18 Oct Estimating Canopy Cover for Two Urban N’hoods in Louisville
The following article was created and originally posted on October 18, 2013 on MapGrapher here!
We’ve been thinking about trees a lot in Louisville recently, especially in light of recent research highlighting Louisville as a city experiencing significantly hotter than average temperatures compared to other US cities. We understand that aggressively increasing our urban tree canopy is one of the best things we can do to mitigate these rising temperatures.
In estimating urban tree canopy cover, researchers and analysts often to turn to imagery from the USDA’s National Agricultural Imagery Program to create vegetation models that can help provide canopy cover estimates for a point in time.
This week, in cooperation with the Urban Design Studio, we finally got a chance to sink our teeth into some USDA NAIP data, with a focus on two urban neighborhoods in Louisville: Portland and Tyler Park. We sort of picked these two random, and we look forward to using this data to perform similar analyses for the rest of Louisville Metro. If you’re interested in the sausage-making, the process we used is called the Normalized Difference Vegetation Index… described here. For technical reasons related to the data, we had to use imagery from 2010.
Some caveats: (1) These are estimates, (2) While this imagery is available for Kentucky biennially from something 2006-2012, only the 2010 quarter quadrangles had the necessary Near Infrared “4th Band” that’s needed to pick up leaves on plants and trees. (3) Also, although I kept tweaking the NDV Index, a bit of grass always seemed to make it into the model. (4) I separated out a portion of uninhabited flood plain within Metro’s Portland boundary, and north of the interstate, where no one lives. If that area is included, then Portland’s 2010 canopy estimate would be 25%.
NOTE: For those of you “in the know” this analysis is not directly related to Urban Design Studio’s work on the Downtown Tree Inventory, which is in the final stages of data cleaning, and to be presented in a few weeks.
PLEA: Does anyone know if 2012 NAIP Imagery with the 4th band is available or even extant?