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.