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TAFTS in CAVIAR2008-09
Paul Green, Ralph Beeby, Alan Last,John Harries, Juliet Pickering
Imperial College London
Stu Newman, Jonathon Taylor @ UK Met. Office Eric Usadi, Tom Gardiner, Marc Colman, @ NPL
FAAM
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
Page 2
Introduction
• IC contribution to CAVIAR• Far-IR science and the TAFTS instrument• Radiometric calibration at NPL• Summer 2009 Flight campaign• Summer 2008 Flight campaign• Closing remarks
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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IC Contribution
• TAFTS instrument upgrade• Flight planning (lots of modelling)• Instrument Calibration
– Purpose built blackbody at NPL, July 2008 and May 2009• 2 flight campaigns
– Aug-Sept 2008, Camborne, UK [R Beeby next term]– July-Aug 2009, Jungfraujoch, Switzerland
• Synthesis of results• Application of new continuum
– Understanding of the impact of the new results on our understanding of present-day climate and climate change.
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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The TAFTS Instrument
• dual-input Martin-Puplett (polarizing) FTS with two spectral bands
• measure both nadir and zenith (+net)• 4 liquid helium cooled detectors
– 80-300cm-1 (2 x Ge:Ga)– 300-700cm-1 (2 x Si:Sb)
• resolution: 0.12cm-1 (apodized)• single scan: 2 secs• 4 internal BB sources• employs Brault sampling scheme• all built in-house (J Murray + A Canas)• UKMO C-130, ARA Egrett, BAe-146
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
Page 5
Tropical Standard Atmosphere cooling rate diagram
Sub-arctic winter Standard Atmosphere cooling rate diagram
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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Current Issues in the far-IR (0-600cm-1)
• UTH variability and far-IR cooling to space– 27-35% OLR from far-IR (Sinha and Harries 1995) – Heating rate diagram (Clough et al. 1992)– Far-IR transmission act as ‘valve’ in climate change scenarios (Shaw
et al. 1999)– Proposed satellite missions - CLARREO
• Water vapour spectroscopy– Continuum measurements down to ~400cm-1 but nothing below (Tobin
et al. 1999, Serio 2008) • Cirrus clouds
– Mean global coverage of ~30%– Contribution coincident with peak of far-IR emission.– Cools or warms depending on altitude, thickness, optical thickness,
particle size and particle shape– Cirrus presence significantly changes spectral fluxes.
History of TAFTS
• Flown on 3 aircraft
C-130 (1999-2001), Egrett (2001-2002), FAAM 146 (2004+)
• Clear-sky campaigns
EAQUATE – UK, Sept 2004
RHUBC – NSA ARM site USA, Feb-Mar 2007
CAVIAR – UK and Switzerland, Summer 2008 / 2009
• Cirrus / Cloud campaignsEMERALD I/II – Australia, 2001 and 2002
WINTEX + CAESAR – UK, 2005 to 2007
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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Radiometric calibration
• At NPL 5th - 15th May 2009• Pre-campaign radiometric
calibration with 2 external blackbody sources. NPLxBB and ICxBB.
• Differential instrument, always measures the difference between two views.
• Temperatures viewed covers those found in flight. (+10 to -55°C)
• Additional runs with both external blackbodies at near-equal but cold temperatures, to isolate the instrument self-emission term.
• 2008 – first dual input calibration and tested new beamsplitters
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
Page 8
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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NPL external calibration blackbody
• Purpose-built traceable temperature standard calibrated BB for use by both TAFTS and ARIES [UKMO 3-16μm FTS]
• Alcohol cooled• Temperature range
– -75 to +30C• Blackbody emissivity
– 0.996 0.002 (λ < 50 μm)– 0.994 0.005 (50 μm < λ <
100 μm)– 0.990 +0.005 / -0.02 (100
μm < λ < 200 μm) Eric Usadi, NPL
Calibration run targets (2009)Run UW BB UW temp
(degC)DW BB DW temp
(degC)Internal BBshot/cold
A1 ICxBB -26.2 NPLxBB +5, -10, -25, -26.2
50/20
A2 ICxBB -31.8 NPLxBB +5, -10, -25,-31.8, -45, -55
60/amb
A3 ICxBB -32.4 NPLxBB +5, -10, -25, -32.4, -40, -55
amb/60(40)
B1 NPLxBB -10, -25, -40, -41.2, -42.2
ICxBB -41.2 50/20
B2 NPLxBB +5 ICxBB -44 60/amb
B3 NPLxBB +5, -10, -25, -40, -55
ICxBB -40 70/40
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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Summer flying 2009
• 13 July – 12 August 2009• Based out of Basel, Switzerland• 38.5hrs over 9 flights
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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Courtesy: Alan Foster
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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Flight Campaigns instrumentation
• FAAM BAe-146– SWS [shortwave]– TAFTS [far-IR]– In-situ measurements
• General Eastern• FWVS• TWC
– ARIES [mid-IR]– MARSS [microwave]– Dropsondes
• Payerne Sonde / GPS • Models (UKMO and
Swiss Met)From www.faam.ac.uk
Jungfraujoch
MönchJungfrau Eiger
Courtesy: Stu Newman
Flight campaign instrumentation
• Ground-based instrumentation– Radiosonde balloons (temperature, water vapour profile, wind)– GPS (water vapour)– NPL 0.7-14μm sun-pointing FTS
• BAe-146 in-situ– Radiometers, TAFTS, ARIES, SWS– In-situ (temp, WV, wind, cloud, aerosol etc.)– Water vapour: General Eastern FPH, FWVS, TWC – Dropsondes– BBRs, surface temp, hemispherical radiance
• Model fields– Swiss Met Office and ECMWF model fields
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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CAVIAR 2009 Flight schedule
Date Flight Meteorology TAFTS performance
02/07/09 B465 N/A Test flight
16/07/09 B466 Clear (partial MC) R6-10 excellent; R1-6, 11,12 good
19/07/09 B467* Some thin Ci, ↓R3-7 R6-11.2 excellent; R1-5 good
20/07/09 B468 Night balloon launch R1,2,6,7 good; R3-5,8,9 ok
25/07/09 B469 StCu later in flight All runs excellent
26/07/09 B470* Occasional thin Ci All runs excellent
27/07/09 B471* Clear R1-4 excellent; R5,6 lost chs; No R7,8
29/07/09 B472 Clear R1-8 excellent; No R9-13 [ARIES]
01/08/09 B473 Clear Did not fly - Helium
04/08/09 B474* Partial MC R1-6 excellent; R7,8 lost chs; No R9-11
CAVIAR Annual MeetingCosener’s House,15th Dec 2009Page 15
MC – mountain cloud
B471 – 27/07/09
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
Page 16Profile 7 ~18kft 09:58UTC
Profile 7 ~20kft 09:55UTC
Profile 2 ~16kft 07:40UTC
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
Page 17
Elevation data from:
http://srtm.csi.cgiar.org/
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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Water Vapour profiles
• Each group (IC, MO, Reading) involved in the flight campaign need to know the water vapour profile (and uncertainty) to compare with measured spectra.
• There are a number of sources of data; dropsonde, models, aircraft in-situ, satellites.
• Need to be compared and combined in an intelligent manner.
• All participants need to be using same profiles, for better cross-comparison…
• Workshop in week 30 Nov – 4 Dec 2009 @ IC involving SN, LT and PG
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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Measuring Water Vapour
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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Measuring Water Vapour
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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Profile philosophy
• Dropsonde are most accurate measures of profile, but only occasional snap-shot.
• Aircraft in-situ measurements from frost-point hygrometer, fluorescence WV spectrometer and Nevzorov TWC, all have different response times and measurement characteristics. Provide profiles in ascents/descents and measure of variation along runs.
• ECMWF analysis model fields – 0.25° grid assimilating all available data, but produced via spherical harmonics scheme – limited detail.
• Swiss Met model• GPS water vapour from JFJ• JFJ surface measurements• Satellite data (SEVIRI, IASI, AIRS etc)• Microwave (MARSS) instrument on FAAM-146• And radiometer data itself – shouldn’t be forgotten.• So how best to combine…
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
Page 22
Profile philosophy
Dropsondes are an accurate snap-shot, ECMWF, even if biased, should give good idea of trend, temporally and spatially. Aircraft in-situ measurements as first check of this.
Initially:
1) define a few points fixed points, representative of segments of the run (Camborne – Ocean N, Camborne, Ocean S). In this case, NW-SE runs, fortuitously follows ECMWF grid diagonal.
2) Sonde drop locations, naturally cluster about these points – so attribute dropsonde data to these locations.
3) Look at time of ECMWF fields analysis/forecast, dropsonde launch and aircraft run pass. Interpolate the ECMWF fields in time between these epochs, and produce a shift in T(p),q(p) from change in ECMWF field.
So, any good?
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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Time variance of assimilation
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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Comparison of ECMWF correct profiles
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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B471 Run 1
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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B471 Run 1
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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Atmospheric Profiling 2008Pre
ssure
/ h
Pa
Water vapour / %RH
Temperature / K
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
Uncertainty in Profiles
• Uncertainty in atmospheric profiles is a source of uncertainty in simulated spectra – this affects comparison between simulations and TAFTS spectra
• Make use of Jacobians in LBLRTM to assess sensitivity of spectra to uncertainties in temperature and relative humidity
• Analytic Jacobians: calculate dR/dx across spectral range where R = radiance and x = atmospheric parameter
• Indicates the change in radiance that would be caused by a change in a given atmospheric parameter (e.g., temperature, relative humidity)
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
Wavenumber / cm-1
Rad
iance
/
mW
/m2.s
r.cm
-1
dR
/d log
[vm
r(H
2O
)] /
m
Wm
2sr
.cm
-1/log
[vm
r]
dR
/d log
[vm
r(H
2O
)] /
m
Wm
2sr
.cm
-1/log
[vm
r]
Wavenumber / cm-1
Rad
iance
/
mW
/m2.s
r.cm
-1
Closing remarks
• Overall a very successful campaign. Best yet in terms of weather, instrument performance (TAFTS and others) and number of flights
• But lots to do…– Concentrate on B471.– Continue analysis of dropsonde / Payerne radiosonde data. – Determine most appropriate profile for each run – last week.– Calibrate B471 runs 2,3,4,5 and 6.– Compare with ARIES data (in cross-over region).– Uncertainty budget calculations with updated ε and ΔT from NPL-based
calibration work.– LBL code updates – HITRAN2008– Make continuum assessment, then validate with other flights.
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
Page 32
THANK YOU
CAVIAR Annual MeetingCosener’s House,15th Dec 2009
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Atmospheric Profiling
• Need to know the distribution of water vapour above and below the aircraft in order to compare TAFTS measurements with LBLRTM1/HITRAN2
• Aircraft performs straight, level runs (SLRs) to take measurements
• Collect data from different sources to produce a “best estimate” :
• Dropsondes released from aircraft• Balloon radiosondes launched from
Camborne 2-3 times daily• ECMWF3 forecast model• Collaboration with Stuart Newman
(Met Office) and Liam Tallis (Reading) to find best scheme for determining profile
Vaisala RD93 dropsonde, courtesy www.vaisala.com