sed samples

We spent a few days on R/V Gulf Challenger (25-26 February and 12 March 2008) collecting bottom samples and bottom videography in Portsmouth Harbor. There are 26 bottom sample + video stations, and 3 stations with bottom sample only.

I plotted up GPS locations from the bottom samples to see how they looked. Two GPS positions were recorded for each sample (one when the Shipek sampler started descending, and another when it came to surface) using a Garmin WAAS-enabled handheld GPS from the stern of the boat. The plot looks something like this:

Obviously, there is sort of a large difference between the deploy and retrieve positions (represented by green and red dots, respectively). Hmmmm. I consulted with Shachak and he recommended that I interpolate between the two, reasoning that the mean position is probably closer to the true sample location. Here’s what I did:

• convert deploy + retrieve positions from dd.dddd to UTM coordinates
• find midpoint between deploy + retrieve positions (interpolation on XY grid)
• calculate XY distance between deploy + retrieve positions
• calculate approximate uncertainty of midpoint position, choosing the greater of the following values:
  • 1/2 of XY distance (e.g. somewhere between deploy + retrieve positions)
  • 5m
• PLOT midpoint with buffer distance equal to (approximate) uncertainty

And here’s the result: