algal mat ecosystem
8
algal mat ecosystem benthic shallow-water system in which the sediment is overgrown with dense layers of filamentous and thallous algae and their associated microorganisms. The occurrence of algal mats is related with the
absence of an active benthic macrofauna with its grazing and bioturbation,
while on the other hand, the dense algal mat prevents benthic animals from
settling in the seabed. Estuarine mudflats have been observed to change
temporarily into algal mats after oil spills. --tbenthic system.
alginates additives to food (cream, pudding) to make fluids firmer, originating
from the Phaeophyta.
aliasing misinterpretation of a recorded signal due to undersampling.
Oceanographic variables generally vary in two or three spatial directions
and in time. If, for instance, a plane wave in the propagation direction is measured, the variance spectrum will contain variance at much smaller wavelengths (--twave characteristics) than if the same wave is measured in a direction
nearly parallel to the wave crests. Therefore additional assumptions or theoretical or empirical knowledge are required to interpret undersampled
recordings of this type. Another type of aliasing can occur in a digitized
analog signal. If a time-varying signal is recorded every time interval6t, the
highest frequency that can be interpreted with this sampling rate is the
Nyquist frequency 1/26t, corresponding to a wave period of 2 6t. Frequencies
above the Nyquist frequency are therefore undersampled, although they will
contribute to the recorded total variance of the parameter. This contribution
may wrongly be attributed to lower frequencies. This type of aliasing can be
compared with the effect of the wheels of a motion picture apparently
revolving backwards.
L-,.;//
Aliasing
...,-
...'"
,-"- .... "- ..........
8
algal mat ecosystem benthic shallow-water system in which the sediment is overgrown with dense layers of filamentous and thallous algae and their associated microorganisms. The occurrence of algal mats is related with the
absence of an active benthic macrofauna with its grazing and bioturbation,
while on the other hand, the dense algal mat prevents benthic animals from
settling in the seabed. Estuarine mudflats have been observed to change
temporarily into algal mats after oil spills. --tbenthic system.
alginates additives to food (cream, pudding) to make fluids firmer, originating
from the Phaeophyta.
aliasing misinterpretation of a recorded signal due to undersampling.
Oceanographic variables generally vary in two or three spatial directions
and in time. If, for instance, a plane wave in the propagation direction is measured, the variance spectrum will contain variance at much smaller wavelengths (--twave characteristics) than if the same wave is measured in a direction
nearly parallel to the wave crests. Therefore additional assumptions or theoretical or empirical knowledge are required to interpret undersampled
recordings of this type. Another type of aliasing can occur in a digitized
analog signal. If a time-varying signal is recorded every time interval6t, the
highest frequency that can be interpreted with this sampling rate is the
Nyquist frequency 1/26t, corresponding to a wave period of 2 6t. Frequencies
above the Nyquist frequency are therefore undersampled, although they will
contribute to the recorded total variance of the parameter. This contribution
may wrongly be attributed to lower frequencies. This type of aliasing can be
compared with the effect of the wheels of a motion picture apparently
revolving backwards.
L-,.;//
Aliasing
...,-
...'"
,-"- .... "- ..........