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CAVIAR: TAFTS flight planning: Pt 1

Paul Green, John Harries, Alan Last, Ralph BeebyImperial College London

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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Flight planning: Introduction

• Points to consider– Which altitudes are most sensitive to the continuum?– Which is dominate? Self or foreign continuum? Does this hold true for both

the far-IR and mid-IR (and SWS), will ARIES have different priority?– Will the atmos. profile / total column, effect the sensitivity?– What sensitivity do we want/need?– Now much co-adding, how much data needed, looking at what scene?– What about profile uncertainty? – What about profile variability? Spatially, temporally? – How do we tell the difference between monomer line strength error and

continuum error? – And many, many more….

• All contribute to the flight plan. Time for some simulations…

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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Simulation Philosophy

• Simulating the atmosphere is best (most accurately) done using line-by-line radiative transfer codes.

• LBLRTM is most up-to-date, latest HITRAN and continuum.

• But does mean we have to work with the MT-CKD continuum parameterisation within its usage in LBLRTM– LBLRTM v9.4, HITRAN 2004, MT-CKD v1.2

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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The questions to answer.

• Need to find some realistic profiles

• What type of measurement?

• Micro-window sensitivity to altitude, profile across far-IR spectrum

• Which continuum, self or foreign-broadened?

• What would an error in the continuum look like, spectrally?

• Are we sensitive to is?

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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Input data

• Obtain realistic profiles from record

• Campaign is August 2008 over Camborne, use Camborne radiosonde record for August 2007.

• Looks for few representative profiles. That cover variability of likely scenarios. Harder than it looks!

• PWV range 1.07 to 3.03cm

• Need clear-sky (RH < 95)

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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The “step” profile

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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The chosen few (profiles)

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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Why net radiance?

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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Net radiance for 3 profiles fn(altitude)

• Overall, look similar, but detail is in the relative progression of the micro-windows

• 33kft spectrum similar for all profiles.

• On this scale hard to see, almost too much information.

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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The chosen few (micro-windows)

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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Micro-window (continuum) sensitivity as function of wavenumber, altitude and humidity profile

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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Continuum contribution fn(altitude)

• What are the source of the micro-window contributions?

• How does it divide up between the monomer lines, self- and foreign broadened continuum?

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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Continuum relative contribution

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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A continuum error (10% foreign)

• What is the sensitivity to the water vapour continuum?

• How accurate can we measure it?

• What is the spectral signature of the error?

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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Radiative signature from error in continuum

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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TAFTS sensitivity

• Levels on aircraft are higher than in laboratory. Need to calculate from recent CAESAR flight data.

• But 32scan average is well below 1mW level throughout LW, with low at 100cm-1 of around 0.05mW/m2.sr.cm-1.

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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Flight planning summary

• Net radiance data gives better sensitivity– But we need to know the profile above us.

• Yes, the profile matters– If there is a high RH step, we want to work near the bottom

of it. – High RH layers increase the sensitivity w.r.t altitude, but

narrows the spectral range of this sensitivity.• Continuum has largest contribution at high wavenumbers, c.f.

monomer, the with the foreign dominating throughout altitude range except lowest level.

• An error in the continuum will have detectable spectral signature.

CAVIAR flight planning meeting20th November 2007, UKMO, Exeter

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What next?

– TAFTS noise levels and sensitivity.• Look at noise level from recent CAESAR flying as guide to noise levels, as

opposed to laboratory spectra.

– Profile sensitivity, variability, [particularly above max. altitude]

• Need to look at uncertainty fn (time and separate) error, any suggestions?

– Monomer line strength error signature• Bit tricker!

– Any more?