Tuesday, July 21, 2009

Google Earth Physics?

I haven't had time to carefully read this preprint since I'm at a workshop, but this looks kinda fun and intriguing. The authors are using Google earth images on boats with wakes behind them to estimate the velocity of these sailing vessels.

Abstract: Google Earth photographs often show ships and their wakes in great detail. We discuss how the images can be used to calculate the velocity of these ships.




J Bowie said...

Now that sounds like an exercise my students would enjoy. I will be looking at this more closely as the school year gets closer.

Canticle said...

Hmm. happens to be close to one of my main areas, and they're missing some important detail. Much of ship design is about prismatic co-efficient and the compromise between wave making resistance and other efficiencies. Two hull shapes doing the same speed will generate different wave patterns, and not just laterally but, more importantly, vertically. The wavelength following astern is proportional to maximum dispacement speed, which can change dramatically with hull design. It's essentially about convincing the water the boat's longer than it is! Water density, salinity etc. also affect it but are much smaller variables. There are also many 'semi displacement' hulls about (we'll ignore planing hulls!). It's not a bad 'rule of thumb' approximation technique, but is also an example of rather superficial research & evidence, and not identifying the major weaknesses, i.e. slightly sloppy scientific methodology. Start with Tony Marchaj.