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Aeolian processes and landforms
Published in Richard J. Chorley, Stanley A. Schumm, David E. Sugden, Geomorphology, 2019
Richard J. Chorley, Stanley A. Schumm, David E. Sugden
There has been a variety of suggested relationships between the mass transport of drifting snow and wind velocity (Figure 16.23) both because of difficulties of measurement and because of the possible range of physical changes undergone by blowing snow. The latter include frictional melting; hardening and entrainment inhibition of snow surfaces at higher wind speeds; the increase of surface snow density with wind speed; differences of surface hardness due to normal melting processes; the variation of the threshold separating saltation and suspension transport; and the important effect of sublimation – the direct evaporation of ice crystals. It has been estimated that snow particles of 0.1, 1.5 and 2 mm diameter will sublimate completely after moving in air through some 450 m, 900 m, and 1400 m, respectively, and wind-blown snow in Wyoming has been shown to lose up to 25 per cent of its mass through sublimation after moving 500 m and some 80 per cent after 3000 m. Another factor affecting snow transport is the rate of snow supply, and it requires at least a length of 100 m of exposed snow surface to initiate a steady state of downwind drift movement. The transport curve of Budd et al. (1966) (see Figure 16.23) implies that most drift transport occurs during a few high-magnitude wind storm events, but it has been shown empirically that significant drifting occurs at lower windspeeds with, for example, 54–69 per cent of the total annual drift accumulation in some small Colorado catchments occurring during five weeks with windspeeds not exceeding 9 m/s.
Multilevel weather detection based on images: a machine learning approach with histogram of oriented gradient and local binary pattern-based features
Published in Journal of Intelligent Transportation Systems, 2021
Md Nasim Khan, Anik Das, Mohamed M. Ahmed, Shaun S. Wulff
Transportation agencies and the Department of Transportations (DOTs) have been using data from RWISs for various safety applications, including VSL and Dynamic Massage Sign (DMS). While the performance of the congestion-based VSL depends on the suitability of fundamental diagram structure (Barua et al., 2017), the performance of the weather-based VSL largely relies on the real-time and accurate identification of road-surface weather conditions. Note that the implementation of weather stations to get real-time weather information for the entire roadway network of a state is not financially viable due to the high installation cost. In addition, sensors on the weather stations are usually not mounted at the road surface level. Many weather conditions, such as blowing snow, may reduce the visibility only at the road surface level due to the accumulation of snow on the side of the road, especially in the mountainous region in the presence of snow fences. In such a case, the visibility at a higher elevation from weather stations might not represent the actual scenario. To overcome this problem, many studies have used in-vehicle sensors, including video cameras, to detect weather conditions at road surface level. However, most of the weather detection studies, as described in the previous sections, require an arbitrary object in front of the vehicle. These detection methods might not be reliable in everyday scenarios because the objects could be obstructed by other vehicles, especially in congested traffic conditions. Keeping these research needs in mind; the main motivation of this paper is to develop an affordable in-vehicle weather detection system that can provide accurate trajectory-level weather information at road surface level in any weather conditions and does not require an arbitrary object in front of the vehicle to function properly. For non-VSL corridors, the proposed weather detection system can provide low-cost advisory VSL. In addition, the system can also be used to disseminate cautionary messages within Advanced Traveler Information System (ATIS) over the DMS to warn the drivers about potentially hazardous weather, especially on roadways with no RWIS.