Status of OMI Operations

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Statusof OMI Operations Jacques
ClaasInstrument Operations TeamKNMI, De
Bilt/The Netherlands
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Instrument status

• Nominal Operations Baseline has not changed.
• CCD temperatures are very stable.
• The thermal settings for CCD and OPB still have
  their initial values.
• The life limited items (calibration source and
  mechanisms) are far within budget.
• There has been one anomaly on Sept. 27th caused
  by an error in the operations software that was
  recently updated.
• Fully operational for more than 99.2 over the
  last year.

OMI flight model
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Instrument topics (1/2)

• Two calibration dark measurements have been
  updated to account for the degradation of the
  CCD- Dark measurements have longer duration
  (120 sec instead of 20 sec)- Solar dark
  measurements have a longer duration (256 sec
  instead of 164 sec)
• All measurements for which the instrument
  mechanisms are used have been updated. Mechanisms
  are operated differently to avoid bouncing
  against the end stop of the mechanisms.
• A special measurement has been developed
  switching on the White Light Source (WLS) for a
  long time 14 minutes. Purpose is to increase
  the WLS output (inner bulb surface gets
  contaminated by the tungsten from the filament).

AURA in fairing
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Instrument topics (2/2)

• Increasing the WLS output by performing special
  WLS long measurements

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Row anomaly (1/13)

• A row anomaly was discovered in September
  2007.This anomaly has persisted since then.
• On May 19th 2008, a new row anomaly was
  discovered.
• Both row anomalies impact specific CCD rows (is
  specific part of the OMI field of view).
• 2007 anomaly 2 rows affected for complete
  illuminated orbit
• 2008 anomaly 4 rows affected for only northern
  part of illuminated orbit
• Data users must carefully read the L1b readme
  file on how to treat the affected CCD rows in
  their retrieval algorithms.

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Row anomaly (2/13) impact on L2
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Row anomaly (3/13) impact on L2
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Row anomaly (4/13) OMI measurements
a
39 ?
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Row anomaly (5/13) OMI L0 data
UV image from April 20
X-track
UV image from September 11
determine average radiance level in box as
function of position in orbit.
wavelength
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Row anomaly (6/13) L0 radiance profile
April 20 2008
tropical
radiance level
midlat
midlat
arctic
arctic
orbit position
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Row anomaly (7/13) L0 radiance profile
September 11 2008
tropical
radiance level
midlat
arctic
Start of anomaly
midlat
arctic
orbit position
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Row anomaly (8/13) when did it start?
Radiance levels for a fixed position in orbit
May 16
May 11
Two radiance jumps- May 11- May 16
radiance
time
X-track
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Row anomaly (9/13) geometry
OMI mounted on the S/C
?
a 39 ?
sun
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Row anomaly (10/13) potential problem area
front view OMI optical bench
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Row anomaly (11/13) potential problem area
area around nadir and solar aperture
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Row anomaly (12/13) potential problem area
MLI construction close to nadir and sun ports
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Row anomaly (13/13) summary / cause

• A small piece of MLI close to the nadir and solar
  aperture has moved into the field of view of the
  nadir port.
• The anomaly causes a partial blocking of the
  field of view of the UV2 and VIS channels
• The anomaly causes a reflection of sunlight into
  the field of view of the UV1 channel.
• Constant timing of the anomaly indicates that the
  blockage / reflection is located close (a few
  centimeters) to the nadir and solar aperture.
• Correcting for the anomaly is complicated because
  it is dependent on
• orbit position
• solar beta angle
• channel
• wavelength

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AURA re-phasing (1/3)

• On NASA instigation, between Dec 5th 2007 and
  May 8th 2008, a relocation of the AURA
  satellite was performed.
• Purpose - Improving the science output by
  combining AQUA and AURA science data
  (overlapping fields of view for particular
  instruments, smaller time difference). -
  distance before 5918 km, distance after 3674 km
• Consequence - the OMI groundtrack has moved
  about 120 km eastwards (about 6 ground pixels).
  - the OMI monthly spatial zoom-in measurements
  now have a different geo-location. - the NOSE
  parameters have to be updated (not done yet!).
• Decision - the timing of the monthly spatial
  zoom-in measurements will not be changed, hence
  will keep the changed geo-location.

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AURA re-phasing (2/3)
Before re-phasing
OMImonthlyspatial zoom-inmeasurements
After re-phasing
De Bilt
Washington
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AURA re-phasing (3/3)
threshold for thedelta irradiance sensitivity
correction(conversion CCD electrons to photons)