Remote Sensing Group
Tropospheric ozone retrieval from
uv/vis spectrometery
RAL Space - Remote Sensing Group
Richard Siddans, Georgina Miles
Brian Kerridge, Barry Latter
21st May 2014 TEMPO 2nd Science Meeting, Hampton, VA
Rutherford Appleton Laboratory
RAL Remote Sensing Group
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Development and application of retrieval schemes to retrieve
trace gases, aerosol and cloud from satellite observations
Ozone:
– Munro et al., 1998 (Nature), demonstrating first
tropospheric ozone profiles
– Role in GOME series (& MAG) since ~1990
– Involved ESA’s Climate Change Initiative Essential Climate
Variable programme
– Developing NRT initiative for MACC/Copernicus
Atmosphere Service
– Involvements in Operational ESA Sentinals 4, 5 and 5
Precursor (S4 & 5 MAG)
© 2010 RalSpace
Remote Sensing Group
RAL UV Ozone Profile
Processor
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3-step retrieval (Hartley bands, surface albedo, Huggins bands)
Designed to fit to high precision in Huggins bands required for
tropospheric ozone information
Currently optimised for GOME, SCIAMACHY and GOME-2A/B
Selected as ESA Ozone CCI prototype nadir profile processor
for sensitivity to tropospheric ozone
Algorithm validation paper about to be submitted to AMTD
(Miles et al, 2014)
A joint IASI+GOME-2 (IR+UV) version is available, currently
developing Chappuis add-on.
Surface - 450hPa
ozone 2008
J
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January 2008
Remote Sensing Group
Ozone retrieval from the
Chappuis bands
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Why?
– Sensitivity to near-surface ozone in visible region
– Typically less Rayleigh scattering/brighter over land than in UV
Why not?
– Broadband ozone feature (1 piece of information, not profiles on
its own)
– Works in theory, but it’s hard to do in practice. Many other
spectral patterns to interfere with ozone fit:
– Surface/scattering/other gases/water vapour…
– Instrumental ‘features’/spectroscopic errors…
Remote Sensing Group
Ozone retrieval using the Chappuis
Bands for near-surface information
Dark
surface in
Chappuis
region
Over
‘grass’
surface
type
Simulated
AKs
AK
0-2km
0-6km
6-12km
UV+Vis retrieval simulations indicate a
signal to noise ratio of ≥300 is needed to
add information to the UV-only profile
retrieval
This implies a Chappuis-only total
column fit precision of 2-4DU is required
for Chappuis bands to add useful
information on near-surface ozone to
UV profile retrieval
(Miles et al., 2012)
Remote Sensing Group
Chappuis-only DOAS slant column fit
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Spectrally averaged GOME-2A B3/4 measurements (450-550nm)
WL range after Richter et al, 2012
Fit 7 leading principle components from land spectral databases
(ASTER/USGS)
Further spectral patterns to fit:
– O2, O3, O4, H2O(2), NO2, Ring(2), liquid water, registration/shifts
parameters(2), , air molecule Ring effect(2) and polynomials to
represent Rayleigh, cloud and aerosol scattering
All parameters are fit in a straightforward least squares manner. A third
order polynomial is subtracted from all patterns (other than the fitted
polynomial. patterns).
© 2010 RalSpace
Remote Sensing Group
Visible-only DOAS retrievals
of total column ozone with GOME-2
Spectral fitting for
ozone is challenging
in the Chappuis
bands, mostly due to
surface effects – so
lots of things need to
be fitted!
→ See O3MSAF VS
Report for details
(Miles et al., 2012)
http://o3msaf.fmi.fi/VS
reports.html
Remote Sensing Group
Column fit results
Remote Sensing Group
Principle of combining UV+Vis
information
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Information from Chappuis
only yields 1 piece of
information
Use RT simulations using
RAL UV-retrieved ozone
profile to predict relative
light-path sensitivity in UV
and Chappuis (AMFs)
Combine with total column
Chappuis fit to inform UV
profile in further (linear)
retrieval step
RT simulation
AMFs at different
wavelengths
550nm
325nm
340nm
450nm
760nm
With cloud
Remote Sensing Group
Combining UV+Vis information
• Use linear retrieval step to combine
information including AMF as weighting
function:
GOME-2 profile
xUV+Vis = x + (Sx-1 + KtSy-1K)-1KtSy-1(y-Kx)
x, Sx: UV retrieved profile and covariance
y, Sy: Chappuis column and fit error
K: weighting functions that map x onto y
Remote Sensing Group
Impact on surface ozone
number density
UV-only
UV+Vis
Difference
All land
pixels
Cloud
screened
20% CF
2km CTZ
Remote Sensing Group
Next Steps
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UV+Vis ozone profile retrievals:
– Process more data
– Plenty of scope for improving quality of Chappuis slant
column fit
– Improvements expected to forward model for linear step
We note the gap in spectral coverage in Chappuis bands for
TEMPO
– This technique probably won’t work with TEMPO spectral
gap. GOME-2B/C will continue to provide data
– 0-2km ozone subcolumn target will be very challenging
This work will be actively progressed in the coming months
within UK National Centre for Earth Observation at RAL
We intend to support TEMPO in parallel to S4 and other
European missions
© 2010 RalSpace
Remote Sensing Group