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There is a growing interest in the far infrared spectral region 17–50 μm as a remote sensing tool in atmospheric sciences, since this portion of the spectrum contains the characteristic molecular rotational band for water vapour. Much of the Earth energy lost to space is radiated through this spectral region. The Radiation Explorer in the Far InfraRed Breadboard (REFIR/BB) spectrometer was born because of the quest to make observations in the far infrared. REFIR/BB is a Fourier Transform Spectrometer with a sampling resolution of 0.5 cm −1 and it was tested for the first time in the field to check its reliability and radiometric performance. The field campaign was held at Toppo di Castelgrande (40° 49′ N, 15° 27′ E, 1258 m a. s. l.), a mountain site in South Italy. The spectral and radiometric performance of the instrument and initial observations are shown in this paper. Comparisons to both (1) BOMEM MR100 Fourier Transform spectrometer observations and (2) line-by-line radiative transfer calculations for selected clear sky are presented and discussed. These comparisons (1) show a very nice agreement between radiance measured by REFIR/BB and by BOMEM MR100 and (2) demonstrate that REFIR/BB accurately observes the very fine spectral structure in the water vapour rotational band.

A simple and compact parallelogram mirror drive based on flexure pivots suitable for intermediate resolution Fourier transform spectroscopy is presented. The system permits 12 mm of mirror translation with a residual tilt of less than ±0.4 mrad in the horizontal plane and ±0.2 mrad in the vertical plane. A system prototype was built and fully characterized for a Fourier transform spectrometer operating on a stratospheric balloon.

The measurement of thermal and mechanical properties of materials at cryogenic temperatures gains more and more importance in the field of the application of novel high-tech materials to aerospace industry and in developing scientific instrumentation. We present a simple and inexpensive interferometric dilatometer for the measurement of the thermal expansion of materials in the 4–300 K range. The dilatometer consists of a Michelson tilt-compensated interferometer in which the path difference is given by the variation in length of a sample enclosed in a 4 K cryostat. The compensation for misalignment permits a fast and simple operation routine that configures the instrument as a valuable tool for materials engineering.

The present work examines downwelling radiance spectra measured at the ground during 2013 by a Far Infrared Fourier Transform Spectrometer at Dome C, Antarctica. A tropospheric backscatter and depolarization lidar is also deployed at same site, and a radiosonde system is routinely operative. The measurements allow characterization of the water vapor and clouds infrared properties in Antarctica under all sky conditions. In this paper we specifically discuss cloud detection and the analysis in clear sky condition, required for the discussion of the results obtained in cloudy conditions. First, the paper discusses the procedures adopted for the quality control of spectra acquired automatically. Then it describes the classification procedure used to discriminate spectra measured in clear sky from cloudy conditions. Finally a selection is performed and 66 clear cases, spanning the whole year, are compared to simulations. The computation of layer molecular optical depth is performed with line-by-line techniques and a convolution to simulate the Radiation Explorer in the Far InfraRed-Prototype for Applications and Development (REFIR-PAD) measurements; the downwelling radiance for selected clear cases is computed with a state-of-the-art adding-doubling code. The mean difference over all selected cases between simulated and measured radiance is within experimental error for all the selected microwindows except for the negative residuals found for all microwindows in the range 200 to 400 cm−1, with largest values around 295.1 cm−1. The paper discusses possible reasons for the discrepancy and identifies the incorrect magnitude of the water vapor total absorption coefficient as the cause of such large negative radiance bias below 400 cm−1.

A ground based FT spectroradiometer with a 5-100 mm spectral range, room temperature detectors, low power consumption and a robust optical and electronic design is operating continuously from the Concordia Station, Antarctica. © 2014 Optical Society of America

The calibration procedure applied to the wideband REFIR-PAD infrared spectrometer is described along with the results obtained in ground-based campaigns performed since 2009 from high-altitude sites in extremely dry air conditions.

In Fourier transform spectroscopy (FTS), nonlinearity amplitude distortions in the interferograms are mainly due to detector. In the case of photoconductive detectors, as for instance, the semiconductor Mercury-Cadmium-Telluride detector (MCT), that is the detector most frequently employed for high-performance infrared measurements, the nonlinearities have been often discussed in the literature. For other infrared detectors, such as bolometers, the effect is not studied with equal attention; nevertheless, also with these detectors some nonlinearity is expected to be present. Amplitude distortions in the interferogram induce, through Fourier transform, radiometric errors in the acquired spectra. In order to eliminate radiometric errors, the interferograms must be corrected before Fourier transformation, by using either a measurement or a model of the real response of the acquisition system. An assessment of nonlinearity errors in FTS can also be made after Fourier transformation using the harmonic features that are introduced in the measured spectra by the nonlinear response. Usually nonlinearity was detected by looking for a nonzero signal in the low-frequency region of the spectrum, where the spectral response should be equal to zero. This procedure may be difficult in presence of 1/f noise, that prevents an accurate identification of the low frequency feature. In this paper, a method for the detection and characterisation of small nonlinearity effects by way of an analysis of the amplitude of the second harmonic feature in the acquired spectral distribution is presented and discussed. The method is applied to real measurements obtained with a far IR interferometer with an 3He-cooled bolometric detector.

Fourier transform spectrometers (FTS), thanks to their intrinsic advantages of high throughput, high spectral resolution and multiplex acquisition of spectral channels, offer a powerful tool for the characterisation of the Earth's atmosphere. The use of photon noise limited detectors in FTS instruments operating in the middle/far infrared spectral region permits high sensitivity emission spectroscopy measurements, without the limitations arising from the use of an external radiation source. The wide operating spectral range of FTS instruments makes possible simultaneous detection of different atmospheric chemical species that show rotational and vibrational spectral bands in the middle/far infrared region. Spatially resolved measurements of the concentration of the interesting species are of fundamental interest in the study of local phenomena in atmospheric chemistry and physics, and can be obtained through the use of various observation and data inversion techniques. Among these, the best results in terms of vertical resolution are achieved through the limb sounding observation technique from airborne platform. As an example of possibilities offered by the above considered technique, results obtained from the SAFIRE-A (Spectroscopy of the Atmosphere using Far InfraRed Emission-Airborne) during the Antarctic campaign APE-GAIA (Airborne Polar Experiment-Geophysica Aircraft In Antarctica, Ushuaia, Argentina, September–October, 1999) are presented.

In an ideal Fourier transform spectrometer the measured spectrum is a scalar combination of two input sources, while, more generally, a vectorial combination occurs in a real instrument. The vectorial combination is caused by the absorption of the beamsplitter which introduces a deviation from π of the relative phase between the two input sources, as well as a third source. Moreover, the asymmetry of the beamsplitter can cause a frequency dependent phase delay adding complexity to the system. A general model of a Fourier transform spectrometer is presented and it is shown that such a complex behaviour can be characterized through the “composite phase parameter” of the beamsplitter. Furthermore, some general rules are identified that can be used to devise more efficient calibration procedures and strategies for the minimization of the distortions caused by the vectorial combination of the spectra.

We used Stycast 1266 in a high-pressure, low-temperature transducer. In order to ascertain the dependence of capacitance and loss on temperature, we measured the temperature behaviour of the dielectric constant and the dissipation factor of Stycast 1266 at 1 KHz between 0.07 and 300 K. We found a smooth decrease of the dielectric constant with decreasing T. The temperature dependence below 1 K is well explained by the tunneling model. The loss tangent showed very low values (always less than 5×10−5), with a peak around 260 K that can be ascribed to dielectric relaxation processes.

We report the most accurate measurement of the helium fine structure splitting. The $2^{3}P_{0}\ensuremath{-}2^{3}P_{1}$ energy splitting is $29616949.7\ifmmode\pm\else\textpm\fi{}2.0\mathrm{kHz}$. Laser saturation spectroscopy, heterodyne pure frequency determination, and fluorescence detection were combined in a novel experimental approach. The absence of external perturbing magnetic fields, used in earlier experiments, lends confidence to our determined value and allows us to discriminate between contradictory results previously reported. This result, when combined with expected advances in theory, should yield a new value of the fine structure $\ensuremath{\alpha}$, which may help clarify a presently puzzling experimental situation.

The accurate measurement of thermal expansion coefficient at low temperatures is fundamental in applications where a high mechanical stability is required over the complete procedure of cooling. Here we report on our measurement of thermal expansion of AISI 420 between 20 and 293 K, measured by an interferometric dilatometer. (C) 2014 Elsevier Ltd. All rights reserved.

This work presents the results concerning the analysis of a set of atmospheric emitted (down welling) spectral radiance observations in the spectral range 180 to 1100 cm(-1) acquired at the Dome-C site in Antarctica during an extensive field campaign in 2011-2012. The work has been mainly focused on retrieving and validating the coefficients of the foreign contribution to the water vapour continuum absorption, within a spectral range overlapping the water vapour rotational band. Retrievals have been performed by using a simultaneous physical retrieval procedure for atmospheric and spectroscopic parameters. Both day (summer) and night (winter) spectra have been used in our analysis. This new set of observations in the far infrared range has allowed us to extend validation and verification of state-of-art water vapour continuum absorption models down to 180 cm(-1). Results show that discrepancies between measurements and models are less than 10% in the interval 350-590 cm(-1), while they are slightly larger at wave numbers below 350 cm(-1). On overall, our study shows a good consistency between observations and state-of-art models and provides evidence toward needing to adjust absorptive line strengths. Finally, it has been found that there is a good agreement between the coefficients retrieved using either summer or winter spectra, which are acquired in far different meteorological conditions. (C) 2014 Optical Society of America

PPG invented and patented a technology for improving the corrosion resistance and the acoustical insulation of some critical parts of a vehicle as underbody and boxed parts. Such an invention, based on a thermoplastic polymeric composition containing heat activated swelling agents, has generated two main coating materials: an expandable underbody coating and a box section gap filler. The immediate performing advantages caused by using these innovative products are: (a) drastic weight reduction of employed materials; (b) remarkably good mechanical performance; (c) improved anticorrosion resistance; (d) increased acoustical insulation level. Together with such an excellent technical behavior, this new PPG technology represents a highly positive innovation also from environmental and toxicological viewpoints. Expandable underbody coating and box section gap filler, both with the common objective of helping create a more silent and durable vehicle, are perfectly integrated into the objectives of a Chemical Industry, i.e. those of proposing safe environment-friendly products safeguarding internal and external surroundings from hazardous materials.

[1] A field experiment was conducted in northern Chile at an altitude of 5.3 km to evaluate the accuracy of line-by-line radiative transfer models in regions of the spectrum that are typically opaque at sea level due to strong water vapor absorption. A suite of spectrally resolved radiance instruments collected simultaneous observations that, for the first time ever, spanned the entire terrestrial thermal spectrum (i.e., from 10 to 3000 cm 1 , or 1000 to 3.3 mm). These radiance observations, together with collocated water vapor and temperature profiles, are used to provide an initial evaluation of the accuracy of water vapor absorption in the farinfrared of two line-by-line radiative transfer models. These initial results suggest that the more recent of the two models is more accurate in the strongly absorbing water vapor pure rotation band. This result supports the validity of the Turner et al. (2012) study that demonstrated that the use of the more recent water vapor absorption model in climate simulations resulted in significant radiative and dynamical changes in the simulation relative to the older water vapor model. Citation: Turner, D. D., et al. (2012), Ground-based high spectral resolution observations of the entire terrestrial spectrum under extremely dry conditions, Geophys. Res. Lett., 39, L10801

[1] The Radiation Explorer in the Far InfraRed-Prototype for Applications and Development (REFIR-PAD) spectroradiometer was operated from the Testa Grigia Italian-Alps station in March 2007 during the Earth Cooling by Water Vapour Radiation (ECOWAR) measurement campaign, obtaining downwelling radiance spectra in the 100–1100 cm−1 range, under clear-sky conditions and in the presence of cirrus clouds. The analysis of these measurements has proven that the instrument is capable of determining precipitable water vapor with a total uncertainty of 5–7% by using the far-infrared rotational band of water. The measurement is unaffected by the presence of cirri, whose optical depth can be instead retrieved as an additional parameter. Information on the vertical profiles of water vapor volume mixing ratio and temperature can also be retrieved for three altitude levels. The ability to measure the water vapor column with a simple, uncooled instrument, capable of operating continuously and with a time resolution of about 10 min, makes REFIR-PAD a very valuable instrument for meteorological and climatological studies for the characterization of the water vapor distribution.

The REFIR-PAD spectroradiometer is based on a misalignment-compensated Mach-Zehnder design with Ge-coated Mylar beamsplitters and uncooled pyroelectric detectors for broadband, room-temperature operation in the mid/far-infrared range.

Fourier transform emission spectroscopy can make an important contribution in the observation of the Earth's atmosphere and in the investigation of atmospheric physics and chemistry. In this paper, we report the measurement performances and the result obtained by a Fourier transform spectrometer, named SAFIRE-A (Spectroscopy of the Atmosphere using Far Infrared Emission - Airborne), operating in the far infrared spectral region from limb sounding observation of the atmospheric emission from a high altitude aircraft. After a short review of the advantages of FTS emission limb sounding in comparison with competing techniques and observation geometries, a detailed description of the instrument is given with the result obtained during the APE-GAIA (Airborne Polar Experiment - Geophysica Aircraft In Antarctica) fi eld campaign carried out over the Antarctic Peninsula.

In this study we present an intercomparison of measurements of very low water vapor column content obtained with a Ground‐Based Millimeter‐wave Spectrometer (GBMS), Vaisala RS92k radiosondes, a Raman Lidar, and an IR Fourier Transform Spectrometer. These sets of measurements were carried out during the primary field campaign of the ECOWAR (Earth COoling by WAter vapor Radiation) project which took place on the Western Italian Alps from 3 to 16 March, 2007.

The measurement of the Earth’s atmospheric emission spectrum is fundamental for the study of the global radiation budget. Up to now, this measurement has typically been limited to the mid‐infrared region because of the technological limitations of space‐borne spectrometers operating in the far infrared (FIR). The uncovered region of the FIR is however very important because most of the radiative cooling of the atmosphere, due to the strong rotational band of water vapor, occurs here.The REFIR‐PAD (Radiation Explorer in the Far InfraRed—Prototype for Applications and Development) instrument is a completely uncooled Fourier transform spectrometer that allows to perform the spectrally resolved measurement of the entire atmospheric emission spectrum including the FIR region with a spectral resolution of 0.5 cm−1. REFIR‐PAD was deployed in June 2005 on board a stratospheric balloon to perform the nadir‐looking spectral measurement of the outgoing longwave radiation in the tropics, near Teresina (North‐East Bra...

During the ECOWAR (Earth Cooling by Water vapor Radiation) measurement campaign, held in March, 2007 from the Testa Grigia station on the italian-swiss Alps, the REFIR-PAD (Radiation Explorer in the Far-InfraRed - Prototype for Applications and Development) spectroradiometer performed spectrally resolved measurements of the downwelling atmospheric radiance in the 100 _ 1100 cm_1 spectral range, with a resolution of 0.5 cm_1 . Measurements were performed both in clear sky conditions and in presence of cirrus clouds, with total columnar water vapor values ranging from 0.5 to 3 mm. The measured spectra were analyzed through a least _ 2 data fitting procedure based on the MINUIT minimization routine and the LBLRTM version 11.3 forward model, providing integrated water vapor content, cloud optical density and information on vertical water vapor and temperature profiles. Fitting residuals from the data analysis process show significant features in the 300 _ 600 cm_1 region, that are well above measurement uncertainty, giving a hint on possible refinements both in the water vapor continuum model and spectroscopy.

Diode lasers offer a lightweight, rugged, and economic alternative to other types of laser source, but they often do not provide long-term stability and spectral purity of emission. We have developed a stabilized, near-infrared diode laser source that is capable of as much as 20 mW of single-mode output power for the effective replacement of a He-Ne laser in the path difference measuring system of a high-resolution (1.25-m maximum path difference) Fourier transform spectrometer. Laser characterization has been performed both in laboratory measurements and in flight tests, resulting in a relative frequency stability of better than 10(-6) on a 6-h flight.

The outgoing long-wave radiation from the Earth's atmosphere in the far infrared spectral region is mostly unexplored, while is well recognized that the water vapour contribution to greenhouse trapping is dominant in this region. The Radiation Explorer in the Far InfraRed (REFIR) study has proven the feasibility of a space-borne Fourier transform spectrometer able to perform the measurement in the 100–1100 cm−1 range with a resolution of 0.5 cm−1. Following this work a prototype of the spectrometer named REFIR-PAD (Prototype for Applications and Development) has been developed to observe the atmospheric radiance from both ground-based sites and from stratospheric balloon platforms. In this work we describe the REFIR-PAD level 1 data analysis procedure, that, starting from raw instrumental data produces the calibrated atmospheric spectral radiance. Performances of the procedure are also described.

The spectroscopy of the constituents of the Earth's atmosphere that are active in the far infrared spectral region, among which the water vapour is the main one, has been validated through the analysis of wide-band nadir-looking spectra acquired with the Radiation Explorer in the Far Infrared—Prototype for Applications and Development (REFIR-PAD) Fourier transform spectroradiometer. The spectra, covering from 100 to 1400 cm - 1 with a 0.475 cm - 1 unapodized resolution, were acquired during a balloon flight performed in a tropical region in 2005. Atmospheric variables, namely water vapour and temperature vertical profiles, were retrieved from the REFIR-PAD data, and the residuals of the fitting are here critically analysed for the search of systematic effects that can be ascribed to spectroscopic errors. In the spectral interval between 150 and 600 cm - 1 nosignificant inconsistency is detected between the residuals and the measurement uncertainty, proving the good quality of the radiative transfer model and of the HITRAN 2004 spectroscopic database. Significant difference are instead observed when the HITRAN 2000 database is used.

The paper presents a novel methodology to retrieve the foreign-broadened water vapor continuum absorption coefficients in the spectral range 240 to 590 cm(-1) and is the first estimation of the continuum coefficient at wave numbers smaller than 400 cm(-1) under atmospheric conditions. The derivation has been accomplished by processing a suitable set of atmospheric emitted spectral radiance observations obtained during the March 2007 Alps campaign of the ECOWAR project (Earth COoling by WAter vapor Radiation). It is shown that, in the range 450 to 600 cm(-1), our findings are in good agreement with the widely used Mlawer, Tobin-Clough, Kneizys-Davies (MT_CKD) continuum. Below 450 cm(-1) however the MT_CKD model overestimates the magnitude of the continuum coefficient. (C) 2008 Optical Society of America

This paper presents the project Earth Cooling by Water Vapor Radiation, an observational programme, which aims at developing a database of spectrally resolved far infrared observations, in atmospheric dry conditions, in order to validate radiative transfer models and test the quality of water vapor continuum and line parameters. The project provides the very first set of far-infrared spectral downwelling radiance measurements, in dry atmospheric conditions, which are complemented with Raman Lidar-derived temperature and water vapor profiles. Citation: Bhawar, R., et al. (2008), Spectrally resolved observations of atmospheric emitted radiance in the H2O rotation band.

Our understanding of global warming depends on the accuracy with which the atmospheric components that modulate the Earth's radiation budget are known. Many uncertainties still exist on the radiative effect of water in the different spectral regions, among which the far infrared where few observations have been made. An assessment is shown of the atmospheric outgoing flux obtained from a balloon-borne platform with wideband spectrally resolved nadir measurements at the top-of-atmosphere over the full spectral range, including the far infrared, from 100 to 1400 cm?1, made by a Fourier transform spectrometer with uncooled detectors. From these measurements, we retrieve 15 pieces of information about water vapour and temperature profiles, and surface temperature, with a precision of 5% for the mean water vapour profile and a major improvement of the upper troposphere-lower stratosphere knowledge. The retrieved atmospheric state makes it possible to calculate the emitted radiance as a function of the zenith angle and to determine the outgoing radiation flux, proving that spectrally resolved observations can be used to derive accurate information on the integrated flux. While the retrieved temperature is in good agreement with ECMWF analysis, the retrieved water vapour profile differs significantly, and, depending on time and location, the derived flux differs in the far infrared (0?600 cm?1) from that derived from ECMWF by 2?3.5 W/m2±0.4 W/m2. The observed discrepancy is larger than current estimates of radiative forcing due to CO2 increases since pre-industrial time. The error with which the flux is determined is caused mainly by calibration uncertainties while detector noise has a negligible effect, proving that uncooled detectors are adequate for top of the atmosphere radiometry.

Observations of very low amounts of precipitable water vapor ( PWV) by means of the Ground- Based Millimeter wave Spectrometer ( GBMS) are discussed. Low amounts of column water vapor ( between 0.5 and 4 mm) are typical of high mountain sites and polar regions, especially during winter, and are difficult to measure accurately because of the lack of sensitivity of conventional instruments to such low PWV contents. The technique used involves the measurement of atmospheric opacity in the range between 230 and 280 GHz with a spectral resolution of 4 GHz, followed by the conversion to precipitable water vapor using a linear relationship. We present the intercomparison of this data set with simultaneous PWV observations obtained with Vaisala RS92k radiosondes, a Raman lidar, and an IR Fourier transform spectrometer. These sets of measurements were carried out during the primary field campaign of the Earth Cooling by Water vapor Radiation ( ECOWAR) project which took place at Breuil- Cervinia ( 45.9 degrees N, 7.6 degrees E, elevation 1990 m) and Plateau Rosa ( 45.9 degrees N, 7.7 degrees E, elevation 3490 m), Italy, from 3 to 16 March 2007. GBMS PWV measurements show a good agreement with the other three data sets exhibiting a mean difference between observations of similar or equal to 9%. The considerable number of data points available for the GBMS versus lidar PWV correlation allows an additional analysis which indicates negligible systematic differences between the two data sets.

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.

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), on-board the European ENVIronmental SATellite (ENVISAT) launched on 1 March 2002, is a middle infrared Fourier Transform spectrometer measuring the atmospheric emission spectrum in limb sounding geometry. The instrument is capable to retrieve the vertical distribution of temperature and trace gases, aiming at the study of climate and atmospheric chemistry and dynamics, and at applications to data assimilation and weather forecasting. MIPAS operated in its standard observation mode for approximately two years, from July 2002 to March 2004, with scans performed at nominal spectral resolution of 0.025 cm−1 and covering the altitude range from the mesosphere to the upper troposphere with relatively high vertical resolution (about 3 km in the stratosphere). Only reduced spectral resolution measurements have been performed subsequently. MIPAS data were re-processed by ESA using updated versions of the Instrument Processing Facility (IPF v4.61 and v4.62) and provided a complete set of level-2 operational products (geo-located vertical profiles of temperature and volume mixing ratio of H2O, O3, HNO3, CH4, N2O and NO2) with quasi continuous and global coverage in the period of MIPAS full spectral resolution mission. In this paper, we report a detailed description of the validation of MIPAS-ENVISAT operational ozone data, that was based on the comparison between MIPAS v4.61 (and, to a lesser extent, v4.62) O3 VMR profiles and a comprehensive set of correlative data, including observations from ozone sondes, ground-based lidar, FTIR and microwave radiometers, remote-sensing and in situ instruments on-board stratospheric aircraft and balloons, concurrent satellite sensors and ozone fields assimilated by the European Center for Medium-range Weather Forecasting. A coordinated effort was carried out, using common criteria for the selection of individual validation data sets, and similar methods for the comparisons. This enabled merging the individual results from a variety of independent reference measurements of proven quality (i.e. well characterized error budget) into an overall evaluation of MIPAS O3 data quality, having both statistical strength and the widest spatial and temporal coverage. Collocated measurements from ozone sondes and ground-based lidar and microwave radiometers of the Network for the Detection Atmospheric Composition Change (NDACC) were selected to carry out comparisons with time series of MIPAS O3 partial columns and to identify groups of stations and time periods with a uniform pattern of ozone differences, that were subsequently used for a vertically resolved statistical analysis. The results of the comparison are classified according to synoptic and regional systems and to altitude intervals, showing a generally good agreement within the comparison error bars in the upper and middle stratosphere. Significant differences emerge in the lower stratosphere and are only partly explained by the larger contributions of horizontal and vertical smoothing differences and of collocation errors to the total uncertainty. Further results obtained from a purely statistical analysis of the same data set from NDACC ground-based lidar stations, as well as from additional ozone soundings at middle latitudes and from NDACC ground-based FTIR measurements, confirm the validity of MIPAS O3 profiles down to the lower stratosphere, with evidence of larger discrepancies at the lowest altitudes. The validation against O3 VMR profiles using collocated observations performed by other satellite sensors (SAGE II, POAM III, ODIN-SMR, ACE-FTS, HALOE, GOME) and ECMWF assimilated ozone fields leads to consistent results, that are to a great extent compatible with those obtained from the comparison with ground-based measurements. Excellent agreement in the full vertical range of the comparison is shown with respect to collocated ozone data from stratospheric aircraft and balloon instruments, that was mostly obtained in very good spatial and temporal coincidence with MIPAS scans. This might suggest that the larger differences observed in the upper troposphere and lowermost stratosphere with respect to collocated ground-based and satellite O3 data are only partly due to a degradation of MIPAS data quality. They should be rather largely ascribed to the natural variability of these altitude regions and to other components of the comparison errors. By combining the results of this large number of validation data sets we derived a general assessment of MIPAS v4.61 and v4.62 ozone data quality. A clear indication of the validity of MIPAS O3 vertical profiles is obtained for most of the stratosphere, where the mean relative difference with the individual correlative data sets is always lower than ±10%. Furthermore, these differences always fall within the combined systematic error (from 1 hPa to 50 hPa) and the standard deviation is fully consistent with the random error of the comparison (from 1 hPa to ~30–40 hPa). A degradation in the quality of the agreement is generally observed in the lower stratosphere and upper troposphere, with biases up to 25% at 100 hPa and standard deviation of the global mean differences up to three times larger than the combined random error in the range 50–100 hPa. The larger differences observed at the bottom end of MIPAS retrieved profiles can be associated, as already noticed, to the effects of stronger atmospheric gradients in the UTLS that are perceived differently by the various measurement techniques. However, further components that may degrade the results of the comparison at lower altitudes can be identified as potentially including cloud contamination, which is likely not to have been fully filtered using the current settings of the MIPAS cloud detection algorithm, and in the linear approximation of the forward model that was used for the a priori estimate of systematic error components. The latter, when affecting systematic contributions with a random variability over the spatial and temporal scales of global averages, might result in an underestimation of the random error of the comparison and add up to other error sources, such as the possible underestimates of the p and T error propagation based on the assumption of a 1 K and 2% uncertainties, respectively, on MIPAS temperature and pressure retrievals. At pressure lower than 1 hPa, only a small fraction of the selected validation data set provides correlative ozone data of adequate quality and it is difficult to derive quantitative conclusions about the performance of MIPAS O3 retrieval for the topmost layers.

[1] HNO3 profiles measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument operating on the Envisat satellite are validated with balloon measurements. An agreement of ±5% is obtained. The two measurements observe HNO3 features in different spectral regions (vibration spectra in the middle infrared and rotation spectra in the far infrared, respectively) and the agreement is obtained after that significant upgradings are made to the spectroscopic database. A stringent test of our understanding of HNO3 spectroscopy for remote sensing measurements is obtained.

The REFIR-PAD (Radiation Explorer in the Far InfraRed - Prototype for Applications and Development) Fourier transform spectroradiometer has successfully performed, at the end of June, 2005, a stratospheric balloon flight from Teresina, Brazil. The instrument has provided 8 hours worth of nadir-looking spectra acquired with a resolution of 0.5 cm -1 in the 100 to 1400 cm -1 spectral range, thus covering both the far-infrared range. containing the radiative signature of the upper tropospheric water vapour, and the better-known mid-infrared range, which provides validation with existing instruments. From the analysis of the calibrated spectra we obtain valuable information on the contribution to the Earth's outgoing long-wave radiation of water, both in the vapour and cloud form, in a region of the atmosphere, the upper-troposphere/lower-stratosphere, in which this contribution has a critical role.

The first spectral measurement of Earth’s emitted radiation to space in the widebandrange from 100 to 1400cm −1 with 0.5cm −1 spectral resolution is presented. The mea-surement was performed from a stratospheric balloon in tropical region using a Fourier 5 transform spectrometer, during a field campaign held in Brazilin June2005. The instru-ment, which has uncooled components including the detector module, is a prototypedeveloped as part of the study for the REFIR (Radiation Explorer in the Far InfraRed)space mission. This paper shows the results of the field campaign with particular atten-tion to the measurement capabilities of the prototype. The results are compared with 10 measurements taken by IASI-balloon (Infrared Atmospheric Sounding Interferometer –Balloon version), aboard the same platform, and with forward model estimations. Theinfrared signature of clouds is observed in the measurements. 1 Introduction The observation of the upwelling emission in the full relevant spectral range, from the

A balloon-borne wide-band Fourier transform spectrometer named REFIR-PAD (Radiation Explorer in the Far InfraRed, Prototype for Applications and Development) has been developed at CNR-IFAC to perform the characterisation of the Earth's outgoing long-wave radiation in the far-infrared region. The spectroscopic characterisation of this region is expected to increase greatly our level of knowledge of the radiative effects of water content in the upper troposphere. The REFIR-PAD instrument provides spectrally-resolved nadir-sounding radiance measurements in the 100-1400 cm-1 range, with a 0.5 cm-1 resolution, covering the most part of the Earth's long-wave emission and including both the far-infrared and the better known middle-infrared region. REFIR-PAD was flown as a piggy-back payload on the CNES IASI-LPMAA stratospheric balloon gondola in June 2005 from Teresina, Brazil. The data collected in this mission, will provide valuable information for the development of a future space mission aimed to the operational monitoring of the upper troposphere water vapour and clouds in order to identify their climate signatures.

During the 2002 environmental satellite Envisat mid-latitude validation campaign, a new upgraded configuration of the Infrared Balloon Experiment (IBEX) Fourier transform spectrometer, which had its first flight in 1978, performed a stratospheric balloon flight across the Mediterranean Sea. Among the substantial upgrades made to the instrument, the use of photon-noise-limited detectors permitted us to reach the theoretical limits in terms of signal-to-noise ratio. Also, important modifications were made to the interferometric system and electronics, such as the installation of a solid-state laser reference source and an onboard data recording system. During the flight, measurement of volume-mixing-ratio vertical profiles of O3, HNO3, N2O, and ClO from an altitude of approximately 38 km were performed with a vertical resolution of approximately 1.5 km.

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.

New measurement capabilities of the SAFIRE-A airborne spectrometer, based on a polarisation sensing optical scheme and suitable for investigation of aerosols and clouds properties, have been implemented and tested in a field campaign. The polarisation measuring configuration is described here with respect to the instrument layout for intensity measurements deployed in several scientific missions to study the chemistry and dynamics of the upper troposphere and lowermost stratosphere. First results of the novel experimental set-up, obtained during the APE-GAIA Antarctic campaign, are presented and discussed and possible measurement scenarios, relying on synergistic use of SAFIRE-A intensity and polarisation measuring modes, are envisaged for future applications.

The work presents measurements obtained with the multi-input spectroradiometer GASCOD/A4p, the Fourier transform far infrared interferometer SAFIRE-A and the two-channel chromatograph HAGAR, on board the M-55 Geophysica stratospheric aircraft during the APE-GAIA measurement campaign, held in September-October 1999 over the Antarctic Peninsula. The paper aims to investigate the gas mixing ratio distributions at the flight altitude, during a recovery phase of the reservoir species in the lower stratosphere in the Antarctic spring. Attention is focused on the daytime flight of 23 September, when the aircraft flew inside the vortex at two different altitudes (about 16.5 and 18.5 km). Concentration distributions were examined for NO2, N2O, O3, BrO, ClO, HCl, H2O and HNO3, during flight inside and outside the vortex. Simultaneous concentration measurements of HNO3 and H2O showed a denitrification but not dehydration inside the vortex core. The reformation of chlorine reservoirs is investigated. It was evident that the re-conversion of HCl was favoured in the Cl+CH4 branches, and its high mixing ratio up to 1 ppbv at 425 K surface confirms that low ozone air masses inside the vortex and strong sunlight greatly favour a more rapid formation of passive chlorine reservoirs.

An upgraded configuration of the SAFIRE-A Fourier transform far-infrared spectrometer was recently set up, and significant improvements in instrument performance were attained during several testing and scientific flights onboard the high-altitude research aircraft M55-Geophysica. New features were implemented in specific instrument subsystems, such as the pointing system, the reference laser interferometer, and the onboard calibration unit, to increase the overall instrument functionality and to obtain reliable operation from both the high-frequency (approximately 120 cm(-1)) and the low-frequency (approximately 23 cm(-1)) detection channels. Other changes, such as those made in the onboard recording system or in the postflight data-transfer procedure, were aimed at expanding the capability of unattended operation and at providing a user-friendly interface for data downloading and ground servicing. A detailed description of these modifications is given, along with a quantitative assessment of the SAFIRE-A instrument performance.

Materials used in the realization of supports for massive cryogenic detectors must have several properties which should be known down to the detector working temperature. This does not always happens, because of the difficulties in the measurement of material characteristics at very low temperatures. We studied the thermal properties of a Polypropylene copolymer (PP) at temperatures as close as possible to the working temperature (10 mK) of CUORE (Cryogenic Underground Observatory for Rare Events), in view of the possible use of PP in the realization of the supports for the TeO2 crystal absorbers (750g). From the data obtained we conclude that, from a thermal point of view, PP is adequate for use as support material in cryogenic massive detectors.

Bolometric infrared detectors are the best choice for sensitive radiometric measurements in the far infrared and millimeter wave spectral region. Nevertheless, these devices, when operating on board high-altitude balloons or aircrafts, are also affected by cosmic-ray crossing of the detector elements. Each of these events degrades the radiometric data on a time scale that depends on the detector's characteristics. In this paper, we describe an automatic procedure based on Discrete Wavelet Transform that can be used to localize cosmic-ray events in the data flow, even when they occur in correspondence with high signal levels, and to optimally remove them for minimum data loss.

Following the experience made on balloon platforms, a far infrared FT instruments for atmospheric studies has been designed for operation on aircraft platforms. Adopted technical choices and experienced problems are discussed.

In Fourier transform spectroscopy, path difference dependent misalignments, such as those due to imperfect mechanical movement of the scanning mirror, can be modelled as path difference dependent apodisation and phase errors. The theoretical model that relates the mirror drive characteristics to the path difference dependent error is used to verify the consistency of the optical instrument line shape with the measurements of the mechanical drive quality. This procedure can be used as a diagnostic and qualification tool.

We report frequency locking of a 1083-nm DBR diode laser on a high-finesse Fabry-Pérot cavity (ℱ ≃ 2800). We used the Pound-Drever FM locking scheme at a modulation rate of 5 MHz. A lock bandwidth of about 1 MHz is obtained by using a three-path servo loop. The laser linewidth is narrowed to ∼ 5 kHz. The root Allan variance σ(τ) of the laser frequency with respect to the cavity reaches a minimum of 4 ± 1 Hz at τ = 10 s. © Springer-Verlag 1998., This work was supported by the European Community contracts GE1*CT920046 and ERB FMGECT950017.

We have investigated atomic coherence effects in the ladder scheme of the triplet transitions 2S-2P-3S of helium. A powerful dressing laser at 706 nm in resonance with the 2P-3S transition induces a transparency on the 2S-2P transition at 1083 nm probed by a weak laser. We have characterised this induced transparency also known as Electromagnetically Induced Transparency (EIT), demonstrating the possibility of reaching 100% of bleaching. Also, we have evidenced the presence of the two photon effect on the EIT process by studying its dependence on the mutual probe-dress polarisation angle. With such a simple level scheme a quantitative comparison with the theory has been made possible and many of the predicted effects have been investigated. Furthermore, polarisation of the dressing laser field has allowed for the first time the study of the electromagnetically induced birefringence which causes a change in the probe laser polarization. The experiments were performed not only in the clean environment of a ...