Monthly Archives: November 2013

White Bear Lake

I've been in an EarthCalc intellectual downswing for a few weeks -- just could not think of anything interesting. It is weird how we have these mental blocks at times. Fortunately, a week ago Saturday I went to the first local Data Visualization Hackathon and had the pleasure of working with some folks to explore the declining level of White Bear Lake.

I've discussed White Bear Lake a bit before in talking about aquifers and rate of change. This weekend at the hackathon we looked more explicitly at the lake level itself, rather than water level in aquifers nearby. White Bear Lake is striking because it has dropped many feet since 2003. That change is visible from space!! Look in particular at the upper left corner of the lake:

The video above simply takes images from the Landsat satellites from 1984 through 2012, and was made by Nate Bird at the data viz hackathon using images from Google. Check out Google's Earth Engine which gave us the idea.

I also put together a very quick graph of lake level (in blue) and precipitation (in green), with clashing scales. It's not the best visualization, but it gives some illustration of the fact that the USGS says that White Bear Lake's average levels used to roughly lag yearly precipitation by a few years, but since the early 2000s has been somewhat decoupled from yearly precipitation.

I have a few more illustrations to put up in the next post, as well as the worksheet. First, though, I'll ask you to think about how we should model the lake! White Bear Lake is very irregular in shape. Should we idealize it and model the surface as a rectangle? a circle? The shape of the bottom is also quite complex. Should we model the lake as a prism -- like a swimming pool -- or as a bowl? What are the right answers to these questions, and how would we be able to know if we answered right or wrong?

Changing tides (the prodigal returns)

There's a reason I started this project over the summer... now that I'm back teaching, there are so many urgent tasks to complete that blogging can fall to the side! I'm used to making a point of carving out time for research: on a personal level, I don't feel like a vital mathematician or teacher if I'm not creating mathematics. I have less practice, though, making time for math communication outside the classroom.

How are your semesters going? It is that time when you might feel that the semester's been going on forever, and yet the end is not near. We all know the end is rushing toward us, though, and it's the time when we try to remind students who might have been slacking or who have started getting discouraged that we have almost two months to wrestle a class into success or let it sink into failure.

In my calculus class right now we're dealing with derivatives of arcsine and arccosine, but I am not going to talk about those today. Instead I'll put up the natural follow-up to the last post, a spreadsheet worksheet on modeling ocean water level over 24 hours.