1. Exploratory study of craters detection on Lutetia using mathematical morphology methods
Małgorzata Jenerowicz
Space Research Centre,
Polish Academy of Sciences
Padova 7-9 March OSIRIS Full Team Meeting

2. Outline Assumptions Study area and Data set Methodology Results
Conclusions
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3. Assumptions
The manual indication of the impact craters is very complex, difficult and time consuming task
The lack of comprehensive catalogs of the impact craters of the diameter less than given threshold value
Craters characteristics:
Dark feature (shadow) attached to the brighter one: B and D regions (Urbach et al.2009)
Classification into „Large” and „Small/Medium” craters based on size criterion
Compact and non-linear shape for both B and D regions
Spatial relation between B and D regions, determinated by their centroids: orientation and distance. Direction consisten with the direction of light source.
IDPs in Somalia. Copyright WFP, 2011
Padova 7-9 March OSIRIS Full Team Meeting

4. Study Area Achaia subunit Ac1
OSIRIS Team (MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA)
Padova 7-9 March OSIRIS Full Team Meeting

5. Data Set NAC_2010-07-10T15.42.47.523Z_ID30_1251276001_F22
Camera system
Time
[UTC T*]
Spacecraft Altitude [km]
Angular resolution [mrad/px]
Spatial Resolution [km/px]
Light Source Phase Angle [o]
Processing Level
Data Type
OSIRIS NAC
15:43:06.520
15:45:00.240
15:45:07.170
3512.6
3121.9
3126.2
18.6
0.066
0.059
52.25
81.10
82.98 L3
PDS
Filter Name
Wavelength
Bandwidth
Spectral Range
Objective
Orange
649.2 nm
84.5 nm
Orange: nm
Red: nm
Surface spectral reflectance
(Credits: ESA 2010 MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA)
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6. Methodology Preprocessing Preliminary selection
AOI selection
Median filter
Image decomposition
Preliminary selection
Contrast filter
Area filter
Compactness criterion
Intensity threshold
Non-craters suppression
Shape filter
Distance and Orientation criterion
Final calculation
Merging craters groups (different spatial scale)
Indication of centroids
Comparison with the results of visual interpratetion
Padova 7-9 March OSIRIS Full Team Meeting

7. Flat Zones, Peaks and Valleys
Flat Zone Lh(f) of a gray-scale image f is a connected component of the level set
At each gray level, there may be multiple flat zones, which are denoted by
,with k some index variable.
Similarly, a peak component
is defined as the kth connected component of the threshold of image f, which is defined as
By analogy, a valley component
is defined as the kth connected component of the threshold
of inversed image f (in the image domain E), which is defined as
Padova 7-9 March OSIRIS Full Team Meeting

8. Preliminary Selection
Craters Features
Proposed series of Mathematical Morphology techniques
Bright region highly contrasting
Dark region highly contrasting
The maximum size criterion
(e.g. 39.6km2 – 600 pixels);
The medium size criterion (e.g. 6.6km2 – 100 pixels);
The minimum size criterion
(e.g. 0.9km2 – 15 pixels);
The compactness criterion;
Infimum reconstruction;
Supremum reconstruction;
Top-hat area opening: the threshold value – 600 pixels;
Top-hat area opening: the threshold value – 100 pixels;
Top-hat area opening: the threshold value – 15 pixels
The disk structuring element d = 3pixels;
Padova 7-9 March OSIRIS Full Team Meeting

9. Preliminary Selection
WFP 2010
WFP 2010
WFP 2010
WFP 2010
Padova 7-9 March OSIRIS Full Team Meeting

10. Non-craters suppression
Shape filter
1: label (B/D) regions: LB LD
2: for LB/D = 1:max
3: calculate 1st Hu’s Invariant phi(1)
phi(1)=m.m20-xbar*m.m10)/m.m00^2 + (m.m02-ybar*m.m01)/m.m00^2;
Where
m.m20=sum(x.^2.*F);
m.m02=sum(y.^2.*F);
m.m10=sum(x.*F);
m.m01=sum(y.*F);
m.m00=sum(F);
4: If phi(1) > 0.5 then // set to the representative
Distance and Orientation criterion
1: Centroids of labeled (B/D) regions: CB CD
2: for CD = 1:max
3: do Euclidean Distance Matrix
4: distance matrix = EDM • CB
5: find distance = min -> rho
6: find index(CB) = rho
7: calculate theta
8: if theta < Ttheta & rho < Trho &
xD < xB then // set to representative
WFP 2010
WFP 2010
WFP 2010
WFP 2010 B D
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11. (a) CRATERS CANDIDATES
Non-craters removal
(a) CRATERS CANDIDATES
(c) INTERSECTION
Medium and Small craters
Large craters
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12. Non-craters removal (b) SHAPE ANALYSIS Medium and Small craters
Large craters
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13. (c) ORIENTATION AND DISTANCE
Non-craters removal
Medium craters
(c) ORIENTATION AND DISTANCE
Large craters
Small craters
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14. Results
NAC_ T Z_ID30_ _F22
NAC_ T Z_ID30_ _F22
WFP 2010
WFP 2010
WFP 2010
NAC_ T Z_ID30_ _F22
WFP 2010
Image
Results
NAC_ T
105
NAC_ T
109
NAC_ T
106
Padova 7-9 March OSIRIS Full Team Meeting

15. Results: Size distribution
Large
Medium
Small
Size [pixels]
Distance [pixels]
<60
< 30
<10
Orientation [o]
<50
< 45
<45
Compactness
Disck dim 3 pixels -
Image
Large
Medium
Small
IMG 12 32 61
IMG 11 26 72
IMG 13 25 68
Padova 7-9 March OSIRIS Full Team Meeting

16. based on visual interpretation of randomly selected samples
Results verification
based on visual interpretation of randomly selected samples
Achaia region with randomly selected grid cells
Grid size 3.5kmx3.5km
Total No of cells: 49 (35%)
The comparative analysis between the results derived by
the semi-automatic detection and visual interpretation for randomly selected samples shows high correlation: 0.70
Total No of craters inside
the verification set:
Image 1
Semi-automatic: 45
Visual interpretation: 53
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17. Conclusions
High correlation between semi-automatically and visually detected craters
The benefits of using mathematical morphology methods for craters detection based on VHR optical data
Problems to solve
simplicity and limited number of descriptors
low computation cost - easy adaptation to different local conditions (illumination, terrain)
- implementation for the entire area
- determination of the crater depth: d (Solar Elevation Angle – 3D model)
- craters statistics: d / D
- crater’s shape reconstruction
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18. Thank you for your attention
Małgorzata Jenerowicz
Padova 7-9 March OSIRIS Full Team Meeting