Ozone Monitoring Instrument spectral UV irradiance products: comparison with ground based measurements at an urban environment

Abstract

Abstract. We have compared spectral ultraviolet overpass irradiances from the Ozone Monitoring Instruments (OMI) against ground-based Brewer measurements at Thessaloniki, Greece from September 2004 to December 2007. It is demonstrated that OMI overestimates UV irradiances by 30%, 17% and 13% for 305 nm, 324 nm, and 380 nm respectively and 20% for erythemally weighted irradiance. The bias between OMI and Brewer increases with increasing aerosol absorption optical thickness. We present methodologies that can be applied for correcting this bias based on experimental results derived from the comparison period and also theoretical approaches using radiative transfer model calculations. All correction approaches minimize the bias and the standard deviation of the ratio OMI versus Brewer ratio. According to the results, the best correction approach suggests that the OMI UV product has to be multiplied by a correction factor CA(λ) are in the order of 0.8, 0.88 and 0.9 for 305 nm, 324 nm and 380 nm respectively. Limitations and possibilities for applying such methodologies in a global scale are also discussed.

Spatial and temporal UV irradiance and aerosol variability within the area of an OMI satellite pixel

“…Satellite ozone and UV data were exhaustively validated by means of GB measurements, regarding TOMS; (Kalliskota et al, 2000;McKenzie et al, 2001;Krotkov et al, 2001;Fioletov et al, 2002;Meloni et al, 2005;Arola et al, 2005;Kazantzidis et al, 2006) and lately OMI; Ialongo et al, 2008;Weihs et al, 2008;Kazadzis et al, 2009;Buchard et al, 2008). All these validation studies converge to the following conclusions:…”

“…The campaign data series include a mix of cloudless, partly cloudy and a few overcast cases. According to the work of Kazadzis et al (2009), OMI exhibits a wavelength dependent overestimation of the irradiance at the surface by up to 30%, 17% and 11% respectively for 305 nm, 324 nm and 380 nm for all atmospheric conditions. Mean irradiance differences at 324 nm between OMI and the ground based instruments at the three campaign sites are shown in Table 1.…”

“…The OMI surface UV algorithm is used for offline production of the global surface UV data using as input the OMI TOMS total column ozone (Bhartia and Wellemeyer, 2002) and reflectance at non-absorbing wavelength (360 nm). A more detailed summary of the OMI-UV retrieval can be found in Kazadzis et al (2009).…”

“…Their results for UV erythemal dose variability within one OMI satellite pixel showed deviations up to ±5%, ±10% and ±50% for cloudless, partly cloudy and overcast conditions, respectively. For the area investigated here Kazadzis et al (2009) have compared spectral ultraviolet overpass irradiances from OMI against ground-based Brewer measurements at Thessaloniki, Greece from September 2004 to December 2007. It is demonstrated that OMI overestimates UV irradiances by 30%, 17% and 13% for 305 nm, 324 nm, and 380 nm respectively and 20% for erythemally weighted irradiance.…”

“…-Linking of possible OMI overestimation of UV irradiances levels with the findings of a three and half year OMI UV validation study (Kazadzis et al, 2009) at the urban area of Thessaloniki, Greece.…”