Remote sensing of the ocean

Measurements of ocean properties from space that use radar or other techniques are generally influenced by ocean waves. Remote sensing is also a way to measure wave properties. IOWAGA uses satellite data to provide a validation for the numerical model results, but also provides parameters, derived from these models, that can be used to correct for wave effects in measurements of sea surface salinity, winds, sea level ...

Infragravity waves and satellite altimetry

"Infragravity waves" are are long gravity waves with periods of 30 to 300 s and wavelengths that typically range from 1 to 50 km in the deep ocean. Their amplitude in the open ocean can be larger than 1 cm, thus contributing to the measured sea level fluctuations that can be measured from space. We are developping a global numerical model of these "IG waves" as part of the preparation for the SWOT mission in order to help
define the measurement errors for ocean currents.

Icebergs and waves

Following the first full map of small iceberg distribution in the Southern Ocean by Tournadre et al. (2008), it was realized that it looked very much like the pattern of errors in the wave model. So what happens to waves in an iceberg field? Well, if the berg is big enough, they just get blocked and partially reflected, like waves smashing against breakwaters in coastal areas. The only difference is that our breakwaters are made of ice and they drift and melt slowly. Actually the icebergs lose 'bergy bits' due to the pounding of waves on their sides.

Jean Tournadre was brave enough to process the 2002-2009 archive of Jason-1 satellite data to detect icebergs in the altimeter signal. These detection provided statistics of iceberg positions and sizes, for icebergs with diameters between 500 m and 4 km. Of course there are also much bigger icebergs and their positions are known because they are easily tracked by other means. However, these giant icebergs are less numerous and should have, except very locally, a smaller impact on ocean waves.

This information about icebergs was then introduced in the numerical wave model WAVEWATCH III^® which is developed jointly with NOAA/NCEP.