International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
where TP: TRUE POSITIVE - Both data sets (detected crater
and comparison data set) classify the pixel as being part of a
crater
TN: TRUE NEGATIVE - Both data sets classify the pixel as
being part of the background
FP: FALSE POSITIVE - Detected data set classifies the pixel
as a crater, comparison data set classifies it as background.
FN: FALSE NEGATIVE - Detected data set classifies the pixel
as background, comparison data set classifies it as a crater
However, if we apply these factors directly to the optical image
results, the detection ratio is likely to be very low, because the
non-detection of large sized impact craters significantly reduces
the detection ratio. So the QA factors are modified for impact
craters, which have higher detection percentages than 50%,
which are considered as true detection. Detection results by this
scheme are shown in Table 1.
(a) Crater detection on MOC- | (b) Crater detection on MOC-
WA level 2 image WA level 2 image (M0203967)
M0203967)
e
(48 E git +
(e) Crater det (f) Crater detection on MOC-
WA level 1 image M0300749 | WA level 2 image (M0900109)
Figure 9. Crater detection examples for craters of various sizes
and shapes. Note that heavily eroded craters are not
currently detected,
3
(a) Centre points of craters in (b) Crater detection results
MCC overlaid on MOLA with MOC-WA level 2 image
DEM (M0101958) same area with
case (b)
Figure 10. Inter-comparison with MCC data sets and detected
craters on MOC WA image (white + ; Barlow data
sets , Black + : Kuzmin data sets)
Manual measurement
MCC Small
; Large
(Barlow) size n
(R «8 ne
v (8 <R<60)
pixels )
True
positively
detected 60 198 120
crater
number
False False positive has no meaning
Dositively for the MCC inter
: comparison, because MCC
detected Smpaîrss Sod s 74 10
data sets don't aim to
crater :
catalogue all craters in target
number
area
False
negatively
detected 12 32 12
crater
number
Detection ;
83% 86% 90%
percentage
Branching
Homns - 0.37 0.08
factor
ualit
Quality j 6596 84%
percentage
*True negative has no meaning for individual crater detection
Table 1. Impact crater detection ratio by intercomparison with
MCC and manual measurement in 12 random MOC
WA images
3.3 Simulation with different illumination condition
As far as we have experienced, the illumination condition is
crucial for the positional accuracy of the detected impact crater.
To assess the robustness of an algorithm with different ranges
of illumination angles, simulated crater DTMs whose diameter
was 100 pixels and which have vertical 3D profiles of well
known craters proposed by Duxbury (1991), was employed.
Hill shaded images were generated at 10° intervals within the
range of 0-360° sun azimuth angle and 20-90° elevation angles
using a Minnaert surface’s reflectance model which is given by
(8).
P = B(cosi )' (cose )'" (8)
where B: brightness coefficient ,
k : the constant of Minnaert exponent
e: emission angle, I ; incidence angle
The results show very good agreement with actual (modelled)
positions except at very high sun elevation angles around 90°,
which rarely occurs for real image acquisitions.
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