CTD Aliasing Investigation
Abstract
The Neil Brown Instrument Systems Mark IIIb Conductivity, Temperature, and Depth (CTD) instrument is used by the Naval Oceanographic Office to satisfy requirements for environmental data. Computed parameters such as salinity are calculated from those directly measured. An investigation is described which evaluates the effect of aliasing on CTD data acquired at the standard sampling rate of 15.63 Hz. A method is developed for determining the transfer functions for conductivity and temperature from a modified CTD at three times the normal data sampling frequency. Because the modified sampling arrangement introduces jitter in the sample timing, it is necessary to use a modified spectral estimation techniques, developed by Shaw, was adopted to estimate the conductivity- and temperature-transfer functions. Conductivity-transfer functions obtained in this way are compared with published results. Agreement is to within the margin of error introduced by sample timing jitter for most frequencies. The temperature- and conductivity-transfer functions are used to predict an upper limit to the spectral error due to aliasing. These results are extended to include a corresponding estimate for salinity. It is concluded that aliasing is not a significant source of error in present data products at 1.0-m resolution, and that error due to aliasing would be less than 10% in products with resolutions as fine as 0.1 m. Thus, limits on high resolution data products are not due to aliasing, but instead are due to other phenomena associated with the instrument.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1985
- Accession Number
- ADA253722
Entities
People
- Ernest L. Burdette