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ALVICE
 
 
RIVM stratospheric ozone lidar in Lauder (New Zealand)

Site description
The RIVM stratospheric ozone lidar is located at the NIWA institute in Lauder, New Zealand (45.04°S, 169.68°E at an altitude of 370 m above sea level). The Lauder site has been a primary NDACC station since the start of NDSC (former name of NDACC) in January 1991 and is participating in various validation projects.

Lauder site

Instrument description
The RIVM stratospheric lidar is a differential absorption lidar (DIAL). Since September 2007, it has a Coherent LPXPro 325C XeCl excimer laser, predominantly emitting light pulses in the wavelength 308 nm. A secondary beam (at 353 nm) is generated through Raman conversion. Subsequently, the system measures the backscatter in these two wavelengths (both measured in near -5% intensity- and far -95% intensity- channels) and at 332 and 385 nm (Raman channels). The instrument is featured in action (third beam in the visible part of the spectrum, not used for scientific purposes) on the image on the right.

Instrument history
The RIVM stratospheric lidar was built in Bilthoven (The Netherlands) and shipped to the NIWA institute in Lauder, where measurements commenced in December 1994. The original laser, a Lambda Physik LPX325i XeCl excimer laser, was replaced in September 2007 by a Coherent LPXPro 325 XeCl excimer laser together with a replacement of the Raman cell.

Campaigns
The Ozone Profiler Assessment at Lauder (OPAL) campaign was held in 1995. During this campaign, two differential absorption lidars, a microwave radiometer, electrochemical concentration sondes and the SAGE II satellite instrument were compared. At altitudes of 20 to 40 km, the measurements agreed within 15% for individual profiles and within 10% for the campaign average. For more details on these validation activities see McDermid et al. 1998.

The Temperature and Ozone Profiler Assessment at Lauder (TOPAL) campaign was held in April 2002. The RIVM lidar was compared with ozone sondes, a NASA/GSFC ozone lidar and a microwave radiometer. Agreement with the sondes was within 3% over the altitude interval 18 to 29 km and 10% (lidar relatively overestimating) outside this interval. Agreement with the GSFC lidar was excellent in the range 12 to 30 km, followed by a gradual increase with altitude of the differences between the two lidars (with the RIVM lidar relatively underestimating ozone). These specific differences have been attributed to Rayleigh scattering, for which an updated implementation has been included in version 8.2 of the RIVM analysis software. Agreement with the microwave radiometer is within 3% over most of the profile.

A third intercomparison campaign was held in June/July 2011 which was limited to the comparison of temperature profiles due to a laser breakdown of the travelling standard. A new measurement scheme optimising operator time, integration time and altitude coverage was initiated. Results of the comparison and the new observation strategy are being analysed together with those of the re-trial of this campaign in April 2012 named Temperature, Water vapour and Ozone Profiler Assessment at Lauder (TWOPAL). Note that the RIVM lidar does not produce water vapour profiles, but that the NDACC travelling standard lidar data were compared with frost point hygrometer data from balloon sondes. 

Observation strategy
Measurements prior to July 2011 were taken in four modes. Distinction between these modes is done using grey filters (see Table 1 for an overview of the used channels). The modes are:
  1. nd05 used when clouds are present
  2. nd20 used in clear sky conditions
  3. mid
  4. high

The first measurement is the mid-measurement, with which it is possible to derive an ozone profile from 28 up to 40-45 km. The nd05 and nd20 measurements allow a good characterisation of the lower profile (both using Raman channels). Finally, the last measurement (high) is used to better capture the part of the profile above the aerosol layer (>28 km, therefore Raman channels are not needed).

Four wavelengths can be used, where the signal of 308 nm and 353 nm can be split into near and far signal segments to reduce the large dynamic range of the return signal.

Table 1: Overview of the used channel combinations for the different measurement modes. + indicates the usage of a given channel for a given mode

  Wavelength [nm]

308 near

308 far

353 near

353 far

332

385

Mode

nd05

+

 

+

 

+

+

nd20

+

+

+

+

+

+

mid

+

+

+

+

+

+

high

+

+

+

+

   
Measurement frequency
Measurements are usually taken 5 to 6 nights a month. The figure below shows the ozone number density measurements in the period 1994 to January 2011.


 

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19 September 2016