AquaVIT 2



International Intercomparison of atmospheric Water vapour instruments

The concept:

The aerosol and cloud simulation chamber AIDA at the Karlsruhe Institute of Technology (KIT) offers a large volume of constant H2O mixing ratio that provides the basis for 3 intercomparison options: (1) in situ ambient instruments without inlets installed inside the AIDA chamber, (2) in situ instruments with inlets configured to sample from a heated manifold flow extracted from the chamber, (3) optical instruments installed outside the chamber that probe a portion of the chamber volume.  A further distinction is that instruments external to the chamber can be either inside or outside the chamber thermal enclosure. The national metrology institute (PTB) will provide intercomparision to a mobile transfer humidity standard at KIT to ensure traceability to primary humidity standards.


Intercomparison of state of the art and prototype atmospheric hygrometers with each other and with independent humidity standards at the aerosol and cloud simulation chamber AIDA to:

  • determine and document sensitivity, precision, and accuracy of the different instruments. KIT will provide comparison to the AIDA water vapour standard (±5% in the range 5-500 ppm; APicT and MBW 373LX) and PTB will provide comparison to a transfer standard ensuring traceability to the national water vapour standard.
  • verify the results of the AquaVIT1 intercomparion 2007 .
  • provide a continued quality control.
  • document the improvement of existing and the development of new instruments.

This includes:·          

  • Intercomparison of open path (water vapour) instruments (TDL).
  • Intercomparison of sampling (total water) instruments. 
  • Quantify the influence of rapid changes in pressure, temperature, and water vapour on instrument response (Not generally possible for the instruments in option 3 above).
  • Humidity measurement in dense clouds in AIDA providing intrinsic saturation reference (Not generally possible for the instruments in option 3 above).
  • Pressure range: 50 - 1000 hPa.
  • Temperature range: 189 - 243 K.
  • Water vapour range: 1 - 1000 ppmv (1 atm).
  • Relative humidity over ice range: 0 – 100 % (and supercooled water clouds).

New compared to AquaVIT1:

  • Test of radiosondes inside AIDA.
  • Intercomparison of calibration devices (in flight, lab type).
  • Intercomparison with national water standard (PTB transfer standard) to determine the accuracy of the instruments as part of the EU project METEOMET.

Similar activities which could be combined with AquaVIT2:

  • Intercomparison of instruments for water isotope ratio measurement.

Organisers: Ottmar Möhler (KIT), Harald Saathoff (KIT), Holger Vömel (DWD), Martina Krämer (FZJ), Ru-Shan Gao (NOOA), David Fahey (NOOA), Volker Ebert (PTB), Thomas Peter (ETH)

Timeframe: April 2nd -19th, 2013 (one week instrument installation and 2 weeks of experiments)