Analog visibility computer

We address the problem of repeated coverage of a target area, of any polygonal shape, by a team of robots having a limited visual range. Three distributed Cluster-based algorithms, and a method called Cyclic Coverage are introduced for the problem. The goal is to evaluate the performance of the repeated coverage algorithms under the effect of changes in the robots' visual range. A comprehensive set of performance metrics are considered, including the distance the robots travel, the frequency of visiting points in the target area, and the degree of balance in workload distribution among the robots. The Cyclic Coverage approach, used as a benchmark to compare the algorithms, produces optimal or near-optimal solutions for the single robot case under some criteria. The results show that the identity of the optimal repeated coverage algorithm depends on the metric and the robots' visual range.

We discuss the farthest objects on Earth observable for the unaided, healthy naked eye during the daytime, i.e., the maximum visual range for observers on Earth. Visual range depends first on the properties of the material between observer and object and its interaction processes with radiation, but second also on our visual perception system. After a rough comparison of ranges in water, glass, and the atmosphere, we focus on the physical basis of visual range for the latter. As a contrast phenomenon, visual range refers to allowed light paths within the atmosphere. It results from the interplay of geometry, refraction, and light scattering. We present a concise overview of this field by qualitative descriptions and quantitative estimates as well as classroom demonstration experiments. The starting point is the common geometrical visual ranges, followed by extensions due to refraction and limitations due to contrast, which depend on scattering and absorption processes within the atmosphere. The quantitative discussion of scattering is very helpful to easily understand the huge ranges in nature from meters in dense fog to hundreds of kilometers in clear atmospheres. Extreme visual ranges from about 300 km to above 500 km require optimal atmospheric conditions, cleverly chosen locations and times, and a sophisticated topography analysis. Even longer visual ranges are possible when looking through the vertical atmosphere. From the ISS, daytime ranges well above 1000 km are possible.

Effect of Visual Range on Driving Speed on Low-grade Highway

The measurement of atmospheric properties from which visual range and thus "visibility" can be inferred reliably is a difficult task. One approach to instrumental measurement of atmospheric properties that can be interpreted in terms of visual range, with appropriate assumptions, is to use an optical transmissometer. Such an instrument provides a measure of the atmospheric extinction coefficient averaged over the propagation path and bandwidth of the instrument. When visual ranges are to be measured, the instrument baseline must necessarily be a significant fraction of the maximum visual range to be resolved and both micro-scale and macroscale beam effects are evident in the measurements. To realize the desired measurement of transmittance due to extinction by aerosol, it is necessary that the errors in measurement of atmospheric transmittance due to gaseous absorption and the macroscale components of atmospheric transmittance due to stochastic and deterministic refraction be minimized. This paper describes the field testing on an 18 km folded baseline of a long-path laser transmissometer parametrically designed for visual range measurements under good visibility conditions. Design parameters, instrument performance, measurements and data interpretations are presented. It is concluded that with large collecting optics, aperture averaging and adjustment of beam divergence, stochastic and refractive effects can be sufficiently minimized to make the transmissometer a useful instrument for visual range measurements.

Visual range and size of atmospheric particles

Atmospheric visibility is one of the indicators used to evaluate the status of air quality. Based on a conceptual definition of visibility as the maximum distance at which the outline of the selected target can be recognized, an image analysis technique is introduced here and an algorithm is developed for visibility monitoring. Although there are various measurement techniques, ranging from bulk and precise instruments to naked eye observation techniques, each has their own limitations. In this study, a series of image analysis techniques were introduced and examined for in-situ application. An imaging system was built up using a digital camera and was installed on the study sites in Incheon and Seoul separately. Visual range was also monitored by using a dual technology visibility sensor in Incheon and transmissometer in Seoul simultaneously. The Sobel mask filter was applied to detect the edge lines of objects by extracting the high frequency from the digital image. The root mean square (RMS) index of variation among the pixels in the image was substantially correlated with the visual ranges in Incheon and Seoul with correlations of <TEX>$R^2$</TEX>=0.88 and <TEX>$R^2$</TEX>=0.71, respectively. The regression line equations between the visual range and the RMS index in Incheon and Seoul were VR=<TEX>$2.36e^{0.46{\times}(RMS)}$</TEX> and VR=<TEX>$3.18e^{0.15{\times}(RMS)}$</TEX>, respectively. It was also confirmed that the fine particles (<TEX>$PM_{2.5}$</TEX>) have more impacts to the impairment of visibility than coarse particles.

This article presents the results of an experimental investigation into the relationship between visual range and the size distribution of ice fog particles at Fairbanks, Alaska. An empirical function is developed for the constant appearing in the Trabert formula. Use of this function gives visual ranges that agree with measured values for size distributions of different width.

The effects of non-standard conditions on visibility measurement

Site specific factors influencing the visual range calculated from teleradiometer measurements

Models of visual range and location distances are crucial for quantification of vision based feeding opportunities and predation risk in the pelagic habitat. We compare an earlier published model with measurements of the reactive distance of Gobiusculus flavescens relative to two species of copepods. Although this model gave reasonable predictions at low light intensities, the measurements of reactive distance at higher intensities were much lower than those predicted by the model. We modified the model to account for saturation at high light intensities. With this additional feature, the correspondence with the G.flavescens observations was significantly improved. Furthermore, the revised model is consistent with earlier published data on fish contrast thresholds obtained over a wide range of target sizes and irradiance levels. Given the values of only two parameters, one sensitivity threshold and one saturation parameter, the model is capable of predicting visual ranges for relatively large intervals of light intensity, prey size and turbidity. Other published visual range models are briefly reviewed and compared with our model.

During the winter of 2008, daily time series of images of five "unit-cell chequerboard" targets were acquired using a digital camera. The camera and targets were located in the Majura Valley approximately 3 km from Canberra airport. We show how the contrast between the black and white sections of the targets is related to the meteorological range (or standard visual range), and compare estimates of this quantity derived from images acquired during fog and mist conditions with those from the Vaisala FD-12 visibility meter operated by the Bureau of Meteorology at Canberra Airport. The two sets of ranges are consistent but show the variability of visibility in the patchy fog conditions that often prevail in the Majura Valley. Significant spatial variations of the light extinction coefficient were found to occur over the longest 570 m optical path sampled by the imaging system. Visual ranges could be estimated out to ten times the distance to the furthest target, or approximately 6 km, in these experiments. Image saturation of the white sections of the targets was the major limitation on the quantitative interpretation of the images. In the future, the camera images will be processed in real time so that the camera exposure can be adjusted to avoid saturation.

How far can we see with the naked eye at night? Many celestial objects like stars and galaxies as well as transient phenomena such as comets and supernovae can be observed in the night sky. We discuss the farthest distances of such objects and phenomena observable with the unaided eye during the night time for Earth bound observers. The physics of night time visual ranges differs from the one of daytime observations because human vision shifts from cones to rods. In addition, mostly point sources are observed, due to the involved large distances. Whether celestial objects and phenomena can be detected depends on the contrast of their radiation and the background sky luminance. We present a concise overview of how far we can see at night by first discussing effects of the earth atmosphere. This includes attenuation of transmitted radiation as well as its role as source of background radiation. Disregarding attenuation of light due to interstellar and intergalactic dust, simple maximum nighttime visual range estimates are based on the inverse square law, which can be easily verified by laboratory and demonstration experiment . From the respective calculations, we find that individual stars within the Milky Way galaxy of up to 15 000 light years are observable. Even farther away are observable galaxies with several billion stars. The Andromeda galaxy can be observed with the naked eye in a distance of around 2.5 million light years. Similarly, the observability of supernovae also allow a visual range beyond the Milky Way galaxy. Finally, gamma ray bursts as the most energetic events in the universe are discussed with regard to naked eye observations.

All modes of surface transportation can be disrupted by visibility degradation caused by airborne volcanic ash. Despite much qualitative evidence of low visibility on roads following historical eruptions worldwide, there have been few detailed studies that have attempted to quantify relationships between visibility conditions and observed impacts on network functionality and safety. In the absence of detailed field observations, such gaps in knowledge can be filled by developing empirical datasets through laboratory investigations. Here, we use historical eruption data to estimate a plausible range of ash-settling rates and ash particle characteristics for Auckland city, New Zealand. We propose and implement a new experimental set-up in controlled laboratory conditions, which incorporates a dual-pass transmissometer and solid aerosol generator, to reproduce these ash-settling rates and calculate visual ranges through the associated airborne volcanic ash. Our findings demonstrate that visibility is most impaired for high ash-settling rates (i.e. > 500 g m−2 h−1) and particle size is deemed the most influential ash characteristic for visual range. For the samples tested (all < 320 μm particle diameter), visibility was restricted to ~ 1–2 m when ash settling was replicated for very high rates (i.e. ~ 4000 g m−2 h−1) and was especially low when ash particles were fine-grained, more irregular in shape and lighter in colour. Finally, we consider potential implications for disruption to surface transportation in Auckland through comparisons with existing research which investigates the consequences of visual range reduction for other atmospheric hazards such as fog. This includes discussing how our approach might be utilised in emergency and transport management planning. Finally, we summarise strategies available for the mitigation of visibility degradation in environments contaminated with volcanic ash.

The visual sense supplies a major part of the information necessary for avoiding traffic accidents and fog impedes this channel of information, even though the invention of radar has removed the limitation to a considerable extent. The closure of airports is caused mainly by reduced visual range and partly by low cloud, or by typhoons in Japan. The length of signal sections on the Japan National Railway (600 m) was determined from a study of the frequency of visual ranges. Nishikura and others have studied the influence of visibility on the probability of marine traffic accidents and conclude that the ratio of the collision danger with a visibility less than 1 km and more than 1 km is in the range of from 30 to 100. Wheatley et al. have also shown the risk of traffic accidents to be high in bad visibility in the Dover Strait.

PurposeTo explore quality of life related with intermediate vision of patients before and after cataract surgery, and to make patients’ experience available for the design of future scales that assess visual function related with intermediate distance.Patients and MethodsA qualitative research methodology based on thematic content analysis was used to explore vision-related quality of life based on the experiences of patients with cataract. Patients were recruited at the Service of Ophthalmology of the Hospital de Sant Pau (Barcelona, Spain). Data were collected through nineteen semi-structured interviews conducted with patients diagnosed with cataract and implanted with a standard aspheric monofocal intraocular lens (IOL) (Tecnis® ZA9003) (n = 6), an enhanced monofocal IOL (Tecnis® Eyhance ICB000) (n = 6), and patients from the waiting list (n = 7). The data analysis consisted in coding, aggregation, and theme development of the transcribed audios.ResultsPatients on waiting lists reported difficulty and insecurity in performing daily and meaningful tasks related to near visual ranges (eg: threading a needle, reading price tags), intermediate (eg: using a computer or dialling numbers on a smartphone), and distant (eg: recognizing faces, walking on uneven surfaces). Patients after surgery with the standard IOL reported improvement in performing activities mainly in the distant visual range, but also the need for a better communication with clinical staff to adjust their own expectations on the results of the surgery. Finally, patients implanted with the enhanced IOL reported satisfaction and improved visual function in performing daily activities, especially those related to the intermediate visual range.ConclusionOur exploratory study found that patients after cataract surgery with the enhanced IOL reported a better performance in activities that require the intermediate vision. These results will inform the development of scales to assess vision-related quality of life in the intermediate visual range prioritizing outcomes according to patients’ daily and meaningful activities.