Golden Valley, Minnesota Image Analysis Heather Hegi and Kerry Ritterbusch

Objectives  Project for City of Golden Valley  Create accurate shapefiles of their historic water features Important for future building projects Necessary for maintenance of current structures

Data/Materials  1937 and 1945 panchromatic images 1937 – used for confirmation 1945 – wetter year (water features easily identifiable)

Data/Materials  May 2009 multispectral image  City boundary  High resolution DEM  Current lakes

Procedures  Put 1937 images into continuous image mosaic (1945 & 2009 images already continuous)  Digitized historic water features employing ’37 & ’45 imagery  Performed unsupervised classification on 2009 imagery  Conducted change detection between the 1945 and 2009 lake shapefiles

Problems with panchromatic images  Running a normal classification as is done with a multispectral image does not work on black and white imagery  Performed Digitization

 One difficulty associated with semi-automated analysis of historical photographs, however, is that these images contain limited information – typically a single, panchromatic spectral band. Traditional methods of analysing such images assume that pixels in the same land-cover class are spectrally similar. This method is sub-optimal for several reasons. Even in relatively simple landscapes, individual land-cover classes (e.g. ‘forest’) may comprise a broad range of pixel spectral values, which may overlap with the ranges of other land- cover classes. (Pringle et al., 2009, p. 545)

Factors in Image Classification of Lakes  Turbidity  Color  Placidity or Roughness of surface Caused by:  Disturbed sediment  Pollution  Aquatic flora  Wind and water speed

Unsupervised Classification  Found that fewer classes were better 7 classes22 classes

Imagery Considerations  2010 NAIP – Many shades of lakes  2010 Landsat – Course resolution

Change Detection  Determined lake surface area change between 1945 and 2009  Use of Intersect and Erase tools  Created 2 maps: The first map displays the distribution of the lakes in 1945 and 2009 The second map focuses more in-depth on the exact changes that have occurred throughout the years

Statistics  66% of the lakes that existed in 1945 are still present today  20% increase in lake area from 1945 to 2009  53% of lakes that exist today existed in 1945  Overall, there was a 58% change in lake distribution (Area of Lake Change) / (Total Lake Area Existing & Historic)

Findings  Increase in lakes, rather than a decrease as we had assumed would be the case

Conclusions  Digitization is the way to go with historical data