GEOGRAPHIE
INNSBRUCK
EGU 2009
Analysis of Airborne LiDAR Data for Digital Soil Mapping in Alpine Valleys
Digital Soil Mapping in Alpine areas
In mountainous areas, the distribution of soils is characterized by a high variability on small scales with relief being the most decisive soil forming factor.
Its heterogeneity must be represented in Digital Soil Mapping approaches (cf. Lagacherie et al. 2007).
Digital Terrain Models (DTM) from airborne LiDAR (Light Detection and Ranging) provide a
source for high resolution relief information that is becoming commonly available for an increasing
number of regions. In this study we analyse the applicabiltiy of DTMs derived from airborne
image
LiDAR
morphometric
LiDAR for Digital Soil Mapping. A comprehensive evaluation is carried out by comparing our
segmentation
DTM
indices
results with a similar analysis based on classical photogrammetric DTMs. Ground truth data on
landforms and soils from field studies is used to verify the relation between soil and topography.
detailed
classification
field work
data
basic
classification
Using Airborne LiDAR for terrain analysis
In theory, the high resolution of LiDAR DTMs (2.5 m cell size in the test area of Bruneck, South
Tyrol - Italy) should allow a very accurate delineation of landform elements. But there are also
certain shortcomings when working with high resolution DTMs;
(a) strongly varying scales of the demanded landform elements
(b) random errors in the DTM (summarized as "noise")
(c) distinctive anthropogenic modifications of the relief
To overcome these difficulties we use object-oriented image analysis, instead of a traditional
pixel-oriented approach (cf. Dragut and Blaschke 2006, Schneevoigt et al. 2008). Rather than
modelling the spatial distribution of soil types or attributes, we try to delineate landform units
relevant for soil development, so called soil-landform entities (cf. MacMillan et al. 2000).
error
assessment
analysis of
photogrammetric
DTM
map of
soil-landform entities
Figure 1: Workflow to derive soil-landform entities from a LiDAR DTM
Basic Classification
investigation area
flat land
moderate slope
steep slope
settlement
river
Object-oriented image analysis
fuzzy
membership function
An object-oriented image analysis is carried out using the commercial remote sensing software Definiens Professional 5.0. Landform elements significant
for soil formation are detected by image segmentation and subsequent classification using both fuzzy membership functions and crisp classifiers. Figure 1
shows the hierarchical workflow (cf. Benz et al. 2004). The necessary inputs - basic and compound geomorphometric indices - are derived using open
source GIS programs. Image segmentation is accomplished by a
multi-resolutional segmentation on two different scale levels (cf. Baatz
Basic Classification
Detailed Classification
and Schäpe 2000) using “slope” and “SAGA wetness index” (cf.
group
parameters
class
parameters
Böhner et al. 2002) as basic criteria.
1 flat land
slope (low)
1.1 floodplain
VDCN* (very low)
In the subsequent two-step classification each segment is assigned
1.2 river terrace
VDCN* (low)
a specific landform unit based on the parameters listed in Table 1.
1.3 flat land
VDCN* (medium/high)
For the basic classification, the segments are grouped by slope
1.4 bog
TWI** (high)
according to the fuzzy membership function shown in Figure 2. The
2 moderate
slope
2.1 moderately
slope (moderate)
detailed classification is used to define specific landform units on the
slope
(moderate)
sloping hillside
basis of the predefined slope classes. Additional information for rivers,
2.2 alluvial fan /
close to floodplain,
toeslope
river terrace or flat land
settlements and roads are taken from a landuse map. Figures 3a and
2.3 mod. channel catchment area (large)
3b show the results of the two classification steps for the test area of
2.4 slope bog
TWI** (high)
Bruneck, Italy.
2.5 moderately
close to river / between
sloping
embankment
steep hillside
steep channel
steep
embankment
1.0
3 steep
slope
slope (steep)
3.1
3.2
3.3
0.5
0.0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
slope (°)
flat land
moderate slope
steep slope
Figure 2: Fuzzy membership function of “slope” for the basic classification
4 river
land use
5 settlement land use
4
5
* VDCN = Vertical Distance to Channel Network
river
settlement
floodplain and terrace
shape of segment
slope (steep)
catchment area (large)
close to river / between
floodplain and terrace
shape of segment
land use
land use
** TWI = Topographic Wetness Index
Table 1: Parameters for a two-step classification of the object-oriented image analysis in the test area of Bruneck, South Tyrol - Italy
References:
Baatz M and Schäpe A, 2000, Multiresolution segmentation – an optimization approach for high quality multi-scale image segmentation. In: Strobl J., Blaschke T, Griesebener G (eds), Angewandte Geographische Informationsverarbeitung
XII. Beiträge zum AGIT-Symposium Salzburg 2000. Herbert Wichmann Verlag, Karlsruhe, 12-23.
Benz C, Hofmann P, Willhauck G, Ligenfelder I and Heynen M, 2004, Multi-resolution, object-oriented fuzzy analysis of remote sensing data for GIS-ready information. ISPRS Journal of Photogrammetry & Remote Sensing, 58:239-258.
Böhner J, Köthe R, Conrad O, Gross J, Ringeler A and Selige T, 2002, Soil regionalisation by means of terrain analysis and process parameterisation, European Soil Bureau – Research Report, 7:213-222.
Dragut L and Blaschke T, 2006, Automated classification of landform elements using object-based image analysis. Geomorphology, 81: 330-344.
Lagacherie P, McBratney AB and Voltz M (eds), 2006, Digital Soil Mapping: An Introductory Perspective. Developments in Soil Science, 31, Elsevier, Amsterdam.
MacMillan R A , Pettapiece W W, Nolan S C, Goddard T W, 2000, A generic procedure for automatically segmenting landforms into landform elements using DEMs, heuristic rules and fuzzy logic. Fuzzy Sets and Systems, 113: 81 -109.
Schneevoigt NJ, van der Linden S, Thamm HP and Schrott L, 2008, Detecting Alpine landforms from remotely sensed imagery. A pilot study in the Bavarian Alps. Geomorphology, 93: 104-119.
0
500 1000
Detailed Classification
investigation area
alluvial fan / toeslope
mod. sloping hillside
floodplain
river terrace
2000m
0
Figure 3a: Soil-landform entities in the test area after the first classification step
500 1000
Gebirgsforschung:
IGF
Mensch und Umwelt
K R I N G E R1 ,
Mar kus
T U S C H1 ,
Clemens
G E I T N E R1,2 ,
2000m
Soil-Landform Classification
DTM: twofold vertical exaggeration
floodplain
river terrace
flat land
alluvial fan / toeslope
mod. channel
mod. s. embankment
mod. sloping hillside
bog
slope bog
steep hillside slope
steep channel
steep embankment
river
settlement
Figure 4: Northern part of the test area
Results and Discussion
Figure 4 shows a section of the valley floor of the investigation area Bruneck, South Tyrol - Italy. The final
detailed landform classification was draped over a twofold vertically exaggerated 3D - visualization of the
terrain. The outcome of this study shows clearly that airborne LiDAR DTMs with high raster resolutions
(cell sizes of 5 m and smaller) can provide valuable information for delineating landform entities with
presumably homogenous conditions for soil formation. Despite specific shortcomings which still need to
be resolved, object-oriented image analysis shows to have advantages over traditional pixel-based
approaches when dealing with high-resolution DTMs.
Acknowledgements
We thankfully acknowledge funding from the Autonomous Province of Bozen/Bolzano - South Tyrol for
project “LASBO - Einsatz von Laserscanning zur Unterstützung der Bodenkartierung in Gebirgsräumen”.
Ger tr aud
M E I S S L1 ,
Mar tin
R U T Z I N G E R3
1 I n s t i t u t e o f G e o g r a p h y, U n i v e r s i t y o f I n n s b r u c k - I n n r a i n 5 2 , A - 6 0 2 0 I n n s b r u c k
2 M o u n t a i n Re s e a r ch : M a n a n d E nv i r o n m e n t Re s e a r ch G r o u p , A u s t r i a n A c a d e m y o f S c i e n c e s - Te ch n i ke r s t r. 2 1 a , O t t o H i t t m a i r - P l at z 1 , A - 6 0 2 0 I n n s b r u ck
3 I n t e r n a t i o n a l I n s t i t u t e f o r G e o - I n f o r m a t i o n S c i e n c e a n d E a r t h O b s e r v a t i o n ( I T C ) - P. O . B o x 6 , 7 5 0 0 A A E n s c h e d e , T h e N e t h e r l a n d s
Mail:
steep hillside slope
mod. s. embankment
steep embankment
settlement
river
Figure 3b: Soil-landform entities in the test area after the second classification step
http://www.uibk.ac.at/geog r a phie/bg l/lasbo
Korbinian
flat land
mod. channel
steep channel
bog
slope bog
[email protected]