Figure 6. Crater Lake Kd ratios from data in Figure 5 (June–September 1996–2002, LI-1800uw). Least squares regression for Kd,320:Kd,380 versus depth (m), y = -0.0031x + 2.32, r2=0.68. Average 0–10 m ratios: Kd,320:Kd,blue, 2.28 (SE=0.007), Kd,380:Kd,blue, 0.98 (SE=0.002), Kd,320:Kd,380 = 2.32 (SE = 0.012). Average 0–40 m ratios: Kd,320:Kd,blue = 2.52 (SE=0.058); Kd,380:Kd,blue = 1.11 (SE=0.029); Kd,320:Kd,380 = 2.27 (SE = 0.016).

Figure 14B. Time series for Kd,320 and Kd,380 (0–40 m) in Crater Lake using direct radiometer measurements (1966, 1969, 1996–2002) and proxy derived from Kd,blue using blue-filter photometer data, (1940, 1969, 1980–1991). For 1966 Kd,380 was estimated from reported Ed,360–390nm vs depth (5–25m) yielding Kd,380=0.024; after adjustment for 0–40 m depth range using recent patterns of Kd versus depth (Figures 5 & 6), Kd,380= 0.027. For 1966 and 1969 the Kd,320 radiometer data were estimated from measured radiometer Kd,380 using Kd,320 = Kd,380 *

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).