        | 2 |                 |           |              |
|             |        | ^ |                 |           |              |
|             |        |   |                 |           |              |
|             |        | 1 |                 |           |              |
|             |        | 3 |                 |           |              |
|             |        | x |                 |           |              |
|             |        | 2 |                 |           |              |
|             |        | 4 |                 |           |              |
|             |        | k |                 |           |              |
|             |        | m |                 |           |              |
|             |        | ^ |                 |           |              |
|             |        | 2 |                 |           |              |
|             |        | ^ |                 |           |              |
|             |        |   |                 |           |              |
|             |        | 1 |                 |           |              |
|             |        | 3 |                 |           |              |
|             |        | x |                 |           |              |
|             |        | 2 |                 |           |              |
|             |        | 4 |                 |           |              |
|             |        | k |                 |           |              |
|             |        | m |                 |           |              |
|             |        | ^ |                 |           |              |
|             |        | 2 |                 |           |              |
|             |        | ^ |                 |           |              |
+-------------+--------+---+-----------------+-----------+--------------+
| *Spatial    |        |   |                 |           |              |
| zoom-in     |        |   |                 |           |              |
| mode*       |        |   |                 |           |              |
+-------------+--------+---+-----------------+-----------+--------------+
| UV-1        | 2600   | 1 |                 | 270 - 310 | Regional     |
|             | km     | 3 |                 | nm        | observations |
| UV-2        |        | x |                 |           | of all OMI   |
|             | 725 km | 2 |                 | 310 - 365 | products     |
| VIS         |        | 4 |                 | nm        |              |
|             | 725 km | k |                 |           |              |
|             |        | m |                 | 365 - 500 |              |
|             |        | ^ |                 | nm        |              |
|             |        | 2 |                 |           |              |
|             |        | ^ |                 |           |              |
|             |        |   |                 |           |              |
|             |        | 1 |                 |           |              |
|             |        | 3 |                 |           |              |
|             |        | x |                 |           |              |
|             |        | 1 |                 |           |              |
|             |        | 2 |                 |           |              |
|             |        | k |                 |           |              |
|             |        | m |                 |           |              |
|             |        | ^ |                 |           |              |
|             |        | 2 |                 |           |              |
|             |        | ^ |                 |           |              |
|             |        |   |                 |           |              |
|             |        | 1 |                 |           |              |
|             |        | 3 |                 |           |              |
|             |        | x |                 |           |              |
|             |        | 1 |                 |           |              |
|             |        | 2 |                 |           |              |
|             |        | k |                 |           |              |
|             |        | m |                 |           |              |
|             |        | ^ |                 |           |              |
|             |        | 2 |                 |           |              |
|             |        | ^ |                 |           |              |
+-------------+--------+---+-----------------+-----------+--------------+
| *Spectral   |        |   |                 |           |              |
| zoom-in     |        |   |                 |           |              |
| mode*       |        |   |                 |           |              |
+-------------+--------+---+-----------------+-----------+--------------+
| UV          | 2600   | 1 |                 | 306 - 364 | Global       |
|             | km     | 3 |                 | nm        | observation  |
| VIS         |        | x |                 |           | of some      |
|             | 2600   | 1 |                 | 350 - 432 | products     |
|             | km     | 2 |                 | nm        |              |
|             |        | k |                 |           |              |
|             |        | m |                 |           |              |
|             |        | ^ |                 |           |              |
|             |        | 2 |                 |           |              |
|             |        | ^ |                 |           |              |
|             |        |   |                 |           |              |
|             |        | 1 |                 |           |              |
|             |        | 3 |                 |           |              |
|             |        | x |                 |           |              |
|             |        | 1 |                 |           |              |
|             |        | 2 |                 |           |              |
|             |        | k |                 |           |              |
|             |        | m |                 |           |              |
|             |        | ^ |                 |           |              |
|             |        | 2 |                 |           |              |
|             |        | ^ |                 |           |              |
+-------------+--------+---+-----------------+-----------+--------------+

**2.3 On-board Calibrators** **and** **Calibration Measurements**

The pre-flight spatial, spectral, and radiometric calibration^5^ has
been done in detail by the Dutch Space, the prime instrument contractor,
and the TNO-TPD team, who have designed and built the optical systems at
TNO-TPD facilities. In addition to the pre-flight calibration, OMI will
also perform the in-flight calibration^5^ measurements. The on-board
calibrators include: *three solar diffusers* for solar measurements (one
for daily use and the others for monitoring the degradation of the daily
used diffuser), *Internal White Light Source (WLS)* observed (on average
once per week) via a transmission diffuser for relative radiometric
calibration of the instrument optics plus detectors, two *Light Emitting
Diodes (LEDs)* observed once a week on average for monitoring the
efficiency of the detectors. *Dark current* measurements are also
performed. OMI also uses a polarization *scrambler* to depolarize the
incoming polarized radiation. *Wavelength calibration* is performed by
using Fraunhofer lines in the solar irradiance and earth radiance
spectra. For geolocation verification purpose the earth radiance
measurements are made in super spatial zoom-in mode (\"small pixel\"
mode, no binning).

**3. Science Data Processing**

The EOS Data and Operations System (EDOS) is responsible for data
capture and initial Level-0 processing of spacecraft data. Level-0
product consists of raw instrument data at original resolution, time
ordered, with duplicate packets removed. Aura data from OMI, MLS,
HIRDLS, and TES are further processed using the algorithms provided by
the individual instrument science teams to convert counts to geolocated
radiances (Level-1B products) and produce geophysical data products
(Levels-2 & 3) from Level-1B. This activity takes place on the Science
Investigator-led Processing Systems (SIPS) centers established for each
instrument. For OMI, two data centers are under development, the OMI
SIPS or OSIPS located at NASA GSFC and the ODPS (OMI Dutch Processing
System) located at the KNMI, The Netherlands. The surface spectral UV-B
flux product will be processed at the FMI, Finland. OSIPS and ODPS will
integrate operational science software, process and reprocess standard
products, and deliver them to the GES DISC for archive and distribution.

**4. OMI Data Products**

The OMI data products are available at four processing Levels: Level-0,
Level-1B, Level-2, and Level-3. Level-0 products are raw sensor counts.
Level-0, Level-1B, and Level-2 products contain orbital swath data,
whereas Level-3 products contain global data that are averaged over time
(daily or monthly) for small equal angle (latitude x longitude) grids
covering the whole globe. OMI Level-2 data files will also contain
temporal, spatial, solar, and viewing geometry parameters, quality
flags, and extensive quality assurance information, in addition to the
standard retrieved geophysical parameters. Brief details of these
products are given below.

**4.1 OMI Radiometrically Calibrated and Geolocated Radiance Products
(Level-1B)**

An extensive calibration and data processing algorithm called the
"Level-0 to 1B Algorithm" has been developed^6^ by Dutch Space in
co-operation with the Dutch OMI team. The Level-0 to 1B algorithm is
used at OSIPS (NASA GSFC) to produce Level-1B OMI products^7^. It takes
the raw sensor measurements (Level-0 data), calibration and spacecraft
ephemeris information and produces radiometrically calibrated and
geolocated radiances. Six types of Level-1B standard products are
produced (Table 2).

Table 2. OMI Calibrated and Geolocated Earth View Radiance, Solar
Irradiance, and Calibration Products (Level-1B)

+---------+------------------------------------------------------------+
|         | **OMI Level-1B Calibrated Radiance & Irradiance**          |
+---------+------------------------------------------------------------+
| *P      | *Product Description*                                      |
| roduct* |                                                            |
+---------+------------------------------------------------------------+
| O       | **Geolocated Earth View UV Radiance, Global-mode Product** |
| ML1BRUG |                                                            |
|         | \- Geolocated earth view radiances from the UV channel     |
|         | detector in the wavelength range of 270 to 380 nm, using   |
|         | the global measurement mode. It will also contain the data |
|         | rebinned from the observations taken using zoom-in         |
|         | measurement modes.                                         |
+---------+------------------------------------------------------------+
| O       | **Geolocated Earth View VIS Radiance, Global-mode          |
| ML1BRVG | Product**                                                  |
|         |                                                            |
|         | \- Geolocated earth view radiances from the VIS channel    |
|         | detector in the wavelength range of 350 to 500 nm, using   |
|         | the global measurement mode. It will also contain the data |
|         | rebinned from the observations taken using zoom-in         |
|         | measurement modes.                                         |
+---------+------------------------------------------------------------+
| O       | **Geolocated Earth View UV Radiance, Zoom-in mode          |
| ML1BRUZ | Product**                                                  |
|         |                                                            |
|         | \- Geolocated earth view radiances from the UV channel     |
|         | detector in the wavelength range of 270 to 380 nm**,**     |
|         | using spectral and spatial zoom-in measurement modes.      |
+---------+------------------------------------------------------------+
| O       | **Geolocated Earth View VIS Radiance, Zoom-in mode         |
| ML1BRVZ | Product**                                                  |
|         |                                                            |
|         | \- Geolocated earth view radiances from the VIS channel    |
|         | detector in the wavelength range of 350 to 500 nm, using   |
|         | spectral and spatial zoom-in measurement modes.            |
+---------+------------------------------------------------------------+
| O       | **Solar Irradiance Product**                               |
| ML1BIRR |                                                            |
|         | \- Averaged sun measurements of the solar irradiances from |
|         | both the UV and VIS channel detectors over a single solar  |
|         | observation in the wavelength range of 270 to 500 nm.      |
+---------+------------------------------------------------------------+
| O       | **Calibration Data**                                       |
| ML1BCAL |                                                            |
|         | \- In-flight calibration measurement results, including    |
|         | the complete CCD readouts for both the UV and VIS channels |
|         | from the areas on the CCD that are intended for the        |
|         | calibration purposes (which is outside of the area         |
|         | normally used by the spectrometer).                        |
+---------+------------------------------------------------------------+
| O       | **Operational Parameter File**                             |
| ML1BOPF |                                                            |
|         | \- Essentially a LUT (look up table) with the information  |
|         | (including pre-flight and in-flight calibration            |
|         | parameters) needed in the Level 0 to 1B processing.        |
+---------+------------------------------------------------------------+

The lead scientists for Level-1B products are: Marcel Dobber
(*dobber@knmi.nl*), R. H. Voors (*voors@knmi.nl*), and J. de Vries
(*JdeVries \@tpd.tno.nl*).

**4.2 OMI Orbital Atmospheric Products (Level-2)**

The OMI Level-2 (orbital swaths) products contain the geophysical
parameters (at ground-pixel resolution) derived from radiometrically
calibrated and geolocated radiances (Level-1B product). The spectral
radiances used for the retrieval of OMI products are given in Table 3.
Each Level-2 product file consists of parameters retrieved from
observations made only in the daytime portion of an orbit (\~ 53 minute
duration). In addition to standard derived parameters, these files also
contain some auxiliary derived parameters, ancillary input parameters,
temporal, spatial, solar and viewing geometry, terrain height, ground
pixel quality flags, and extensive quality assurance information. In the
OMI global operational mode the spatial resolution is 13 x 24 km^2^ at
nadir. Almost all Level-2 products will contain data at 13 x 24 km^2^
(nadir pixel size) resolution with the exception of few. Level-2
products will be available at higher spatial resolution using the OMI
spatial zoom-in mode data 13 x 12 km^2^. These products will have their
short name with "Z" (for the Zoom) at the end.

Table 3. The spectral regions used for the retrieval of OMI products

  ----------------------------------- ------------- ---------------- -------------
  ***Products***                      ***Spectral   ***Products***   ***Spectral
                                      Range (nm)***                  Range (nm)***

  Surface spectral irradiance &       290 - 400     O~3~ profile     270 - 340
  Erythemally weighted UV Flux                                       

  Ozone column: DOAS method           320 - 340     SO~2~            300 - 330

  Ozone column: TOMS Version 8 method 310 - 380     HCHO             335 - 360

  Aerosol: near-UV and                330 - 500     BrO              344 - 360
  multi-wavelength method                                            

  Cloud Fraction and Cloud Pressure:  320 - 500;    OClO             355 - 385
  O~2~-O~2~ absorption method         470 - 485                      

  Cloud Fraction and Cloud Pressure:  392 - 398     NO~2~            405 - 465
  Rotational Raman method                                            
  ----------------------------------- ------------- ---------------- -------------

**Ozone Products**

There are four Level-2 ozone products (Table 4) that are based on the
algorithms that have heritage from Total Ozone Mapping Spectrometer
(TOMS), Global Ozone Monitoring Experiment (GOME), and Scanning Imaging
Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY). These
ozone products are column ozone, ozone profile, and tropospheric total
ozone. Two algorithms are available for the total ozone retrieval,
enhanced TOMS Version 8 (V8) algorithm used for more than 25 years for
the TOMS, and Differential Optical Absorption Spectroscopy (DOAS)
technique used for the GOME and SCIAMACHY ozone retrievals. TOMS V8
algorithm^8^ retrieves vertical column ozone data essentially using
317.5 and 331.2 nm wavelengths. OMI's additional hyper-spectral
measurements will help in better estimates and corrections of the
factors that induce uncertainty in ozone retrieval (e.g., cloud and
aerosol, sea-glint effects, profile shape sensitivity, SO~2~ and other
trace gas contamination). DOAS technique^9^ is based on the fitting of
the satellite measured gases absorption structure at number of
absorption lines in the spectral region 331.1 to 336 nm to the one
measured in the laboratory. First slant column density is determined
then it is translated into a vertical column density, using air mass
factor. This air mass factor is computed using radiative transfer
models.

Ozone profile retrieval^10^, is based on the Optimal Estimation method
(also referred to as Rodger\'s maximum-likelihood estimation technique),
uses all ozone sensitive wavelengths radiances (in spectral region 270
to 340 nm), a priori ozone profile, radiances, and a Jacobian matrix
computed from the radiative transfer model. Hyperspectral capabilities
provide better vertical resolution below 20 km compared to SBUV which
has a limited number of wavelengths.

Tropospheric Total Ozone (TTO) retrieval^11^ is based on an improved
version of Tropospheric Ozone Residual (TOR) method. TOR method uses
stratospheric ozone column obtained from high vertical resolution ozone
profile (HIRDLS retrievals) and subtracts it from the OMI retrieved
total column ozone.

**Clouds, Aerosols and Surface UV Irradiance Products**

OMI produces cloud fraction and cloud pressure that are used in OMI
trace-gas retrievals and by other Aura sensors. Two methods are used for
the cloud pressure retrieval, O~2~-O~2~ absorption & Rotational Raman
Scattering methods. O~2~-O~2~ absorption method^12^ is based on spectral
fitting of O~2~-O~2~ absorption band at 477 nm using DOAS technique.
Rotational Raman Scattering (RRS) method^13^ is based on the least
square fitting of the Ring spectrum (filling-in of Fraunhofer lines in
the range 392 to 398 nm due to rotational Raman scattering.

OMI also provides aerosol information that is needed by the other Aura
algorithms. Two algorithms^14^ (near-UV and multi-wavelength methods)
are used for the retrieval of aerosol characteristics over the ocean and
land. The availability of the near-UV wavelengths 330 to 490 nm makes
the aerosol retrieval over the desert area also possible since the land
reflectance is small at these wavelengths. Besides being able to provide
information on the aerosol absorption and single scattering albedo, OMI
aerosol algorithms can differentiate between sulfate, smoke and dust
aerosols, and characterize the type of urban aerosols.

Spectral surface irradiance (at 305, 310, 324, and 380 nm) reaching the
ground and the erythemally weighted irradiance (covering 290-400 nm) are
produced using the enhanced version of TOMS Surface UV-B flux
algorithm^15^. Measured earth-atmosphere radiances are used in
conjunction with radiative transfer model to retrieve UV spectral
irradiances reaching the ground. The OMI algorithm uses actual snow
thickness information from the ECMWF (European Centre for Medium-Range
Weather Forecasts) analysis which improves the values for the high
latitudes. The erythemal UV exposure is calculated using a model for the
susceptibility of Caucasian skin to the sunburn (erythemal). Some
highlights of clouds, aerosols and surface irradiance exposure products
are also provided in Table 5.

Table 4. OMI Ozone Products (Level-2)

+-------+--------------------------------------------+----------------+
| **OMI |                                            |                |
| Ozone |                                            |                |
| (     |                                            |                |
| Total |                                            |                |
| c     |                                            |                |
| olumn |                                            |                |
| &     |                                            |                |
| Profi |                                            |                |
| le)** |                                            |                |
+-------+--------------------------------------------+----------------+
| ***   | ***Parameters***                           | ***Lead        |
| Produ |                                            | Scientist***   |
| ct*** |                                            |                |
+-------+--------------------------------------------+----------------+
| OMTO3 | **O~3~ total column (TOMS V8 method)**,    | P. K. Bhartia  |
|       | also other derived and ancillary           |                |
|       | parameters including N-values, effective   | Pawan.K.Bh     |
|       | Lambertian scene-reflectivity, UV aerosol  | artia@nasa.gov |
|       | index, SO2 index, cloud fraction, terrain  |                |
|       | and cloud pressure, ozone below clouds,    |                |
|       | geolocation, solar and satellite viewing   |                |
|       | angles, and quality flags.                 |                |
+-------+--------------------------------------------+----------------+
| OM    | **O~3~ total column (DOAS method),** ozone | P. Veefkind    |
| DOAO3 | slant column density and its precision     |                |
|       | (for data assimilation), also other        | ve             |
|       | derived and ancillary parameters e.g.      | efkind@knmi.nl |
|       | ozone ghost column density, air mass       |                |
|       | factor (all, clear, and cloudy scenes),    |                |
|       | scene reflectivity, radiance over the DOAS |                |
|       | fit window (331.1 to 336.1 nm), root mean  |                |
|       | square of DOAS fit, cloud fraction, cloud  |                |
|       | radiance, terrain & cloud pressure,        |                |
|       | geolocation, viewing angles, and quality   |                |
|       | flags.                                     |                |
+-------+--------------------------------------------+----------------+
| OM    | **O~3~ profile (Optimum estimation         | R. van Oss     |
| PROO3 | method),** a priori profile (including     |                |
|       | uncertainties) for 17 layers, correlation  | o              |
|       | coefficients, averaging kernel, root mean  | ssvanr@knmi.nl |
|       | square of fit, total ozone (obtained by    |                |
|       | integrating the profile), geolocation,     | R. H. Voors    |
|       | solar and satellite viewing angles, and    |                |
|       | quality flags.                             | voors@knmi.nl  |
|       |                                            |                |
|       | *-This product will be produced at KNMI    |                |
|       | and will be archived at the NASA GES DISC  |                |
|       | as a standard product*.                    |                |
+-------+--------------------------------------------+----------------+
| OM    | **Tropospheric total ozone,** ozone        | J. Ziemke      |
| TROO3 | profile, total column ozone & other        |                |
|       | parameters including geolocation, viewing  | z              |
|       | angles, & quality flags.                   | iemke@umbc.edu |
+-------+--------------------------------------------+----------------+

Table 5. OMI Clouds, Aerosols, and Surface UV Exposure Products
(Level-2)

+-------+--------------------------------------------+----------------+
| **Clo |                                            |                |
| uds** |                                            |                |
+-------+--------------------------------------------+----------------+
| ***   | ***Parameters***                           | ***Lead        |
| Produ |                                            | Scientist***   |
| ct*** |                                            |                |
+-------+--------------------------------------------+----------------+
| OM    | **Cloud fraction and cloud pressure        | J.F. de Haan   |
| CLDO2 | (O~2~-O~2~ absorption method),** slant     |                |
|       | column O~2~-O~2~ & O~3~, Ring              | h              |
|       | coefficients, and uncertainties in derived | aandej@knmi.nl |
|       | parameters; terrain and geolocation        |                |
|       | information; solar & satellite viewing     |                |
|       | angles; and quality flags.                 |                |
+-------+--------------------------------------------+----------------+
| OM    | **Cloud fraction and cloud pressure        | J. Joiner      |
| CLDRR | (Rotational Raman scattering method),**    |                |
|       | other derived and ancillary parameters;    | Joanna.Joi     |
|       | terrain and geolocation information; solar | ner-1@nasa.gov |
|       | & satellite viewing angles; and quality    |                |
|       | flags.                                     |                |
+-------+--------------------------------------------+----------------+
| **Aer |                                            |                |
| osols |                                            |                |
| over  |                                            |                |
| Ocean |                                            |                |
| and   |                                            |                |
| L     |                                            |                |
| and** |                                            |                |
+-------+--------------------------------------------+----------------+
| OM    | **Aerosol optical thickness & single       | O. Torres      |
| AERUV | scattering albedo for the clear sky        |                |
|       | (Near-UV and multi-wavelength methods),**  | Omar.Tor       |
| &     | near-UV index (based on 342.5 and 388 nm)  | res-2@nasa.gov |
|       | similar to TOMS aerosol index; visible     |                |
| O     | aerosol index (based on 388 and 494.5 nm); | P. Veefkind    |
| MAERO | dominating aerosol type (carbonaceous,     |                |
|       | mineral dust, or sulfate) based on aerosol | ve             |
|       | indices; aerosol layer height (ancillary); | efkind@knmi.nl |
|       | uncertainties in the derived parameters;   |                |
|       | quality flags; solar and satellite viewing | G. de Leeuw    |
|       | angles; and geolocation information. The   |                |
|       | aerosols indices will be reported even in  | dele           |
|       | the case of cloud contaminated pixels.     | euw@fel.tno.nl |
|       |                                            |                |
|       | *-In the beginning, near-UV aerosol        |                |
|       | algorithm will start production at the     |                |
|       | OSIPS (NASA GSFC) and the multi-wavelength |                |
|       | algorithm will be used at the ODPS (KNMI). |                |
|       | Later the two methods will be combined and |                |
|       | it will be used at the OSIPS to produce    |                |
|       | standard aerosol products.*                |                |
+-------+--------------------------------------------+----------------+
| **Su  |                                            |                |
| rface |                                            |                |
| UV-Ir |                                            |                |
| radia |                                            |                |
| nce** |                                            |                |
+-------+--------------------------------------------+----------------+
| OMUVB | **Surface Erythemal UV Exposure (TOMS      | A. Tanskanen   |
|       | algorithm):** Downward spectral            |                |
|       | irradiances (W/m^2^/nm) at the ground for  | Aapo.ta        |
|       | 305, 310, 324, & 380 nm; Erythemally       | nskanen@fmi.fi |
|       | weighted UV irradiance (W/m^2^) covering   |                |
|       | 290 to 400 nm spectral region ( noontime   |                |
|       | values & daily averages).                  |                |
|       |                                            |                |
|       | *-This product will be produced at FMI     |                |
|       | (Finland), and will be archived at NASA    |                |
|       | GES DISC as a standard product.*           |                |
+-------+--------------------------------------------+----------------+

**Trace Gases Products**

Total column and slant column values of trace gases, NO~2~, BrO, HCHO,
OClO, and SO~2~ will be produced using absorption spectrum fitting
techniques. Highlights of these products are provided in Table 6. The
OMI algorithm will detect volcanic ash and sulfur dioxide produced in
volcanic eruptions with up to 40 times more sensitivity than TOMS and
GOME.^18^

Table 6. OMI Trace Gases Products (Level-2)

+-------+---------------------------------------------+----------------+
| **    |                                             |                |
| Trace |                                             |                |
| Gases |                                             |                |
| (N    |                                             |                |
| O~2~, |                                             |                |
| BrO,  |                                             |                |
| HCHO, |                                             |                |
| OC    |                                             |                |
| lO,** |                                             |                |
| and   |                                             |                |
| **SO~ |                                             |                |
| 2~)** |                                             |                |
+-------+---------------------------------------------+----------------+
| ***   | ***Parameters***                            | ***Lead        |
| Produ |                                             | Scientist***   |
| ct*** |                                             |                |
+-------+---------------------------------------------+----------------+
| OMNO2 | **NO~2~** **total & tropospheric**          | J. Gleason     |
|       | **column**, slant column density, one sigma |                |
|       | fitting uncertainties for the NO~2~ and the | James.F.Gl     |
|       | other species varied in the fitting window, | eason@nasa.gov |
|       | correlation of other fitted species to the  |                |
|       | NO~2~, fitting root mean square (rms),      | P. Veefkind    |
|       | surface reflectivity, cloud top height,     |                |
|       | geolocation , and solar and satellite       | ve             |
|       | viewing angles.                             | efkind@knmi.nl |
+-------+---------------------------------------------+----------------+
| OMBRO | **BrO** **total column** and slant column   | K. Chance      |
|       | abundance, one sigma fitting uncertainties  |                |
|       | for the BrO and the other species varied in | kchance@c      |
|       | the fitting window, correlation of other    | fa.harvard.edu |
|       | fitted species to the BrO, fitting rms,     |                |
|       | surface reflectivity, cloud top height,     |                |
|       | quality flags, geolocation , and solar and  |                |
|       | satellite viewing angles.                   |                |
+-------+---------------------------------------------+----------------+
| O     | **HCHO total column** and slant column      | K. Chance      |
| MHCHO | abundance, one sigma fitting uncertainties  |                |
|       | for the HCHO and the other species varied   | kchance@c      |
|       | in the fitting window, correlation of other | fa.harvard.edu |
|       | fitted species to the HCHO, fitting rms,    |                |
|       | surface reflectivity, cloud top height,     |                |
|       | quality flags, geolocation , and solar and  |                |
|       | satellite viewing angles.                   |                |
+-------+---------------------------------------------+----------------+
| O     | **OClO slant column** and one sigma fitting | K. Chance      |
| MOCLO | uncertainties for the OClO and the other    |                |
|       | species varied in the fitting window,       | kchance@c      |
|       | correlation of other fitted species to the  | fa.harvard.edu |
|       | OClO, fitting rms, surface reflectivity,    |                |
|       | cloud top height, quality flags,            |                |
|       | geolocation, and solar and satellite        |                |
|       | viewing angles.                             |                |
|       |                                             |                |
|       | *-This product is not global (retrieved for |                |
|       | polar regions only).*                       |                |
+-------+---------------------------------------------+----------------+
| OMSO2 | **Total column SO~2~**, prescribed SO~2~    | A. Krueger     |
|       | layer height, fitting rms, convergence      |                |
|       | flags, total ozone, surface reflectivity,   | akr            |
|       | cloud top height, quality flags,            | euger@umbc.edu |
|       | geolocation, and solar and satellite        |                |
|       | viewing angles.                             |                |
+-------+---------------------------------------------+----------------+

**4.3 OMI Global Gridded Atmospheric Products (Level-3)**

OMI Level-3 product will be produced for almost all Level-2 standard
parameters. 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 product will be 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 will also contain the
corresponding statistical parameters (number of pixels, minimum,
maximum, and sigma).

**4.4 Other OMI Data Processing & Data Products**

In addition to the standard data processing at the OSIPS (NASA GSFC) and
at the ODPS (KNMI, Netherlands) together with "standard data products"
archival at NASA GES DISC, there will be two other types of product
generation.

**Near Real Time Products (NRT)**

KNMI will produce a daily global Near Real Time **(**NRT) ozone product
(Ozone total column). This product will be retrieved from "rate buffered
data" (Level-0 data, not time ordered and without duplicity removed) and
will be available within three hours of data capture. These NRT products
will be used for several operational applications. For example
assimilating these measurements in numerical weather prediction models
will provide improved wind-field information for regions where
wind-field measurements are scarce. OMI NRT products^2^ can also
contribute to the operational forecasting of the UV-index.

**Very Fast Delivery Products (VFD)**

FMI will produce "regional" Very Fast Delivery (VFD) products (Ozone
total column, Surface UV-B flux, and UV spectra) using Direct Broadcast
Data from the satellite. Finland will access Direct Broadcast (DB) data
once a day as the spacecraft flies overhead. A ground station is built
in Sodankylä to receive OMI data. These products will be retrieved from
Direct Broadcast raw telemetry data and will have limited geographical
coverage (2600 km swath from the Arctic Ocean to the Alps, covering most
of the northeastern Europe).

**4.5 Additional Total Column Ozone Products**

The "Enhanced TOMS V8 algorithm" will be used to process the OMI\'s
data. It has gone through three decades of refinements. This algorithm
will also be used to reprocess all the BUV, SBUV and TOMS data taken
since April 1970 for the continuity of more than 25-year long-time data
record. TOMS has produced total ozone with r.m.s. of 2% for most
conditions. OMI data will add more than 5 years (or longer) to this data
record. These data will be reprocessed at OSIPS and will be archived at
GES DISC. In the first phase, data will be processed for the TOMS
measurements (Table 7). These TOMS products contain total ozone, SO~2~,
aerosol indices, and surface reflectivities, in addition to the quality
flags and geolocation information.

Table 7. TOMS Total Ozone Products (Level-2)

+-------+--------------+--------+-------------------+---------------+
| ***   | ***I         | *      | ***Spectral       | > ***Lead     |
| Produ | nstrument*** | **Data | Bands***          | >             |
| ct*** |              | Per    |                   |  Scientist*** |
|       |              | iod*** |                   |               |
+-------+--------------+--------+-------------------+---------------+
| TOM   | TOMS Nimbus7 | 1978 - | 312, 317, 332,    | P. K. Bhartia |
| SN7L2 |              | 1993   | 340, 360, 380 nm  |               |
|       |              |        |                   | Pawan.K.Bha   |
|       |              |        |                   | rtia@nasa.gov |
+-------+--------------+--------+-------------------+---------------+
| TOM   | TOMS         | 1991 - | 312, 317, 332,    |               |
| SM3L2 | Meteor-3     | 1994   | 340, 360, 380 nm  |               |
+-------+--------------+--------+-------------------+---------------+
| TOM   | TOMS ADEOS-1 | 1996 - | 309, 313, 318,    |               |
| SA1L2 |              | 1997   | 322, 331, 360 nm  |               |
+-------+--------------+--------+-------------------+---------------+
| TOM   | TOMS Earth   | 1996 - | 309, 313, 318,    |               |
| SEPL2 | Probe        | P      | 322, 331, 360 nm  |               |
|       |              | resent |                   |               |
+-------+--------------+--------+-------------------+---------------+

> **5. Data Validation & Field Campaigns**

For algorithm development, testing, and evaluation, synthetic test data
bases have been generated using radiative and chemical transport models
and GOME data. OMI validation activities have been at high priority. The
Aura Validation Working Group^19^ has been developing a more "specific
strategy" that will first focus on validation under quiet atmospheric
conditions then it will be followed by comparison campaigns under more
"challenging" conditions.

An OMI validation plan is well underway as part of the overall Aura
validation activity. The creation of coincident satellite overpasses
(i.e. TOMS, GOME, SCIAMACHY) for specific data validation sites are
already planned^19^. Many field campaigns (involving high and low Level
aircrafts, satellite overpasses, and in-situ balloons and sondes, and
other surface measurements) are designed for testing OMI algorithms, for
algorithm enhancement and data validation.

**6. OMI DATA PRODUCT SUPPORT AVAILABLE FROM THE NASA GES DISC**

**Long-term Atmospheric Chemistry and Dynamics Data Records at the GES
DISC**

The data from the Aura instruments (OMI, MLS, HIRDLS), as well as the
data from the other future missions such as, NPOESS Preparatory Project
(NPP), will be archived at the NASA GES DISC. The atmospheric data
products from several past and present atmospheric data missions (Table
8) , including Nimbus-4 IRIS and BUV, Nimbus-7 SBUV and LIMS, a series
of TOMS instruments, SME, UARS instruments (CLAES, HALOES, ISAMS, MLS,
HRDI, WINDII), ERS-2 GOME (courtesy of DFD/DLR ), Terra and Aqua
instruments (MODIS, AIRS, AMSU, HSB), TOVS pathfinder, SSBUV, ATMOS, and
DAO, are also archived at the NASA GES DISC.
![](media/image1.wmf){width="8.699305555555556in"
height="2.9305555555555554in"} The continuity of the long-term
atmospheric ozone, trace gases, clouds, aerosols, solar and surface UV
spectral irradiances, and erythemal surface UV-B flux data, will be
maintained with the launch of Aura spacecraft in early 2004. Some of the
atmospheric chemistry and dynamics related climate products available
from the NASA GES DISC are listed in Table 8.

**Data Support**

The NASA GES DISC has been engaged in the collection, archive,
distribution, and support of satellite-based remote sensing data since
its inception in 1993. The GES DISC\'s key objective has been to
facilitate data access, provide data in the format compatible with the
user requirements, explore and promote the potential applications, and
reach the broader satellite data user community.

The standard climate data sets, as well as special products such as
regional subsets, applications products in GIS compatible format,
related ancillary data sets, and data analysis tools are freely
available to the public for the Earth System Science studies,
environmental applications, and educational use. Detailed information
pertaining to the availability of climate data sets is available from
the GES DISC (*<http://disc.gsfc.nasa.gov/>* ).

Table 8. Atmospheric Chemistry & Dynamics, and Other Climate related
Data Sets, at the NASA GES DISC

  ------------ ----------------------------- ---------- ------------------------
  **Sensor**   **Sensor Name**               **Data     **Key Products**
                                             Period**   

  NPP          NPOESS Preparatory Project    launch     atmosphere, ocean, and
                                             2009       land products

  OMI          Aura Ozone Monitoring         2004 -     ozone, trace gases,
               Instrument                    present    aerosol, cloud, UV flux

  HIRDLS       Aura High Resolution Limb     2004 -     total ozone & profile,
               Sounder                       present    trace gases, aerosols

  MLS          Aura Microwave Limb Sounder   2004 -     ozone, trace gases,
                                             present    humidity, temperature

  AIRS         Atmospheric Infrared Sounder  2002 -     ozone, atmospheric
                                             present    profiles, cloud, SST

  AMSU-A       Advanced Microwave Sounding   2002 -     temperature and humidity
               Unit                          present    profiles

  MODIS        Moderate-Resolution Imaging   2000 -     ozone, aerosol, cloud,
               Spectroradiometer             present    ocean, land products

  GOME         Global Ozone Monitoring       1995 -     ozone, trace gases,
               Experiment (DFD/DLR)          present    surface UV flux

  TOMS         Total Ozone Mapping           1978 -     ozone, SO~2~ and aerosol
               Spectrometer                  2006       indices, UV-B flux

  SBUV         Solar Backscatter Ultraviolet 1978 -     ozone profile, SO~2~
               Spectrometer                  1990       index, UV-B flux

  BUV          Nimbus-4 Backscatter          1970 -     ozone, surface
               Ultraviolet Spectrometer      1977       Lambertian reflectivity

  IRIS         Infrared Interferometer       1970 -     infrared radiances for
               Spectrometer                  1971       ozone retrieval

  LIMS         Limb Infrared Monitor of the  1978 -     O~3~, NO~2~, water
               Stratosphere                  1985       vapor, temperature

  SME          Solar Mesospheric Explorer    1981 -     total ozone and ozone
                                             1986       profiles

  CLAES        Cryogenic Limb Array Etalon   1991 -     O~3~, trace gases,
               Spectrometer                  1993       temperature, aerosols

  ISAMS        Improved Stratospheric and    1991 -     O~3~, trace gases,
               Mesospheric Sounder           1992       temperature, aerosols

  MLS          UARS Microwave Limb Sounder   1991 -     ozone, trace gases,
                                             1999       humidity, temperature

  HALOE        Halogen Occultation           1991 -     O~3~, trace gases,
               Experiment                    2005       temperature, aerosols

  HRDI         High Resolution Doppler       1991 -     temperature and wind
               Imager                        2005       fields

  WINDII       WIND Imaging Interferometer   1991 -     temperature and wind
                                             2005       fields

  SSBUV        Shuttle Solar Backscatter     1989 -     O~3~ & trace gases
               Ultraviolet Spectrometer      1996       profiles; solar
                                                        irradiances

  ATMOS        Atmospheric Trace Molecule    1985 -     profiles of ozone &
               Spectroscopy                  1986       trace gases

  TOVS         TIROS Operational Vertical    1985 -     O~3~, atm-profiles,
               Sounder (Path Finder)         1995       wind, SST, cloud,
                                                        rainfall

  DAO          Data Assimilation Office      1980 -     O~3~, atm-profiles,
                                             1993       wind, SST, cloud,
                                                        rainfall

  MSU          Microwave Sounding Unit-      1979 -     temperature and humidity
               Limb93                        1994       profiles

  TRMM         Tropical Rainfall Measuring   1997 -     surface rain fall and
               Mission sensors               present    drop size distribution

  SeaWiFS      Sea-Viewing Wide              1997 -     ocean color, sediments,
               Field-of-View Sensor          present    chlorophyll

  CZCS         Coastal Zone Color Scanner    1978 -     ocean color, sediments,
                                             1986       chlorophyll

  SORCE        Solar Radiation and Climate   2003 -     solar total and spectral
               Experiment Sensors            present    irradiance

  SUSIM        Solar Ultraviolet Spectral    1991 -     solar UV spectral
               Irradiance Monitor            2005       irradiance

  SOLSTICE     Solar Stellar Irradiance      1991 -     solar UV spectral and
               Comparison Experiment         2005       stellar irradiance

  ACRIM        Active Cavity Radiometer      1980 -     total solar irradiance
               Irradiance Monitor            2002       

  PEM          PEM - Particle Environment    1991 -     x-rays, high energy
               Monitor                       2005       particles deposition
  ------------ ----------------------------- ---------- ------------------------

**Data Read Software and Data Mining Tools for OMI Products**

A majority of the data sets archived at the NASA GES DISC are in the
Hierarchical Data Format-Earth Observing System (HDF-EOS) format. This
format has been adopted by NASA for standard data product distribution
since it is able to handle multiple types of data objects and at the
same time is independent of the platform or operating system the file
has been created on. Two versions of HDF-EOS format, HDF-EOS 2.x (based
on native HDF4 format) and HDF-EOS 5.x (based on native HDF5 format) are
in use and are usually referred as HE4 and HE5 format, respectively. OMI
Level 1B data files (radiances, irradiance, and calibration files) will
be written in HE4 format and OMI Level-2 & 3 products (derived
geophysical parameters) will be in HE5 format and the file names will
have extension ".he4" and ".he5", respectively.

Many software and tools have been developed by the NASA data centers and
software developers to read HDF-EOS files. Following the Terra and Aqua
EOS missions, NASA data centers (including GES DISC) have developed a
number of tools for accessing and analyzing HE4 files. Some new tools
are now being developed to handle data products in HE5 data format.
These tools can examine and modify the HE4 and HE5 file contents, dump
the files, extract the required data objects (images, orbital swath
data, gridded data, and tables), can display the content, convert files
from old HDF format to new format and vice versa or convert the file
into familiar ASCII or binary format.

For example, *HE5View* and *HDFView* are file viewing tools developed
for viewing the contents of HE5 data files. The HE5View application
allows the user to convert HDF-EOS data files to various formats
including binary and ASCII. Another popular software is *HECONVERT*. It
is a command-line conversion utility used to convert HE4 files to HE5.
Complete list of the old and new software and tools for HDF-EOS file are
available from the GES DISC web site
*<http://acdisc.gsfc.nasa.gov/tools.shtml>*

The Atmospheric Composition Data Support Team at GES DISC provides
assistance to the user in the areas of accessing data products,
documentation, and data browse and data analysis software. For users
convenience "Read Software" and data analysis tools have been developed
by GES DISC Data Support Team in the C, Fortran, and IDL languages.
These programs are capable of data extraction, subsetting, analysis,
reprojection, and format conversion (binary, GIS, or ASCII file). Some
(e.g. *atmos, hdf_reader*) are simple command-line based data browse and
data extraction programs and consist of only a few lines which users can
easily insert in their data analysis code. Some tools with sophisticated
visualization and analysis capabilities though developed for some other
sensors are modified to handle OMI Level-1B products created in HE4
format.

For example, a new multifunctional data processing and visualization
tool (an enhanced version of HDFLook), has been developed for the data
products in HE4 format. The capabilities of this tool include: automatic
detection of the fill values and masks, re-mapping of swath data to
world map, geo-projection conversion, interactive and batch mode
processing capabilities, subsetting features (availability of parameter,
band, and spatial subsetting), multi-file processing (mosaic and stitch
capabilities), capability of producing enhanced false and true color
(RGB) images with option of map and grid overlays, data conversion from
scaled quantities to physical units, format conversion from HDF-EOS to
ASCII, Binary, JPEG, or GeoTIFF. This tool and other data analysis
software are available free from the NASA GES DISC
(*<http://disc.gsfc.nasa.gov/> )*. Similar tools are being developed at
the GES DISC for OMI Level-2 & 3, and other Aura products created in HE5
format.

**Web based Interactive Data Mining Capabilities Applicable to OMI Data
Products**

To promote wider distribution and use of the NASA remote sensing data
archived at the GES DISC, web based servers (*WebGIS, OpenGIS,
WMT-DODS*) have been developed to provide on-line, interactive
capabilities for data searching, visualization, mapping, analysis, and
retrieval of data in user requested formats. For example*, WebGIS* is
developed to provide on-the fly format conversion of data from large
data sets (including the HDF format). For different type of data
requested, WebGIS searches the DISC online data holdings and creates
maps of spatially subsetted data in Geographic Information System (GIS)
formats. The users can create images overlaid on top of each other (with
desired transparency). The GES DISC also provides a Near-line Archive
Data Mining (*NADM*) system (*http://disc.gsfc.nasa.gov/services/*). The
*NADM* enables registered users to test and execute their own data
mining algorithms against the data pool of Earth sciences data for
long-term studies, including seasonal and annual variability.

**Data Access**

One of the main goals of the NASA GES DISC is making the data easily
accessible to the wider user community. All of the data sets archived at
GES DISC are freely made available to the public and science user
communities. These data sets may be accessed via several mechanisms
including:

\- *GES DISC Search and Order*

A user friendly Web-based search and order system, with full-features of
spatial & temporal search. For users' convenience, features such as
parameter extraction and spatial subsetting are also provided.
(*<http://disc.gsfc.nasa.gov/Aura/>* ).

\- *Mirador*

Uses Google-Like Keywords (Ozone, Aerosol, Trace Gases, OML1B,
Hurricanes, etc ) to find satellite or model data that are available
from the GES DISC
([*http://mirador.gsfc.nasa.gov/*](http://mirador.gsfc.nasa.gov/)).

\- *EOS Warehouse Inventory Search Tool (WIST)*

This interface provides access to satellite and ground based data that
are available from all NASA data archive centers and NASA affiliated
centers (*<http://wist.echo.nasa.gov/>* ).

> **7. SUMMARY**

OMI is a new instrument, with a heritage from the European satellite
instruments GOME and SCIAMACHY, and US satellite instruments SBUV and
TOMS. OMI's unique capabilities for measuring important trace gases with
a small footprint and daily global coverage, in conjunction with the
other Aura instruments, will make a major contribution to our
understanding of stratospheric and tropospheric chemistry and climate
change. OMI will provide data continuity to more than 30-year of ozone
data record from TOMS and other BUV instruments. In addition to the
total ozone column, OMI will provide several key parameters for
stratospheric and tropospheric chemistry and climate research, including
the ozone profile, columns of NO~2~, SO~2~, OClO, BrO, HCHO, surface UV
Erythemal irradiance, and aerosol and cloud properties. Extensive data
validation activities are planned to evaluate and improve algorithm by
comparing products derived from in-situ observations. OMI products will
be used by the scientific community to monitor ozone, air quality and
detect subtle signatures of climate change. OMI atmospheric products,
including calibrated and geolocated radiance products, will be archived
at the NASA Goddard Earth Sciences (GES) Distributed Active Archive
Center (DISC) and will be freely available (*http://disc.gsfc.nasa.
Gov/* ) to the scientific and other data user communities.

The Atmospheric Composition Data Support Team at the NASA GES DISC has
been providing science and data support to assist users in accessing and
using the atmospheric data products. A number of tools for data access,
subsetting, reprojection and mapping of orbital (level-1B & 2) products,
visualization of global gridded (Level-3) products, and data analysis
have been developed at the NASA GES DISC and are provided free to the
data user communities (*http://disc.gsfc.nasa.gov*).

> **Acknowledgements**

The authors would like to acknowledge the OMI Science Team Members and
OSIPS Team Members for their help in providing the information. This
work is supported by the NASA GSFC Earth Science Enterprise.

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[^1]: Suraiya.Ahmad-1@ nasa.gov; phone 301-614-5284; fax 301-614-5268;
    http://disc.gsfc.nasa.gov/