Deriving and Evaluating City-Wide Vegetation Heights from a TanDEM-X DEM

Johannes Schreyer,Tobia Lakes

doi:10.3390/rs8110940

Abstract

Vegetation provides important functions and services in urban areas, and vegetation heights divided into vertical and horizontal units can be used as indicators for its assessment. Conversely, detailed area-wide and updated height information is frequently missing for most urban areas. This study sought to assess three vegetation height classes from a globally available TanDEM-X digital elevation model (DEM, 12 × 12 m spatial resolution) for Berlin, Germany. Subsequently, height distribution and its accuracy across biotope classes were derived. For this, a TanDEM-X intermediate DEM, a LiDAR DTM, an UltraCamX vegetation layer, and a biotope map were included. The applied framework comprised techniques of data integration and raster algebra for: Deriving a height model for all of Berlin, masking non-vegetated areas, classifying two canopy height models (CHMs) for bushes/shrubs and trees, deriving vegetation heights for 12 biotope classes and assessing accuracies using validation CHMs. The findings highlighted the possibility of assessing vegetation heights for total vegetation, trees and bushes/shrubs with low and consistent offsets of mean heights (total CHM: −1.56 m; CHM for trees: −2.23 m; CHM bushes/shrubs: 0.60 m). Negative offsets are likely caused by X-band canopy penetrations. Between the biotope classes, large variations of height and area were identified (vegetation height/biotope and area/biotope: ~3.50–~16.00 m; 4.44%–96.53%). The framework and results offer a great asset for citywide and spatially explicit assessment of vegetation heights as an input for urban ecology studies, such as investigating habitat diversity based on the vegetation’s heterogeneity.

Highlights

Urban vegetation is an important property of urban ecosystems that delivers functions for city residents by providing ecosystem services [1] and natural functions, mainly as a diverse habitat for the local fauna [2,3]
Since this study aims to proof the capacities of the TanDEM-X digital elevation model (DEM) for urban vegetation height assessment on spatially explicit units, this study does not include the already existing very high resolution UltaCamX vegetation layer for assessment of vegetation heights on biotopes
Area-wide canopy height models (CHMs) and CHMs for two vegetation height classes were obtained. Both CHMs are displayed with a building layer made using the UltraCamX data in Figure 3, which shows the spatial distribution of both vegetation height classes throughout Berlin

Summary

Introduction

Urban vegetation is an important property of urban ecosystems that delivers functions for city residents by providing ecosystem services [1] and natural functions, mainly as a diverse habitat for the local fauna [2,3]. Negative effects, so-called ecosystem disservices, are associated with urban vegetation and incur financial, social, and environmental costs [1]. Vegetation-related ecosystem services and disservices can be assessed using vegetation parameters as indicators. These indicators include genus/species, age, location, leaf coverage, stem diameter, crown diameter, and height [1,4]. The height of vegetation types is crucial to assess the vertical distribution of vegetation and to extend spatial distribution patterns of vegetation using three-dimensional information for volume or surface measurement [5]. In the context of ecosystem effects, single urban vegetation types, such as trees, bushes, and shrubs, differ due to their size, amount of woody components, biomass, and foliage and have to be taken into account separately [6]

Objectives

Methods

Results

Discussion

Conclusion