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An old-fashioned technology such as the "searchlight profiler", which was used in the 1960s for the early profiling of atmospheric backscatter, recently modified for its use with lasers and CCD cams1, has been revisited in the telemetric-LIDAR described here. The instrument is intended for the low-cost monitoring of urban aerosols, with a limited useful range of 100-200 meters. A modulated CW laser beam is used to probe the atmosphere, and a refractive telescope is used to collect the backscattered light on a photodiode array. Like in a telemetric system, the distance between the laser beam and the telescope axis determines the range resolution and the distance of the measurement volume corresponding to each pixel of the array. The system was used in conjunction with in-situ PM10 instruments for several months of continuous operation in Prato and Florence (Italy). The comparison between LIDAR-derived and conventional PM10 measurements is shown.

The spectrally-resolved characterization of the atmospheric emission has a fundamental role in the study of the Earth radiation balance, and only a measurement performed in a wide spectral range enables us to separate the contributions to the radiative balance due to the different altitudes, constituents and physical phases. The REFIR-PAD (Radiation Explorer in the Far InfraRed-Prototype for Application and Development) Fourier transform spectroradiometer can perform a characterization of the broadband radiative signature of clouds and aerosols, with the only limitation of the need of low levels of water vapour like those that are obtainable in high altitude stations during winter. The capabilities of this kind of measurement have been assessed in a series of test campaign performed in Tuscany during the winter of 2006/2007 when atmospheric emission spectra have been acquired in various transparency conditions and the evidence of transparency in the far-infrared region below 600 cm -1 has been demonstrated. REFIR-PAD operates in the spectral range extending from 100 to 1400 cm -1 with a resolution of 0.5 cm -1 , using room-temperature detectors and optics and a compact, misalignment-compensated design. The instrument, developed at IFAC-CNR, Florence, has been successfully deployed in several campaigns, both in the ground based zenith-looking geometry and in the nadir-looking balloon borne configuration. The operating spectral range of the REFIR-PAD spectroradiometer encompasses great part of the atmospheric emission spectrum, from the relatively unexplored far-infrared region below 400 cm -1 , dominated by water vapour rotational band, to the atmospheric transparency window, where a number of atmospheric instruments are already operating and can provide intercomparison data.

In recent years the Italian Space Agency funded a feasibility study for an aerospace imaging interferometer for Earth Observation. The instrument, named ALISEO (Aerospace Leap-frog Imaging Stationary Interferometer for Earth Observation), belongs to the class of the so called "stationary interferometers," and it operates in the common path Sagnac configuration not employing any moving parts to generate phase delay. ALISEO acquires the target image as modulated by a pattern of autocorrelation functions of the energy coming from each target's location. The complete interferogram is retrieved introducing relative source-observer motion. In order to calibrate the optical-path-difference (OPD) axis of the raw interferograms, a set of measurements have been carried out illuminating a double planar diffuser system by He-Ne lasers operating at different wavelengths. Standard reflectance tiles together with diffusers doped with Holmium and Rare Earths have been used to verify the wavelength calibration of the instrument. Finally, a procedure for raw data pre-processing aimed at retrieving at-sensor radiance spectra is developed taking into account the issues of dark signal subtraction, spectral instrument response compensation, effects of vignetting, and Fourier back-transform algorithm.

The fundamental component of a stationary interferometer is a beam-splitter semi-transparent plate that provides phase-delay between the two interfering rays. The phase-delay changes with varying the incident angle of the entering ray, thus producing the entire interference pattern while moving the device over the surface of the observed target. Due to their technical characteristics these interferometers can reliably be adapted for aerospace remote sensing applications. Their ability to produce the interference of the incoming radiation over a broad spectrum of optical wavelength together with the possibility to accommodate the spectral resolution by changing its optical aperture and the sampling step make these instruments interesting for Earth remote sensing. This paper describes the results coming from laboratory experiments and numerical simulations carried out in order to investigate the use of the static interferometers for remote sensing purposes.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A statistically significant data set of backscattering LIDAR and ground-based information has been obtained for the planetary boundary layer (PBL) of Florence (I). The summer LIDAR backscattering data at 532 and 1064 nm have been used to estimate both the size and the number concentration of the urban aerosols in the accumulation mode. This technique seems to be relatively insensitive to the aerosol composition. The time-height evolution of the PBL [mainly the stable (SL) and the mixed (ML) layers] has been plotted, together with the meteorological and ground-based pollution data for the 200 measurement days. The ground-based hourly pollution data (NOx, CO) have been compared with the hourly-averaged 1064 nm backscattering at 25 meters above the ground. A correlation, R equals 0.65, was obtained between NOx and 1064 nm backscattering during the summer period when the traffic aerosols do not grow considerably after their production. The correlation is not significant during winter, when the growth of the particles is much faster. During winter, the RH variations are more important than aerosol number variations to determine the backscattering evolution.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The depolarization-backscatter lidar reported here is developed for application in the polar stratospheric and high- tropospheric studies. That includes the following operations: detection of the stratospheric background aerosol, detection of high-altitude cirrus clouds and polar stratospheric clouds (PSC), detection of Rayleigh backscatter signal for subsequent stratospheric temperature retrieval algorithm application. The lidar is stationed in Sodankyla, Finland (67N) and intended for a 2-year operation at that site. It operates with one Nd:YAG laser with second and third harmonics conversion. The detection of the backscatter atmospheric signal is performed at the fundamental, second and the third harmonics of the laser (1 micrometer, 532 nm and 355 nm), as well as the vibrational Raman backscatter from the nitrogen pumped by the third harmonic at 387 nm. The backscatter signal at 532 nm is detected separately in (p) and (s) polarization.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Consideration is given to a novel inversion algorithm to determine the aerosol size distribution from lidar signals obtained at several wavelengths. This algorithm is based on a nonlinear fit of the backscattered measurements using a set of predetermined functions. Size distribution profiles of tropospheric aerosols in different meteorological conditions - clear, hazy, and cloudy atmosphere - are determined on the basis of lidar measurements made in central Switzerland, which is characterized by a specific microclimate. Measurements of stratospheric clouds and aerosols created by the Pinatubo eruption were measured above Berlin and Sodankyla, Finland. These measurements are used to characterize the size distribution of these volcanic aerosols in order to estimate their influence on radiative transfer.

Two years evolution of the stratospheric aerosol loading are presented; this study started after the eruption of the volcano El Chichon. Measurements were carried out in Florence, Italy, from the end of April 1982 to today. The increase of stratospheric aerosols at our latitude up to December 1982-January 1983 and the following decay has been monitored. Scattering Ratio and Integrated Backscattering, from the tropopause to 28 Km height has been corn puted. Due to the characteristics of the IROE Lidar system short time fluctuations in the lidar signatures could be observed, obtaining information on stratospheric inhomogeneities and structures.