The CDIP system was operated as a "hardwired" system. Signals from the 

 pressure sensors are sampled at 1-2 Hz (Table 1) via submarine cables from an 

 onshore field data logging station. The field station was designed to operate 

 independently, under locally resident program control, as a software-driven, 

 autonomous, data acquisition system. Its primary function is to locally acquire, 

 log, and, in response to a call from a host computer, upload the stored data. The 

 data are received through a phase lock loop, electronically conditioned and 

 optimally compacted, according to the header block instructions, and stored 

 locally in 16 K-bytes of RAM. Storage is based on the "first in, first out" 

 principle, with the oldest word overwritten by the latest word as the storage 

 buffer is filled. Two-way communication between the field station and the 

 central station in La Jolla is accomplished via modem connections, through 

 normal phone service. In response to a phone query from the central station, 

 typically every 3 hr, the field station uploads the latest data buffer. Since each 

 record is over 2 hr long, this allows for nearly continuous sampling (gaps of 

 several minutes occur during downloading). The central station data collection 

 computer, a Sun workstation, superficially examines the incoming data for 

 obvious defects, such as incomplete transmissions and failed phone connections. 

 A detected fault will trigger a retry call to the field station. After additional 

 quality control, final data are transferred monthly to CERC via Internet. 

 Additional details of the CDIP operation are given by Seymour et al. (1993). 



Data collection commenced for the NDBC buoy in January 1993, was 

 interrupted briefly in May 1993, and continued through May 1994. Repairs were 

 effected in September 1994, and the buoy continued operation through 1995. 

 Table 2 provides summary statistics for the deployment with 20-year hindcast 

 statistics for comparison (Corson et al. 1986). ' Figure 1 1 is a rose plot of the 

 mean significant wave height and occurrence by direction (convention is 

 direction waves are coming from, with respect to true north). 



The CDIP system was installed in October 1994 and operated without 

 interruption through the duration of the study. As planned, the adequacy of the 

 measurements was assessed after the first year of operation (McGehee 1995). 

 The principal issues were the range of different types of incident conditions 

 measured by the buoy, and the level of infragravity energy measured by the 

 harbor gages. 



While a reasonable variety of incident wave directions and frequencies was 

 captured, it was not a particularly energetic year. One event sufficient to affect 

 harbor operations occurred, on 14-15 March 1994, reportedly due to wind wave 

 conditions in the entrance. Figure 12 expresses the total measured infragravity 

 energy for each record (high-energy cases only) at each site as an equivalent 

 wave height during the first 8 months of record. Infragravity wave heights 

 experienced in mid-March were exceeded in other months without reported 

 problems. It is not clear whether the lack of reported impacts on operations in 



For convenience, mathematical symbols used in Table 2 and throughout this report are listed in the notation 

 (Appendix I). 



12 



Chapter 2 Field Wave Measurements 



