a, Histogram of the number of observations. b, Number of observations by lake area (in km2). Note that observations are aggregated to monthly time steps and therefore the actual number of ICESat-2 observations is slightly higher. In b, the x axis is plotted on a log scale. In total, 43% of lakes receive two observations, 24% receive three observations, and 32% receive four or more observations. There is a strong positive correlation with lake area, as shown in b. For example, although the average across all water bodies is 3.3 observations over the 22-month period, lakes larger than 10 km2 average 11.2 observations.