M. Viterbini

Multiwavelength Aerosol Scatterometer for Airborne Experiments to Study the Optical Properties of Stratospheric Aerosol

In the recent past the role of polar stratospheric clouds (PSCs) and of stratospheric aerosol in polar ozone depletion raised the attention of the scientific community (Solomon 1990; Fiocco et al. 1997). The understanding of PSCs in terms of concentrations of particles, sizes, optical parameters, formation processes, and microphysics is relevant for evaluating their contribution to chlorine activation, dehydration, and denitrification of the lower polar stratosphere. In view of a better understanding of PSC properties, during the last few years joint lidar and optical particle counters (OPC) measurements were carried out in Antarctica (Deshler et al. 1991; Adriani et al. 1992). While the OPC was able to assess particle concentrations and sizing, the lidar could give a contemporary measurement of the aerosol volume cross section for backscattered signals and information on the depolarizing properties of the particles, hence their thermodynamical phase. In the approximation of the Mie theory, the two measurement techniques were compared to estimate the refractive index of the particles (Adriani et al. 1995). However, the comparison between lidar and balloon-borne measurements needs some care, due to differences in the sampling technique. The lidar is a ground-based instrument and the OPC is carried by balloons and moves with respect to the ground, so that the two measurements are not taken on the same air mass. Ancillary information about the wind speed profile have to be used to choose, among the lidar temporal sequence, the best lidar profile to be compared—at a given altitude—with data from the balloon-borne OPC, drifting with the

Balloonborne lidar for cloud physics studies

An innovative balloonborne microjoule lidar (MULID) has been developed within the framework of the HIBISCUS project to provide nighttime measurements of visible and subvisible cirrus and aerosols. MULID has been designed to be a low-cost and an ultralow consumption instrument, due to the remote possibilities of payload recovery and the necessity of a low-weight battery power supply. Ground tests have been performed at the Observatory of Haute Provence (France), and the first technical flight has been made from Trapani, Italy, on a stratospheric balloon; finally, the instrument has been scientifically deployed during the pre-HIBISCUS and HIBISCUS tropical campaigns in Bauru, Brazil, in February 2003 and February 2004, respectively. A description of the instrument is provided together with the results of the ground-based and flight tests as well as an overview and discussion of the first results.

Single photon detection and timing system for a Lidar experiment

An instrument for photon counting measurements in a Lidar experiment is described. Single events can be stored up to rates of 25 MHz and it is capable of 4096 data acquisitions for each measurement. Time information by two successive photons is achieved with an accuracy better than 14 ns. The system is interfaced with an HP 1000F series computer. A window discriminator/shaper for formatting the photomultiplier pulses is also described.

Planetary Fourier spectrometer: An interferometer for atmospheric studies on board Mars 94 mission

SummaryPFS is a two-channel Fourier spectrometer operating in the infra-red wavelengths between 1.25 and 45 μm. The instrument will be used mainly in the study of the Martian atmosphere. The principal goals are the measurements of the atmospheric temperature and pressure, atmospheric constituents, aerosol and clouds, ground pressure for surface topography, optical and thermophysics properties of the Martian soil. PFS will fly on the Mars 94 spacecraft which should be launched in 1994 and reach the planet in 1995. It is essentially constituted by two different interferometers located in the same box which is divided into two parts. A dichroic placed on the PFS entrance is used to separate the spectral range into two parts, a division needed by the different optical materials which have to be used in each spectral range. The optical layout of the experiment is very compact. Each channel uses two cubic mirrors mounted on an L-structure pivoted on a motor. The motor moves the mechanics and permits the optical-path difference between the arms to be varied. Each interformeter operates in a different spectral range, respectively, between (1.25÷4.8) μm (8000÷2083cm−1) and (6÷45)μm (1666÷220)cm−1). The spectral resolution is 2 cm−1. The entrance aperture area is 30 cm2 per channel and the field of view is 2 and 4 degrees. Every measurement lasts about 4 s. The time and, therefore, the relative optical-path difference for the measurement of every point of the interferogram is given by the zero crossings of the interferogram of a reference monochromatic channel at 1.2 μm which uses a laser diode as source. The two interferograms are double-sided and will have 16384 and 4096 points, respectively, corresponding to spectra of 6250 and 1823 useful points.

Observation of polar stratospheric clouds over McMurdo (77.85°S, 166.67°E) (2006–2010)

Polar stratospheric clouds (PSCs) have been observed in the Antarctic winter from 2006 to 2010 at the Antarctic base of McMurdo Station using a newly developed Rayleigh lidar. Total backscatter ratio and volume depolarization at 532 nm have been measured from 9 km up to 30 km with an average of 90 measurements per winter season. The data set was analyzed in order to evaluate the occurrence of PSCs based on their altitude, seasonal variability, geometrical thickness, and cloud typology derived from observed optical parameters. We have adopted the latest version of the scheme used to classify PSCs detected by the CALIPSO satellite-based lidar in order to facilitate comparison of ground-based and satellite-borne lidars. This allowed us to approximately identify how processes acting at different spatial scales might affect the formation of different PSC particles. The McMurdo lidar observations are dominated by PSC layers during the Antarctic winter. A clear difference between the different type of PSCs classified according to the observed optical parameters and their geometrical thickness was observed. Ice and supercooled ternary solution PSCs are observed predominantly as thin layers, while thicker layers are associated with nitric acid trihydrate particles. The same classification scheme has been adopted to reanalyze the 1995–2001 McMurdo lidar data in order to compare both data sets (1995–2001 versus 2006–2010).

Combined System for Observations of Tropospheric and Stratospheric Thin Clouds

Abstract A balloonborne sonde and a polarization lidar have been developed to make combined observations of thin tropospheric and stratospheric clouds. In their first application these instruments have been used in a campaign organized to study Antarctic polar stratospheric clouds (PSCs), which are deeply involved in the process of ozone depletion. The sonde collects cloud particles larger than 4 µm in diameter on a transparent impactor and observes them by means of a CCD (charge coupled device) camera microscope. Images are transmitted in real time to the ground station for recording and analysis. Shape, dimension, and size distribution of the particles are obtained from these frames. The lidar provides complementary information about the cloud optical depth, backscattering, depolarization, vertical distribution, and temporal evolution. Characteristics of both instruments are described. The experiments performed during the 1990 spring campaign at McMurdo Station, Antarctica, are discussed, and some resul...

Voltage breakdown follower avoids hard thermal constraints in a Geiger mode avalanche photodiode

A novel approach to single-photon detection by means of an avalanche photodiode is described and preliminary results obtained by implementation of a prototype are reported. The electronic circuit (breakdown voltage follower) avoids the use of complex temperature controls typically used with these devices, thus reducing system complexity and cost. Data obtained without any thermoregulation show the same behavior with respect to systems thermoregulated to within a few hundredths of a degree celsius.

Integrating multichannel scaler for photon counting in laser radar application

A multichannel scaler for photon counting is described. Single photon pulses can be collected up to rates of 100 MHz during a programmed dwell time and an integration versus time can be done for each of the 999 channels on a user‐programmable number of successive measurements. A live, dynamic display is provided. Data can be easily sent to any computer for recording or to a telemetry system for remote transmission.

Polar stratospheric clouds and ozone depletion: Relevance of extendedin situ observations

SummaryThe occurrence of a springtime ozone depletion over Antarctica appears to be the result of a chain of processes leading to catalitic destruction of the gas by the action of halogen radicals, in particular chlorine oxide. High abundances of ClO in the stratosphere are determined by abnormally low concentrations of nitrogen compounds; such denitrification is likely to be caused by heterogeneous reactions and transport carried out by the clouds present in the polar stratosphere. Stratospheric clouds form during most of the winter and the beginning of spring over the polar regions. Due to scarce accessibility, knowledge of their properties is still poor. Information on extent, particles shape and size distributions is, however, fundamental for the understanding of the magnitude of their contribution to the destruction chain. A balloon-borne experiment, aimed at thein situ observation of cloud particles from 2 to 200 microns in radius, is presented. This would be the first system to provide on-line TV images of cloud particles. The first measurement campaign in Antarctica is planned for the period August–October 1990.

Lidar Measurements of Stratospheric and Mesospheric Density: Preliminary Results

Lidar measurements of atmospheric density and temperature in the stratosphere and middle atmosphere are presented. The lidar system operating in Frascati is described and some results of high altitude soundings are reported.