What is a 2D Wave Spectrum?
A 2D wave spectrum is a representation of the energy distribution of ocean waves in both frequency and direction. It provides a detailed view of how wave energy is distributed across different wave frequencies and directions. This information is invaluable for various offshore activities, including vessel operations, platform design, and safety assessments.
2D wave spectrum presented as function of time in ODST:
Basic Theory of 2D Wave Spectra
Frequency vs. Direction:
The horizontal axis of a 2D wave spectrum represents the wave frequency, which is the number of wave cycles passing a point per unit time. The vertical axis represents the wave direction, usually measured in degrees relative to true north.
Energy Density:
Each point on the spectrum represents the energy density of waves within a specific frequency and direction range. The color or height of the point indicates the energy level, with brighter colors or higher points signifying higher energy.
Significance and Dominant Directions:
By analyzing the spectrum, it's possible to identify the significant wave height, which is the average height of the highest one-third of waves. Additionally, the dominant wave directions, where most of the energy is concentrated, can be determined.
Swell and Wind Waves:
The spectrum helps differentiate between swell waves (longer period waves generated by distant storms) and wind waves (shorter period waves generated locally by wind).
The below example spectrum has a swell wave coming from south-west and a wind wave coming from north-east.
Wave Forecasting:
Utilizing historical data and numerical models, 2D wave spectra aid in forecasting sea states, providing critical information for safe offshore operations.