Detection and measurement of wave breaking - Breaking and Dissipation of Ocean Surface Waves - page 98

breaking probability and statistics, to study breaking severity, turbulent mixing and air-sea
exchanges due to the breaking. Needless to say, it can be used to obtain dynamic properties
of wave breaking, such as

( (3.30) , Jessup & Phadnis , 2005 ). It is also applicable to
micro-breaking (to which most of the other breaking-study techniques are not), and this is
basically how it started.
So why do we still, more than 10 years after infrared sensing was introduced, refer to this
technique as promising and having a great potential? This question is equally applicable
to the other remote-sensing methods described in this section, and to some extent to the
acoustic techniques of Section 3.5 . In this regard, it is worth quoting Melville et al. ( 1988 )
who investigated both acoustic and microwave-radar signatures of breaking waves and
wrote:

( c )

“Our results imply that these remote sensing techniques ultimately may be used to measure the
dynamics of breaking waves, and are not restricted simply to obtaining the statistics and kinematics
of breaking”.

More than 20 years after these words, the remote-sensing methods mentioned have still
not made breaking statistics, kinematics and dynamics well understood or even well
described.
In this regard, it is perhaps not the researchers who developed the remote-sensing meth-
ods of studying breaking, and not the engineers who design the technical means of sensing
who should bear sole responsibility. The methods are well developed, proved, tested and
validated, and the instrumentation, for example infrared cameras, are quite sensitive, reli-
able and no longer very expensive. In our view, it is now the physicists who have to share
the blame for the lack of progress. Once there is a clearer understanding of the physics, of
what oceanic properties and features are to be sought and measured, the modern techni-
cal capabilities, including remote-sensing techniques, will be able to effectively investigate
them, address issues and deliver results.

3.7 Analytical methods of detecting breaking events in surface elevation records

The analytical methods for detecting breaking events in surface elevation records, which
are the subject of this section, could potentially provide a powerful means for study-
ing wave breaking, or at the very least breaking statistics and probability. There are vast
amounts of wave records accumulated over decades of wave observations and measure-
ments, and most of them undoubtedly have the breaking events embedded.
In this section, the Black Sea field experiment is described, since its data will be broadly
employed here and throughout the topic. Also, conversion of the acceleration-based break-
ing criteria from deep water to shallow water waves is done analytically and has shown
convincing agreement with observations.
The analytical techniques for breaking detection do exist, but like almost everything else
related to breaking they have to rely on empirical criteria and therefore are semi-empirical
rather than strictly theoretical methods. The theoretical approaches have to be able to deal