Resolution:
standard / ## Figure 1.
Amplitude and temporal frequency of the light flicker of downward irradiance are wavelength
dependent. (A,B) Examples of light flicker time series of downward irradiance at 1 m depth and light
wavelengths of 400 and 600 nm. Each time series constitutes of 3,000 measurements
acquired over 173 s. The amplitude of the light flicker at 600 nm is larger than at
400 nm. (C) The amplitude (estimated as the coefficient of variation) of light flicker of downward
irradiance decreased with growing water depth (across the 1 to 10 m depth range),
and increased monotonically toward longer light wavelengths. The ratio between the
amplitude at the longest and shortest wavelengths was calculated for each depth. This
ratio did not vary considerably across depths, and ranged between 2.5 and 3.0 (presented
next to each spectrum). (D) The frequency distribution of the flicker at a depth of 1 m differed across the light
spectrum. For clear graphical presentation, the power spectrum of light flicker, normalized
to the dominant frequency (1.54 Hz), is presented for different wavelengths at 50
nm intervals. See Additional file 1A-D for the frequency distribution of flicker at 2, 4, 6, and 10 m depth. (E) The frequency distribution of light flicker at 500 nm differed across water depths,
with the dominant frequency (1 m, 1.54 Hz; 2 m, 1.54 Hz; 4 m, 0.83 Hz; 6 m, 0.80 Hz;
10 m, 0.67 Hz) and the relative power at high frequencies decreasing with growing
depth. (F) The wavelength dependence of light flicker became weaker with growing depth. Wavelength
dependence was assessed as the reciprocal of the root mean square error (RMSE) and
the normalized RMSE (NRMSE) between the power distribution at 500 and 550 nm.
Sabbah and Hawryshyn |