Gilles Larcheveque

Influence of the photomultiplier tube spatial uniformity on lidar signals

Measurements of the spatial uniformity of Hamamatsu H5783-06 photosensor modules were performed by the flying spot method. The results were used to simulate the influence of the photomultiplier tube on a lidar signal. A simple method for improving the spatial uniformity is proposed.

Development of a multiwavelength aerosol and water-vapor lidar at the Jungfraujoch Alpine Station (3580 m above sea level) in Switzerland

The Jungfraujoch Research Station (46.55 degrees N, 7.98 degrees E, 3580 m above sea level) for decades has contributed in a significant manner to the systematic observation of the Earths atmosphere both with in situ measurements and with trace gas column detection. We report on the development of a lidar system that improves the measurement potential of highly resolved atmospheric parameters in both time and space, with the goal of achieving long-term monitoring of atmospheric aerosol optical properties and water-vapor content. From the simultaneously detected elastic-backscatter signals at 355, 532, and 1064 nm, Raman signals from nitrogen at 387 and 607 nm, and water vapor at 408 nm, the aerosol extinction and backscatter coefficients at three wavelengths and a water-vapor mixing ratio are derived. Additional information about particle shape is obtained by depolarization measurements at 532 nm. Water-vapor measurements by use of both nitrogen and water-vapor Raman returns from the 355-nm laser beam are demonstrated with a vertical range resolution of 75 m and an integration time of 2 h. The comparison to the water-vapor profile derived from balloon measurements (Snow White technique) showed excellent agreement. The system design and the results obtained by its operation are reported.

Water vapor vertical profile by Raman lidar in the free troposphere from the Jungfraujoch Alpine Station

The water vapor content in the atmosphere is an important criteria for the validation of predictive results obtained from global scale atmospheric models. Due to its non-homogeneous distribution in the troposphere, both in space and time, the water vapor content in the atmosphere may still be considered today as the largest uncertainty in our understanding of the earth radiation budget. This paper presents new results obtained by Raman lidar measurements as one of the attractive method for long-term continuous observation of the water vapor content in the atmosphere. A powerful pulsed laser beam at 355 nm is emitted and the inelastic back-scatter signals (Raman shift) from nitrogen and water vapor are recorded respectively. The ratio between the water vapor Raman shifted wavelength at 408nm and the nitrogen at 387nm gives a first estimate of the relative water vapor mixing ratio with good vertical resolution. The absolute water vapor vertical profiles are retrieved using an additional in situexternal reference value directly obtained from a local meteorological station. The Raman lidar system, operated at an altitude of 3′580 m above see level in the Swiss Alpine region at the Jungfraujoch research station, is presented, and two typical water vapor vertical profiles obtained in clear sky and in cloudy conditions are discussed and directly compared with radio sounding measurements performed by the Swiss Meteorological Station from Payerne (80 km West). A first estimate of the statistical (signal to noise) and systematic error sources is presented.

A Raman Differential Absorption Lidar for Ozone and Water Vapor Measurement in the Lower Troposphere

A new way of measuring ozone and water vapor in the Planetary Boundary Layer (PBL) is proposed. The method is based on the simultaneous measurement of the Raman backscattering in the UV by O2, N2 and H2O, using a single pump beam at 266 nm. The ozone concentration is retrieved from the differential absorption of the N2 and O2 Raman backscattered signals, while the water vapor is measured using the classical Raman scheme. We present some preliminary results showing daytime ozone measurements in good correlation with a point monitor. | A new way of measuring ozone and water vapor in the Planetary Boundary Layer (PBL) is proposed. The method is based on the simultaneous measurement of the Raman backscattering in the UV by O2, N2, and H2O, using a single pump beam at 266 nm. The ozone concentration is retrieved from the differential absorption of the N2 and O2 Raman backscattered signals, while the water vapor is measured using the classical Raman scheme. We present some preliminary results showing daytime ozone measurements in good correlation with a point monitor.

Photo-oxidant formation in the Milan metropolitan area

During the Limitation of Oxidant Prodn. (LOOP) campaign, different instruments were deployed, providing a complete data set. This will be used to evaluate the model and its ability to reproduce pollution events. Then, the complete data set will be used for a better definition of the model inputs. The final aim of the LOOP project is to use the model to test different abatement strategies, particularly by defining the region where ozone prodn. is NOx or VOC sensitive.

UV ozone DIAL based on a Raman cell filled with two Raman active gases

A configuration of a UV ozone DIfferential Absorption Lidar (DIAL) based on a single cell filled with two Raman active gases has been developed. The cell is filled with a mixture of hydrogen and deuterium as active gases and argon as a buffer gas. The cell is pumped with the fourth harmonic of a Nd:YAG laser. The partial pressures of the gases are chosen to achieve even energy for the first Stokes of hydrogen (299 nm) and deuterium (289 nm), which are used as DIAL wavelengths. The ON and OFF beams, produced in this way, have identical spatial intensity distribution, identical temporal power profiles and the ability to probe the same air volume at the same time, which contributes to the decrease of systematic errors. Special care is taken to diminish the negative influence of the crosstalk between channels in the receiving part and the spatial nonuniformity of the receiving photosensors. Lidar measurements of tropospheric ozone concentration with vertical resolution ranging from 15 to 150 m and distances from 200 to 1200 m are performed. The results are compared with ground based punctual measurements and with DIAL measurements from a system with two Raman cells.

Raman DIAL measurement of ozone and water vapor in the lower troposphere

A new lidar for the measurement of tropospheric ozone is proposed, based on the differential analysis of the Raman backscattered signals on nitrogen and oxygen, which is far less sensitive to the aerosols than the classical DIAL system. Using a third Raman channel, the system is able to measure the water vapor mixing ratio simultaneously. The transmitting section of the instrument is composed of a single wavelength at 266 nm, generated by a quadrupled Nd:YAG laser, while the receiving section is the combination of a 20 cm Newton telescope, a polychromator, custom made band pass filters and miniature photomultiplier, giving a compact and efficient optical layout. The cross-talk between the different channels, and the rejection of the 266 nm wavelength have been measured in detail and will be presented. Time series of ozone and water vapor vertical profile during some days have been performed in the early spring 99.