Direct solar irradiance and IR atmospheric radiance have been measured during different measurements campaigns,
conducted in three mountain sites in Italy, far from anthropogenic sources. Direct solar irradiance has been measured by
a high resolution (1.5 nm) AVANTES radiometer, working in the spectral range 400 nm-900 nm, while down welling
IR sky radiance measurements has been measured by an MR100 BOMEM Fourier Transform Spectrometer covering the
spectral ranges 500 cm-1-5000 cm-1 and 1 cm-1 of resolution. At least two Radiosonde launches per day furnished
temperature and water vapour profiles. The instruments were located on a mobile laboratory, specifically projected to
host them. The parameters obtained from direct solar irradiance are Aerosol Optical Depth, Angstrom parameters and
Aerosol Size Distributions retrieval, while from IR data water vapour and temperature profiles have been retrieved.
Different orographic characteristics and different air-masses circulation on the measurement sites influenced Aerosol
Optical Depth values and variation. Infrared radiances inversion allows the water vapour content retrieval and a
correlation between aerosol effective radii and water vapour content has been looked for.
The international experiment EAQUATE (European AQUA Thermodynamic Experiment) was held in September 2004 in Italy and in the United Kingdom. The Italian phase, performed in the period 6-10 September 2004, was mainly devoted to assessment and validation of performances of new IR hyperspectral sensors and benefits from data and results of measurements of AQUA and in particular of AIRS. It is also connected with the preparatory actions of MetOp mission with particular attention to calibration and validation of IASI products (as water vapour and temperature profiles), characterization of semitransparent clouds and study of radiative balance, demonstrating the role of ground-based and airborne systems in validation operations.
The Italian phase of the campaign was carried out within a cooperation between NASA Langley Research Center, University of Wisconsin, the Istituto di Metodologie per l'Analisi Ambientale (CNR-IMAA), the Mediterranean Agency for Remote Sensing (MARS) and the Universities of Basilicata, Bologna and Napoli. It involved the participation of the Scaled Composites Proteus aircraft (with NAST thermal infrared interferometer and microwave radiometer, the Scanning HIS infrared interferometer, the FIRSC far-IR interferometer), an Earth Observing System-Direct Readout Station and several ground based instruments: four lidar systems, a microwave radiometer, two infrared spectrometers, and a ceilometer. Radiosonde launches for measurements of PTU and wind velocity and direction were also performed as ancillary observations. Four flights were successfully completed with two different AQUA overpasses. The aircraft flew over the Napoli, Potenza and Tito Scalo ground stations several times allowing the collection of coincident aircraft and in- situ observations.
KEYWORDS: Interferometers, Sensors, Fourier transforms, Signal to noise ratio, Spectroscopy, Calibration, Signal detection, Pyroelectric detectors, Far infrared, Space operations
In the framework of the Radiation Explorer in the Far InfraRed space mission for the characterization in the far infrared of the Earth outgoing emission, a breadboard version of the Fourier transform spectrometer, which is the core instrument of the payload package, has been developed. The Fourier transform spectrometer operates in the spectral range of 100-1100 cm-1 with a resolution of 0.5 cm-1, 6.5 s acquisition time, and signal-to-noise ratio better than 100. It is a compact prototype designed both for laboratory applications and for field campaigns, in particular for operations in high-altitude ground-based sites and on-board of stratospheric balloon platforms.
This paper describes the instrument characterization performed in laboratory conditions and under vacuum. The study has allowed to study the trade-off among all the instrument parameters and to test the new optical design of the interferometer, with particular attention to the photolithographic beam splitters and the room-temperature pyroelectric detectors.
The instrument was operated for the first time in a field campaign in June 2004 from 1247~m altitude ground-based site located in the South of Italy. The results of this test and the comparison with the measurements taken with a BOMEM spectrometer, that partially overlaps the REFIR bandwidth in the higher spectral region, are reported. Info can be found at http://radiation.ifac.cnr.it.
An intensive aerosol and water vapour measurement campaign, started on June 2002, is in progress at IMAA in Tito Scalo (PZ) (Southern Italy, 40°36'N, 15°44'E, 820 m above sea level) in the frame of the validation program of ENVISAT. Systematic measurements, using both active and passive ground based instruments, will be performed for a period of 12 months, in coincidence with ENVISAT overpasses. A Raman lidar system is used to perform both aerosol and water vapour measurements; aerosol backscatter and extinction coefficients are retrieved from simultaneous elastic signals at 355 nm and inelastic N2 Raman backscatter lidar signals at 386.6 nm, whereas, water vapour mixing ratio measurements are retrieved from simultaneous H2O and N2 Raman signals. A sun-photometer based on a Mechelle spectrometer is used to measure direct solar irradiance in the wavelength range 300 ÷ 1100 nm and a Fourier infrared spectrometer is used to measure vertical sky radiance in the range 500 ÷ 3000 cm-1. All the observations are complemented with radio-sonde launches. Two measurements per week are scheduled for the first six months of the validation campaign, while one measurement per week is scheduled for the last six months. First results of the measurement campaign are presented.
A comparison between simulated data and measurements performed by means of a spectroradiometer has been done. We searched a correlation between Aerosol Optical Depth, measured the over a wide spectral range, and TOMS Aerosol Index, which is satellite retrieved. This comparison has been done for both desertic aerosol (measurements taken in Namibia, 1998) and rural aerosol (measurements realized in Southern Italy, 2000 and 2001). At the same time, the simulation code MODTRAN has been used, in order to obtain both synthetic Aerosol Optical Depth and Aerosol Index. Finally, we compared measured and simulated correlation, finding, a good agreement for desertic aerosol.
Direct solar radiation measurements were performed both in a moderately polluted location of Southern Italy. We use a spectro- photo-radiometer covering the range 400nm-110nm, with a resolution of 3nm, to obtain the aerosol optical depth. We use this data to compare two inversion techniques to deduce the aerosol size distribution.
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