Foggy Conditions Research Articles

Lapland longspur mortality at an oil well drilling rig site, Laramie County, Wyoming

ABSTRACTTwo hundred fifty‐one Lapland longspur (Calcarius lapponicus) carcasses were recovered around an oil well drilling rig in Laramie County, Wyoming, USA, on December 13–14, 2010, apparent victims of a winter storm and “light entrapment” from the lights on the drilling rig during foggy conditions. We found Lapland longspur carcasses distributed around the drilling rig from 33 m to 171 m. Investigators did not find evidence of bird carcasses on the drilling rig deck or equipment immediately adjacent to the drilling rig. We ruled out chemical toxins and disease as a cause of mortality. Weather conditions, the circular depositional pattern of carcasses around the drilling rig, and bird necropsy results led investigators to conclude that the Lapland longspur mortality was the result of the migrating birds entering the area illuminated by the drilling rig lights in freezing fog and the birds repeatedly circling the drilling rig until they fell to the ground in exhaustion and dying from subsequent trauma. Further research is needed to understand how to most effectively adjust lighting of onshore drilling rigs to reduce the potential for avian light entrapment. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Foggy Port Surveillance Video Clearness Algorithm Based on Wavelet Packet Decomposition

Port surveillance videos are degraded seriously in foggy conditions. This paper presented a clearness algorithm based on wavelet packet decomposition. Firstly, we extracted the background image from degraded videos and established the updated model; Secondly, we detected the moving objects as foreground images; Thirdly, we defogged these images based on wavelet packet decomposition; Finally, we fused the background and foreground images together. The experimental results show that our method is more effective.

Review on Visibility Monitoring in Expressway under Foggy Condition

Visibility monitoring under foggy condition is very essential to traffic safety on expressway. The definition and influence factor of visibility are summarized. The main advantages and disadvantages of three common methods- transmission method, scattering method, digital imaging method and related visibility meters are analyzed and compared here. The domestic and foreign status and trends of visibility research on foggy expressway are mainly introduced from thick fog forecast, warning and monitoring system, visibility detection device. Aiming at the existing problems of visibility monitoring in expressway, some suggestions for improvement are put forward at last.

Effects of foggy conditions on drivers’ speed control behaviors at different risk levels

Driving in foggy weather is a potentially dangerous activity that has been investigated using various approaches. However, most of the previous research has focused on the driver’s response in a particular situation under foggy conditions and lacks a systematic analysis of driving performance, especially speed-related behaviors. This paper presents a hierarchical driving performance assessment method to investigate the effects of foggy conditions on drivers’ speed control behaviors. With this method, driving behaviors were tested in three simulated driving scenarios classified into three risk levels: basic speed control while driving along road segments at a low risk level, dynamic speed adjustment in car-following situations at a medium risk level, and emergent speed responses to precrash situations at a high risk level. The driving simulation experiment results indicated that the drivers intended to reduce their speeds in order to lower the driving risk in foggy conditions at all three risk levels. However, due to the limited visibility in fog, the drivers could not observe and respond to impending changes in road geometries in a timely way, which resulted in higher operating speeds than in clear weather conditions. At the medium risk level, the drivers’ dynamic speed adjustment behavior was degraded in the fog, with both acceleration and deceleration rates lower than in the clear conditions; therefore, more rear-end collisions happened in the foggy conditions than in the clear conditions. At the high risk level, the experiment results showed that drivers’ speed compensation in foggy conditions does not sufficiently reduce their crash-involvement risk, but it can effectively lower the crash severity, as indicated by a significantly lower collision speed.

Spatio-temporal detection of fog and low stratus top heights over the Yellow Sea with geostationary satellite data as a precondition for ground fog detection — A feasibility study

An accurate cloud top retrieval from geostationary (GEO) and low earth orbit (LEO) platforms is still a pending problem. This particularly holds for low level clouds. Furthermore, cloud top height is a crucial parameter to calculate cloud immersion of underlying terrain from GEO/LEO data and thus, for the discrimination between low level stratus and ground fog, where the latter is a main obstruction for air, land and sea traffic. All problems are particularly evident for ocean areas such as the Yellow Sea where no ground observations are available. In this paper, a novel method is presented to retrieve low stratus/fog top heights with special reference to the Yellow Sea and its surroundings, based on GEO data of MTSAT-1 and MTSAT-2 (JAMI sensor) and LEO data (MODIS sensor on Terra and Aqua) using the infrared (IR) water vapor and split-window bands. Two cases with very good data coverage are discussed where the retrieved low stratus/fog heights are compared to CALIPSO cloud top heights, and simulated data using the mesoscale model WRF. The comparison of JAMI retrievals with the spatial data sources used shows an encouraging accuracy (root-mean-square error, RMSE, around 300m) in comparison to other retrieval schemes base on IR data hitherto published. A validation of the retrievals for the position of two radiosonde stations using available sounding data of seven foggy days revealed an even better performance with an average deviation of 184m (standard deviation of 132m). However, the validation revealed that the application of the underlying equations to retrieve inversion strength and thickness under foggy conditions would need some adjustments because the equations taken from the work of Liu and Key (2003) were originally developed for clear sky situations. Thus, the adaptation of the original scheme during future work should especially address cloudy conditions under moderate inversion strengths which could lead to an improvement of the retrieval accuracy.

Detection of Runway and Obstacles using Electro-optical and Infrared Sensors before Landing

For safe aircraft operations, detection of runway incursions especially during landing and takeoff is essential. And it is important that such detection technique is capable of detecting the distant objects so that pilot has enough response time to take corrective action. This paper presents techniques to detect runway and runway incursions using electro-optical color camera and medium wave infrared sensor on-board the aircraft during approach for landing. The detection process consists of horizon detection to reduce runway search space in sensor image and then detect runway and obstacles. The information is then presented to the pilot to improve pilot situational awareness. The performance of the proposed techniques are evaluated in flight simulators with simulated images of electro-optical and infrared sensors on-board the aircraft during approach for landing at a distance of 3 nautical miles from runway threshold during day/night and in low visibility CAT II foggy conditions. Effectiveness of the techniques with statistics of runway detection, miss detection and false alarm for different case studies have been provided and discussed.

Aerosol Number Concentrations and Visibility during Dense Fog over a Subtropical Urban Site

There is now enough evidence of greater frequencies and extent of fog formation in urban areas. These could easily be linked to rapid increase in aerosol number concentration (ANC) peculiar to polluted urban environments. It is therefore pertinent to study ANC and visibility alongside the meteorological parameters in order to investigate the relationships which may possibly exist between these parameters especially during foggy conditions. This study based on field measurements of ANC for aerosol spectrum varying from 0.3 µm to 20 µm attempts to investigates whether a threshold ANC could be associated with a given visibility range during low visibility conditions including dense fog episodes. Thus, the present work explores relationship between ANC size spectrum and visibility (100 m–4500 m) in a polluted urban environment in India with specific reference to episodes of dense fog during winter period. The study depicts a threshold minimum value of ANC during foggy conditions. A power relationship between ANC and visibility is obtained. Further, aerosol number distribution and size distribution function are also studied and empirical relation is compared with previous studies. Further work is suggested to strengthen the findings presented here.

Latitudinal and Size Segregated Compositional Variability of Aerosols over the Indian and Southern Ocean during 2010 Austral Summer

To characterize the spatial variations in size segregated aerosols, samples were collected over the Indian and Southern oceans (7°N to 68°S) during the Indian expedition to Southern Ocean (January–February 2010). The chemical and mass concentrations of ions were measured in nine size classes (0.4–> 10 µm) of aerosols through ion-exchange chromatographic system and gravimetric estimates, respectively. Mass concentrations of coarse aerosols increase towards the Antarctic coast which is well correlated with the increasing humidity suggesting growth of particles. The study area was found to be predominately impacted by sea salt aerosols with a sea salt load of 91%. F–, Cl– and NO3– reflected anthropogenic impact within the fine mode aerosols but the marine influence dominated the coarse mode. Methanesulphonic (MSA) was predominantly of biogenic origin but a substantially low MSA/nssSO42– ratio suggested that DMS contribution to the total nssSO42– concentration was low. NH4+ concentrations showed a shift from fine to coarse particles, with a trimodal distribution over the Southern Ocean. Our study reports a significant Cl– depletion in the aerosols and the degree of Cl– deficit was size-dependent, increasing with decreasing particle sizes. The neutralization ratios suggested differential behavior of ions with respect to the prevailing meteorological conditions. The coarse mode aerosols were neutralized by ammonia leading to the formation of NH4NO3 particles. The fine modes were predominately composed of NH4HSO4 and its formation is favored by the high humidity and foggy conditions over the study area. Factor analysis support that the Southern Indian Ocean (10°S to 59°S) had the highest loading of anthropogenic and sea salt aerosols, which lead to the formation of secondary aerosols through gas to particle transformations. The rocky Antarctic coastline, act as a source of coarse crustal aerosols over the Southern Ocean (60°S to 65°S).

Suppression of transpiration due to cloud immersion in a seasonally dry Mexican weeping pine plantation

Cloud immersion affects the water budget of fog-affected forests not only by introducing an additional source of water (via cloud water interception by the canopy), but also by suppressing plant transpiration. The latter effect is often overlooked and not routinely quantified, restricting a complete understanding of the net hydrological effect of cloud immersion and the possible consequences of projected reductions in cloud immersion under drier and warmer climates in tropical montane regions in the coming decades. This paper describes an approach to quantify the suppression of stand-level tree transpiration (Et) due to cloud immersion using measurements of sapflow, fog occurrence (visibility), leaf wetness, and near-surface climate. Estimates of fog-induced Et suppression in a 10-year-old Pinus patula plantation in the montane cloud belt of central Veracruz, Mexico, are presented for two contrasting dry seasons and a wet season. Fog occurred for 32% of the total study period, although showing pronounced seasonal variation (e.g. 44% during the second dry season). When fog occurred it was accompanied by rainfall during three quarters of the total time. Although the canopy was wet for almost a third of the time, fog-induced canopy wetness constituted only a very small portion of this total (2%). Relative to sunny conditions, Et was suppressed by 90±7% under conditions of dense fog versus 83±7% under light fog and 78±10% during overcast conditions. Quantification of the potential change in annual Et associated with two scenarios for future cloud immersion at the study site revealed that: (i) when all fog occurrence is replaced by overcast conditions, mean annual Et (645±50mm) is likely to increase by only 2±1%; and (ii) when sunny conditions replace all foggy conditions, the likely increase in annual Et is 17±3%. As the rise in the regional lifting condensation level is likely to be on the order of only a couple of hundred meters and will probably result in a shift to overcast rather than clear-sky conditions, the present results suggest that the corresponding impact on Et may be relatively small. Consequently, a climate change-related reduction in dry-season precipitation, through the associated potential reductions in soil water reserves, presents a more worrisome prospect for plant–water relations and water yield from headwater catchments than diminishing cloud immersion alone. The present results highlight the need for better projections of climate change-related alterations in cloud cover and immersion, as well as rainfall patterns for tropical montane regions.

Research on the Enhancement and Processing of Faint Laser Signal in Foggy Conditions

For the echo of the laser signal was relatively weak and accompanied by a lot of noise in a foggy condition, a multi-pulse cumulative method for enhancing weak laser signal was proposed. The enhancement principle and method of multi-pulse signal accumulation was studied, and with it the weak signal was processed. The matched filter algorithm was used to extract the characteristics of laser echo signal, the original signal and the accumulated signal was processed by the matched filter, respectively, which greatly improves the signal to noise ratio (SNR). The experimental results show that: four separate laser signals accumulated together enhance SNR by twice; the accumulation of multi-pulse laser signal can effectively improve SNR, and the matched filter can strengthen the signal while suppressing noise.

The Processing of Laser Signal Based on Spatial Correlation Threshold Filtering in Foggy Media

with the difficulties of extracting the feature of faint laser signal reflecting from non-cooperative target in foggy conditions, the spatial correlation threshold filtering approach was proposed based on spatial correlation filtering. The thought, theory and implementation methods of the spatial correlation threshold filtering was elaborately studied, especially, the selection of the threshold for the filter was analyzed. A comparative study of threshold filtering, spatial correlation filtering and spatial correlation threshold filtering was carried out to verify the filtering effect for the laser signal reflecting in the foggy environment, the experiment results shows that: spatial correlation threshold filtering method has the most effective filtering. The processing results show that the new method can effectively eliminate noise and keep weak laser signal characteristics, which lays solid foundation for identification of target nature.

Physical and chemical characterization of ambient aerosol by HR‐ToF‐AMS at a suburban site in Hong Kong during springtime 2011

An Aerodyne high‐resolution time‐of‐flight aerosol mass spectrometer (HR‐ToF‐AMS) has been employed in a field sampling campaign at a suburban coastal site in Hong Kong in springtime 2011 to provide insights into the size‐resolved chemical composition of nonrefractory submicron aerosol species. This is the first time that such detailed real‐time measurements have been made in Hong Kong. The total nonrefractory PM1 was dominated by sulfate (51.0%) and organics (28.2%) with considerable acidity (average in situ pH = 0.95) and a characteristic bimodal particle size distribution with peaks at 200 and 570 nm of vacuum aerodynamic diameter (Dva). Source apportionment of organic aerosol yielded three characteristic aerosol fractions (hydrocarbon‐like organic aerosol, semivolatile organic aerosol and low‐volatile organic aerosol) with distinct temporal patterns and distributions in different particle size regions. The influence of air mass origin on species concentrations, particle size distributions and elemental ratios was investigated using backtrajectory analysis. Larger particle diameters, greater fractions of oxygenated organic aerosol and higher organic‐to‐carbon ratios were observed during coastal and continental air mass influence. Three major pollution events with elevated nonrefractory PM1 concentrations were observed in the sampling period, which were related to distinct meteorological and circulatory conditions. Accumulation and redistribution of local and regional pollutants were notable in a period of strong land‐sea breeze over the Pearl River Delta region, with considerable photochemical activity and particle aging. Increased fractions of oxygenated organic aerosol were apparent in foggy conditions, illustrating the importance of aqueous phase oxidation processes in a cooler and more humid time period.

The Research on Defogging Algorithm Based on Dark Channel in Color Space

In order to restore degraded image quality under foggy conditions, this paper proposes an improved defogging algorithm based on dark color knowledge in color space. According to the scene depth relationship between objects in a foggy image, the algorithm can repair the dark color figure, in which the grey scale line distance is used to judge edges, the most similar point of dark colors is selected as new value of dark value based on the character of the adjacent dark color, and the dark color image is used to obtain atmospheric light value automatically. Finally, the defogging purposes have been achieved based on the inverse process of the model. Experimental results show that improved algorithm effectively improves the visual effect of fog-degraded images.

Satellite-Based Technologies in Use for Extreme Nocturnal Mountain Rescue Operations: a Synergetic Approach Applying Geophysical Principles

Mountain-rescue operations require rapid response whilst also ensuring the security of the rescue teams. Rescuing people in a big rock-face is even more difficult if night or fog prevent sight. The paper presents a technical solution to optimally support, under these aggravated conditions, the location of the casualties and the navigation of the rescue team(s) in a rock-face from a coordination station. In doing so, standard components like a smartphones with GPS functionality, a data communication on a client–server basis and VR visualisation software have been adapted to the specific requirements. Remote support of the navigation in steep rocky terrain requires a highly accurate wall model which permits the local experts of the coordination station to dependably estimate geometry and structure of the rock along the rescue route and to convey necessary directives to the retrieval team. Based on terrestrial laser-scans from different locations, such a model has been generated for the mighty Dachstein South Face (Austria) and texturised with digital photographs. Over a twelve-month period, a transdisciplinary team of the Dresden University of Technology (Informatics, Electrical Engineering, Cartography) developed and integrated the various technical modules of the mountain-rescue support-system (digital rock-face model, optimised GPS data transmission between mobile device, server and client, data filtering, and dynamic visualisation component). In summer 2011 the proper functioning of the prototype was demonstrated in a rescue exercise under foggy dusk conditions.

Comparison of sonic anemometer performance under foggy conditions

A sonic anemometer comparison was performed at a mountain cloud forest site in Taiwan to evaluate the effect of fog on sonic anemometers performance, with particular emphasis to their employment in eddy-covariance applications. Four sonic anemometers (Campbell CSAT3, Gill R3-50, METEK USA-1, and R.M. Young 81000VRE) were tested for 15 consecutive days with an overall fog duration of 86h.Four aspects were analyzed: (1) spike statistics during foggy and non-foggy conditions, (2) spectral and co-spectral analyses before, during, and after 16 fog events, (3) correlations between turbulence characteristics of wind and temperature, and (4) flux error estimations.All sonic anemometers produce more spikes when the visibility is below 1000m, compared to conditions with visibilities above 1000m. However, the overall number of spikes caused by fog is generally low and therefore of no concern for any of the tested sonic anemometers.Spectral analyses showed that for most anemometers fog mostly affects spectra of the sonic temperature. Here, the high frequency range is either damped or amplified. These effects worsen with increasing duration and density of fog. In case of the 81000VRE and the USA-1, all three wind component spectra, sonic temperature spectra as well as the co-spectra of w’T’ and w’u’ show white noise in the high frequency range during dense fog. The CSAT3 shows noise only in the high frequency range of the sonic temperature and the co-spectra of w’T’. Smallest sensitivity to fog was observed for the R3-50. Nevertheless, differences in resulting fluxes are usually smaller than the flux error of the measurements. Due to the results of the spectral analysis and small flux errors the R3-50 seems to be suited best for eddy covariance measurements and process studies under dense foggy conditions.

Single Image Haze Removal Method for Inland River

Due to environmental pollution, the climate is worsening. The fog days up to 60% of the year in inland certain segments, which it has seriously affected the marine electronic cruise normal operation and navigation safety. According to the inland video image becomes gray and lack of visibility in foggy weather conditions, and in order to remove the haze to get a clear image color and contour, this paper presents a method based on Jones Extension Matrix and the Dark Channel Prior. First, we obtain the light intensity in the atmosphere and the estimated concentration of the haze by using Dark Channel Prior, and via using the Jones Extension Matrix and the parameters of Stokes' Law to eliminate part of the scattered light. At last, we have completed the function of image dehazing by brightness adjustment factor based on N pixels in the field of step brightness and improve the brightness based on Retinex Principle for the recovered image. Experimental results show this algorithm improves scenery visual effect in condition of haze. It is provided a clear video image for the marine electronic cruise in the foggy day. DOI: http://dx.doi.org/10.11591/telkomnika.v11i1.1908

Fast Single Image De-Hazing Using Characteristics of RGB Channel of Foggy Image

Images captured under foggy conditions often exhibit poor contrast and color. This is primarily due to the air-light which degrades image quality exponentially with fog depth between the scene and the camera. In this paper, we restore fog-degraded images by first estimating depth using the physical model characterizing the RGB channels in a single monocular image. The fog effects are then removed by subtracting the estimated irradiance, which is empirically related to the scene depth information obtained, from the total irradiance received by the sensor. Effective restoration of color and contrast of images taken under foggy conditions are demonstrated. In the experiments, we validate the effectiveness of our method compared with conventional method.

Distributions of low molecular weight dicarboxylic acids, ketoacids and α-dicarbonyls in the marine aerosols collected over the Arctic Ocean during late summer

Abstract. Oxalic and other small dicarboxylic acids have been reported as important water-soluble organic constituents of atmospheric aerosols from different environments. Their molecular distributions are generally characterized by the predominance of oxalic acid (C2) followed by malonic (C3) and/or succinic (C4) acids. In this study, we collected marine aerosols from the Arctic Ocean during late summer in 2009 when sea ice was retreating. The marine aerosols were analyzed for the molecular distributions of dicarboxylic acids as well as ketocarboxylic acids and α-dicarbonyls to better understand the source of water-soluble organics and their photochemical processes in the high Arctic marine atmosphere. We found that diacids are more abundant than ketoacids and α-dicarbonyls, but their concentrations are generally low (< 30 ng m−3), except for one sample (up to 70 ng m−3) that was collected near the mouth of Mackenzie River during clear sky condition. Although the molecular compositions of diacids are in general characterized by the predominance of oxalic acid, a depletion of C2 was found in two samples in which C4 became the most abundant. Similar depletion of oxalic acid has previously been reported in the Arctic aerosols collected at Alert after polar sunrise and in the summer aerosols from the coast of Antarctica. Because the marine aerosols that showed a depletion of C2 were collected under the overcast and/or foggy conditions, we suggest that a photochemical decomposition of oxalic acid may have occurred in aqueous phase of aerosols over the Arctic Ocean via the photo dissociation of oxalate-Fe (III) complex. We also determined stable carbon isotopic compositions (δ13C) of bulk aerosol carbon and individual diacids. The δ13C of bulk aerosols showed −26.5‰ (range: −29.7 to −24.7‰, suggesting that marine aerosol carbon is derived from both terrestrial and marine organic materials. In contrast, oxalic acid showed much larger δ13C values (average: −20.9‰, range: −24.7‰ to −17.0‰) than those of bulk aerosol carbon. Interestingly, δ13C values of oxalic acid were higher than C3 (av. −26.6‰) and C4 (−25.8‰) diacids, suggesting that oxalic acid is enriched with 13C due to its photochemical processing (aging) in the marine atmosphere.

Visibility enhancement using an image filtering approach

Abstract The misty, foggy, or hazy weather conditions lead to image color distortion and reduce the resolution and the contrast of the observed object in outdoor scene acquisition. In order to detect and remove haze, this article proposes a novel effective algorithm for visibility enhancement from a single gray or color image. Since it can be considered that the haze mainly concentrates in one component of the multilayer image, the haze-free image is reconstructed through haze layer estimation based on the image filtering approach using both low-rank technique and the overlap averaging scheme. By using parallel analysis with Monte Carlo simulation from the coarse atmospheric veil by the median filter, the refined smooth haze layer is acquired with both less texture and retaining depth changes. With the dark channel prior, the normalized transmission coefficient is calculated to restore fogless image. Experimental results show that the proposed algorithm is a simpler and efficient method for clarity improvement and contrast enhancement from a single foggy image. Moreover, it can be comparable with the state-of-the-art methods, and even has better results than them.

Implementing FDWS(Fog Detect & Warning System) with LED Module Structure : Estimation of Safety Effects

도로상의 운전자는 눈을 통하여 90% 이상의 정보를 취득한다. 하지만 안개로 인하여 전방 시야가 제약될 경우 운전자에게 치명적인 결과를 초래한다. 안개는 시간적, 공간적으로 빠르게 변화하는 특성이 있어 1~2개소에서 측정된 시정거리로 대다수의 구간을 예측하는 것에는 무리가 있다. 이러한 안개에 대한 대책으로 개별차량의 주행속도와 차두거리를 인식하고 대응할 여건을 제공, 안개시 사고발생 가능성을 줄여주는 안개도로 안전운전 지원시스템을 개발하였다. 본 시스템은 차량검지기, 시정계, 안개등, 메인컨트롤러 등 4가지로 구성되어 있다. 시정계는 안개 발생시 가시거리를 측정하고 안개등은 30 m 간격으로 설치되어 시정거리별 적정 휘도를 LED에 표출시킨다. 본 논문은 국도 37호선(파주-적성 1 km 구간)에 설치된 안개도로 안전운전 지원시스템에 대한 운전자 행태 및 효과 평가를 실시하였다. 운전자 행태 측정의 척도는 평균주행속도, 서면설문을 이용하였다. 결과적으로 시스템 설치 후 주간에는 3 km/h, 야간에는 10 km/h의 평균 감속도를 보였다. Although drivers use various sensory channels to control and navigate their vehicles, they acquire most of all driving-related information visually. In fog, no matter what visual acuity is, the visual channel is useless due to the induced poor visibility. Drivers react differently to the adverse weather, resulting in high speed variation. That is why it has the high fatal rate during foggy conditions. Then, it is imperative to provide drivers positive guidance in fog. In this study, the Fog Detect and Warning System (FDWS), being called as the fog lighthouse, was conceived to inform drivers of safety speeds and distances between each vehicle. FDWS includes visibility meters, light bars, and vehicle detectors. The visibility meters calculate sight distances when fog occurs and the estimated sight distances inform drivers through the light bars which are installed at every 30m intervals. The light bars which display red warning lights inform a following vehicle of the position of the leading vehicle to keep the safety distance between the two vehicles. Since the main lights with the high-bright LED (Light Emitting Diode) have high visibilities, drivers can easily recognize far away. Also microwave sensors together with the light bars are installed to detect the presence of vehicles at every 30m intervals. The aim of this paper was to evaluate the effectiveness of the fog system on driver behavior and consciousness. As a pilot study, FDWS was implemented on a 1km section of National Highway No. 37 with a divided four-lane, rural highway. The analysis of the driver behavior was based on mean speed with standard deviation, and a questionnaire survey was conducted to estimate the driver consciousness. The results indicates that FDWS significantly led to an about 3kph (for daytime) and 10kph (for nighttime) reduction in mean speed compared to the system turned off. Also the consciousness survey shows that FDWS was useful helping drivers guide safely in fog.