Partial Least Squares Modeling of Lunar Surface FeO Content with Clementine Ultraviolet-Visible Images - Planetary Exploration and Science: Recent Results and Advances - page 8

( R 2 ) of this model is 0.918, and RMSE is 1.44 wt%, indicating a good regression of
iron abundance has been achieved:

t

X

8

y i y i / k . b

i D 1

RMSECV k D (1.6)

8

t

8

X

y i y i / 2 . b

iD1

RMSE D (1.7)

8

1.4.2 Results and Analysis

We apply the PLS model mentioned in Sect. 1.4.1 to a small area near the southern
rim of Mare Crisium (Fig. 1.4a ) for preliminary check and validation. This region is
chosen for two reasons. First, its location is near the boundary of mare and highland,
so bimodal distribution of FeO is expected to exist; moreover, there are many small
spectrally fresh craters (low maturity degree) in the mare area, which could be used
as an indicator for the maturity-suppressing ability of our model (Ling et al. 2011 ).
PLS-derived iron map is shown in Fig. 1.4c in comparison with the result
of Lucey's work (Fig. 1.4b ). Considering the maturity-suppressing ability can be
indicated by the small fresh craters in the mare region, the difference between our
model and Lucey's is subtle, i.e., most of small fresh craters (bright spots in the
750 nm reflectance image (Fig. 1.4a )) are invisible in the PLS-derived FeO map
in Fig. 1.4b, c . The distribution of FeO in the mare area is relatively homogenous,
which indicates that the maturity-suppressing ability of our model is comparable to
Lucey's algorithm.
It can be seen from Figs. 1.4 and 1.5 that FeO abundance is high in mare regions
and low in highland regions. Generally, FeO abundance of mare regions is higher
than 10 wt%, which is due to the large concentration of iron-bearing silicates in
mare basalts such as pyroxene, olivine, ilmenite, etc. Highland region is deficient in
iron, as its rock type is dominated by anorthosite (Lucey et al. 1995 , 1998 ). From the
histogram of iron abundance (Fig. 1.5 ), we can distinguish a bimodal distribution of
FeO in this region; the peak on the left represents FeO concentration in highland
region and right peak represents that in mare region. Comparing the PLS model
to Lucey et al.'s ( 2000 ) algorithm, it can be recognized that the two models have
similar peak positions for the mare region (right peak), and the peak FeO abundances
are about 16.5 wt%; while the FeO abundances for the highland (left peak) have a
little difference, our result is around 9 wt%, about 1 wt% higher than Lucey's. This
discrepancy may result from various causes such as model input parameters (e.g.,
different bands or sampling sites). Further discussions will be given in Sect. 1.4.3 .