Vitel Soil Moisture Probe: Measurement and Data Processing
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SamplingYou must first decided on the number and location of samples within your study area. Since we are interested in both the spatial average and spatial patterns of soil moisture content, it is necessary to assign coordinates to each sampling location. In this way, we can map the surface and subsurface distribution of soil moisture content across the study area. Local or relative coordinates will suffice, and the coordinate system should be the same as that used to collect thaw depths. If possible, the soil moisture measurements should be made at the same time as the end-of-season thaw depths.
Field MeasurementOnce you have decided on your sampling locations, it is a relatively simple procedure to make measurements. To sample the soil from 0-10 cm (since the probe tines are 10 cm long), orient the probe vertically and carefully insert the tines into the soil. Then, switch on the power source and wait several seconds. Set the channel selector switch to 1, then read and record the first voltage. Change the selector switch to channel 2. Repeat the procedure until all four voltages have been recorded. Turn off the power to conserve battery life. Further details are available in the handout.
In many cases, it is also desirable to obtain measurements of soil moisture at greater depth from the same location. To do this, a tulip bulb planter has been provided. At a nearby (~0.5 m) location, use the tulip bulb planter to extract a plug of soil 15 cm long. It may be necessary to first use the larger unit to cut the organic mat, then the shorter bulb planter to grip and remove the plug. Try to minimize disruption of the hole and plug. Insert the Vitel probe into the borehole, switch on the power, and record the four voltage readings. Re-insert the soil plug.
You may wish to mark the sites so that you can return to the same locations each year. Furthermore, it is useful to record the type of soil that you encountered near the surface (0-10 cm) and at depth (15-25 cm). Finally, if you are collecting both surface and subsurface readings from the same site, it is probably best if you separate the readings since you will have two resulting data sets.
Data Entry in SpreadsheetThe next step is to record the data in a spreadsheet. The file format is:
STATION # [space] SOIL [space] V1 [space] V2 [space] V3 [space] V4
The STATION # (number) is simply the sample number. SOIL refers to the soil type, and V1-4 are the measured voltages at that site. Further details are available in the Hydra Soil Moisture Probe User's Manual. Be sure to enter the station# and soil type as an integer and voltages as a real number (1.000 instead of 1). In general, use a soil type of sand (=1) if you are dealing with organics. An example is given below, and there are sample input and output data files included on the disk. Note that there are no column headings or commas to separate the fields.
If you have collected two data sets, they should be separated. However, the first column will be identical and the second column may be the same.
166 1 2.107 1.993 1.942 2.15
167 1 2.069 1.992 1.943 2.151
168 1 2.052 1.989 1.942 2.151
169 1 2.037 1.987 1.944 2.15
170 1 2.022 1.984 1.946 2.15
171 1 2.009 1.983 1.948 2.149
Once the data has been entered, save the file(s) as an ASCII text file, with an appropriate name, to the same directory where HYD_FILE.EXE is located. The file should have a (.DAT) extension. Do not retain any column headings, and use a space as a delimiter (no commas).
Processing the DataThe data file you created in the spreadsheet will be used as input into the DOS program HYD_FILE.EXE, which is provided on the disk. Follow the instructions in the User's Manual. When running this program, keep in mind that you must use a different output filename than the input filename, and be sure to use the extension (.DAT) for both input and output files.
Prompt: Enter Filename to be converted: SITE1.DAT
Prompt: Enter Output Filename: OSITE1.DAT
The resulting output data file should be sent to the CALM WWW site via electronic transfer or disk. In addition, be sure to include the coordinates of the sampling sites.