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The Radiation Explorer in the Far Infrared – Prototype for Applications and Development (REFIR-PAD) is a Fourier transform spectroradiometer that has been designed to operate from both stratospheric balloon platforms and the ground. It has been successfully deployed in a stratospheric balloon flight and several ground-based campaigns from high-altitude sites, including the current installation at the Italian–French Concordia Antarctic station. The instrument is capable of operating autonomously with only a limited need of remote control and monitoring and provides a multiyear dataset of spectrally resolved atmospheric downwelling radiances, measured in the 100–1500 cm−1 spectral range with 0.4 cm−1 resolution and a radiometric uncertainty of better than 0.85 mW(m2srcm-1)-1.

Measurements have been performed at eight laboratories on Raman-shifted radiation from frequency-quadrupled Nd:YAG and KrF lasers. Each of these sources is a possible candidate for making differential-absorption lidar measurements of ozone in the free troposphere. The spectral purity, efficiency and divergence of the different sources are compared and explained using a simplified model of the Raman interaction. Particular attention has been given to the use of buffer gases to optimize the Raman gain and divergence. The experimental results show that the operating conditions required to optimize the output energy of each of these types of laser source can be quite different. In the case of the KrF laser, it has been shown that high energies can be generated at low active gas pressures, and that increasing the pressure increases the beam quality, but decreases the energy. (Less)

A four wavelength backscattering depolarization LIDAR designed for polar stratospheric cloud and stratospheric aerosol measurement is described. The system uses the following wavelengths: 355 nm, 532 nm, 750 nm, and 850 nm. These wavelengths, obtained by means of the third- and second-harmonic of a Nd: YAG laser and by means of a tunable Ti: Sapphire laser, are chosen in a way to better characterize the particel size of such stratospheric aerosols. They are not emitted simultaneously as the LIDAR system is designed with only two detection channels permitting to detect, in the analog and in the photon counting mode, both the direct and the depolarized backscattered signal. The system has been operational in northern Finland since the end of November 1991.

In this paper we describe a new instrument named ALISEO (Aerospace Leap-frog Imaging Stationary Interferometer for Earth Observation), which belongs to the class of the “stationary interferometers”. ALISEO has been selected as the main payload for a novel Italian Space Agency (ASI) optical mission based on a micro-satellite (MIOSat) with steering capability. The mission is constituted by a micro-satellite equipped with advanced payloads, among which there are an extensible telescope, a MEMS Mach-Zehnder non-imaging interferometer, and ALISEO. MIOSat is expected to provide the scientific community with the technological demonstration of this new remote sensing technology.

ALISEO (Aerospace Leap-frog Imaging Stationary Interferometer for Earth Observation) belongs to the stationary interferometers representing a promising architecture for future Earth Observation (EO) sensors due to their simple optical layout. ALISEO has been selected by the Italian Space Agency as the principal payload for a new optical mission based on a micro-satellite (MIOsat). Payloads planned for MIOsat are an extensible telescope, a high-resolution panchromatic camera, a Mach-Zehnder MEMS interferometer, and ALISEO. MIOsat is expected to provide a platform with pointing capability for those advanced sensors. ALISEO operates in the common-path Sagnac configuration, and it does not employ any moving part to generate phase delay between the two rays. The sensor acquires the target images modulated by a pattern of autocorrelation functions: a fringe pattern that is fixed with respect to the instrument's field of view. The complete interferogram of each target location is retrieved introducing relative source-observer motion, which allows any image pixels to be observed under different phase delays. Recent laboratory measurements performed with ALISEO are described and discussed in this paper. In order to calibrate the optical path difference (OPD) of raw interferograms, a set of measurements have been carried out using a double planar diffuser system and several coloured He-Ne lasers. Standard reflectance tiles together doped with Holmium and Rare Earths have been used for validating the wavelength calibration of the instrument and proving the reliability of the reflectance retrieving procedure.

A cryogenically operated laser diode spectrometer (COLD) for the airborne measurement of carbon monoxide is described. The instrument is designed, and fully qualified, for operation on a high-altitude aircraft and the scientific mission is the in situ measurement of trace gases in the upper troposphere and lower stratosphere. Sensitivities achieved so far during in-flight operation are a few ppbV with a time resolution of 4 s, coupled with a good reliability. Airborne data, obtained by COLD during research campaigns in Australia and Brazil in the frame of international projects, are also presented to demonstrate COLD in-flight performance.

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.

In preparation for a possible space mission, a breadboard version named REFIR-BB of the Radiation Explorer in the Far Infrared (REFIR) instrument has been built. The REFIR is a Fourier-transform spectrometer with a new optical layout operating in the spectral range 100-1100 cm(-1) with a resolution of 0.5 cm(-1), a 7-s acquisition time, and a signal-to-noise ratio of better than 100. Its mission is the spectral measurement in the far infrared of the Earth's outgoing emission, with particular attention to the long-wavelength spectral region, which is not covered by either current or planned space missions. This measurement is of great importance for deriving an accurate estimate of the radiation budget in both clear and cloudy conditions. The REFIR-BB permits the trade-off among all instrument parameters to be studied, the optical layout to be tested, and the data-acquisition strategy to be optimized. The breadboard could be used for high-altitude ground-based campaigns or could be flown for test flights on aircraft or balloon stratospheric platforms. The breadboard's design and the experimental results are described, with particular attention to the acquisition strategy and characterization of the interferometer. Tests were performed both in laboratory conditions and in vacuum. Notwithstanding a loss of efficiency above 700 cm(-1) caused by the poor performance of the photolithographic polarizers used as beam splitters, the results demonstrate the feasibility of using the spectrometer for space applications.

In this paper, mid-infrared spectrometer based on a liquid nitrogen cooled lead-salt diode laser, emitting at 2190 cm/sup -1/ for the in-situ measurement of stratospheric nitrous oxide is developed. The system operates unattended for several hours under changing ambient conditions: during flight, the pressure is ranging from 1000 down to 30 mbar, temperature ranges from +70/spl deg/C to -90/spl deg/C. Typical flight measurements are performed between 10000 and 22000 m of altitude and at an aircraft speed of 160-190 m/s.

In this paper, compact near-infrared distributed feedback diode-laser, emitting at 1.651 micron for the measurement of atmospheric methane profiles on an airborne platform is developed. The detection technique is based on two-tone frequency modulation spectroscopy. The calibration procedure for the analyser with respect to pressure changes during the flight mission is also discussed.

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.

In the present paper a Lidar (light detection and ranging) system is described. It allows high-speed data acquisition of Lidar signals and meteorological parameters by means of standard instrumentation. The Lidar, controlled by a computer, utilized two laser sources (Nd: Yag and ruby), a modified Ricthey-Chretien telescope and signal detection, storage and real-time monitoring equipment. The whole system was installed in a container for field experiments.