Figure 3: (a) This figure illustrates the laboratory surface, referred to as the black-and-white boundary pattern, with known albedo, which consisted of two regions: a black region on the left and a white region on the right separated by a sharp linear boundary. (b) This illustrates the four sensor orientations used to collect data for the estimation of the SSF along with the symbols used to indicate the measured values plotted in Figure 5. The top row views the sensors as if looking up from the table so that the photodiode placement in the sensor package can be visualized. Below these the gray sensor shapes illustrate how they are oriented looking down at both the sensors and the albedo surface. Measurements were taken as the sensor was incrementally moved, with one-millimeter steps, in a direction perpendicular to the boundary (as indicated by the arrow at the bottom of the figure) from a position of 5 cm to the left of the boundary (well within the completely black region) to a position 5 cm to the right of the boundary (well within the completely white region). This process was repeated four times with the sensor in each of the four orientations.