Day Three: Theory at Duke University

The main thing I did today was travel to Duke in order to meet with Chris, Henry, and Poy to talk about theory and learn how to analyze data once I begin to collect it.  We began by going over the Oishi articles that I read yesterday.  Fortunately, my analysis seemed to mesh pretty well with the way that Chris was describing it.  I understand most of the concepts, except maybe the empirical computations behind the Granier Temperature Dissipation Probes.  I had to think a little bit about the area of the rotated solid using a theorem that incorporated the centroid of the sap flux curve.  I eventually got it, though.  Once we finished talking about both of the articles, I chatted with the entire team for a while about how exactly the installl at NCSSM was going to be carried out.  The maintenance team had began to mount wire Wednesday morning, but I wasn't sure if they would be done by the end of the day.  We tentatively set tomorrow as the day where Chris, Henry, and Poy would come to help me install the probes into the trees.

After this discussion, we moved into using the software to collect data and convert it into sap flux values that accounted for non zero flux at night.  Three main pieces of software were used.  PC200W, SCWin, and BaseLiner.  PC200W is a program from Campbell Scientific that is purpose-built to interface with the CR1000 data logger that I have in the REX lab.  I learned how to plug it in to COM 3, use the interface between RS232 and USB, and how to connect to the data logger.  I learned how to extract the data from the logger and export it to a tab-delimited text file in order to view in other programs.  SCWin was the program used to actually program the datalogger to take fifteen second intervals, average them over 30 minutes, and plot the data in one space of memory.  The programming is not in any common programming language - it is in some kind of Campbell proprietary language.  However, the GUI based interface made it a little easier to set the datalogger the way I wanted it.  I created a program to import onto the logger, however, without a working logger in the REX lab, it may be a little difficult to implement this until tomorrow.  Finally, I learned how to use BaseLiner, which is an incredibly important program for converting change in voltage to a sap flux value while accounting for non-zero flux at night time.  The program takes raw data from the datalogger and allows you to manipulate the base line based on several variables such as Photosynthetically Active Radiation and Vapor Pressure Deficit.  Manually controlling this base line is actually a pretty difficult job - there are a bunch of different things to consider while doing it.  Chris Oishi walked me through the process pretty well, but I'm sure that I won't do a very good job at the very beginning.  I left duke and came back to NCSSM and practiced BaseLiner for the next few hours on some data that Chris gave me from the Duke site.

I got everything set up for the visit tomorrow to install the probes.  The wire is in the tree, so everything should go off without a hitch (hopefully).  I looked at the dogwood again, and everything seems to be OK!  We talked about mounting sap flux probes on the dogwood, and this may happen with either a car batter or the vernier data loggers.