detection of burial mounds in high-resolution satellite images of ...
detection of burial mounds in high-resolution satellite images of ...
detection of burial mounds in high-resolution satellite images of ...
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DETECTION OF BURIAL MOUNDS IN<br />
HIGH-RESOLUTION SATELLITE IMAGES<br />
OF AGRICULTURAL LAND<br />
Øiv<strong>in</strong>d Due Trier (NR), Anke Loska (NDCH),<br />
Siri Øyen Larsen (NR), and Rune Solberg (NR)<br />
Collaborators:<br />
The Norwegian Directorate for Cultural Heritage, NDCH (also fund<strong>in</strong>g)<br />
The Norwegian Space Centre (also fund<strong>in</strong>g)<br />
Vestfold County Adm<strong>in</strong>istration<br />
Museum <strong>of</strong> Cultural History - University <strong>of</strong> Oslo<br />
www.nr.no<br />
remotesens<strong>in</strong>g.nr.no
Outl<strong>in</strong>e<br />
►<br />
►<br />
►<br />
►<br />
Background<br />
Methods<br />
▪<br />
▪<br />
▪<br />
contrast enhancement<br />
template match<strong>in</strong>g<br />
classification experiments<br />
Results<br />
Conclusion<br />
www.nr.no<br />
remotesens<strong>in</strong>g.nr.no
CultSearcher<br />
►<br />
►<br />
►<br />
►<br />
►<br />
S<strong>of</strong>tware for computer assisted<br />
potential cultural heritage sites<br />
Agricultural<br />
Soil<br />
Crop<br />
marks<br />
marks<br />
fields<br />
Circular patterns<br />
<strong>burial</strong> <strong>mounds</strong><br />
–<br />
could<br />
be rema<strong>in</strong>s<br />
<strong>detection</strong><br />
<strong>of</strong><br />
<strong>of</strong><br />
www.nr.no<br />
remotesens<strong>in</strong>g.nr.no
Quickbird <strong>images</strong><br />
Lågen-<br />
dalen<br />
April 27<br />
2005<br />
10:45AM<br />
Gardermoen<br />
July 29, 2003<br />
10:23 AM<br />
www.nr.no<br />
remotesens<strong>in</strong>g.nr.no
Cross section <strong>of</strong> ditch that has<br />
surrounded bronze age <strong>burial</strong> mound<br />
www.nr.no<br />
remotesens<strong>in</strong>g.nr.no
Detail <strong>of</strong> Lågendalen image<br />
RGB<br />
2.4 m<br />
Near <strong>in</strong>frared<br />
2.4 m<br />
Panchromatic<br />
0.6 m<br />
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remotesens<strong>in</strong>g.nr.no
Where to look<br />
►<br />
We<br />
only<br />
consider<br />
agricultural<br />
fields<br />
=<br />
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remotesens<strong>in</strong>g.nr.no
Test data<br />
►<br />
►<br />
Altogether<br />
▪<br />
▪<br />
▪<br />
The<br />
▪<br />
▪<br />
▪<br />
▪<br />
▪<br />
15 strong<br />
10 fairly<br />
10 weak<br />
35 r<strong>in</strong>gs <strong>in</strong> the<br />
r<strong>in</strong>gs (clear<br />
strong<br />
r<strong>in</strong>gs (poor<br />
appearance<br />
radius,<br />
thickness,<br />
two<br />
visibility)<br />
<strong>images</strong>:<br />
r<strong>in</strong>gs (moderate visibility)<br />
<strong>of</strong><br />
gray tone <strong>in</strong>tensity,<br />
degree<br />
contrast<br />
<strong>of</strong><br />
visibility)<br />
different<br />
completeness,<br />
to the<br />
local background<br />
r<strong>in</strong>gs varies<br />
greatly:<br />
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remotesens<strong>in</strong>g.nr.no
Example r<strong>in</strong>g marks<br />
Strong<br />
r<strong>in</strong>gs:<br />
Fair<br />
r<strong>in</strong>gs:<br />
Weak<br />
r<strong>in</strong>gs:<br />
The contrast has been adjusted to <strong>high</strong>light the r<strong>in</strong>gs<br />
www.nr.no<br />
remotesens<strong>in</strong>g.nr.no
Local contrast enhancement<br />
►<br />
►<br />
The pixel value pCE x,<br />
image is computed as<br />
p CE<br />
( x,<br />
y)<br />
=<br />
( y)<br />
<strong>in</strong> an N ×<br />
N neighbourhood<br />
<strong>in</strong> the<br />
p(<br />
x,<br />
y)<br />
− μ(<br />
x,<br />
y,<br />
N)<br />
σ ( x,<br />
y,<br />
N)<br />
Achieves more or less constant<br />
entire image.<br />
contrast<br />
centered<br />
local<br />
on<br />
enhanced<br />
( x,<br />
y)<br />
contrast<br />
.<br />
over the<br />
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remotesens<strong>in</strong>g.nr.no
Local contrast enhancement<br />
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remotesens<strong>in</strong>g.nr.no
Template match<strong>in</strong>g<br />
►<br />
►<br />
A r<strong>in</strong>g filter is convolved<br />
with<br />
the<br />
image<br />
Correlation image; pixel value <strong>in</strong>dicate how well the<br />
r<strong>in</strong>g filter agrees with the image when centered on<br />
the respective location<br />
Square boundary Circular boundary<br />
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remotesens<strong>in</strong>g.nr.no
Locat<strong>in</strong>g potential r<strong>in</strong>g sites<br />
►<br />
►<br />
►<br />
Locations with<br />
Threshold<br />
▪<br />
▪<br />
The<br />
▪<br />
τ:<br />
correlation<br />
correlation<br />
threshold<br />
<strong>high</strong><br />
correlation<br />
image > τ bright r<strong>in</strong>g<br />
image < -τ dark r<strong>in</strong>g<br />
τ<br />
may<br />
be adjusted<br />
by the<br />
user<br />
<strong>in</strong>fluence true r<strong>in</strong>g recognition rate vs. number <strong>of</strong><br />
false <strong>detection</strong>s<br />
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remotesens<strong>in</strong>g.nr.no
Classification experiments<br />
►<br />
►<br />
Are there features that can<br />
positives from true r<strong>in</strong>gs?<br />
discrim<strong>in</strong>ate<br />
false<br />
Features extracted from 4r4r sub <strong>images</strong><br />
(panchromatic + b<strong>in</strong>ary) conta<strong>in</strong><strong>in</strong>g r<strong>in</strong>g candidates<br />
True r<strong>in</strong>g False r<strong>in</strong>g<br />
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remotesens<strong>in</strong>g.nr.no
Classification experiments<br />
►<br />
►<br />
►<br />
Features <strong>in</strong>clude:<br />
▪<br />
▪<br />
▪<br />
▪<br />
r<strong>in</strong>g cover; overlap between b<strong>in</strong>arized sub image<br />
and b<strong>in</strong>ary version <strong>of</strong> the r<strong>in</strong>g filter<br />
mean<br />
x-<br />
and y-coord<strong>in</strong>ates<br />
Hu moment <strong>in</strong>variants<br />
Real weighted<br />
Desicion<br />
Results<br />
tree<br />
Fourier<br />
classifier<br />
discourage<br />
the<br />
<strong>of</strong><br />
moments<br />
use<br />
<strong>of</strong><br />
b<strong>in</strong>arized<br />
image<br />
classification<br />
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remotesens<strong>in</strong>g.nr.no
Scatter plots<br />
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remotesens<strong>in</strong>g.nr.no
Flowchart <strong>of</strong> algorithm<br />
Def<strong>in</strong>e<br />
Construct<br />
Threshold<br />
Threshold<br />
Local<br />
Convolve<br />
Remove<br />
masks <strong>of</strong><br />
agricultural<br />
Do band pass filter<strong>in</strong>g?<br />
contrast<br />
No<br />
r<strong>in</strong>g templates<br />
image with<br />
convolution<br />
convolution<br />
enhancement<br />
<strong>of</strong><br />
result<br />
<strong>detection</strong>s<br />
result<br />
fields<br />
<strong>in</strong>creas<strong>in</strong>g<br />
r<strong>in</strong>g template<br />
to f<strong>in</strong>d<br />
to f<strong>in</strong>d<br />
outside<br />
sizes<br />
Yes<br />
dark r<strong>in</strong>gs<br />
masks<br />
Merge new r<strong>in</strong>g with exist<strong>in</strong>g if less<br />
than 5 pixels apart<br />
bright r<strong>in</strong>gs<br />
2D fast Fourier<br />
transform<br />
Band pass filter<strong>in</strong>g<br />
Inverse 2D FFT<br />
Yes<br />
More r<strong>in</strong>g templates?<br />
(FFT)<br />
No<br />
Validation:<br />
Operator deletes false <strong>detection</strong>s<br />
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remotesens<strong>in</strong>g.nr.no
Results<br />
band corr. strong fair weak true false<br />
pass thresh. r<strong>in</strong>gs r<strong>in</strong>gs r<strong>in</strong>gs r<strong>in</strong>gs r<strong>in</strong>gs<br />
no 0.30 11 5 0 16 450<br />
no 0.33 11 5 0 16 109<br />
no 0.35 10 2 0 12 39<br />
no 0.40 8 0 0 8 3<br />
yes 0.35 12 3 0 15 174<br />
yes 0.38 11 2 0 13 48<br />
yes 0.39 10 2 0 12 31<br />
yes 0.40 9 1 0 10 12<br />
ground truth<br />
15 10 10 35<br />
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remotesens<strong>in</strong>g.nr.no
Verification<br />
Detected r<strong>in</strong>gs Verified r<strong>in</strong>gs<br />
Bright<br />
r<strong>in</strong>gs<br />
Dark<br />
r<strong>in</strong>gs<br />
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remotesens<strong>in</strong>g.nr.no
Conclusion<br />
►<br />
►<br />
►<br />
►<br />
Detection <strong>of</strong> r<strong>in</strong>gs is a challeng<strong>in</strong>g task.<br />
Local contrast enhancement<br />
Template match<strong>in</strong>g<br />
Archaeologists state that the s<strong>of</strong>tware tool is<br />
helpful.<br />
▪ Avoid manual <strong>in</strong>spection <strong>of</strong> entire <strong>images</strong>.<br />
▪ Easy to remove false <strong>detection</strong>s.<br />
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remotesens<strong>in</strong>g.nr.no
Thank you for your attention<br />
www.nr.no<br />
remotesens<strong>in</strong>g.nr.no