the Kongsfjorden area, Svalbard First results

lameubiquityMechanics

Feb 21, 2014 (3 years and 6 months ago)

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Technique and precision

At

all

sites

a

fixed

point

for

global

reference

were

established
;

a

bolt

was

drilled

into

the

bedrock

and

its

position

measured

by

GPS
.

The

positions

of

the

camera

stations

were

measured

by

GPS

and

surveyed

from

the

fixed

point

to

create

both

a

global

and

a

local

reference
.

The

photos

were

acquired

with

a

stereo

overlap

by

using

a

Hasselblad

camera

with

a

60

mm

lens
.

Photogrammetric

control

points

were

established

using

bolts

drilled

into

the

cliff

wall
.


Results


The

automatically

generated

DTM

from

2002

for

site

4

is

shown

below

as

a

shaded

relief

model
.

Above

the

erosion

rate

for

site

1

is

shown

as

the

difference

between

the

2002

and

2004

DTMs
.

At

site

1

the

measurements

reveal

an

overall

stable

cliff

wall,

with

patches

of

erosion

of

up

to

11
.
9

cm/y
.

Below

the

erosion

rate

of

site

4

is

shown

and

it

also

reveals

a

spot

like

erosion

of

up

to

3
.
8

cm/year

in

the

otherwise

stable

rock

wall
.

At

both

sites

there

are

also

areas

of

sedimentation
.

This

is

probably

due

to

actual

sedimentation,

and

to

some

extent

also

small

inaccuracies

of

the

technique
.

The

photo

distance

for

site

1

is

14

meters

and

for

site

4

it

is

7

meters,

giving

a

theoretical

accuracy

of

some

3
.
0

mm/year

for

site

1

and

some

1
.
5

mm/year

for

site

4

for

the

DTM

differencing

over

the

two

year

time

interval
.

The

mean

values

for

the

erosion

rates

are

5

mm/y

at

site

1

and

0
.
5

mm/y

at

site

4
.

Meaning

the

overall

erosion

rate

at

site

4
not

being

significant

compared

to

the

accuracy
.


Abstract

Four

sites

for

measuring

coastal

cliff

erosion

in

the

Kongsfjorden

area

on

Svalbard

(
79
°
N,

12
°
E)

were

established

in

August

2002

and

revisited

in

August

2004
.

Sites

with

cliffs

in

unconsolidated

material

and

cliffs

in

bedrock

where

chosen
.

Photos

were

taken

at

distances

ranging

from

7

to

15

meters

from

the

cliff

walls

with

a

Hasselblad

camera
.

At

each

site

photographs

were

taken

from

two

or

three

different

camera

positions

to

be

able

to

create

3
D

digital

terrain

models

of

the

cliffs
.

The

photos

were

scanned

and

digital

terrestrial

photogrammetry

applied

to

construct

digital

terrain

models

(DTMs)
.

The

erosion

rate

can

then

be

estimated

by

taking

the

difference

between

two

DTMs

of

different

years
.

Due

to

the

short

distance

between

camera

and

cliff,

the

accuracy

is

in

the

millimeter

to

centimeter

range
.

Results

from

site

1

and

4

show

a

generally

stable

rock

wall

with

spot

like

erosion

of

up

to

11
.
9

cm/y

and

3
.
8

cm/y

respectively
.


Measuring coastal cliff erosion using terrestrial photogrammetry in
the Kongsfjorden area, Svalbard


First results

B. Wangensteen
¹
, T. Eiken
¹
, R. S. Ødegård
²

and J.L Sollid
¹


1.Department of Geosciences, University of Oslo, P.O.Box 1047 Blindern, NO
-
0316 Oslo, Norway

2. Gjøvik University College, Norway. P.O. Box 191, NO
-
2802 Gjøvik, Norway

E
-
mail: bjorn.wangensteen@geo.uio.no




Location of Svalbard and the sites in the Kongsfjorden area


The

camera

was

mounted

on

top

of

a

theodolite

with

a

special

device

making

it

possible

to

measure

the

exact

position

of

the

camera

and

to

ensure

that

the

photo

stations

are

on

a

line

parallel

to

the

cliff

wall
.

Photo

distances

in

the

range

of

7
-
14

m

gives

a

scale

of

1
:
117

to

1
:
233

and

a

XY
-
resolution

in

the

order

of

1
.
2



2
.
3

mm
.

The

theoretical

elevation

accuracy

(Z
-
direction)

is

in

the

range

1
.
4



5
.
6

mm

for

the

given

photo

distances

(
0
.
20
-
0
.
40



of

the

photo

distance)
.


The overlapping photos of site 4 from 2002. The erosion rate is
calculated for the rock wall of this site.


Conclusions and future work

The method of close up digital terrestrial photogrammetry seems suitable
for creating accurate digital terrain models of coastal cliffs and hence
promising for detecting changes in the order of mm to cm/year. André
(1997) reports of Holocene rock wall retreat in the range 0 to 1.58 mm/y
in the same area.



Reference:
André, M.
-
F. (1997) Holocene Rockwall Retreat in Svalbard: A triple
-
rate evolution.
Earth Surface and Processes and Landforms

22.


Acknowledgement:

The fieldwork was financially supported by the INTAS
-
project
“Arctic coasts of Eurasia: dynamics, sediment budget and carbon flux in connection
with permafrost degradation” (INTAS
-
2001
-
2329) and by two scholarships from the
Norwegian Research Council on behalf of the Norwegian Polar Committee .