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 ID: 543992
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classification of Historic Lakes and wetlands
Golden Valley, Minnesota Image Analysis
Heather Hegi and Kerry RitterbuschSlide2
Objectives
Project for City of Golden ValleyCreate accurate shapefiles of their historic water featuresImportant for future building projectsNecessary for maintenance of current structuresSlide3Slide4
Data/Materials
1937 and 1945 panchromatic images1937 – used for confirmation1945 – wetter year (water features easily
identifiable)Slide5
Data/Materials
May 2009 multispectral imageCity boundary High resolution DEM
Current lakesSlide6
Procedures
Put 1937 images into continuous image mosaic (1945 & 2009 images already continuous)Digitized historic water features employing ’37 & ’45 imageryPerformed unsupervised classification on 2009 imagery
Conducted change detection between the 1945 and 2009 lake shapefilesSlide7
Problems with panchromatic images
Running a normal classification as is done with a multispectral image does not work on black and white imageryPerformed DigitizationSlide8
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)Slide9
Factors in Image Classification of Lakes
TurbidityColorPlacidity or Roughness of surfaceCaused by:
Disturbed sediment
Pollution
Aquatic flora
Wind and water speedSlide10
Unsupervised Classification
Found that fewer classes were better
7 classes
22 classesSlide11
Imagery Considerations
2010 NAIP – Many shades of lakes2010 Landsat – Course resolutionSlide12
Change Detection
Determined lake surface area change between 1945 and 2009Use 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 yearsSlide13Slide14Slide15
Statistics
66% of the lakes that existed in 1945 are still present today20% increase in lake area from 1945 to 200953% 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)Slide16
Findings
Increase in lakes, rather than a decrease as we had assumed would be the caseSlide17
Conclusions
Digitization is the way to go with historical data