Fig. 2: Observation geometry at the lunar surface.
From: Direct observations of negative ions on the Lunar surface by Chang'E-6
The surface-looking NILS field-of-view is projected onto the lunar surface, approximately to scale (top panel: side view, bottom panel: top view). Local north is towards the right. The light and dark red areas correspond to 20% and 50% sensitivity levels of the footprint, respectively. The red arrow in each view indicates the average direction of solar illumination and is a proxy for the flow direction of the solar wind. Well defined craters are shown as solid lines, degraded craters as dashed lines. The black dot represents a small rock.
