Figure 14A. Regressions show that Crater Lake Kd,320 and Kd,380 can be calculated from Kd,blue (400–500 nm) using data averaged over 0–40 m for July–August 1996–2002: Kd,320 = 1.65 * Kd,blue + 0.027, r2=0.66; Kd,380 = 1.16 * Kd,blue – 0.001, r2=0.92.

Figure 15A. Crater Lake regression of photometer Kd,blue against inverse Secchi depth (units m-1; annual averages for only same-day measurements, 1968–1991). Equation: Kd,blue = 2.08/ZSD – 0.026 (r2=0.54, N=13 years).

Figure 15B. Crater Lake time series of Kd,blue from direct photometer (gray circles) and radiometer (black circles) measurements and proxy using Secchi depth (open circles). The spike in 1995 follows heavy summer rain in June and July (see Figure 10A). Many of the comparison points are for measurements made on different days in the same month.