دانلود رایگان مقاله انگلیسی تصویر برداری از راه دور در مقابل عکاسی چشمی: روابط میان معیار های تراکمی روکش درخت - الزویر 2017

abstract

The easy availability and widespread use of remotely-sensed imagery, especially Google Earth satellite imagery, makes it simple for urban forestry professionals to assess a site and measure tree cover density without visiting the site. Remotely-sensed tree cover density has become the dominant criterion for urban forestry regulations in many countries, but it is unclear how much such measures match the eyelevel tree cover density that people experience; or the information gained through site visits, eye-level photography, or from consulting with citizens. To address this uncertainty, we assessed associations among two remotely-sensed and three eye-level tree cover density measures for 140 community street sites across the Midwestern United States with low, medium, or high tree cover coverage by using linear regression analysis. We found significant associations among the two remotely-sensed measures and the three eye-level measures across the three levels of tree cover. The associations between any pair of remotely-sensed and eye-level measures, however, diminish dramatically as canopy cover increased. At high levels of canopy cover, all associations between the remotely-sensed measures and the eye-level measures became statistically insignificant. These findings suggest that measures from remotely-sensed imagery fail to represent the amount of tree cover people perceive at eye-level when canopy cover is medium or high at the site scale. Therefore, the current urban forestry planning regulations, which rely heavily on remotely-sensed tree cover density measurements, need to be revised. We suggest strategic spots where eye-level measures of tree cover density should be emphasized.

5. Conclusion

This study was an initial effort to understand the relationships among multiple measures of tree cover density. At the site scale, measures calculated using remotely-sensed images were not strongly associated with eye-level measures of tree cover density when tree canopy cover was medium (15.1%–30.0%) or high (30.1%–62.0%). The findings presented here challenge the widespread use of remotely-sensed tree cover density as the dominant tool for guiding the design and management of urban forests, at least at the site scale. One promising way to overcome the challenges identified here would be to integrate measures of tree density from remotely-sensed imagery and eye-level photography and develop a comprehensive index of greeness that can more sensitively depict the urban tree canopy that people experience on site. Our findings should caution designers, planners, and urban forest professionals that heavy reliance on digital aerial photographs and maps may lead to landscape assessments and decisions that do not represent individuals’ experience of a site. Using eye-level photographs and visting a site in person are still indispensible tools when tree cover density is at medium or high levels.