Carmine Serio

Global Solar Radiation Estimation from Relative Sunshine Hours in Italy

Abstract We examine the existing measurements of global solar radiation and sunshine duration for Italy, and evaluate the errors made in estimating global solar radiation from sunshine hours measurements. We find that the Angstrom–Black linear relation in the form F/Fext = 0.23 + 0.37n/N can be used to predict global solar radiation over all of Italy with a relative error of ∼10%; whereas, if the average value of F/Fext for all stations is used as a simple predictor, the relative error turns out to be ∼15%.

Feasibility of the spaceborne radiation explorer in the far infrared (REFIR)

The REFIR (Radiation explorer in the far infrared) project is a study, funded by European Union, of feasibility of a novel space-borne instrument that will measure the atmospheric spectral radiance of the Earth in the broad spectral range 100-1100 cm-1 from space with sufficient spectral resolution (0.5 cm-1) and signal-to-noise ratio (SNR > 100). The main scientific objectives of the REFIR experiment are the measurement of the outgoing FIR radiation at the top of the atmosphere and the improvement of our knowledge of the principal drivers of this flux, e.g. temperature structure, water vapor, and clouds throughout the troposphere-surface system. The REFIR concept consists of a far infrared Fourier transform spectrometer (FTS) as the core instrument, of an embedded imager operating in an infrared window, sharing the same bore-sight as FTS, for scene/cloud signature identification in the FIR, of an add-on imager to provide multi-channel imagery, and of an absolute single-pixel radiometer with a single broad-band channel, used to measure the emitted radiation contextually with the spectral measurements. The integration of all the systems leads to a very compact satellite instrumentation, working at room temperature, with an estimated overall mass of 70 kg and a power consumption of 80 W, including electronics. The overall data rate toward the ground station is foreseen to be of 170 kbps before on-board data compression. This work highlights the main technical results at the end of phase-B0 study. The technical solutions adopted for the instrument are outlined and an accurate analysis of performances is shown.

Statistical Predictability and Parametric Models of Daily Ambient Temperature and Solar Irradiance: An Analysis in the Italian Climate

Abstract Stochastic–dynamic models are discussed for both air temperature and solar irradiance daily time series in the Italian climate. Most of the methodologies discussed in this paper are well known and established for processes having a Gaussian distribution. However, a technique is presented that allows statistical inferences for non-Gaussian processes. Applying these models to 20-year time series, their predictability is analyzed for five meteorological stations of the Areonautica Militare Italiana. The following results were obtained: 1) the seasonalities in both the mean and the standard deviations of measured data are well fitted by simple periodic models; 2) the short range statistical fluctuations of the analyzed variables are well described by first order autoregressive processes whose parameters have constant values for all five stations. For the sake of brevity results are presented only for one station (Napoli).

Cloud Clearing of Infrared Sounder Radiances

Abstract The paper compares the performance of three different schemes for computing clear-sky brightness temperature from cloud-affected measurements. Both the ability to detect clouds and to estimate the equivalent clear-sky brightness temperature are examined. Simulated brightness temperatures computed from the ECMWF operational analysis are used as a reference, together with Advanced Very High Resolution Radiometer (AVHRR)-derived sea surface temperature and cloud content within High-Resolution Infrared Radiation Sounder (HIRS) fields of view. Cloud masks obtained from the cloud-detection schemes are compared with cloud masks obtained from AVHRR data; clear-column brightness temperatures for HIRS/2 channels 4, 7, and 13 are compared with the simulated ones; simulated clear-column brightness temperatures in the HIRS/2 window channel 8 are validated with equivalent products from AVHRR data. The comparison highlights some problems in the operational implementation of the NESDIS cloud-clearing scheme and ...

Assessing the impact of radiometric noise on IASI performances

Abstract The performances of the Infrared Atmospheric Sounding Interferometer (IASI) which is under development at the aboratories of the French National Space Agency and Italian National Space Agency have been evaluated. An error analysis has been carried out on the basis of the expected radiometric noise. To this end, a linear form of the radiative transfer equation has been formulated for the direct and simultaneous estimation of temperature, water vapour and ozone profiles.

An Advanced Optimal Spectral Estimation Algorithm in Fourier Spectroscopy with Application to Remote Sensing of the Atmosphere

Remote sensing of the atmosphere from satellite to improve numerical weather prediction demands objective data handling methods, as the effectiveness of satellite data ultimately rests on our ability to process the data in real time. In this paper a procedure to recover high-resolution spectra from infrared Fourier spectrometer data is presented. The technique relies on the generalized cross-validation criterion and retains all the computational characteristics that are proper to the fast Fourier transform. The procedure yields adaptive apodizing functions that improve the convergence of the Fourier transform. Numerical examples are carried out using synthetic spectra computed by a high-resolution radiative transfer code. The effect of additive noise is also analyzed. The application of the technique to remote sensing of the atmosphere is discussed. Although our applications of the method emphasize the problem of recovering radiance spectra from interferogram signals, the procedure also applied in a general context, for example, to the estimation of variance spectra of stochastic processes from their autocovariance functions. 14 refs., 5 figs., 4 tabs.

A three-step cloud clearing procedure for infrared sounder measurements

Abstract A new cloud clearing procedure applied to High-resolution Infrared Radiation Sounder (HIRS/2) radiance measurements is presented, based on knowledge of the typical statistical features of both clear and cloud contaminated radiance fields and on the application of some well known techniques for the statistical handling of data. The procedure consists of three sequential steps. In the first, the clear sky latitudinal gradient is restored using statistical correlation among HIRS/2 and MSU measurements. In the second step the scene variability (i.e. the dynamics along the longitudinal gradient) is retrieved by a discrete Fourier developments and a recursive Kalman filter. Finally, the characteristic smoothness of clear fields is introduced using a low-pass filter (third step). Applications of the whole filtering technique to measured HIRS/2 channel 5, 6 and 7 brightness temperatures are discussed and its performance is checked by comparing sets of filtered and stimulated data.

Solar direct irradiance at the ground: A parametric approach

Abstract A parametric model, giving the solar direct irradiance at the ground, using as input parameters the precipitable water vapour and the optical thickness of particulate matter is presented. The validity of the parametrization is tested against a spectral model checked during field studies.

Sensitivity of broadband and spectral measurements of outgoing radiance to changes in water vapor content

Broad band radiance measurements at top of the atmosphere are simulated using two diverse line-by-line codes for a number of standard atmospheric conditions to evaluate the sensitivity of broad band spectral and spectrally integrated radiometry to realistic changes of water vapor content in the troposphere and of other parameters of climatic significance. . It is shown that the rotational band is very sensitive to realistic changes in upper tropospheric water vapor. Moreover our ability to retrieve middle and upper troposphere H2O is enhanced if spectral measurements in the water vapor rotational band are compared to measurements in the strong 6.3 micrometers vibrational band, which has been used exclusively since the early 1970s.

Spectral estimates in Fourier spectroscopy applied to remote sensing of the atmosphere: a parametric autoregressive modelling approach

Abstract A procedure to recover high resolution spectra without any intervening window from infrared Fourier spectrometer data is presented. The technique relies on the maximum entropy principle in information theory. A parametric autoregressive modelling approach is used. Numerical examples are carried using synthetic spectra computed by an high resolution radiative transfer code. The effect of additive noise is also analysed. The application of the technique to remote sensing of the atmosphere is discussed.