What is OMI? OMI Instrument? OMI Project?
- 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
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
Where can I find information about the OMI instrument?
- See the OMI web site, and also the article by
Dobber, Marcel J. et al. "Ozone Monitoring Instrument Calibration
", IEEE. Trans.
Geosci. Rem. Sens. 44 (5), 1209-1238 (May 2006).
OMI Instrument Description
||UV-1: 264-311 nm
UV-2: 307-383 nm
VIS: 349-504 nm
| Spectral Resolution
| UV-1: 0.63 nm
UV-2: 0.42 nm
VIS: 0.63 nm
|UV-1: 1.9 px
UV-2: 3.0 px
VIS: 3.0 px
|| 115° (2600 km on ground)
||12 km x 6 km (flight direction x crossflight
||CCD: 780 x 576 (spectral x spatial)
| Duty Cycle:
|| 60 minutes on daylight side
10-30 minutes on eclipse side
|| 0.8 Mbps (average)
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
What is a OMI 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.
What is a OMI 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.
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
Where can I find spectral response information for
the OMI bands?
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. 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. 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.
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).
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.
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 = 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.
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.
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).
- 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
- 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
- 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.
- Download the "FTP script for full size granules" provided after the
table of granules below.
- On SGI or Linux machines, run: ftp -p -n aurapar2u.ecs.nasa.gov < script
- 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:
- Download the FTP_script: order_xxx....txt
- On SGI or Linux machine, run:
ftp -p -n aurapar2u.ecs.nasa.gov < order_16498.txt
- 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.
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.
What OMI products are currently available? What is
meant by Level 1, 2, and 3 data products?
- 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.
How do I decide which 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.
- What 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.
- What Level 2 Products are available?
Level-2 products can be divided into products in 3 different categories.
A complete list of Level 2 products is available at
DISC web site.
- Ozone products
- Clouds, Aerosols and Surface UV Irradiance products
- Trace Gases Products
- What types of 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).
- What tools are available to work with OMI data products?
- The OMI data products are in HDF-EOS format.
Aura Tools site lists
available tools for reading and working with OMI data. Tools are also available