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© Crown copyright Met Office CAVIAR field campaigns meeting Stuart Newman Exeter, 29 April 2010.

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Presentation on theme: "© Crown copyright Met Office CAVIAR field campaigns meeting Stuart Newman Exeter, 29 April 2010."— Presentation transcript:

1 © Crown copyright Met Office CAVIAR field campaigns meeting Stuart Newman Exeter, 29 April 2010

2 © Crown copyright Met Office Contents This presentation covers the following areas NPL laboratory calibrations Field campaign profile selection Initial continuum results

3 © Crown copyright Met Office NPL lab calibrations

4 © Crown copyright Met Office CAVIAR work package 3.2 Low temperature blackbody calibration ARIES calibrated against NPL low temperature blackbody Range of temperatures relevant to atmospheric remote sensing – we achieved a range of -75 to +30 ºC ARIES blackbody target temperatures also varied as a test of target emissivity

5 © Crown copyright Met Office ARIES target emissivity tests Positive bias with hot target at 81ºC, cold target at 20ºC Negative bias with hot target at 12ºC, cold target at 41ºC (c.f. NPL target with emissivity at -74.8ºC)

6 © Crown copyright Met Office Finding best fit target emissivities

7 © Crown copyright Met Office ARIES target emissivity results hot target at 81ºC, cold target at 20ºC hot target at 12ºC, cold target at 41ºC

8 © Crown copyright Met Office Merge results ExperimentNPL target temperature Fitted (CBB)Fitted (HBB) N May ºC N May ºC N May ºC

9 © Crown copyright Met Office Account for calibration uncertainty?

10 © Crown copyright Met Office Best estimate for uncertainty? Standard deviation gives very large uncertainty Standard deviation of mean (standard error) reduces this by N but for measurements this is an over-constraint May be appropriate to use number of independent calibrations (blackbody views) as N, approx per set of conditions Mean & std. dev.

11 © Crown copyright Met Office Field campaign profile selection

12 © Crown copyright Met Office Summary of flights FlightDateWeather conditionsComments B Cloud at times over JungfraujochPartial NPL data B Initially thin cirrus which clearedGood NPL data B Good clear sky conditionsFLASH sonde* + MetOp overpass B Cloud at times over JungfraujochPartial NPL data B Some thin cirrus encroachingGood NPL data B Excellent clear sky conditionsMetOp overpass B Excellent clear sky conditionsARIES failure B Excellent clear sky conditionsNo TAFTS B Partial cloud over JungfraujochCancelled am flight, pm only * Institute of Applied Physics in Bern launch radiosondes from Payerne equipped with RS92, Snow White and FLASH-B (Lyman-alpha) hygrometers

13 © Crown copyright Met Office Meeting at IC in December Identify sources of profile information (dropsondes, aircraft probes, model fields) Agree a method for sub-selecting data (three areas: NW, over JFJ & SE, different profile for each aircraft run) Agree a method for combining profile information (as a first attempt use the nearest co-located dropsonde and perturb using model spatial-temporal evolution… however, see next slides)

14 © Crown copyright Met Office Model biases Statistics of model fields versus 55 dropsondes ECMWF mean biases are small (though with large scatter) Cosmo mean biases are larger, particularly for humidity

15 © Crown copyright Met Office Model biases cont. Really bad example for Cosmo

16 © Crown copyright Met Office Model biases cont. Better example for Cosmo Cosmo particularly bad on 27/7/09 and 1/8/09 (for some reason) So far have used ECMWF exclusively

17 © Crown copyright Met Office Profile issues Using model to evolve dropsonde profile only works if model is close to true atmosphere If model biases are present, and profile is extrapolated too far in time and space, errors can be introduced It seems best to concentrate first on situations where the spectrometer data are closely located with a dropsonde (or aircraft profile)

18 © Crown copyright Met Office Can we use FWVS data? Dropsondes are widely recognised as most accurate source of humidity data from the aircraft However, for runs immediately after a profile descent (e.g ft down to ft) FWVS may be more representative Attempt to use FWVS humidity data in LBLRTM simulations of ARIES at ft

19 © Crown copyright Met Office CAVIAR example B Jul-2009 Initial run at high level for radiance measurements (here looking up) Spiral descent over Jungfraujoch observatory measuring in situ water vapour (rapid response FWVS probe used here) Subsequent run at lower level for radiance measurements (here looking up) Determine change in radiance due to water vapour in atmospheric path Derive continuum strength, compare to MT_CKD model in LBLRTM

20 © Crown copyright Met Office CAVIAR example B Jul-2009 Consistent discrepancy in centre of water vapour band for channels at 1586 and 1598 cm -1 (MT_CKD continuum is relatively strong at 1586 cm -1 compared with measurements)

21 © Crown copyright Met Office Humidity information from MARSS Helpful to constrain humidity above the aircraft using microwave observations at 183 GHz Microwave Airborne Radiometer Scanning System (MARSS)

22 © Crown copyright Met Office MARSS humidity channels B467 (19/7/09) Good agreement for channel centred closest to 183 GHz line B471 (27/7/09) Worse agreement for channel 183±1 GHz, better for 183±3 GHz

23 © Crown copyright Met Office CAVIAR example B Jul-2009 Inconsistent results here, all retrieved continuum strengths < MT_CKD Is this because LBLRTM profile is too moist? Possible to use MARSS data for profile constraint?

24 © Crown copyright Met Office Initial continuum results from Jungfraujoch flights and satellite data

25 © Crown copyright Met Office 8 MetOp cal/val flights Sea – Gulf of Mexico Land – Oklahoma 2 night, 6 day flights All MetOp collocated Joint Airborne IASI Validation Experiment (JAIVEx) – April-May 2007

26 © Crown copyright Met Office IASI water vapour band Flight B290, 30-Apr-2007

27 © Crown copyright Met Office IASI water vapour band Flight B285, 19/20-Apr-2007

28 © Crown copyright Met Office IASI water vapour band Flight B290, 30-Apr-2007 Coudert et al. water vapour spectroscopy updates since HITRAN2004 MT_CKD_2.5 in LBLRTM_v11.7 Continuum channels relatively insensitive to spectroscopic database

29 © Crown copyright Met Office IASI water vapour band Implied continuum strength is less than MT_CKD 1900 cm -1 Retrieved continuum is sensitive to uncertainties in atmospheric profile

30 © Crown copyright Met Office Preliminary results Selected data from flights B467-B474

31 © Crown copyright Met Office Questions and answers

32 © Crown copyright Met Office IASI atmospheric retrieval

33 © Crown copyright Met Office Spectral retrieval


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