Broadband lidar measurements of tropospheric water vapor profiles

Abstract

Abstract. A new technique has been developed for the measurement of vertical profiles of water vapor in the troposphere. The method, which is also appropriate for the measurement of gases such as ozone and nitrogen dioxide, is based on the application of differential optical absorption spectroscopy (DOAS) to backscattered photons from a broadband lidar (10-20 nm at full width half maximum) operating in the UV-visible region of the electromagnetic spectrum. ANd: YAG pumped broadband dye laser is used as the light source, and backscattered photons from the atmosphere are both time and spectrally resolved using an imaging spectrometer with a chargecoupled device (CCD) detector. The new broadband lidar circumvents many of the difficulties and inaccuracies involved with traditional narrowband differential absorption lidar (DIAL) water vapor observations, for example, the laser bandwidth and wavelength-positioning requirements demanded by the narrowness of the water vapor transitions. Water vapor mixing ratio profiles measured over Cambridge, England, in 1996 with the new instrument demonstrate good levels of agreement with quasi-simultaneous radiosonde profiles from nearby weather stations.

DIAL and GNSS observations of the diurnal water‐vapour cycle above Iqaluit, Nunavut

“…The derivation of Equation 1 can be found in Newsom et al (2020). While Vaisala's water-vapour retrieval algorithm is proprietary, it is similar to the broad-band water-vapour DIAL solution presented in South et al (1998). Solving for the water-vapour transmission profile provides the number-density profile for water vapour via the Beer-Lambert law.…”

“…Both techniques have their advantages and disadvantages, but for the purposes of this study we will focus on the DIAL technique. The DIAL technique has been applied to water‐vapour measurements since the early 1990s for both ground‐ and air‐based lidars (South et al ., 1998; Wulfmeyer and Bösenberg, 1998; Wagner and Pruß, 2002; Spuler et al ., 2015). Water‐vapour DIALs are now starting to be developed for automated and operational use (Spuler et al ., 2015; Newsom et al ., 2020).…”

Radical chemistry at night: comparisons between observed and modelled HO<sub>x</sub>, NO<sub>3</sub> and N<sub>2</sub>O<sub>5</sub> during the RONOCO project

“…While a number of nighttime studies at ground level close to local sources of NO have observed a limited role of NO 3 in nighttime radical production owing to surface losses of NO 3 and the rapid reaction between NO 3 and NO (Salisbury et al, 2001;Fleming et al, 2006;Sommariva et al, 2007;Kanaya et al, 1999Kanaya et al, , 2002Kanaya et al, , 2007aEmmerson and Carslaw, 2009;Faloona et al, 2001;Martinez et al, 2003;Ren et al, 2003Ren et al, , 2005Ren et al, , 2006Volkamer et al, 2010), several studies of NO 3 and N 2 O 5 above ground level and in more remote regions have indicated a more significant role for NO 3 in nighttime radical production and tropospheric oxidation (Platt et al, 1980;Povey et al, 1998;South et al, 1998;Aliwell et al, 1998;Allan et al, 2002;Stutz et al, 2004;Brown et al, 2003Brown et al, , 2004Brown et al, , 2007Brown et al, , 2009Brown et al, , 2011Aldener et al, 2006;Sommariva et al, 2009;Stutz et al, 2010).…”

Radical chemistry at night: comparisons between observed and modelled HO<sub>x</sub>, NO<sub>3</sub> and N<sub>2</sub>O<sub>5</sub> during the RONOCO project

“…Measurements of NO 3 have been overestimated by model calculations in several studies (Mihelcic et al, 1993;Sommariva et al, , 2007, with those of nighttime OH and HO 2 radicals typically underestimated, indicating poor understanding of nighttime tropospheric oxidation processes (Kanaya et al, 1999(Kanaya et al, , 2002(Kanaya et al, , 2007aEmmerson and Carslaw, 2009;Geyer et al, 2003;Faloona et al, 2001;Martinez et al, 2003;Ren et al, 2006). While a number of nighttime studies at ground level close to local sources of NO have observed a limited role of NO 3 in nighttime radical production owing to surface losses of NO 3 and the rapid reaction between NO 3 and NO (Salisbury et al, 2001;Fleming et al, 2006;Sommariva et al, 2007;Kanaya et al, 1999Kanaya et al, , 2002Kanaya et al, , 2007aEmmerson and Carslaw, 2009;Faloona et al, 2001;Martinez et al, 2003;Ren et al, 2003Ren et al, , 2005Ren et al, , 2006Volkamer et al, 2010), several studies of NO 3 and N 2 O 5 above ground level and in more remote regions have indicated a more significant role for NO 3 in nighttime radical production and tropospheric oxidation (Platt et al, 1980;Povey et al, 1998;South et al, 1998;Aliwell et al, 1998;Allan et al, 2002;Stutz et al, 2004;Brown et al, 2003Brown et al, , 2004Brown et al, , 2006Brown et al, , 2007Brown et al, , 2009...…”