July 8 – Soil Moisture Measurements

Joined: 23 Mar 2004 Posts: 74 Location: Barrow, AK

Well today we finished another set of field measurements at CMDL. Jenny had done the UNISPEC yesterday, so we just had soil moisture and thaw depth to do. I learned how to take and download the soil moisture data, but I think that I have as many questions now as I started with this morning, but I'll tell you what I DID figure out. Smile

The soil moisture instrument is a Vitel Hydra-Logger, which is basically an 8” x 5” x 3” box electrical taped to the top of a piece of PVC pipe about 4 feet long. A cord runs from the box through the PVC pipe to a set of probes at the bottom. The probes look like a large electrical plug with 5 prongs.

The soil moisture probe

To take a measurement, you push the prongs into the ground, push the MEASURE button and it quickly reads off a bunch of raw measurements before it comes up with a Percent Volume reading.

Soil moisture readout

Then you push ENTER and give the data point a name tag. Since we were doing the measurements at CMDL the tags were all xxx-yy, where the x’s are the cardinal direction of the transect line (000, 045, 090, 180, 225, or 270) and the y’s are the reading number (1-81, remember there are 3 readings taken for each of 27 points).

Me taking measurements (Photo by Kim Davis)

It was a cold, rainy, windy day at CMDL. It reminded me of many a day I spent in my youth digging clams on Washington beaches.

View toward CMDL from the end of the transect

Dora Nelson, a former TEA teacher, has brought some of her students to the Arctic for a few weeks to experience field science first-hand. So Kate, Rachel and Hanna joined us and divided up the thaw depth measurements so everything went MUCH faster and we finished in about 3 hours.

Dora Nelson’s students, Kate, Hanna and Rachel, receiving instructions on doing thaw depth measurements from Jenny (Photo by Dora Nelson)

After lunch, we went to the lab that SDSU has in the Racquetball Court (yes, another leftover NARL building name) and Jenny and Kim helped me to download the data from the logger.

Me downloading the data at the Racquetball Court (Photo by Jenny Richards)

After the data had been downloaded, I ran the data through a DOS program that did a bunch of fancy calculations on it and created more numbers. At that point, we viewed the data in an Excel file, but all of the columns were unlabelled so I had no idea what I was really looking at or what it meant. Then we discovered that we all really didn’t know:
1) how the soil moisture probes work,
2) what the volume percent readouts really mean, since they range from 25-700 or
3) what the DOS program was doing and what it produced.

So we sent an email to Hyojung Kwon in San Diego. She is the PhD student who has worked for several years with the data that we are sending and knows the most about the systems.

Then Kim, Dora and her students went out to the BEO tower to do the field measurements there while Jenny and I tried to work on some more preliminary data analysis. Jenny showed me how to set up the working files from the raw data, how to run the macro, remove flagged errors and outliers from the data set and how to fill the gaps back in, which Kim and I had done the day before with some other data. I am looking forward to going to Atqasuk tomorrow morning to that Kirstin can answer more of my questions about the data, since it is also her PhD area.