Application of Ground-Penetrating-Radar, Electrical Resistivity Imaging and 3D aerial photos to study paludification in northern

boreal forests of Canada

Ahmed Laamrani1,2, Osvaldo Valeria1,2, Yves Bergeron1,2 & Li Zhen Cheng1

Université du Québec en Abitibi-Témiscamingue1 , Chaire Industrielle en aménagement forestier durable2.

445 boul. de l'Université, Rouyn-Noranda (Québec) J9X 5E4

INTRODUCTION

This research attempts to link stand structure characteristics to Ground Penetrating Radar (GPR) and Electrical Resistivity

Imaging (ERI) data in order to produce very precise numerical models of the mineral slope and organic layer thickness of

nine sites (250 m x 250 m) on the Clay Belt

CONTEXTE

Black spruce forests located on the Clay Belt, a region of eastern North America, are characterized by a decline in forest productivity

Paludification leads to a significant decrease in forest productivity

Topography of the mineral soil is thoughtto have a major influence on the occurrenceof paludification

Needs for a better understanding of thefactors that reduce forest productivity :

Structure of vegetation

Degree of paludification

Relate mineral soil slope, productivity &degree of paludification

+++: Sampling paludified plots (Simard et al. 2009)

The results of this ongoing research will:

1. Allow a more accurate determination of the impacts of paludification on the landscape and on forest productivity

2. Improve forest management practices in the northern boreal forest

GPR method = Explore the shallow

subsurface

12 GPR transects will be collected with a

high-speed pulseEKKO 100 system in each site.

500 MHz antenna Investigation depth ~ 2-3 m

GPR interpretation is primarily based on

Imaging: nature & origin of reflections

Interpolate between 12 GPR by kriging 3D

model for each study site spatial variability

of organic layer thickness & mineral soil slope

UAF 85-51 &

85-62

(~11790 km2)

ERI method (depth~ 3 m)

12 ERI transects with

OhmMapper instrument

Resistivity measurement

PLANAR & DVP system

3D digital images (resolution

of 30 cm)

3D photo interpretation

(Planar-DVP)

Map drainage, cover type,

tree height, spruce-moss, slope

Establish a relation between

geophysical and photo-

interpreted variables

Extrapolate these results at

the landscape level

Planar SD Stereo/3D

EXPECTED OUTCOMES

OBJECTIVES

1.Use GPR and ERI methods to elaborate a

numerical model of the organic layer thickness at

the site level

2. Interpolate a 3D model for each study site in

order to determine the spatial variability of

organic layer thickness

3. Assess the combined effects of slope and

organic layer accumulation on forest productivity.

4. use 3D aerial photos to extrapolate these

results at the landscape level

Using very-high-resolution geophysical (GPR&ERI)

& RS 3D data

STUDY AREA

: Study site # 1Organic layer (paludified site)

Schematic of the OhmMapper instrument and

data acquisition

Inversion

process

Inverted electrical resistivity (ρ):

Low ρ ( 1 to100 Ωm = Clay-silt

ρ >100 Ωm = coarse sand &

gravel

InterpolationInterpretation

Example of 3D modelling representation of the pre-lacustrine topography of the basin of Le Lautrey,

France, in relation to the types of bedrock (Jp,J9, n2)

(Bossuet et al. 2000)

Data processing 2D cross-section.

Amato et al. 2008

Minéral

Air wave Ground wave Neige

Tourbe

Tim

e (

ns)

Dep

th(m

, v=

0.4

0m

/ns)Minéral

Air wave Ground wave Neige

Tourbe

Tim

e (

ns)

Dep

th(m

, v=

0.4

0m

/ns)

Peat

Snow

Mineral

soil

Dallaire 2007

Peatland.

Photo : D. Paré

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ERI survey divided in 12 transects

50 m

1 2 3 4 5 6

12

11

10

9 8

7

Study site

(250 x 250 m)

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ERI survey divided in 12 transects

50 m

1 2 3 4 5 6

12

11

10

9 8

7

Study site

(250 x 250 m)

Study area limitClay Belt region

APPROACH