The OSSI-010-022 probe measures the ambient pressure thus is fixed at the bottom of the sea bed. In standard, it is delivered with a temperature sensor and a pressure sensor.
The OSSI-010-022 wave recorder measures the electrical variations generated by pressure variations on a pressure sensor. The measures are stored in the flash memory of the recorder. Once out of the water, the data is uploaded to a computer through the RS 232 connector.
The wave recorder is timely retrieved (around 2 years and a half of battery life). It is built to be placed at relatively shallow depths (maximal depth is 58m) and minimal depth is 25m to minimize the influence of the reef.
The recorder measures at 4Hz during 2 minutes every 15 minutes.
Installing the wave recorder
Depths and temperature readings take place every 15 minutes. The wave recorder is attached using plastic cable ties (like Colson) to 6 stainless steel bars installed in 3 crosses in the sand.
The probe is installed by scuba divers at about 10 cm above ground. It is important to measure the distance to the ground for later use in computations.
Despite the GPS coordinates, the probe is not deployed using a stable geodisic reference, very useful if one wanted to study the elevation of the sea level. The depth is verified using a dive computer (precision +/- 1m-).
There is no control of the probe (levelling, depth in time, etc.) during the whole period of recording. However, it is the same probe that takes the measures during the whole period.
Retrieving the probe is also done by scuba diving. Only the cable ties linking the stakes to the probe are cut and the probe is taken back to the surface.
The data is directly copied from the Compact Flash cards and an algorithm is used to transform the pressure measures into actual wave significant height and period.
Derived variables are :
Hs (m) - Significant height in meters
Tpeak (s) - Peak period in seconds
Hrms (m) - RMS Height in meters
H1/10 (m) - mean of the 10th biggest waves
H1/100 (m) - mean of the 100th biggest waves
Hmax (m) - estimation of the biggest wave
|In the South Pacific||In French Polynesia|
|Christmas (Kiribati)||Moorea - Pointe Sud|