TAFTS: Comparison of Camborne Spectra with Simulations

Ralph Beeby, Paul Green, Juliet Pickering

CAVIAR Field Campaign Meeting, Reading University, 6/12/10

Outline

• Introduction

• LBLRTM Simulations

• TAFTS Flight Data (Flight B400)

• Comparing LBLRTM spectra with TAFTS

• Conclusions

Introduction

• TAFTS mounted onboard FAAM BAe-146 during CAVIAR field campaigns; Camborne (2008), Jungfraujoch (2009)

• Used to measure in-situ far-infrared radiances, alongside Met Office ARIES (mid-IR)

• Camborne data: Flight B400 (18th September 2008) selected for case study

• Radiance data from TAFTS used to assess water vapour continuum

• Compare measured radiances with those from a simulation (LBLRTM)

Simulating Atmospheric Spectra

• LBLRTM simulates spectra for a user-defined atmospheric profile

• This profile defined using T and RH data from

– Radiosondes (launched from Camborne)

– Dropsondes (released from aircraft)

– ECMWF model data

• Uncertainties in profiles calculated from

– Instrument uncertainty– Variability over course of run

(from aircraft onboard instrumentation)

– Analytic Jacobian Uncertainty in simulated radiance

TAFTS Flight Data

• 7 straight level runs performed during B400

• Good TAFTS performance for first 5 runs

• Data calibrated for – Run 4 (34kft / 251mb), UW and DW– Run 1 (20kft / 444mb), UW– Run 2 (5.5kft / 800mb), DW

• Improved calibration routine removes ‘amplitude beamsplitter effect’ from spectra

• Spectra phase-corrected at higher resolution

TAFTS Spectra

• 34kft UW• TAFTS in blue• LBLRTM in red

• LBLRTM underestimating radiances at longer wavelengths, overestimating at shorter wavelengths

RH profile in need of adjustment?

Profile

• Analytic Jacobian for 34kft UW simulation (LBLRTM); RH profile superimposed in black• Indicates sensitivity of windows to changes in water vapour concentration• TAFTS / LBL comparison suggests atmosphere more opaque looking down from 250mb• Sensitive to 4 significant ‘lobes’ in profile: adjust profile lobe by lobe

TAFTS Spectra

• 34kft DW (TAFTS in blue, LBLRTM in red)

• LBLRTM underestimating radiances profile needs to be less opaque

• Jacobian suggests simulation very sensitive to changes in water vapour content

TAFTS Spectra

• Cross-comparison: 20kft UW and 5.5kft DW

• TAFTS in blue, LBLRTM in red

• TAFTS suggests atmosphere much less opaque than sim – reduce water vapour content in middle of profile?

Profile

• Distribution of RH with altitude

• Use 20kft UW and 5.5kft DW to constrain ‘middle section’ of profile – both suggest profile needs to be less opaque

• Calculate required adjustments to profile from Jacobians – do different views agree?

• Remaining differences after profile adjustment - continuum?

Conclusions

• TAFTS spectra from flight B400 compared with simulated spectra from LBLRTM

• LBLRTM spectra calculated from estimated atmospheric profiles

• Differences between TAFTS and LBLRTM spectra suggest profiles need some adjustment

• Use Analytic Jacobians to calculate size of adjustments

• After adjustment, look at remaining differences between spectra – continuum?