The DGA (Delegation Generale de l'Armement) is interested in the determination of sky-ground characteristics. In particuliar, optical clouds properties as well as land-surface and sea-surface temperatures must be determined with accuracy. To obtain a statistical description of the cloud properties, we have created a cloud database called SALIC (SAtellite-LIdar-Clouds). Two algorithms, one for sea-surface temperature and one for land-surface temperature were recently included in the database. Three different kinds of measurements are used to built up the database: radiosoundings, ground-based lidar measurements, and satellite data obtained from the radiometer AVHRR3 boarded on the NOAA-16 polar orbiting satellite. This paper presents the results for a period covering two years.
Since Sarajevo's sadly famous events (sniper alley), the military tried and hoped to detect snipers before they hit. The principle of the detection is based on the 'cat's eyes' effect according to which the light emitted by the system and incident on the sniper's sight reflects backward in the direction of the source. The system is thus composed of a laser emitter and a CCD array detector. Already existing equipment has been tested in operations and they present too low a probability of detection for the false alarm rate we want to reach. In order to specify equipment characteristics to industrials, it has been necessary to develop a sight laser detector model. The model presented here takes into account all the various elements of the system, from the laser emission to the CCD detection, and atmospheric propagation (ie attenuation and turbulence). The signal and noise probability density functions are calculated by combining the different elementary probability density functions encountered on the double-pass propagation. This Matlab coded model gives the probability of detection of the system for given geometrical (monostatic or bistatic) and electronic characteristics of the system and for a given probability of false alarms. In addition to this, measurements in the field made it possible to validate the budget link of the model and improve it. Those measurements also permitted to underline the importance of the target optical signature, namely its Laser Cross Section. The most significant parameters necessary to the validation of the model are measured. This study allows us to answer the question 'why is the probability of detection of existing systems too low and how could we increase it's efficiency?'
For a long time fluorescence techniques have provided interesting information in oceanography. Lidar (LIght Detection And Ranging) has been used to have fast profiling tools over several meters especially in high dynamic water masses. While fluosensors provide the fluorescence response to a well defined excitation in a small volume, remote sensing operates over several meters and their power to excite fluorescence at a range R depends on optical properties of the medium during the light propagation. In order to study the influence of the propagation properties of the aquatic medium on spectra from fluorescence Lidar a new ranging concept was realized. The presented study is focused on the bistatic design of Lidar combined with a spectral analysis of the backscattered signal for tomoscopic applications. The data were obtained with a frequency doubled Nd:YAG ((lambda) equals 532 nm) and a gated angular resolved detection. While the time base of the system can be compared to ranging by other on-axis Lidar, the spatial dimension of the signal brings complementary information of the light flux distribution as a function of the angle of incidence. The bistatic configuration of this Lidar permits geometrical ranging by a set of detection channels, detecting simultaneously the spectrum (532 nm - 720 nm) with the same system time base. The analysis of fluorescence by the bistatic angular resolved detection is focused on the temporal aspects of fluorescence in near field data of this Lidar. First sea trials with this Lidar have shown the potential for the investigation of fluorescence profiles even in very turbid estuaries.
The aim of this poster is to determine the droplet size distribution in low water clouds from measured optical parameters. Those measurements are obtained by a Lidar system. It consists of two reception telescopes: the first is near the beam send to the atmosphere, the second is at 7.7 m-distance from the first. The backscattering signal collected by the first telescope gives after an Klett's inversion, the volume extinction coefficient profile in the cloud. The double- scattering signal collected by the second telescope associated with the volumique extinction coefficient profile, gives by an inversion method, the double-scattering phase function which is correlated to a log-normal size distribution. The collected signals are detected simultaneously. A verification of the water phase is made by the depolarization ratio. Because of the situation of Lannion city, near the sea, swept by predominant winds from West, frequent fronts are present. So, a large diversity of clouds exists, which is a good experimental ground for testing and validating the theory presented here. Results from ENSSAT Lidar measurements will be presented.
Lidar returns from clouds include successive scattering order contributions. Under several assumptions, they can be evaluated by a simple analytical model, where only forward and backward scattering events are considered. Such a model has been developed, which moreover accounts for realistic receiver/emitter characteristics. Two experimental settings, enabling multiple scattering contribution identification, are considered. They are referred as <<2-FOV>> and <<off-axis>> methods. The latter requires no special additional feature to common lidar devices. Both are examined through a simple simulated case, and two measurements performed on cirrus clouds layers. 2-FOV method leads to an accurate estimate of ice crystals diffraction peak width. Off-axis approach, although theoretically efficient and experimentally less requiring, proved to be rather critical, and has to be properly improved.
This paper presents comparisons between aerosols measurements and aerosols in Lowtran7. Desert aerosols are natural aerosols that can be found throughout the atmosphere; they are a mixture of different kinds of materials. The model used in Lowtran7 separates the desert aerosol into its three major components: carbonaceous particles, pure quartz and quartz contaminated with a small amount of hematite. Recent measurements have been carried out for three samples of desert aerosols from the Middle East and give prominence to a complex composition of the sands. Thanks to an accurate analysis, we present features of the sands and compare them with values introduced in Lowtran7 desert aerosol model.
This paper presents field measurements taken during last winter with a Barnes transmissometer. Transmission data in four infrared bands were recorded; a description of the instrument is presented along with the measured transmissions. The atmospheric transmission over a 200 m path has been calculated on a PC with FASCOD2 using `winmaker:' substitution of maker by an interactive editor under windows.