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Row anomalies

Row anomalies. Marcel Dobber (KNMI). TN-OMI-KNMI-893, issue 1, 11 September 2007 TN-OMI-KNMI-893, issue 2, 19 September 2007 TN-OMI-KNMI-913, issue 1, 22 May 2008 TN-OMI-KNMI-913, issue 2, 30 May 2008. Row anomaly row 53 (UV2, VIS). In row 53 in UV2 and VIS in level-1b data (0-based).

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Row anomalies

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  1. Row anomalies Marcel Dobber (KNMI) TN-OMI-KNMI-893, issue 1, 11 September 2007 TN-OMI-KNMI-893, issue 2, 19 September 2007 TN-OMI-KNMI-913, issue 1, 22 May 2008 TN-OMI-KNMI-913, issue 2, 30 May 2008

  2. Row anomaly row 53 (UV2, VIS) • In row 53 in UV2 and VIS in level-1b data (0-based). • Suppresses signals by 20-30% in UV2 and VIS over complete illuminated orbit. • At the north pole the signal decrease changes into signal increase (sun light reflection). • Not visible in UV1. • Not visible in sun or WLS measurements. • First appeared around 25-27 June 2007. • Seems to have optical origin rather than electronical. • Can be seen in level-0, level-1b and level-2 data.

  3. Row anomaly row 53 (UV2, VIS)

  4. Row anomaly May 2008 • Rows 18-21 in UV1, 38-41 in UV2 and VIS in level-1b data (0-based). • First appears on 11 May 2008 and further increases on 16 May 2008. • In UV2 and VIS similar as row 53 anomaly, but: • new anomaly appears only after nTimes=1140 on northern hemisphere (14 minutes prior to sun_elev_angle=0 degrees). • New anomaly shows strong sun light reflection in UV1, UV2, VIS, only after nTimes=1140, almost 10x more signal than radiance in UV1.

  5. Row anomaly May 2008 Row 40 nadir Row 53 West East Solar port

  6. Row anomaly May 2008 Row 40 nadir West Row 53 East Solar port

  7. Row anomaly May 2008

  8. Row anomaly May 2008 • Stability (in rows and in time) of the row anomaly: UV1

  9. Row anomaly May 2008

  10. Row anomaly May 2008 • Evolution of reflected sun light in UV1 in an orbit for 5 different orbits.

  11. Row anomaly May 2008 • Spectral dependence of reflected sun light

  12. Row anomaly May 2008: Level 2 data • DOAS O3.

  13. Row anomaly May 2008: Level 2 data • Aerosol index • Also observed in NO2, SO2, cloud products.

  14. Conclusions (1) • After September 2007 anomaly now a more severe May 2008 anomaly. • The May 2008 anomaly affects several (4) binned rows in all channels. • Both anomalies seem to be caused by some kind of optical blockage. This blockage also reflects sun light into the nadir port. • It can not be excluded that more row anomalies appear in the future. • It is worrying that the cause for the onset of the row anomalies is not at all understood. • Impact of EOS-Aura rephasing / maneuvers (e.g. DMU) unknown.

  15. Conclusions (2) • The May 2008 anomaly may be correctable in UV2 and VIS, but ...... • The row anomaly is highly variable in time within one orbit as well as long-term (between orbits). • UV1 is saturated in the affected rows, which is can not be corrected. • The correction requires an additive correction (reflected sun light) as well as a multiplicative correction (optical blockage), both of which are highly variable within an orbit as well as long-term, and row dependent. • Corrected rows in UV2 and VIS will not be of the same quality as before the blockage. • A 0-1b data processor change is required. • A Time-Dependent OPF (TDOPF) change is required. • Different corrections may be required for forward processing and for reprocessing. • It will take considerable time before a potential correction algorithm can be implemented and used.

  16. UV part

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