Acajutla, El Salvador

Sea level; Wave height and period statistics

Wave recorders; sea level recorders

The data set comprises wave height and period statistics, and sea level measurements collected near Acajutla, El Salvador. Accurate positions are not known and the location of both instruments is approximated as 13 ° 32.0 N, 89 ° 57.0 W. There is no other information available regarding these sites. The data were collected between 1 December 1974 and 30 November 1975 using an Institute of Oceanographic Sciences (IOS) frequency modulated (FM) pressure recorder deployed in the harbour at Acajutla and a waverider buoy deployed offshore from the harbour. The IOS FM pressure recorder uses a pressure sensitive diaphragm to vary the gap of a parallel plate capacitor, resulting in a frequency modulation of a nominal 100 KHz carrier signal. This signal is recorded on a shore-based magnetic tape data logger linked to the pressure unit by armoured cable. Data were recorded for ten minutes every three hours and analysed later as described by Hardcastle (1978). Some uncertainty surrounds the ability of the pressure recorder to respond accurately to the surface waves since the transfer function from pressure to surface wave height is incompletely understood. Draper (1957) has derived a factor to correct for the hydrodynamic attenuation of the pressure signal. This factor varies with mean zero up-crossing period and may increase wave heights by up to 15 percent compared with classical wave theory (Fortnum and Hardcastle, 1979). This data set has not been corrected. The waverider buoy generates a heave signal via an internal accelerometer to an accuracy of better than five percent. This signal is used to amplitude modulate a 27-30 MHz radio signal which is transmitted continuously and can be received by the recording device at a range of up to 50 km depending on local conditions (Driver, 1980). The data were collected by Livesey and Henderson (now incorporated with Binnie and Partners, 65 London Rd., Redhill, Surrey, RH1 1LG, UK) and are stored at the British Oceanographic Data Centre.

L. Draper (1957) Attenuation of sea waves with depth, La Houille Blanche, 12; B.C.H. Fortnum & P.J. Hardcastle (1979) Waves recorded at Aldeburgh, Dunwich and Southwold on the east coast of England, Institute of Oceanographic Sciences, Report No. 65; P.J. Hardcastle (1978) Sea wave recording system using magnetic tape cassettes, Institute of Oceanographic Sciences, Report No. 61; J.S. Driver (1980) A guide to sea wave recording, Institute of Oceanographic Sciences, Report No. 103

British Oceanographic Data Centre
Joseph Proudman Building 6 Brownlow Street
Liverpool
Merseyside
L3 5DA
United Kingdom