High-speed real-time data acquisition for vector measuring current meters
Additional Document Info
Recent observations indicate that rapidly varying small-scale velocity structures in the upper ocean may be important in the heat and momentum balances near the air-sea interface. Observation of small-sale velocity structure in the upper ocean requires high-speed sampling to resolve rapidly varying flows and to reduce aliasing from surface wave orbital velocities. Since these flows may be temporally transient and vary over short spatial scales, obtaining and displaying the data in real-time are critical to implementing proper sampling strategy. This paper describes an integrated hardware and software approach used to provide real-time acquisition and display of vector measuring current meter (VMCM) data at high sample rates (0.5 Hz) along with supporting data from other instruments at somewhat slower rates. The hardware component consisted of a new circuit board for the VMCM that captured the VMCM data output, stored it, and retransmitted it at high speed in response to a request from the data acquisition computer. The data acquisition software ran on a Masscomp 5600 computer under the UNIX operating system. A central control program provided timing information to several software processes that handled serial data acquisition, display, and storage for one or more instruments. Deployed as a part of the Surface Waves Processes Program (SWAPP) experiment, the integrated data acquisition system successfully collected, processed, stored and displayed data from 19 VMCM’s and four other instruments over a 22-day period in February and March of 1990.