Continuous quality assessment of atmospheric water vapour measurement techniques: FTIR, Cimel, MFRSR, GPS, and Vaisala RS92

摘要

At the Izaña Observatory, water vapour amounts have beenmeasured routinely by different techniques for many years. Weintercompare the total precipitable water vapour (PWV) amountsmeasured between 2005 and 2009 by a Fourier Transform Infrared(FTIR) spectrometer, a Multifilter Rotating Shadow-band Radiometer(MFRSR), a Cimel sunphotometer, a Global Positioning System (GPS)receiver, and daily radiosondes (Vaisala RS92).The long-term characteristics of our study allowsa reliable and extensive empirical quality assessment oflong-term validity, which is an important prerequisite whenapplying the data to climate research. We estimate a PWVprecision of 1% for the FTIR, about 10% for the MFRSR, Cimel, andGPS (when excluding rather dry conditions), andsignificantly better than 15% for the RS92 (the detection ofdifferent airmasses avoids a better constrained estimation).We show that the MFRSR, Cimel and GPS dataquality depends on the atmospheric conditions (humid or dry) andthat the restriction to clear-sky observations introduces asignificant dry bias in the FTIR and Cimel data. In addition, weintercompare the water vapour profiles measured by the FTIR and theVaisala RS92, which allows the conclusion that both experiments areable to detect lower to upper tropospheric water vapour mixingratios with a precision of better than 15%.