BSA Flow Software Installation and User's Guide - CSI

Figure 6-59 shows results from the experiment repeated with the highest
seeding rate that could be produced in the wind tunnel. All three curves
agree well up to about 6 kHz. Above this frequency, sample and hold
overestimates the spectral density, whereas the refined sample and hold
agrees with the CTA except for larger variance.
Effect of sample size
The variance of the refined sample and hold is closely related to the sample
size, as can be seen in Figure 6-60 and Figure 6-61.
Figure 6-60: Data rate 75 kHz, 121k samples
Figure 6-61: Data rate 75 kHz, 1M samples
For clarity only the CTA and refined sample and hold curves are shown
here, since the sample and hold curves are, in both cases, virtually identical
to the one shown in Figure 6-59
Figure 6-61 shows that by increasing the sample size from 120k to 1M, the
variance of the spectrum is reduced, and the CTA and LDA spectra are
practically identical up to 20 kHz. Above that frequency the LDA spectral
values are lower than the CTA values. This may be due to particle lag rather
than the data processing method.
6-64 BSA Flow Software: Options and Add-ons