Haze Conditions Research Articles

Visual air quality simulation techniques

Abstract Visual air quality is primarily a human perceptual phenomenon beginning with the transfer of image-forming information through an illuminated, scattering and absorbing atmosphere. Visibility, especially the visual appearance of industrial emissions or the degradation of a scenic view, is the principal atmospheric characteristic through which humans perceive air pollution, and is more sensitive to changing pollution levels than any other air pollution effect. Every attempt to quantify economic costs and benefits of air pollution has indicated that good visibility is a highly valued and desired environmental condition. Measurement programs can at best approximate the state of the ambient atmosphere at a few points in a scenic vista viewed by an observer. To fully understand the visual effect of various changes in the concentration and distribution of optically important atmospheric pollutants requires the use of aerosol and radiative transfer models. Communication of the output of these models to scientists, decision makers and the public is best done by applying modern image-processing systems to generate synthetic images representing the modeled air quality conditions. This combination of modeling techniques has been under development for the past 15 yr. Initially, visual air quality simulations were limited by a lack of computational power to simplified models depicting Gaussian plumes or uniform haze conditions. Recent explosive growth in low cost, high powered computer technology has allowed the development of sophisticated aerosol and radiative transfer models that incorporate realistic terrain, multiple scattering, non-uniform illumination, varying spatial distribution, concentration and optical properties of atmospheric constituents, and relative humidity effects on aerosol scattering properties. This paper discusses these improved models and image-processing techniques in detail. Results addressing uniform and non-uniform layered haze conditions in both urban and remote pristine areas will be presented.

Temporal and spatial variations of the atmospheric dust loading throughout West Africa over the last thirty years

Abstract. The dust haze conditions, typical of the African atmosphere south of the Sahara, are a result of wind-generated dust from arid lands. The magnitude of the dust haze is evaluated for the 30-year period beginning in 1957 by calculating the number of occurrences where the observed visibility was reduced below threshold values of 10 km and 5 km. The frequency of low visibility was several times greater for the 1977-1986 period than for the 1957-1966 period. Large decreases in visibility are observed after the severe droughts of 1972-1973 and 1982-1984. Contrasting regional differences of the dustiness evolution are noticed. These differences are closely related to the differences in the regional rainfall evolution. The increase in dustiness is believed to arise from dust produced in new desertic areas which result from rainfall shortages along the southern border of the Sahara.

Atmospheric condition and its influence on reflectance of bare soil surfaces in southern Tunisia

Abstract The variation in the influence of the atmosphere on ground reflectance appears to be small for a stable atmosphere al different haze conditions in the study area. For a comparison of field with simulated and actual satellite data the model of Verhoef was used, which requires as input the ratio of measured diffuse to total irradiation. Relative difference in planetary reflectance of Landsat TM predicted with an atmospheric model for a specific ground reflectance and the observed range of stable atmospheric conditions turned out to be small. In situ measured ground reflectance and the ground reflectance derived from planetary actual TM reflectance are in good agreement.

The capabilities of colour infrared film as a negative

Since 1982, the authors have conducted studies at the Ontario Centre for Remote Sensing, Toronto, Canada, on the processing of Kodak Aerochrome Infrared 2443 film as a negative, using modifications to the Kodak C-22 and Aero-Neg processes. In 1984, an interpretation test was conducted to compare Kodak Double X Aerographic 2405 film and negative-processed Kodak Aerochrome Colour IR 2443 (CIR) film, taken simultaneously over areas of conferous and mixed forest, under a range of haze conditions. The results of the test demonstrated that CIR film was much less affected by the presence of atmospheric haze than traditional panchromatic photography, and that this difference represented a distinct imrpovement for forest inventory interpretation. It was concluded, however, that to obtain full advantage of the CIR negative, while printing in black and white, a panchromatic print paper is needed which has a greater range of contrast grades than currently available. Successful tests were also conducted on the production of CIR black and white prints enhanced for specific interpretation purposes using different combinations of subtractive filters.

The Effects of Aerial Perspective on Altitude Estimation

Recent interest in the importance of visual displays within specified flight simulations and scenarios has led to increased emphasis on the identification of pertinent cues within these displays. Through the identification of these cues and their usage in altitude estimation, more effective simulation and hence training programs can be developed. The present explanatory study investigated the use of a psychophysical methodology in the evaluation of aerial perspective as a possible cue in altitude estimation. Specifically the effects of two levels of aerial perspective (present and reduced) and flight experience on estimations were examined. Based on the linear functions of log estimated vs. log actual altitude, differences were found between levels of flight experience in the aerial perspective-present condition. Subjective responses suggest that individuals are aware of the presence/absence of haze conditions and this information influences their altitude estimations.

Lidar determinations of extinction in stratus clouds

A field test has been carried out to compare calculations made from lidar data to direct sensor measurements as tools for determining extinction as a function of altitude in the first kilometer of the earth’s atmosphere during the presence of haze layers and stratus clouds; 1.06-μm wavelength lidar returns were reduced using methods based on the stable solution to the lidar equation proposed by Klett. Direct sensor data were obtained from particulate spectrometers and a point visibility meter carried aloft by a tethered hydrogen balloon. The extinction profiles obtained from reduced lidar data are qualitatively in excellent agreement with those from the airborne payload. At moderate to high extinction values encountered in stratus clouds quantitative agreement is reasonably good; in haze conditions the agreement is less satisfactory, not only between the lidar results and those from the direct sensors, but between the results from the particle size distribution data and visibility meter data as well. Nevertheless, considering that extinction can vary over 4 orders of magnitude in such profiles, it is concluded that lidar is a quantitatively useful tool for studying stratus layers and is a particularly good means for determining ceiling altitude.

Surface aerosol measurements at Barrow during AGASP

Surface aerosol measurements were made at the Barrow GMCC Observatory during the AGASP flight series in March 1983. The condensation nucleus, scattering extinction coefficient, size distribution, and total aerosol optical depth measurements all clearly show conditions of background Arctic haze for March 9‐11, a series of haze episodes during March 12‐16, and a return to background haze for March 17‐18. Angstrom exponents calculated from scattering coefficient data were low during March 9‐11, relatively higher during March 12‐14, and highest during March 15‐18. Surface aerosol data and aerosol optical depth data are in good qualitative agreement for the 10‐day period studied. Background haze was present when trajectories circled the Arctic basin, and haze episodes occurred when trajectories originated in western Asia and Europe.

Effect of humidity on the scattering indicatrix of haze near the earth's surface in the region of ranging angles

In the presented paper are given the results of experimental investigation of the scat- tering indicatrices ~E~ of haze next to the earth in the angle region 0 = 178 ~ for the wavelength ~ ~ i.i ~m. The apparatus for measurement of the coefficient of the directional light scattering (~) and the procedure of its calibration and of the measurements are analogous to those described in (I). The measurements were performed under conditions of haze during twilight and nighttime in May-October, 1979-1980. Simultaneously with the measurements of ~ (8), a base method was used to determine the volume coefficient of attenuation of the atmosphere o~ (~) at wavelengths 0.63 and i.i ~m and also the relative humidity I of the air. The meteorological visibility ~ varied in this case in the range from 3 to 20 km, with ~ in the range from 55 to 98%. To determine the dependence of the absolute scattering indicatrix ~(178 ~ on humidity its values were defined as ~(178 ~ = ~(178~ O~ (~) and averaged over all the realizations for the following ranges of /: 50-60, 60-70, 70-80, 80-87, 87-93, and 93-98%. The results of such an averaging (see Fig. i) with an error not larger than 10% are ap- proximated by the function

Coeficiente de Extinção Fotométricos para o Céu do Rio de Janeiro

Coefficients for atmospheric extinction using B and V Johnson filters were obtained and our results indicate the possibility of determining particle densities in suspension in the atmosphere over the city of Rio de Janeiro. Preliminary data, referred in the present study, are favourably compared to densities of both aerosols in conditions of slight haze, and tropospheric dust in clear conditions.Extinction coefficients are comparable to the ones determined by Chabot Observatory in the San Francisco bay area, here taken as a comparison term due to the similarities between both cities.

Modeling attenuation and phase of radio waves in air at frequencies below 1000 GHz

Moist air is characterized for the frequency range 1–1000 GHz as a nonturbulent propagation medium described by meteorological parameters. An adequate spectroscopic data base for air consists of three terms: (1) resonance information for 29 H2O lines up to 1097 GHz and 44 O2 lines up to 834 GHz in the form of intensity coefficients and center frequency for each line; (2) an empirical water vapor continuum spectrum; and (3) a liquid water attenuation term for haze and cloud conditions. This data base is the heart of two computer programs which calculate and plot attenuation rates (in decibels per kilometer), refractivity (in parts per million), and refractive dispersion (in parts per million). The first covers the troposphere and requires pressure, temperature, and relative humidity as input data. The second addresses isolated line behavior in the mesosphere wherein the geomagnetic field strength H is an additional input parameter due to the Zeeman effect of the O2 molecules. Each oxygen line splits proportionally with H into numerous sublines, which are juxtaposed to form Zeeman patterns spread over a megahertz scale. Patterns of three main polarization cases are considered. Various typical examples for a model atmosphere demonstrate the utility of the approach, provide new information, and underline the serious role that water vapor plays above 120 GHz.

Lichens and Air Quality in Big Bend National Park, Texas

This study was undertaken because of reports of decreased visibility due to haze and the possibility of increased air pollution in the park. Numerous localities where lichens had been collected 10 years ago were revisited in 1980 to look for any changes in the lichen flora. Photographs were taken from scenic vistas where photographs had been taken earlier. Permanent photographic points for lichens were established for long term monitoring. It is argued that fruticose li- chens are just as useful for monitoring air quality in arid areas as in wetter areas. There has been no loss of lichen species at any locality over the past 10 years and haze conditions have not changed much. It is concluded that no significant increase in air pollution has occurred within the park over the past 10 years. In 1966, 1969 and 1970, complete lichen collections were made at 38 localities in Big Bend National Park. Label data for all collections are stored in a computer data base at the University of Minnesota (Wetmore 1979) and a report on the macrolichens (foliose and fruticose lichens) from these localities has been published (Wetmore 1976). Even though the general climate in the park is quite dry, several species of fruticose lichens were found at numerous localities in the mountains. At the time these collections were made, color photographs were taken from various scenic vistas throughout the park. Recent observations by various people have reported the visibility in the park has been degraded due to increased haze conditions. There has also been concern that the haze might be associated with air pollutants that could damage the vegetation of the park. Possible sources of the air pollution are Carlsbad, New Mexico, and El Paso, Texas, These cities are about 400 km northwest of the park and wind patterns are such that air masses from these cities could blow into the park. Lichens are slow growing and remain alive for many years, and therefore can be used as long-term indicators of air quality. They are also known to be very sensitive to many atmospheric pollutants. Some lichens are damaged or killed by low levels of sulfur dioxide (0.5 ppm, Nash 1973), nitrogen oxides (2-4 ppm, Nash 1976) and other strongly oxidizing compounds (Nash 1972, 1975; Ferry et al. 1973). The algae of the thallus seem to be the

The effects of non-standard conditions on visibility measurement

The effects of non-standard visibility observation conditions upon computed visual range (meteorological range) were investigated using data from an eastern U.S. visibility study sponsored by the Electric Power Research Institute. Data collected by multi-wavelength telephotometry was specially marked in the field when non-standard conditions were observed. The non-standard conditions explored were those which violate the assumptions implicit in routine visual range calculations. These conditions include bright and dark clouds behind the target, bright haze, shadowed targets, and snow-covered targets. The errors caused by non-standard conditions were evaluated by comparing derived visual ranges and observed luminances along affected and non-affected viewing paths. The factors introducing error into visual range calculations during bright haze and bright cloud conditions were found to depend strongly on the relative degrees of light scattering in front of and behind the target. Large errors were noted in visual ranges derived for snow-covered targets if an intrinsic contrast of − 1.0 was assumed; a method for approximating intrinsic sky/target contrast was applied to correct these errors. Recommendations are provided for recognition of non-standard conditions and field flagging of data.

Vertical Structure in Atmospheric Fog and Haze and Its Effects on Visible and Infrared Extinction

Abstract Vertical structure of the size distribution and number concentration of particulates in atmospheric fog and haze near Grafenwohr, West Germany, were measured with a balloonborne light-scattering aerosol counter for periods spanning parts of eight days in February 1976. For haze (∼5 km visibility) conditions, little vertical variation is seen; but for low visibility (<1 km) fog conditions, significant vertical increases in concentration of droplets with radii larger than 4 μm are seen over the first 150 m altitude. For haze, the particle size distribution is approximated by a log-normal with geometric mean radius rg≈0.2 μm and geometric standard deviation σg≈1.9. For fog, a bimodal distribution is found with a relative maximum for the larger particle mode at radii of 4 to 6 μm and corresponding values rg≈5 μm and σg≈1.6; the smaller particle mode has values of rg≈0.3 μm to rg≈0.6 μm and σg≈1.8 to σg≈2.5. Liquid water content values for haze and fog range from 10−4 to 0.45 g m−3. Extinction calcula...

Spectral Dependance of Inverse Problem in Radiant Energy Transfer Through Haze

The spectral distribution of source intensity needed to obtain a prespecified irradiance at the receiver for different atmospheric haze condition has been calculated on the basis of semi-empirical expression due to Eldridge and Johnson (1962). Variations in the spectral distributions at the receiving end due to a general service lamp for different atmospheric condition are removable by use of matched filters in front of the source. For this study the scattering media are assumed to consist of uniform water dropl.ts of 0.1 (0.1) 0.6 micron radii with a concentration of 103 particles per c.c. The receiving distances are 0.25 (0.25) 1.0 (0.5) 4 0 Km. Attempt has been made to find out a suitable single matched filter for particular atmospheric haze condition to obtain uniform receiving illumination (with 5 percent variation) for all distances upto 1 Km.

Ozone absorption coefficients and haze corrections for total ozone measurements with Dobson spectrophotometer

From laboratory measurements of absorption in an ozone cell with a Dobson spectrophotometer and their comparison with the results of observations made with atmospheric ozone, Dobson has concluded that the absorption coefficients of ozone (from Vigroux' work) for the Band C wave lengths are too high and have to be revised. Observations made at Ahmedabad confirm this, Accepting that the difference of ozone absorption coefficients for A and D is 1.388 and assuming that by using the AD difference method the haze correction is eliminated, we determine the total ozone amount. Combining this With measurements of apparent total ozone with A wave.lengths alone, the haze correction is calculated. With this haze correction and known , ozone amount, the absorption coefficients for C and B wave lengths can be calculated.. The same absorption coefficients are obtained under varying conditions of haze. They are nearly the same as those obtained by Dobsonfrom his laboratory measurements with an ozone cell.

Photogrammetric Determination of Azimuths

Precise azimuth determination to ±1.0 sec of arc over distances of 70 nm to 300 nm is very desirable where electronic survey techniques, such as HIRAN, are used. In January 1962 a series of tests designed to prove the feasibility of a technique of photographic azimuth determinations was conducted by AFCRL. A B-57 aircraft equipped with a flashing stroboscopic light was flown at night at altitudes as high as 35,000 ft between ground camera sites located at Homestead AFB, at Vero Beach, Florida, and at West End, Grand Bahama Island. Six PC-1000 cameras, two located at each site, attempted to photograph the flashing light on the aircraft against a background of stars. The PC-1000 camera has a 1000 mm focal length, and an f/5 lens. Navigation of the aircraft was accomplished by directions from a radar site in the Miami, Florida area. Results of these tests are evaluated from the standpoint of planning this kind of mission, taking into careful consideration haze conditions, star backgrounds, height above horizon for visibility of stars, maximum distances between ground sites and high intensity of the flashing lights.

Observations of the Green Flash

A Letter published in theJournal(Vol. IV, No. 2, p. 211) from Captain Brett Hilder refers to the use of the phenomenon known as the green flash for obtaining longitude at sea, and an editorial comment on the letter suggests that accurate descriptions of what has actually been observed at different times at sea might be of value to meteorologists. The following notes, though they contain no reference to using the observations for navigational purposes, may be of some interest as they are the result of a great many observations of the phenomenon.Numerous reports on observations of the green flash have been published in meteorological publications where, as a general rule, it is accepted that it is only seen under conditions of extreme visibility and clearness of the atmosphere. From numerous personal observations it has been ascertained that this is in fact not so, and that the green flash can be observed under conditions of extreme cloudiness, haze and humidity so long as the horizon is visible at the time of rising or setting of the heavenly body. Another factor affecting the actual sighting of the green flash is the intensity of light emanated by the body, for the flash is of very weak intensity when compared to the normal brilliance of the body observed.