Infrared Limb Sounding MIPAS and HIRDLS - ECMWF 2 Atmospheric, Oceanic & Planetary Physics,...
Transcript of Infrared Limb Sounding MIPAS and HIRDLS - ECMWF 2 Atmospheric, Oceanic & Planetary Physics,...
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Infrared Limb SoundingMIPAS and HIRDLS
Anu DudhiaAtmospheric Oceanic and Planetary Physics
University of Oxford
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
MIPASMichelson Interferometer for Passive Atmospheric Sounding
Fourier Transform InterferometerLaunched on Envisat 1st March 2002~1 000 profiles per day
HIRDLSHigh Resolution Dynamics Limb Sounder
Filter RadiometerTo be launched on Aura early 2004 ~10 000 profiles per day
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
IntroductionLimb Viewing GeometryChannel SelectionRadiative Transfer ModellingRetrieval Schemes
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Limb-sounders compared to nadir-sounders
Better vertical resolution – 3km MIPAS, 1km HIRDLSBetter upper vertical range – mesosphereWorse horizontal resolution – 100s kmMore sensitive to cloud – fewer gaps in limb view
Also: radiative transfer & retrieval more complicated (2D)
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
(satellite moving clockwise in both figures)Limb Viewing Geometry
HIRDLS – fast limb scanTangent point slopes upwardstowards satellite
MIPAS – slow limb scan Tangent point slopesdownwards following satellite
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
MIPAS Nominal Scan
-1000 -500 0 500 1000Distance along-track [km]
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tude
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
HIRDLS Scan (single azimuth track)
-1000 -500 0 500 1000Distance along-track [km]
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Spectral CoverageMIPAS685-2410cm-1 at 0.025cm-1 spacing, 5 bands2-7 Microwindows up to 3cm-1 width selected for each species
HIRDLS21 filter channels from 570-1600cm-1
1-4 Filters up to 120cm-1 width assigned to specific species
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Radiance Contributions for 21km Tangent Height
500 1000 1500 2000 2500
0.1
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Rad
ianc
e [n
W/(
cm2 s
r cm
-1)]
Total Radiance
CO2 H2OO3 CH4N2O NO2HNO3
500 1000 1500 2000 2500Wavenumber [cm-1]
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tude
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A AB B C D
MIPAS Microwindows
HIRDLS Channels
MIPAS Microwindows
HIRDLS Channels
MIPAS Microwindows
HIRDLS Channels
MIPAS Microwindows
HIRDLS Channels
MIPAS Microwindows
HIRDLS Channels
MIPAS Microwindows
HIRDLS Channels
MIPAS Microwindows
HIRDLS Channels
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Radiance Contributions for 21km Tangent Height
500 1000 1500 2000 2500
0.1
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Rad
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cm2 s
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-1)]
Total Radiance
F11 F12 CLONO2N2O5 CONO
Aerosol
500 1000 1500 2000 2500Wavenumber [cm-1]
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tude
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A AB B C D
MIPAS Microwindows
HIRDLS Channels
MIPAS Microwindows
HIRDLS Channels
MIPAS Microwindows
HIRDLS Channels
MIPAS Microwindows
HIRDLS Channels
MIPAS Microwindows
HIRDLS Channels
MIPAS Microwindows
HIRDLS Channels
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
MIPAS Microwindows
Selected to minimise total retrieval error for given CPU cost
Use spectral masks to exclude measurements
Computer, rather than human, selection
Also results in systematic error budget
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
PT__0004 Microwindow
Radiance spectrum
Temperature Jacobian
Pressure Jacobian
H2O Interference
Spectral masks
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
0 500 1000 1500 2000dI/dT [nW/(m-2 sr cm-1) K-1]
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tude
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Ch5 Ch4 Ch3 Ch2
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45 km
50 km
HIRDLS pT ChannelsLarge area = good S/N
Sharp peak = good resolution
Require 4 CO2 Channels to cover complete vertical profile
Temperature Jacobians
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Radiance Modelling
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Ray TracingNo analytical solution for limb geometry- numerical integration required
Usually adequate to consider atmosphere locally spherical- radius of curvature varies by ±0.5% around orbit
Refraction is significant- deflection 70m at 25km, increases in proportion to density
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Transmittance CalculationsLimb viewing requires high spectral resolution calculations- typically 0.0005cm-1 to capture Doppler broadened lines
1650 1651 1652 1653Wavenumber [cm-1]
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Rad
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e [n
W/(
cm2 s
r cm
-1)]
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1650 1651 1652 1653Wavenumber [cm-1]
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Rad
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W/(
cm2 s
r cm
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MIPAS measurement Atmospheric spectrum
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Irregular Grids
1652.65 1652.70 1652.75 1652.80 1652.85 1652.90 1652.95Wavenumber [cm-1]
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W/(
cm2 s
r cm
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15km30km47km
MIPAS solution is to compute radiative transfer only at a subset of fine gridpoints, determined from spectral structure in eachmicrowindow
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Look Up TablesMIPAS uses look-up tables of absorption coefficient k(ν,p,T) for transmittance of each cell, containing absorber amount u
τc = exp ( - k u )
Path transmittance is then product of cell transmittances (Beer’s Law) τ = ∏ τc
Finally radiance is convolved with instrument line shape ΨR = ∫ ∫ B Ψ dτ d ν
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Band ModelHIRDLS solution is to use channel-averaged transmittances
∫ ∫ B Ψ dτ dν ≈ ∫B dτ
where τ = ∫ Ψ τ dν and B = ∫ B Ψ dν, Ψ is channel spectral response
Band transmittances are pretabulated τ(u,p,T) where p,T arepath-averaged quantities (Beer’s Law not valid for ∏τc )
This removes the spectral integration from the retrieval forward model, but has limited accuracy.
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Pressure-Temperature RetrievalInfrared radiances are highly sensitive to temperature (4%/K)and pressure (1-2% / %)
Nadir sounders retrieve T(p) directly, but limb-viewinggives T(z) or p(z)
Always start with joint pT retrieval for profiles p(z),T(z),
Use CO2 channels since concentration is known
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Retrieving two parameters requiresat least two independent pieces ofinformation.
Difficult at high/low altitudes
Usually use some relative pointingknowledge and hydrostatic constraint
d lnp = -(gM/RT) dz180 200 220 240 260 280 300
Temperature [K]
1000.000
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Pre
ssur
e [m
b]
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HIRDLS Ch3 Ch4Hydrostatic Constraint
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Current MIPAS Retrieval
Least Squares Fit – no explicit a priori or regularisation
One dimensional – assume no horizontal gradients
Sequential – pT, then H2O, O3, HNO3, CH4, N2O, NO2
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Baseline HIRDLS Retrieval
Optimal Estimation – loose climatological a priori constraint
1D retrieval, 2D forward model – 2 passes, model gradients in 2nd pass
Sequential/Joint – pT, Aerosol, H2O, O3, NO2, (HNO3+F11+F12),
(CH4+N2O+ClONO2+N2O5)
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
Future MIPAS Retrieval ?
Optimal Estimation – otherwise too many indeterminate parameters!
2D forward model – tomographic retrieval of complete orbit
Joint – pT+all species, including additional gases
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Atmospheric, Oceanic& Planetary Physics,University of Oxford
ECMWF Workshop 23-26 June 2003A Dudhia
Infrared Limb SoundingMIPAS and HIRDLS
SummaryInfrared limb sounding provides good verticalresolution and measurements of additional species
Main disadvantages are poor horizontal resolution and cloud sensitivity
Limb viewing geometry generally adds another dimension to the complexity of radiance modelling
Someday someone will assimilate limb radiances …