Visual signal is speedy and requires sunlight hours with no obstructions.
Visual obstruction is the blocking of views or foreshortening of views.
Visual obstruction is defined via peripheral visible area testing regular with the advocated documentation requirement.
1994; 'Robel pole': Best et al. 1998) with alternating 1 dm bands painted darkish and light. The lowest decimetre mark visible on the pole was once recorded as the obstruction measurement. Visual obstruction is commonly used as a measure of cover density (Higgins et al.
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