Department of Forest Resources and Environmental Conservation
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- A Comparison of Geospatial Methods for Tree Canopy Assessment: A Case Study of an Urbanized College CampusHwang, Won; Wiseman, P. Eric (2019-04-03)Urban tree canopy (UTC) assessment is essential for understanding the structure and function of urban forests and devising management strategies. Geospatial techniques are routinely utilized for UTC assessment, yet their capabilities and limitations may not be apparent to urban forestry practitioners. In this paper, we provide an overview of two primary methods of geospatial UTC assessment: photo interpretation (PI) and computerized image classification (IC). We then evaluate these methods through a case study of an urbanized college campus in the eastern United States. We examined the web-based application i-Tree Canopy as a PI method. Because this method relies on statistical point sampling, we performed independently replicated assessments of our study area at various point sample sizes to examine the effect of sample sizes on accuracy and certainty of the land cover estimates. We further evaluated two IC methods: a proprietary analysis using high-spatial resolution imagery and a low-spatial resolution analysis using the web-based application i-Tree Landscape. Tree cover assessed in our study area (3.58 km2) with i-Tree Canopy began stabilizing around the weighted mean (14.7%) at a sample size of 100 points but required 250 points or more to reach a tolerable standard error for the estimate. By comparison with the proprietary analysis of high-resolution imagery (16.1%, considered the most robust form of assessment), i-Tree Canopy slightly underestimated tree cover (14.7%), and i-Tree Landscape substantially underestimated tree cover (11.3%). Possible causes of variation in estimates amongst the methods and practical considerations for choosing a UTC assessment method are discussed.
- Sound transmission loss of gypsum wallboard wall partitionsGreen, David W.; Sherry, C. W. (Acoustical Society of America, 1977)Using the data bank of the acoustic laboratory of Domtar Research, statistical equations based on frequency and surface density were derived for predicting sound transmission loss (STL) and sound transmission class (STC) of double leaf wall partitions constructed using gypsum wallboard and either steel or wood studs. The equations show close agreement with experimental data for all frequency bands except those near the coincidence dip. Results predicted using these equations also agree closely with experimental results published by other laboratories. Using these equations the effect of frequency, surface density and cavity filler on STL and STC is easily seen. However, the study also revealed some unexpected results whether or not a partition was (1): Balanced- as to board placement did not significantly affect the STC of either steel or wood stud partitions. (2) For multilayer wood stud partitions attaching the second layer of board to the first with screws, rather than using glue, dramatically reduced the STL at higher frequencies. For higher surface density partitions this decrease may negate any benefits to be derived from adding fiberglass to the cavity space.