Science Requirements OMI dataproducts

Science Requirements for the "normal" OMI products

Data Product	Priority Status	Accuracy of Observations ¹⁾	Ground pixel size at nadir (km × km)	Vertical resolution	Remarks
Irradiances	A	< 2 %	N/A	N/A
Radiances ²⁾	A	< 2 %	< 20 × 20	N/A
Ozone column	A	< 2 % / 4 DU	< 20 × 20	N/A
Ozone profile	A	< 30 % (T) < 10 % (S)	< 40 × 40	> 10 km (T) > 5 km (S)	Vertical Range is 0 - 50 km
Aerosol optical thickness	A	< 30 % / 0.1 ⁶⁾	< 20 × 20	N/A	At 400 nm At 500 nm: 30 % or 0.08
Aerosol single scattering albedo	A	< 0.1	< 20 × 20	N/A
NO₂ column ⁴⁾	A	< 10 % / 10¹⁴ mol. cm^-2	< 40 × 40	N/A
Cloud scattering pressure	A ⁵⁾	< 100 hPa	< 20 × 20	N/A
Cloud fraction	A ⁵⁾	< 0.1	< 20 × 20	N/A
Surface UV-B flux	A	< 4%	< 20 × 20	N/A
SO₂ column	B	< 20 % / 0.4 DU	< 40 × 40	N/A	Pollution, volcanic
BrO column	B	< 10 % / 10¹³ mol. cm^-2	< 40 × 40	N/A
OClO column	B	< 20 % / 10¹³ mol. cm^-2	< 40 × 40	N/A	Polar vortex
HCHO column	B	< 20 % / 10¹⁵ mol. cm^-2	< 40 × 40	N/A	Pollution
Surface reflectance	B	< 5 / 0.01	< 20 × 20	N/A
UV spectra	B	< 10-20 % (wavelength dependent)	< 20 × 20	N/A	Accuracy is wave- length dependent

Notes:

The valid requirement on accuracy will be the largest of the given percentile or absolute number.
The requirements for radiance and irradiance follow from Chapter 4.
Irradiance is not a separate data product.
The required accuracy for the NO₂ column is about 10% in unpolluted areas, but about 20% in polluted areas.
Cloud scattering pressure and cloud fraction are also needed for the retrieval of other products by OMI and other instruments.
The requirement on the accuracy of the aerosol optical thickness (AOT) has been changed after the ATBD review in February 2002 with respect to the original values in the OMI Science Requierements Document (Version 2). The original values (10 % or 0.08 at 400 nm) were considered to be too strict.

Data Product	Priority Status	Accuracy of Observations ¹⁾	Ground pixel size at nadir (km × km)	Vertical resolution	Remarks
Ozone column	A	< 5 % / 10 DU	< 20 × 20	N/A
Ozone profile	A	< 10 % (S)	< 40 × 40	> 5 km (S)	Vertical Range is 10 - 50 km

Notes:

The valid requirement on accuracy will be the largest of the given percentile or absolute number.

Data Product	Priority Status	Accuracy of Observations ¹⁾	Ground pixel size at nadir (km × km)	Vertical resolution	Remarks
Ozone column	A	< 5 % / 10 DU	< 20 × 20	N/A	Over Northern Europe
Surface UV-B flux	A	< 10%	< 20 × 20	N/A	Over Northern Europe
Ozone profile	B	± 10 % (S)	< 40 × 40	> 5 km (S)	Vertical Range is 10 - 50 km Over Northern Europe
HCHO column	B	< 20 % / 10¹⁵ mol. cm^-2	< 40 × 40	N/A	Over Northern Europe
UV spectra	B	< 10-20 % (wavelength dependent)	< 20 × 20	N/A	Over Northern Europe Accuracy is wave- length dependent

Notes:

The valid requirement on accuracy will be the largest of the given percentile or absolute number.

In column 2, priorities are listed for each product (in the context of the OMI mission objectives):

All products are level 2 products, except the (ir)radiances which are level 1b products.
The pragmatic definition of the accuracy is:
the RMS difference between 1) product values retrieved from simulated ("measured" and calibrated) theoretical Earth radiance spectra generated with a state of the art radiative transfer model (including well-defined atmospheres) and 2) the input product values used for the generation of these spectra. The theoretical spectra should be fed into instrument simulation software ("measured"), with all known error sources included; and calibrated with level 0-1b software.
With column is meant the vertical column. (T) stands for "in the troposphere", (S) stands for "in the stratosphere".
1 DU = 2.687 10¹⁶ mol. cm^-2; mol. stands for molecules
Each product has a global coverage of one day, except for the Very Fast Delivery (VFD) products.
Product delivery requirements are for Near Real Time (NRT) products less than 3 hours after observation and less than 30 minutes after the data receipt for the VFD products, for other products less than two days after observation.