Cardigan Bay Wave Height Measuremnets Using a Telescope

(supervisor: Tony Cook)

Nature of project: experimental, data analysis

Available to full-time physicists or joint students.

Project description and methodology

Wave energy will become an especially important area of renewable resources in the next few years. However in order to be able to site wave energy projects, a cheap and effective method must be found to monitor wave heights. Your task will be to use video images of buoys in Cardigan Bay in order to determine wave heights. The video imagery will be acquired through a robotic telescope.

Knowing the telescope position, and determining the dip angle to buoy, with respect to the sea surface, simple trigonometry can be used to determine the distance to the buoy, and hence image scale (cm/pixel). So if the image scale, at that distance, is say 3 cm/pixel, and the buoy bobs up and down by 20 pixels in the image, then the wave peak to trough range will be 60cm. The top or centre of figure of the buoy will be used as a reference point to measure sea wave height envelopes.

A successful project will develop beyond the above in one/some of the following directions:
1) Compare measured wave heights to those available from surf predictions

2) Evaluate the contribution to wave height noise from telescope wind shake and atmospheric turbulence. Can you compensate for these by calibrating against the position of a fixed landmark, placed in the camera field of view?

3) Can a Fourier spectrum be used to separate out wind/atmospheric effects from the true wave height component?

4) Can you evaluate the effects of tides, and atmospheric refraction on the image geometry and wave height measurements - the latter is more relevant over towards the horizon.

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

Additional scope or challenge if taken as a Year-4 project: Currently with the telescope, once it is pointing away from the shoreline, we lose the ability to identify where on the sea we are looking at, and the telescope orientation encoders are not sufficiently accurate to be relied upon to give us a precise azimuth and elevation angle. On top of the telescope tube is a separate wide angle finder scope camera, which will cover the area of the sea being imaged by the telescope, but also fixed landmarks of known position on the shoreline. If you can calibrate/calculate a rotation and scaling matrix to go from telescope camera pixel coordinates into finder scope camera pixel coordinates (and vice versa), then anything that you find in the sea, through the telescope, you can find its location in the finderscope too. If the finderscope contains landmarks on the shore line of known longitude, latitude and height, then you should be able to calculate a precise bearing and range to the object in the sea - hence solving the location problem.

Initial literature for students:

  1. McCormick, M., (2007). Ocean Wave Energy Conversion. Dover. pp256
  2. Gailey, G. and Ortega-Oritz, J. (2000) PYTHAGORAS Theodolite Cetacean Tracking, Marine Mammal Research Program, Texas A&M University: http://www.cetaecoresearch.com/Software/Pythagoras/Pythagoras_manual.pdf
  3. Cook, A.C., Vickers, M. & Stevens-Bulmer, G. (2009) Applications of Statistical Imaging of the Sea using a Robotic Telescope, Proceedings of RSPSoc 2009 Annual Conference, 8-11th September 2009, Leicester, UK . pp. 653-660 .
  4. Hydrographic Office, (2010-2011) Admiralty Tidal Tables, NP201-204. http://www.admiraltyleisure.co.uk/rya_chart_plotter.asp

Novelty, degree of difficulty and amount of assistance required

The project difficulty will depend upon how far you wish to work away from the shore. Close to the shore you have landmarks that can be used for removing wind shake. However the further out that you go towards the horizon, the more that you must consider the effects of terrestrial refraction on the dip angle and the effects of tidal heights on the image scale. Some programming may be neccessary in IDL or LabView in order to track and measure buoy (or other target) wave heights. If you do not do this then manual measurements will be acceptable, although somewhat manually intensive to make. Help will be given on telescope training and an introduction to video data capture and processing.

Project milestones and deliverables (including timescale)

milestoneto be completed by
Find out all you need to know about tides, surf predictions, wave heights, and on-line sites to get this data fromend of November
Telescope Training and decide how to navigate around Cardigan BayChristmas
Evaluate extraneous noise using Fourier Spectrumend of February
Compare measured wave heights to those from on-line wave height predictorsmid-March

Students taking this project will have to submit a full risk assessment form