1 / 17

Objectives

Intercomparison of GlobVapour total column water vapour (TCWV) and Envisat RA2-MWR measurements (preliminary results) Bruno Picard (CLS), Jean-Rémi Deboer (CLS) Martin Stengle (DWD), Marc Schröder (DWD) Estelle Obligis (CLS), Marie-Laure Frery (CLS) bpicard@cls.fr (+33)5 6139 3737. Objectives.

ashlyn
Download Presentation

Objectives

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Intercomparison of GlobVapour total column water vapour (TCWV) and Envisat RA2-MWR measurements(preliminary results)Bruno Picard (CLS), Jean-Rémi Deboer (CLS)Martin Stengle (DWD), Marc Schröder (DWD)Estelle Obligis (CLS), Marie-Laure Frery (CLS)bpicard@cls.fr(+33)5 6139 3737

  2. Objectives • A comparison of GlobVapour TWVC against RA2-MWR product (microwave radiometer on Envisat) • The present study is focusing on 4 monthly SSMI/Meris combined products • The results are preliminary and show what metrics could be used when more data will be available

  3. Context • Altimetry missions usually embed a microwave radiometer in charge of providing the wet tropospheric correction ([cm]) to the radar signal • MWR are 2-bands (23.8/36.5 GHz, ERS-1/2, RA2-Envisat [ESA]) or 3-bands (+18.7GHz, Topex, Jasons [NASA/CNES])

  4. Context • Altimetry missions usually embed a microwave radiometer in charge of providing the wet tropospheric correction ([cm]) to the radar signal • MWR are nadir 2-bands (23.8/36.5 GHz, ERS-1/2, RA2-Envisat [ESA]) or 3-bands (+18.7GHz, Topex, Jasons [NASA/CNES])

  5. Wv for altimetry • The wet tropospheric correction  6 cm of wet tropo. corr = 1 g/cm2 TWVC • « dry » term (2m) provided by meteorological models with a good accuracy • « wet » term, almost proportional to the integrated water vapor (1cm = 1.66 kg/m2), highly variable in space and time, ranging from a few cm to about 50 cm, not provided with enough accuracy by meteorological models (actual resolution of 50km/6hours)

  6. Altimetry requirements • To provide the wet tropospheric corrrection : • with a good accuracy (≈ 1 cm rms) • with a good stability (≈ 1 mm/year) • with no geographically correlated errors • GCOS recommandation: < 0.05mm/yr !

  7. RA2-MWR • RA2-MWR is a 2-bands (23.8/36.5 GHz) nadir Dicke radiometer (resolution of about 20 km) • Wet tropo. corr and TWVC are retrieved by a neural network algorithm developed by CLS E. Obligis, L. Eymard, et al, “First three years of the microwave radiometer aboard ENVISAT: In-flight calibration, processing, and validation of the geophysical products,” J. Atmos. Ocean. Technol., vol. 23, no. 6, pp. 802–814, Jun. 2006. • Data are available since 2002

  8. Reminder • BUT, when using RA2-MWR products, precaution should be taken on the coherency of the dataset • Algorithms have been constantly improved leading to discontinuities  some RA2-MWR events since BOM • Oct.24, 2005, v5.02, 1st day of cycle 42, L1b upgrade: • MWR Side Lobe correction upgrade • Jan.12, 2010, v6.02, 1st day of cycle 86, L1b/L2 upgrade: • new in-flight calibration / new NN algorithm

  9. Reprocessing • Envisat RA2 whole mission reprocessing in on-going • The present RA2-MWR data have been reprocessed using the CLS ESL MWR L1B reference prototype applying a consistent set of algorithms

  10. SSMI/Meris combined product • 4 monthly mean 0.5°x0.5° SSMI/Meris combined TWVC product (prototype): July 2007, August 2007, January 2008, August 2008 (missing data ?) January 2008

  11. RA2-MWR (reproc) product • Along-track nadir TWVC over a month has been averaged on a 0.5°x0.5° map • Altimetry validity flag has been used to edit data of poor quality January 2008

  12. RA2-MWR (reproc) - GlobVapour • mean bias = -0.74 kg/m2 • mean rms = 7.11 kg/m2 • no geographical pattern January 2008

  13. RA2-MWR (reproc) - GlobVapour • mean bias = -0.74 kg/m2 • mean rms = 7.11 kg/m2 • larger dispersion around 15 kg/m2

  14. RA2-MWR (reproc) - GlobVapour • Impact of the reprocessing • official product • reprocessed product • larger bias with thereprocessed product • BUT, more stable in time mean of diff [kg/m2] std of diff [kg/m2] months since 07/2008

  15. Conclusion • Comparison of SSMI/Meris with RA2-MWR shows good agreement • a bias of about 0.8 kg/m2, constant in time (?)no geographical pattern

  16. Further study • Expected improvement for this study • > 15 kg/m2 dispersion ? • more data from GlobVapour ! • SSMI/Meris but also MWR 1D-Var • daily product ? • validation against: • model: ECMWF TWVC • in-situ measurements: radiosonde

  17. THANK YOU! bpicard@cls.fr(+33)5 6139 3737

More Related