Showing papers on "Haze published in 1998"

Improving image quality in poor visibility conditions using a physical model for contrast degradation

Abstract: In daylight viewing conditions, image contrast is often significantly degraded by atmospheric aerosols such as haze and fog. This paper introduces a method for reducing this degradation in situations in which the scene geometry is known. Contrast is lost because light is scattered toward the sensor by the aerosol particles and because the light reflected by the terrain is attenuated by the aerosol. This degradation is approximately characterized by a simple, physically based model with three parameters. The method involves two steps: first, an inverse problem is solved in order to recover the three model parameters; then, for each pixel, the relative contributions of scattered and reflected flux are estimated. The estimated scatter contribution is simply subtracted from the pixel value and the remainder is scaled to compensate for aerosol attenuation. This paper describes the image processing algorithm and presents an analysis of the signal-to-noise ratio (SNR) in the resulting enhanced image. This analysis shows that the SNR decreases exponentially with range. A temporal filter structure is proposed to solve this problem. Results are presented for two image sequences taken from an airborne camera in hazy conditions and one sequence in clear conditions. A satisfactory agreement between the model and the experimental data is shown for the haze conditions. A significant improvement in image quality is demonstrated when using the contrast enhancement algorithm in conjuction with a temporal filter.

Process for reducing haze point in bright stock

Abstract: A dewaxing process for lowering the haze point of a bright stock which includes contacting a bright stock in the presence of added hydrogen gas with a Zeolite EU-1 catalyst in combination with a ZSM-48 and/or SSZ-32 catalyst.

Overview of atmospheric conditions during the Smoke, Clouds, and Radiation-Brazil (SCAR-B) field experiment

Abstract: The Smoke, Clouds, and Radiation-Brazil (SCAR-B) field experiment was conducted in central Brazil and southern Amazonia during the period August 15 to September 20, 1995. This paper presents an overview of atmospheric conditions during the SCAR-B period. A meteorological office was established in Brasilia to support the mission flights and field activities. All the meteorological data collected during the SCAR-B have been archived and are available to the scientific community. The meteorological conditions throughout the SCAR-B period of August and September 1995 were near climatological conditions. Few synoptic-scale waves traveling from southeastern Pacific reached Brazil, therefore the SCAR-B period was characterized by long periods of low humidity, dryness, little cloudiness, or rain, and haze events. The stable situation was interrupted due to the penetration of a frontal system on September 20, 1995, and a second and more rain-producing one on September 28, 1995. Those two frontal systems in a period of 10 days brought an end to the dry season. Air particle trajectories show that most of the smoke below 4 km from Amazonia was transported to the south and then to the east exiting the continent at 25°S–30°S. Radiative transfer calculations carried out for the clear sky gaseous and aerosol atmosphere show the decrease of the solar radiation absorption in the atmosphere-surface system due to smoke aerosol loading at the value from 5 to 50 W m−2 depending on the aerosol optical thickness, single-scattering albedo, and solar zenith angle.

Effect of drought and haze on the performance of oil palm

Abstract: One of the most important events occurring during 1997, which affected oil palm cultivation, is related to the "El Nino" phenomenon This climatic incident resulted in a dramatic drought in many parts of South East Asia Subsequently uncontrolled development of fires in Indonesia led to the development of haze which spread across neighbouring countries of the region The first part of the paper presents a tentative estimate of the impact of the drought on future yields (1998 and 1999) of the palms, based on several studies made in the recent past in West Africa and Indonesia These studies used statistical models about the relationship between the water deficit calculated on a determined period, and the subsequent production of the palms Seasonal variations are considered, in relation with periods of particular susceptibility of inflorescences during their development It appears that the age of the palms is also an important factor to take into consideration The second part of the study deals with the impact of the haze on the performance of oil palms An estimate of the negative effect on yield is proposed, using an agro-climatic model set up by CIRAD's physiologists A major short-term impact of the haze was the significant negative effect on oil extraction rate (OER) observed at factories A statistical model of OER variations according to global radiation is presented and discussed Although drought and haze occurred during the same period, a tentative split of the corresponding effects has been made (Resume d'auteur)

Vertical distribution of the spectral aerosol optical depth in the Arctic from 1993 to 1996

Abstract: During the period from summer 1993 to spring 1996, 51 profiles of spectral aerosol optical depth were measured with airborne Sun photometers throughout the Arctic. This period was influenced by volcanic aerosols after the Pinatubo eruption and the removal of volcanic material from the stratosphere into the troposphere. By 1996, stratospheric aerosol concentration has decreased to pre-Pinatubo levels. Mean values of aerosol optical depth have changed during the period from 1993 to 1996 from 0.09 to 0.02 at 403 nm and from 0.065 to 0.01 at 1041 nm/ 1057 nm, respectively. Size spectra of stratospheric aerosol also show the influence of volcanic aerosols. A bimodal distribution was found with main radius modes at 0.1 μm to 0.3 μm and 0.75 μm to 0.9 μm. The typical vertical distribution of tropospheric aerosols in the Arctic in this time period and inferred size spectra are presented. The seasonal change in the spectral aerosol optical depth with a minimum in summer and high values in spring is shown, as well as the high extinction and distinct layering of Arctic haze up into the free troposphere. Size spectra of Arctic haze also change with height and show, in addition to particles with radii smaller than 0.1 μm, main radius modes between 0.1 μm and 0.2 μm and between 1 μm and 2 μm. Possible influence of tropospheric aerosols on the radiation balance is also discussed for the spring and summer season. While in summer the influence on the radiation balance of the very small amount of tropo-spheric aerosols is negligible, in spring, haze layers with high extinction can result in a slight warming.

Mid-Infrared Sky Brightness Site Testing at the South Pole

Abstract: During the austral summer of 1996, the mid-infrared imaging polarimeter NIMPOL was operated at the Amundsen-Scott South Pole Station, to obtain quantitative measurements of the 10 and 20 μm sky brightness and stability. These observations were conducted as part of the Joint Australian Centre for Astrophysical Research in Antarctica (JACARA) site testing program on the Antarctic Plateau. The results of this site testing program are presented. The observations show that the mid-infrared sky brightness at the South Pole Station is much less than comparison sky brightness observations made at the Canberra base of the instrument. This reduction in sky brightness is attributed largely to the low emissivity of the atmosphere (because of its dryness and lack of aerosols), and the effect of the reduced atmospheric temperature (there is an expected decrease by a factor of 2.5 from the temperature difference between the two sites alone). The measured 11 μm sky emissivity at the South Pole is also lower than previous measurements of the sky emissivity at Mauna Kea Observatory in Hawaii. The sky brightness was also found to be more stable than at the warmer, mid-latitude site (Canberra), and it is expected that "stare" mode operation of the instrument for astronomical observations would be quite feasible under these conditions. Measurements were also made during a period of "ice haze," and the suspended ice crystals were observed to increase the sky background by 16% compared with clear weather and to add low-frequency brightness variations. However, this variability could be removed by slow (2 Hz) chopping, allowing high-sensitivity observing to continue through the "ice haze."

Analysis of temporal variations of the polarization of Venus observed by Pioneer Venus Orbiter

Abstract: Time variations of the disk-averaged polarization of Venus at wave- lengths of 270, 365, 550, and 935 nm have been analyzed in terms of average haze optical thickness, cloud-top pressure, and cloud absorption optical thickness at 270 nm (presumably due to gaseous SOe absorption). The polarization data were deduced from observations made by the Pioneer Venus Orbiter between 1978 and 1990. Newton-Raphson iteration was used to derive the atmospheric parameter values from these observations. The required multiple scattering calculations were performed using the adding/doubling method. The atmospheric model consists of a cloud layer and a haze layer. The cloud and haze particles are composed of a concentrated sulfuric acid solution and have an effective radius of 1.05/m and 0.25 /m, respectively. It was found that the disk-averagedhaze optical thickness, cloud- top pressure, and cloud absorption optical thickness at 270 nm varied Eregularly between 1978 and 1990. No trends were identified for the cloud-top pressure and cloud absorption optical thickness at 270 nm, but we did deduce a decrease in haze optical thickness during this 12 year period. Specific numbers are: (1) a haze optical thickness at 365 nm of about 0.25 in 1978 and less than 0.1 in 1990, (2) a cloud-top pressure that varies between 5 and 20 mbar, and (3) a cloud absorption optical thickness that varies between 0.0 and 4.0. Finally, our analysis revealed that the disk-averaged cloud-top pressure and haze optical thickness behaved anomalously in 1983.

Changes in submicrometer particle distributions and light scattering during haze and fog events in a highly polluted environment

Abstract: The changes in submicrometer atmospheric particle size distributions measured with a Differential Mobility Particle Sizer (DMPS) system during a polluted fog experiment during November, 1994 are presented in this study. Results reveal three modes commonly evident in the size distribution (3 < DN < 843 nm) measurements; the ultrafine, Aitken and accumulation with respective geometric diameters, (Dgn), of 17, 110 and 400 nm. An additional mode, appears between the ultrafine and Aitken modes (Dgn = 52 nm) in approximately one quarter of the measurements and is linked to several industrial cities upwind of the measurement site. A stabile ultrafine mode appears consistently (84% of measurements) at 16-17 nm throughout the campaign, suggestive of a source, such as a highway in the near vicinity. During fog and haze periods number concentrations for particles less than 25 nm and greater than 400 nm decrease by 78 and 95%, respectively. These changes do not affect the aerosol scattering efficiency significantly. The overall aerosol mass scattering efficiency determined for the Po Valley region is 4.3 ± 0.6 m2 g-1. Closure is achieved for light extinction predicted from droplet distributions and measured with a transmissiometer in 37 of 39 cases during fog periods. Measured and calculated light extinction, bext, covary strongly with an R2 of 0.92. (Less)

Sampling of fog droplets by cascade impactors

Abstract: Cascade impactors are suitable instruments for sampling haze and fog droplets at ambient conditions. Evaporation of water from the particles, and condensation on them, may distort the size distributions of the droplets. For an impactor with a flow rate of 80 1 min-' and a working range from 0.5 μm to 32 μm, the aspiration efficiencies and the changes of particle sizes are investigated theoretically. The sizes of droplets above 2 μm diameter are rather well preserved in this impactor. Aspiration efficiencies are improved by a horizontal disc inlet. The analysis shows that specific configurations, that is, baffled apertures and slotted apertures, are most efficient for sampling coarse particles in the size range of fog droplets.

Characteristics of haze, mist and fog

Abstract: An aerosol and fog data set from a field experiment in November 1994 at San Pietro Capofiume, Northern Italy was analysed. With objective criteria developed from visibility measurements average aerosol characteristics in the dry and wet state were calculated for haze, mist and fog conditions which can be seen as representative for continental air masses in an industrialised region. Dry particle size distributions between three and 800 nm and ambient size distributions between and 50 μm were measured with a system consisting of the three size-segregating particle sensors differential mobility particle sizer, droplet aerosol analyser and FSSP. Systematic changes in particle properties were found for the transition from haze to fog that can be used to derive internally consistent optical aerosol properties. The analysis of the data set demonstrates that atmospheric sensors which have been developed for cloud and fog studies yield useful data for haze conditions.

Aerosol Particle Scavenging by Fog and Haze Droplets

Abstract: Droplet imprints in thin gelatin layers have been used for the investigation of coarse particles embedded in fog (haze) droplets in comparison to interstitial particles Droplet samples were taken in less polluted regions of Missouri and Illinois and also in more polluted marine-urban environment in Italy Considerable differences in particle size distribution and particle location inside the droplets have been found in samples collected on four sampling sites The deduced relationships can be applied for the description of the aerosol scavenging process in fogs The pollution of fog (haze) droplets may be related to the droplet mean volume radius and may depend on temperature and on atmospheric humidity An orientative study of the deposited particle composition indicated important relationships between coarse particles of different origin (soil minerals, industrial and urban pollutants, sea salt)

Low haze, speckle free polyester film

Abstract: A low haze, speckle free polyester film suitable for use in solar windows is disclosed The film comprises a mixture of calcined silicone particles and fumed silica agglomerates in which essentially all of the calcined silicone particles have a particle size below about 7 microns; and essentially all the fumed silica agglomerates have a discrete agglomerate size below 1 micron The film very clear and has a minimum amount of haze

Formation of chain-like structures in apple juice haze.

Abstract: Red Delicious apple juice made by exclusion of oxygen (anaerobic juice) was stored in the presence of air at 21 °C for 67 d. During this period, a haze developed in the juice and partially sedimented at the bottom of the glass container. This haze/deposit contained 12 g/kg protein and the remainder was butanol–HCl and/or vanillin reactive material. Electron microscopic examination using negative staining with uranyl acetate showed that the haze/deposit preparations consisted of branched chain-like aggregates of globular particles of variable size. The particles had sufficient electron density to be examined in detail without staining. Their three-dimensional structure was confirmed by shadow casting. A mechanism of formation of these particles is proposed and discussed and a model for formation and aggregation suggested.

Reflection Measurement Problems Arising from Haze

Abstract: Irreproducibility in some reflection measurement methods arises from the observance of the haze component of reflection (non-regular-specular, non-Lambertian). Because of the haze component, the measured reflection is sensitive to the apparatus configuration. We show the effects of detector lens aperture and detector distance on the measurement of the reflected luminance. Only for detectors with small subtense angles can reproducibility be assured when haze reflection is nontrivial.

Particulate emissions — optical and other methods for continuous monitoring from a point source

Abstract: All particles emitted from a stack or vent give rise to various nuisances, depending upon the size, quantity and chemistry of the particles. Plume visibility and haze are a major nuisance resulting mainly from the emission of finer particles, whereas larger particles give rise to local ground level deposits.

THE NATURE AND MANAGEMENT OF CORNEAL HAZE FOLLOWING PRK: An Electron Microscopic Analysis

Abstract: Corneal haze following excimer laser photorefractive keratectomy is commonly seen in the anterior stromal surface of the cornea 1 to 3 months after treatment. Although corneal haze may develop late in the postoperative course, it is rarely problematic and usually does not produce visual disabling symptoms. Clinically significant haze, on the other hand, may decrease vision by one or more lines, decrease contrast sensitivity, reduce night vision, induce astigmatism, and produce ghost images. Even though the incidence of "clinically significant" haze is low, it may present a clinical challenge to manage and alleviate these visual disturbing symptoms. The development of corneal haze is thought to represent the normal healing process and sometimes has been referred to as scarring. The source of the haze is thought to be type III collagen resulting from fibroblast proliferation and inflammatory cell invasion. Mechanical debridement or additional excimer ablation has been reported to be the most successful treatment of clinically significant haze, but does not prevent its recurrence. This study reports the findings of electron microscopy of human corneal haze in an attempt to further understand the source and nature of corneal haze following photorefractive keratectomy (PRK). The electron microscopy of corneal haze in human corneas has never been reported before.