INCORPORATING MULTIPLE DATASETS INTO TRADITIONAL GEOMORPHIC MAPS: THE VESTA EXAMPLE (Invited Presentation)

The primary geologic process for many small, airless, rocky bodies is impact cratering. This means traditional mapping approaches can be problematic, because differences in morphological characteristics among cratered surfaces can be subtle to absent, and surface morphology is muted by the regolith’s physical and mechanical properties. An additional problem is that previous mapping efforts were informed by mapping Earth’s Moon, where a general correlation exists between albedo, composition, and topography. By contrast, no such general correlation exists on many smaller bodies, and thus the bulk of compositional information is not carried by the morphology, the topography, or even by a combination of the two. Using a lunar-based approach leads to unique information provided by other data (multispectral, visible color, etc.) being lost in the mapping process and as a result, not being incorporated synergistically into interpretations.

In constructing a global geologic map of Vesta at 1:300,000-scale, we utilized an approach that required creating two maps independently. For the first map we used morphology and topography to define map units; for the second, spectral data defined units. The unique results of each map were then combined into map units that contain key information from both datasets.

For Vesta, multispectral data provide unique insight into stratigraphy (material brought up through cratering processes) that can be lost when using an albedo mosaic as the basemap. However, solely using a “color” ratio mosaic as a basemap can magnify potentially misleading data, because spectroscopy in the UV-VIS-near IR samples only the upper few µm of the surface. Thus, clear criteria were established to define hybrid map units. The crucial exercise in retaining unique data when combining the two maps was to create a decision tree for determining which data would be primary in drawing unit boundaries.

In mapping other airless rocky bodies we recommend the following: (1) create maps of each available dataset independently, including defining unique units; (2) define criteria to draw geologic unit boundaries based on the datasets that retain the most unique information; (3) utilize these criteria to create a map combining the most geologically informative data from each map.