page 1 tafts in caviar 2008-09 paul green, ralph beeby, alan last, john harries, juliet pickering...

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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

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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

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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

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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

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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

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Elevation data from:

http://srtm.csi.cgiar.org/

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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

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Measuring Water Vapour

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Measuring Water Vapour

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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…

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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?

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Time variance of assimilation

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Comparison of ECMWF correct profiles

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B471 Run 1

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B471 Run 1

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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.

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THANK YOU

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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