Change Detection in Mire Ecosystems: Assessing Changes of Forest Area using Airborne Remote Sensing Data

Abstract

The objective of this paper is to present an approach for assessing tree growth and shrub encroachment between 1997 and 2002 inopen mire land using CIR-aerial images, DSMs and LiDAR data. The study area is located in the Pre-alpine zone of Central Switzerland. The present study was carried out in the framework of the Swiss Mire Protection Program, where changes of forest area are a key issue. Automatic DSMs were generated from CIR- aerial images of 1997 and 2002. This automated DSM generation is based on high accuracy, intelligent matching methods developed at ETHZ which are able to produce very dense and detailed DSMs that allow a good 3D modelling of trees and shrubs, and a multitemporal analysis of their growth pattern. Forest masks from both years of various levels of detail were then generated combining canopy covers derived from the DSMs using multi-resolution segmentation and a fuzzy classification. On the basis of these forest masks fractional tree/shrub covers were generated using explanatory variables derived from the DSMs and logistic regression models. The models reveal a general decrease of forest area between 1997 and 2002. On the other side, the models also indicate real shrub encroachment and tree growth in open mire land.