Several different instruments are necessary to extract a full set of cloud properties, such as cloud boundaries, cloud optical thickness, particle size and particle phase. The sensor synergy used in this study is a combination of active and passive instruments. Both radiative and intrinsic cloud properties are extracted, and the relation between the two is studied for liquid water clouds. The experimental method for extracting IR emissivity (epsilon) form IR radiometer and lidar measurements will be explained. Cloud Liquid Water Path (LWP) can be extracted from the microwave radiometer. Comparing the two leads to a clear relation between (epsilon) and LWP in the case of liquid water clouds. This can be understood if one considers a simple approximation to the extinction efficiency of liquid water droplets in the IR, leading to an RI emissivity that solely depends on LWP, and not on the particle size distribution. Similar methods can be applied to space-based observations, such as combining LITE and Meteosat measurements to derive IR emissivity. First results are shown.

This work is a preliminary study of the viability of retrieving macro physical and micro physical cloud parameters from nighttime radiances provided by MODIS sensor, onboard Terra spacecraft. It is based on the analysis of the sensitivity of every MODIS IR band to each of the parameters that describe the different layers composing the earth-cloud-atmosphere system. IN order to make this analysis, an atmospheric radiative transfer model that makes use of the discrete ordinates method DISORT is employed. Multiple simulations are performed for a great variety of clouds and atmospheric conditions, taking into account the main absorbers in each band. As a first result, the more adequate bands for our purpose are select and, using these channels, the proposed method extracts the parameters characterizing the different layers through a numerical inversion of the radiative model based on an evolutionary method for solving optimization problems called scatter search. In addition, a sensitivity analysis is carried out in order to estimate the impact on the retrieved values of the uncertainties in model inputs and assumptions.

In low spatial resolution remote sensing the plane parallel albedo bias caused by sub-pixel cloud inhomogeneities leads to underestimation of cloud properties. RF Cahalan et al. Have suggested the effective thickness approximation as a method of correcting this bias, assuming a single parameter fractal cloud model.. The magnitude of the reduction factor applied to the optical depth in this method is dependent on the cloud fractal parameter, determined from spatial liquid water distribution. We present here a study using in situ aircraft liquid water measurements in northern Tasmania, Australia, to first locally determine the cloud fractal parameter in local conditions, and then to test the satellite retrieval of cloud properties using these results. Four categories of cloud with different fractal parameters are identified and the retrieval method showed encouraging results, with further testing and refinement required.

This study investigates the prospect of retrieving ice cloud properties using the far IR part of the outgoing longwave radiation spectrum. Ice optical properties in the far IR are such that ice clouds not only absorb but also scatter radiation. Thus, the far IR offers unique remote sensing opportunities for ice particle size and shape retrieval. Calculations of top of the atmosphere brightness temperatures are made at high spectral resolution for a variety of atmospheric profiles, cloud heights, particle size, and ice contents, and integrated over narrow spectral bands. We define two bands where the scattering effect is particularly obvious and compare their signals to the 11 micrometers band signal. The results indicate that the far IR is more sensitive to changes in particle size for optically thick ice clouds than is the IR window.

CLOUDS is a project co-funded by the EC under FP-4, conducted by 12 European partners, also cooperating with NOAA/ETL. It is the mission study of a monitoring satellite to perform measurements necessary to describe cloud-radiation interaction in operational models for climate and long-term weather prediction. Complementary to missions for process study, CLOUDS addresses the monitoring aspect. As such, it has to comply with requirements of sufficiently frequent observing cycle, and operational sustainability. This prevents using active systems and leads to consider passive radiometry only, however exploiting as much as possible of the em spectrum, with more polarizations and more viewing geometries. The paper reports on the effort to demonstrate that, by these means, the main ingredients of the cloud-radiation interaction mechanism may be observed with sufficient accuracy. The optimal channels are determined. Clouds, aerosol radiation and precipitation are observed under identical geometry with in a range of the em spectrum spanning from 340 nm to 4.3 cm, i.e. over five orders of magnitudes, for a true multi- spectral approach.

Accurate cloud detection is needed for many geophysical applications. Unfortunately, a significant source of residual error in such satellite-based products is undetected cloud. Here, a new computationally efficient cloud detection procedure for both daytime and nightime Advanced Very High Resolution Radiometer data is developed. It differs substantially from out prior related work. First, a new clustering procedure is used which produces very homogeneous and distinct clusters. Second, the input information vector is reduced in size, incorporates both radiance and spatial components and each components is normalized. Third, the enhanced performance makes possible the use of a multipass procedure which is very effective in identifying the complex multilayer cloud structures common in satellite data. Validation with independent lidar observations confirms the accuracy of the new procedure. Marine low stratiform clouds also are detected effectively.

Many uses of satellite data, including atmospheric sounding of temperature and humidity for operational meteorology, require the detection of cloudy pixels so that these measurements can be either 'cloud cleared' or omitted. However, optically thin cirrus cloud can remain undetected by standard cloud detection algorithms using either visible or IR data, but such clouds can still have a significant detrimental effect on the use of the data and introduce errors in the retrieval of other variables, if they remain undetected. Here we address the problem of detecting optically thin cirrus cloud in high spectral resolution IR interferometer data.

Due to restricted visibility time of remote sensing polar platforms from earth reception station, on ly a limited number of images can be transmitted. On the case of optical images, an in- board cloud cover detection module will allow to transmit only useful images. In order to derive such a module, we propose a method to detect cloudy areas from subsampled images. For a pixel ground surface of about 110 by 100 m², cloudy areas appear as the highest radiometric value homogeneous areas. The algorithm presented in this paper is based on the k-means Method. Its main originality is to improve classical results by introducing isotropic spatial information. Input data are the sorted components of a vector composed of radiometric values for each pixel and its neighbors. Then a classical k-means method with constraints on the cloudy class gravity center is used on these vectors. We tested the method on a set of 206 subsampled SPOT XS and 138 SPOT P images and their manmade interpretation masks. To evaluate the quality of our results, we used the probability of false alarm (PFA) depending on the number of pixels which have been wrongly declared cloudy. We obtained rather good PFA and PND, and compared these values with result obtained with other methods.

When mapping geophysical variables with satellite imagery, it is common practice to create composite maps depicting seasonal or monthly temporal averages. Using data form multiple satellite passes, each location on the earth is represented by a vector of several measurements acquired over the composing period. Removing the cloud-contaminated values form each measurements vector is a common preprocessing task. The objective of this research is to detect and remove hydrometeor contamination in time-composite 85 GHZ SSM/I data of the Amazon Basin without reference to any other SSM/I channel. To develop the cloud removal algorithm, a feed- forward neural network was trained using 85 GHz SSM/I brightness values produced through simulation. Since the data was synthetic rather than real, the correct mean brightness value of each vector was known, as well as the level of contamination for each measurement in the vector. The network inputs included several measures designed to emphasize the atypical cool measurements diagnostic of hydrometeor contamination. The desired output of the network was a binary flag indicating whether the presented measurement was contaminated or clean. Whenthe network was tested, 92 percent of the synthetic measurements were correctly classified as clean or dirty. The average error remaining in the decontaminated vectors was less than 0.1K.

The GOME instrument on board of the European Space Agency's ERS-2 satellite is a nadir viewing across track scanning spectrometer measuring the reflectivity of the earth in the visual spectral range and it has a spatial resolution of 320 by 40 km. The same wide swath is also seen by three broad band Polarization Measurement Detectors (PMDs) in the same instrument with a higher spatial resolution of 20 by 40 km, thus dividing the wide swath into 16 smaller sub-pixels. The polarization cloud recognition algorithm is used to calculate a cloud cover fraction. This work shows some results of a comparison between calculated cloud fractions from the PMDs and co-located surface observations in the Netherlands for August 1997, 1998 and 1999.

Astronomical observatories are extremely dependent on sky transparency. As the expensive new very large telescopes enter into operation, flexible observing modes are being introduced, which allow each 'observing block' to be scheduled at the most appropriate time. In such modes, it makes sense to develop tools for forecasting ambient conditions. We present here the operational water vapor and cirrus cloud forecast model developed for ESO observatories in Northern Chile.

The asymmetry factor, the hemispheric backscattering to total scattering ratio and the backscatter fraction are key parameters for the climate model calculations. The inversion method of King et al. has been modified to retrieve these key parameters from scattering coefficients at four wavelengths. The inversion of multi wavelength aerosol optical properties is an alternative way to obtain the asymmetry factor, the hemispheric backscattering to total scattering ratio and the backscatter fraction, using the retrieved size distributions as an intermediate step.

A program to measure with the highest accuracy the line parameters of high resolution Fourier transform spectra recorded in the laboratory has been written. Tests of the accuracy of the calculated parameters have been performed by comparing the results of the analysis of the 2-0 band of CO and of the v3 + v4 band of CO₂. The line position accuracy has been found to be 9 by 10^-6, and the line intensity accuracy is of the order of 1 percent or better.

On 5 October 1984, the US' first woman in space, Dr. Sally Ride, inserted the Earth Radiation Budget Satellite (ERBS) into a 57 degree inclined orbit using the shuttles remote manipulator arm. The orbital precession period of the satellite was 72 days. The nonscanner instrument aboard the ERBS has acquired earth-emitted and reflected radiant flux data since that time, having exceeded its designed lifetime of three years by a factor of five. During these 15 years, the ERBS nonscanner has become a de-facto standard to which much remotely sensed radiative flux data is compared. This paper compares the fifteen year history of the ERBS wide and medium field-of-view non-scanner detectors with the solar irradiance data acquired by the co-located ERBS solar monitor and with the National Climatic Data Center's earth- surface temperature dataset for the same period.

This work reports on the analysis of the near-UV and visible absorption spectrum of water vapor. Obtained by combining a high- resolution FT spectrometer and a long path White multiple- reflection cell. A large number of water vapor lines belonging to highly excited vibrational levels are identified. Most of these lines have not been observed previously and do not appear in the spectroscopic databases HITRAN and GEISA, widely used for atmospheric calculations. All identified lines are fitted with a Voigt profile using the WSPECTRA program and their cross section and self-broadening parameters at 291 K are determined. A particular attention is give to the integrate cross section over the total spectral range investigated, in order to estimate the contribution of the weak UV-visible water vapor absorption lines to the earth's radiation balance. Preliminary measurements of cross section in the 20000-16000 cm^-1 spectral range are also presented.

In this paper, we present an analytical scheme for the computation of Hessian for skin temperature, temperature profile and water vapor profile. It is possible to retrieve atmospheric parameters from IR radiance achieving the quadratic convergence for a pure Newton algorithm.

The IASI has 8461 potential channels to be exploited for inversions of geophysical parameters. In this paper we analyze two different strategies for their reduction. The first one looks for suitable spectral ranges where the inverse problem is as linear as possible; the second one is based on the cluster analysis theory. Our aim is to minimize the potential information loss evaluated by directly comparing the retrieved temperature and water vapor profiles on a complete set of test atmospheres.

Presented is a ground-based measurement technique for quantifying the directional properties of the IR radiation regime within a forest canopy with regard to mapping the canopy transmission over the upwards facing hemisphere. Implications are discussed for remotely sensed canopy temperature measurements and models of canopy transmission. The technique involves taking narrowband measurement scans throughout the hemisphere using a narrow view angle, narrow spectral band radiometer that measures predominantly within the water vapor transmission window. Measurements made under both clear skies and within a dry sclerophyll Eucalyptus canopy are presented and discussed.

The present work empirically deals with the challenging problem of the integration of data obtained from passive and active microwave sources, in order to develop procedures to suitably calibrate and validate satellite-based passive microwave rainfall algorithms by means of multi parameter radar information over midlatitude areas. Furthermore, this research tires to analyze the well-known beam-filling problem and the different microwave channel penetration top9ic. SSM/I passive microwave radiometer precipitation related parameters were analyzed against multi parameter radar Zh and Zdr 3D maps, obtained from the POLAR-55C multi parameter radar set near Florence, Italy. SSM/I-derived parameters, related to rainfall over land were analyzed by means of information derived form radar volume data. We faced several statistical analyses of the obtained data sets. Results report the effectiveness of Montagnana radar and SSM/I data fusion. In particular, it is assessed the utility of utilizing both active and passive microwave hydrometeor-related information in order to improve the inferences about monitored phenomena. Results are valuable in order to better calibrate and validate passive microwave algorithms for rainfall rate estimation and for cloud detection over land. Correlation values may be improved by filtering radar data according to several parameters thresholds, in order to tackle beam-filling problem and statistical issues.

Textron Systems, under the US Army Space and Missile Defense Command's Field Ladar Tactical Transition Demonstration program, has been evaluating coherently detected, atmospheric aerosol backscattering as a method to extend the utility of the DIAL technique. This paper present recently obtained long range, multi-wavelength DIAL measurements utilizing cloud formations and a laboratory positioned absorption test cell. Good agreement between cloud and continuous wave laboratory measurements of the absorption spectra of ammonia have been obtained.

This article is aimed at describing the technology, system architecture and specifications of a new 3D Nd:YAG scanning lidar. Main features of the system are interspersed low-range and far-range exploration, open user-configuration scanning tools and a specific architectural design based on parallel CPU control, a LabView user interface and a digitally controlled optoelectronic receiver. The latter provides key advantages to the whole system architecture such as calibration of lidar returns in terms of absolute power and repeatability. Issues concerning system responsivity calibration, receiver gain self-calibration, automatic gain control and synchronization offset-drift zeroing and the like, all of which are of prime importance for the lidarist, are presented. As far as we know, these contributions are new to the state-of-the-art of the community of optical and electronic lidar system designers.

Results presented in this contribution correspond to the first measurements made with the transportable lidar system developed by the Universitat Politecnica de Catalunya, which were collected during the eyra 2000 in the city of Barcelona. The system uses a Nd:YAG laser at 1064 nm wavelength and 0.35 J pulse energy at a 20 Hz pulse repetition rate, has a 20 cm diameter telescope and a scanning range of 120 degrees in elevation and 300 degrees in azimuth. In this study only vertical profiles of atmospheric extinction will be shown. Data were acquired under several meteorological situations, showing the influence that this factor has in the arrangement of aerosols in the vertical dimension, and the distributions of backscatter extinction coefficients obtained from the lidar. Data have also been compared to radiosonde profiles acquired in Barcelona at a near time and have shown how the vertical arrangement of aerosols is correlated with changes in atmospheric stability condition, water content and wind direction.

A nighttime operating Raman/Rayleigh/Mie lidar system for the measurement of profiles of the water vapor mixing ratio and the aerosol backscatter ratio is described. The transmitter utilizes two laser beam at 532 nm and 355 nm from a Nd:YAG pulsed laser and the receiver consists of three Newtonian telescopes. Optical fibers carry the signal to the detectors. The system, which is installed in two containers, is transportable. Data are recorded with resolutions of 75-m in altitude and 1-min in time. Water vapor profiles from 200 m above the lidar altitude up to the upper troposphere and aerosol profiles form 500 m up to the lower stratosphere were obtained also at the lowest resolution. The lidar was deployed and used in the 'Target Area of the Lago Maggiore' during the MAP-SOP international campaign. Measurements taken during that campaign are reported to show the lidar performance. Improvements of the system by employing an array of nine 50-cm diameter telescopes are planned. These should effectively enhance the lidar performance.

Structural and optical properties of aerosols and clouds can be retrieved by active remote sensing systems, such as lidars. Such parameters are of importance in the study of dynamics and radiation budget of the atmosphere. In that respect, a small, portable, eyesafe, unattended, elastic-backscatter lidar is being developed at Cimel Electronique, in collaboration with CNRS. It sues a compact, low-energy laser in the visible. The detection is made by a high-gain, high-speed PMT, and a single electronic card for fast acquisition. The aim of the system is also to be tunable to various pointing angles. A variational method was developed to make use of the multiangle measurements and tested on data collected during the INDOEX campaign in March 1999. The optical thickness and backscatter coefficient profiles were retrieved up to 1 km with a total uncertainty of 18 percent. The system has been assembled and first measurements have been made beginning of 2000 for comparison with the theoretical predictions. The system has shown it was satisfactory and the signal profiles obtained are in agreement with the ones simulated with the system parameters.

Emission indices of aircraft engine exhausts must be known to calculate precisely the emissions of aircraft on airports during different operational scenarios. FTIR emission spectroscopy of exhausts was developed further as a remote sensing multi- component analysis method. Measurements at different aircraft engines were used to develop basically and optimize the measurement and analysis procedure during run up tests at ground level. The measured main engines are GE90-85B and RB211 as well as APUs of the B777 and B747. A temperature stabilized spectrometer in a van collected good quality spectra at 0.2 cm^-1 resolution. The FTIR instrument was aligned to the engine nozzle exit with a two axis movable entrance mirror. Setting up the system needs about 10 to 20 minutes, if all systems are running on standby. Total measurement times at one thrust level should be around 5 minutes to obtain reliable results. The FTIR engine measurement results for CO₂, CO, and NO have been proven to be in agreement with intrusive measurement data collected during engine runs in a test rig. The deviations were generally in the order of +/- 30 percent, i.e. comparable to the day-to-day variations of the engine emissions.

A method for the passive remote monitoring of chemical vapors by differential FTIR radiometry is explored. This approach is based on the use of a double-beam Fourier transform IR spectrometer optimized for optical subtraction. The method is described with a particular emphasis on its capabilities for differential detection and background suppression. The algorithm developed for on-line detection and quantization of chemical vapor plume is presented and tested. The method has been successfully used to map the integrated path-concentration of a vapor plume of ammonia.

The aim of their work is to develop non-intrusive methods to determine the presence of unburnt hydrocarbons in the emissions from aero-engine combustion systems. In addition to the detection of UHCs for legal certification of aero-engine performance, the consequences of their release into the upper atmosphere has environmental considerations.

An applicability analysis of a DF laser in atmospheric remote control of SO₂ is performed: experimental absorption factors of SO₂ are given at various emission lines of a DF laser; possible errors from the spectral reflectance dependency for topographic objects are considered and the method of their correction is offered.

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.

This contribution reports on some recently achieved results in aerosol size distribution retrieval in the Anomalous Diffraction Approximation to Mie scattering theory. This approximation is valid for spherical articles that are large compared to the wavelength and have a refractive index close to 1.

Aerosols in the upper troposphere and low stratosphere have been monitored continuously during the past 26 years by a ground-based lidar system at the NASA Langley Research Center in Hampton, Virginia. The measurements were started in 1974 to support NASA's ongoing atmospheric research programs, and have produced one of the world's longest continuous lidar records on northern mid- latitude aerosols. The 26-year record spans periods during which the stratospheric aerosol loading was greatly enhanced by highly explosive volcanic eruptions including, Fuego in 1974, El Chichon in 1982, and Mt. Pinatubo in 1991, each of which injected enormous quantities of aerosols and gases into the stratosphere. These lidar observations of volcanic aerosol plumes in the stratosphere over long time periods have provided insight into their potential impact on global climate and other atmospheric processes.

Measurements from ground-based sun photometer networks can be used both to provide a ground-truth validation of satellite aerosol retrieval sand to produce a land-based aerosol climatology which is complementary to satellite retrievals that currently are being performed mostly over ocean. The MFRSR has become a popular network instrument in recent years, several existing networks operate about a hundred instruments providing good geographical coverage of the US. We describe and validate a retrieval algorithm for processing MFRSR data from clear and partially cloudy days. This method uses consistency between direct normal and diffuse horizontal measurements together with a special regression technique for retrieval of daily time series of column mean aerosol particle size, aerosol optical depth, NO₂, ozone and water vapor column amounts together with the instrument's calibration constants. This method has bene successfully used to analyze MFRSR measurements from a number of instruments both from large networks and those operated by individual users. The analysis of long-term MFRSR measurements provides a description of seasonal and inter-annual changes in aerosol parameters and in column amounts of ozone, NO₂ and water vapor as a function of geographical location. Application of this analysis method to the measurements from growing numbers of MFRSR opens the possibility to build large-scale climatologies basing on MFRSR network data.

Remote sensing of atmospheric trace gases form geostationary orbit has unique scientific value and unique measurement interpretation advantages. This paper describes a proposed measurement method and analysis strategy for inferring CO concentration in the troposphere. Gas filter correlation radiometry is found to be very well suited for remote sensing using full globe images from geostationary orbit. Strengths of the gas correlation technique include measurement efficiency, effective high spectral resolution, excellent spectral calibration, manageable data rate, and measurements over the full spectral bandpass simultaneously.

The Michelson Interferometer for Passive Atmospheric Sounding will be operated onboard the polar orbiting ENVISAT. The instrument will measure the IR emission of various atmospheric trace gases by limb scans covering the altitude region from 6 to 68 km altitude.

The SAGE II, whose first flight is planned to be launched in Winter 2000-2001 on the polar orbit spacecraft METEOR 3M, is a part of NASA's Earth Observing Systems (EOS). A preliminary outcome for the LOA inversion has been obtained for resolved channel for the retrieval of daytime and nighttime constituents such as O3, NO2, NO3, OCIO and aerosols, with good quality, from simulated transmission profiles. An opportunity for testing the inversion algorithm on real measurements is offered by the SALOMON team of the LPCE to validate the method. The purpose of this paper is to present the LOA inversion of SALOMON real measurements, performed in February 2000 from Kiruna, Sweden. The retrieved gas densities and aerosol extinction profiles are compared to the corresponding retrieved values by the SALOMON team.

One of the most important reservoirs of chlorine in the stratosphere is HCl, which sequesters active species and affects the rate of catalytic reactions with ozone. HCl presents a vibro- rotational absorption spectrum, in the near IR; for this reason it is possible to use a Fabry-Perot Interferometer as a multiple narrow band filter with an appropriate free spectral range so its transmission bands overlap the HCl absorption lines.

UV-visible ground-based spectrometers were developed at the ISAO Institute and they are used for application of differential optical absorption spectroscopy (DOAS) methodology to detect stratospheric trace gases involved in the ozone cycle such as NO₂, OClO, and BrO. Observations of the light scattered from the zenith-sky were performed with the instrumentation above mentioned, in various stations situated in both the hemispheres. Some problematics connected to data validation and results analysis are introduced. Considerations about the temperature dependency of the cross-section used for the determination of the trace gases slant column are carried out. Results for nitrogen dioxide abundances at different season and various Solar Zenith Angle in their seasonal and diurnal variation are presented and discussed. Finally, the behavior of the sunrise nitrogen dioxide abundance over the sunset slant column is shown and examined.