OMI slit function product
Description of the product
This package contains the Instrument Spectral Response Function (ISRF) or the slit function of the Ozone Monitoring Intrument (OMI). The slit function depends on wavelength and viewing angle and is given separately for two wavelength bands of OMI:
* UV2 = 310 - 380 nm
* VIS = 350 - 500 nm
To account for the viewing angle dependency, the slit function is given separately for each of the 60 detector rows (00, 01, ..., 59), with the following filename convention:
* BND-bind/row_NN_omi_BND_slit.dat
where BND specifies the band ('uv2' or 'vis') and NN the row number.
If the viewing angle dependency of the slit function is not needed to be or cannot be taken into account, an average slit function can be used. This average is computed from the slit functions rows 12 through 47, and can be considered representative for most rows; for the 4 or 5 rows on either side of the detector the average may be less representative.
Filename convention for the average slit function:
* BND-bind/row_12-47_omi_BND_slit.dat
Each data file gives the wavelength dependent slit function. The slit function value is given for a set of nominal wavelengths, in steps of 5 nm over the range of the spectral band. For each nominal wavelength, the slit function is given over an interval of -1.50 nm to +1.49 nm in steps of 0.01, i.e. with a total of 300 data points. To find the slit function at other nominal wavelengths, linear interpolation between two given nominal wavelengths should be used.
Note that the slit function has not been normalised: the integral over the slit function is not equal to one. This means that when convolving spectra, one has to divide by the the integral over the slit function. The header of each data file provides further details on the data format.
Example of the row-average OMI slit function (ISRF) at selected wavelenghts in the UV2 and VIS bands.
Data source
The slit function data is derived from the parametrisation described in RP-OMIE-KNMI-704:
"Parameterization of the OMI spectral slitfunction & comparison to in-flight solar irradiance data," issue 6 of 17 August 2005, KNMI, De Bilt.
See also:
"Pre-launch characterization of the Ozone Monitoring Instrument transfer function in the spectral domain," Dirksen, R., Dobber, M.R., Voors, R. and Levelt, P.: 2006, Applied Optics, vol. 45, no. 17, 3972-3981, doi:10.1364/AO.45.003972
The average slit finction is introduced in:
"Improved spectral fitting of nitrogen dioxide from OMI in the 405 - 465 nm window," Van Geffen, J.H.G.M., Boersma, K.F., Van Roozendael, M., Hendrick, F., Mahieu, E., De Smedt, I., Sneep M. and Veefkind, J.P. Atmos. Meas. Techn., vol. 8, 10619-10671, doi:10.5194/amt-8-1685-2015