Using ASCAT Wind and Other Data in Marine Forecasting

3.0 System Identification and Model Evaluation Using Observational Data » 3.4 Jason-2 Significant Wave Height » 3.4.1 Introduction

When do ocean waves become hazardous to an ocean-going vessel? The height of a wave that someone considers significant and potentially hazardous depends on the size and shape of the vessel. Mariners know the physical limits of their vessels in terms of both wind speed and wave height. This allows them to reduce their risk of encountering wind and waves that exceed those limits by applying the best available analyses and forecast information on changing weather conditions and associated sea state.

Forecasting wave conditions (especially in the open ocean) is done primarily with NWP model output. Altimeters provide an important source of remotely sensed observation data, and can be used in conjunction with the model output to improve the analysis and forecast of the sea state. However, NWP models still provide forecasts for very large contiguous ocean areas. Therefore, we’ll use WAVEWATCH III data from NOAA-NCEP Environmental Modeling Centre’s Marine Modelling and Analysis Branch (MMAB) in the case since it can be configured to generate higher resolution output.

On the next page, we’ll compare significant wave height from the Jason-2 altimeter and WAVEWATCH III model. But before we do that, let’s quickly review what significant wave height (SWH) is.

SWH is the mean height of the highest one third of the waves in a wave spectrum. It is well correlated with the wave height that a skilled observer would see. The diagram shows the relationship between significant wave height and other pertinent wave characteristics.

Image graphically shows how wave height are classified

The diagram also identifies more hazardous wave characteristics, such as the highest 10% of the wave heights (H1/10), the highest 1% of the wave heights (H1/100), and a theoretical maximum wave height (HMAX), that mariners should be aware of.