Utility of laser altimeter and stereoscopic terrain models: Application to Martian craters

• Laser (MOLA) and digital terrain models (HRSC) compared for crater topography.
• MOLA is accurate for craters with diameters >10 km.
• MOLA can resolve features ~8 px across, HRSC fails for craters ~20 px across.
• Revisit the crater depth versus diameter ratio for Mars.

The use of numerical datasets of the same type derived from remote sensing instruments is often treated as equivalent in value and utility, within the limits of their spatial resolution. Surface topography is a good example of this. We used gridded digital terrain models (DTMs) derived from both laser altimetry and stereo pairs as well as the original laser data points to quantify the topography of impact craters, which have well-studied morphometry. The primary purpose was to test the accuracy of laser data given an image-based DTM with approximately a factor of 10 better spatial resolution; we used the Mars Orbiter Laser Altimeter and High-Resolution Stereo Camera datasets for this work. We found that the ability to derive accurate topographic information in laser altimetry diminished well before the ability to visually resolve the feature in the dataset, but we also found that laser point and gridded data-based results were in good agreement down to their resolution limits. Relative to the image-based DTM, pixel-for-pixel, the laser data were more useful in their ability to visibly resolve the impact craters. This work has implications for remote sensing in general, but specifically the application to limited sources of data for planetary surface topography, such as Mercury where the northern hemisphere topography is being measured with a laser altimeter but the southern hemisphere topography is based only on stereo pairs.