a: Viking lander heights are taken as from the top of
the cameras (Huck et al., 1976), which we expect to cast a more
consistent shadow than the full 2 m height from the top of the antenna.
b: From Golombek et al., 2008
4.2. Comparison to Prior Manual
Results
Manual measurements are an essential calibration step when applying
MBARS. However, the manual analyses presented here were taken with an
understanding of how MBARS detected boulders, creating some bias in how
the boulders were measured. It is worthwhile to compare MBARS results to
other manual boulder counts to determine if existing manual datasets are
useful for calibration. Some discrepancies are expected between the two
manual methods, since the user was directly outlining the bright boulder
faces, rather than using shadows to measure the boulders. We measured a
separate area within the same images to determine whether discrepancies
between MBARS and prior manual boulder measurements were related to a
difference in measurement technique or fundamental challenges with the
image (Section 2.2). The comparison between automated and manual results
is shown in Fig. 7, using four areas within HiRISE image
PSP_007718_2350.