How to measure the height of a wave from a photo

The height is; is one of the fundamental wave parameters for its characterization. She is obtained by the difference between crest and trough. 

In the deep ocean and after the waves leave the generation area, the waves propagate like a sinusoid (the origin of the wave being at zero). This means that the distance from the pit to the the crest (front view) or from the crest to the top. The armhole (posterior view or from behind) are the same. Using wavegraphs that record this type of wave, we can calculate the height of the waves by crossing the water level by the ascending or descending zero. 

However, as already mentioned. we explored before, when the wave begins to feel the bottom there is There are several modifications that alter its shape and this becomes much more evident on the bench, that is, at the place where the wave breaks. In this way, the wave breaking height parameter was created, which corresponds to the sum of all effects that modify the shape of the wave before its dissipation.  ;

At the moment the wave breaks, the trough suffers a lowering effect in relation to the local level, called setdown in science. The wave speed decreases so quickly that the energy is lost. It is concentrated in a reduced horizontal space, which forces vertical stacking, resulting in an increase in wave height. At this point, the difference between trough and crest will be is greater than the crest and trough relative to any other location along the wave propagation.

É It is very difficult to measure the wave breaking height at the breaking point using the same equipment installed on the platform or offshore. There are studies that managed to install electronic equipment (pressure sensor, acoustic sensor) in the surf zone on a rigid bench, which provided fixation support and safety for measurements ;es (Nemes et al., 2016; Nemes et al., 2019). Otherwise, it's too late. It is extremely difficult to maintain a sensor at the bottom of the wave breaking zone, due to the high vertical (more than 2m) and horizontal (more than 60m) morphodynamics of the sand. Now Surface sensors, such as buoys, for example, suffer from horizontal drag, whipping and diving of the equipment, which compromises the reliability, efficiency and accuracy of the data obtained. 

There is scientific studies being carried out at universities in Brazil, Australia, the United States and New Zealand for the development of techniques capable of measuring wave breaking height with cameras. One of the products of these types of studies would be to point your cell phone camera at the wave and obtain the height. But there is still There is a lot to be tested, calibrated and validated.

One of the techniques for estimating the breaking height of waves most used today is wave breaking. through an image with reference. A photo of the wave breaking with asurfer, whose height is; known, has become one of the main tools for obtaining the value of wave breaking height. However, for this technique to be applied correctly, it is necessary to do so. Some care must be taken to ensure precision and accuracy in the final value:

b) the quality of the camera will be improved. This is fundamental to obtain the best possible sharpness and resolution of the height reference present in the wave. This is The main point that defines the accuracy of the method, that is, the value closest to the real one;

c) know the surfer's height and validate its angular decomposition in the wave (image), this is ;, the actual height in your surfing position on the wave will increase; the accuracy of the final value.

d) Finally, the challenge is; be able to transform a two-dimensional moment (photo) into a three-dimensional measurement with a referenced system of measurable spatial scale;

 

The uncertainty of the value of the wave breaking height calculated by the imaging technique (photo) is the sum of items a-b-c-d.

 

See examples of waves that had their height measured through a photo:

 

 

 

- How to measure the height of a wave

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Douglas Nemes is He is a former competitive surfer, who had the opportunity to take all the empirical knowledge acquired in the waves of countless beaches he visited on this planet into the academy. Douglas graduated as a Physical Oceanographer at UNIVALI. He completed a Master's degree in Coastal and Ocean Systems at the Federal University of Paraná. UFPR in 2011. In 2016, he completed his PhD in Oce & acirc; nica Engineering at the Federal University of Rio de Janeiro UFRJ, COPPE Research and Engineering Institute, whose research institute & eacute; the most important in the Americas. Finally, in 2018 he completed a post-doctorate in Coastal Engineering, in a partnership between UFRJ and the Federal University of Pará. UFPA. Over almost 20 years of academic work, Dr. Nemes developed techniques to qualify wave breaking on ocean beaches, published national and international scientific works on the main meteorological phenomenaseawater developments on the southern coast of South America and the development of a multifunctional coastal protection technology capable of recovering eroded beaches, generating perfect conditions for the practice of water sports. Currently works on coordinating hydrographic surveys and data processing for coastal engineering in Brazilian ports and waterways, in order to be used by the Hydrography Center of the Brazilian Navy to update nautical charts .

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