OMI in-flight wavelength calibration and the solar reference spectrum
Robert Voors(1), Ruud Dirksen(1) and Marcel Dobber(1)
(1) KNMI, PO Box 201, 3730 AE De Bilt, Netherlands
The Ozone Monitoring Instrument (OMI) was launched in July 2004 and is
one of four instruments onboard NASA's EOS-Aura satellite. OMI is
a nadir-viewing UV-VIS spectrometer ranging from 270 to 500 nm,
with a spectral resolution of roughly 0.5 nm. OMI obtains daily global
coverage with a nominal sampling at nadir of 13x24 km.
This presentation discusses the in-flight wavelength calibration and the
solar reference spectrum. Wavelength calibration is performed by means
of fitting Fraunhofer structure in the radiance and irradiance spectra.
It was found that when observing rapidly changing radiance signals,
the wavelength scale changed in tune with this. We describe the details
of this effect, explain the underlying optical mechanism and show that
we can (and do) correct for it with a high degree of accuracy. This effect
will be observable in any spectrometer with similar optics as that of OMI.
A prerequisite for any in-flight wavelength calibration method that uses
Fraunhofer lines in the observed spectra, is a good quality high
resolution solar reference spectrum. We describe how we calculate
such a spectrum, based on combining high resolution ground based data,
and medium resolution satellite mesurements.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,