¶ Soil Temperature and Moisture Profiles (STAMP)
¶ Instrument Description
The Soil Temperature and Moisture Profiles (STAMP) is a soil profiling instrument that measures a wide array of variables at 5, 10, 20, 50, and 100cm depths for three (west, south, and east) profile sites. Specifically, the instrument measures soil temperature, soil specific water content, loam soil water content, plant water availability, soil conductivity, and real dielectric permittivity. There are currently STAMPs at several SGP sites.
* For more information see the STAMP Instrument web page.
¶ Expected Operations
¶ Metrics
The STAMP generally runs smoothly with little to no problems. As such, the metrics should appear green for all variables for routine data. When individual variables flag as red (bad data) or grey (missing data), a problem may be ongoing. Please see the STAMP Known Issues or STAMP Past Problems pages for more information.
¶ Plots
There are a large number of plots for the STAMP. You do not need to look at every single one but instead the plots from which you feel you best understand the data. The STAMP is best monitored through looking at the summary plots first, and then looking at the more specific individual plots when data are suspect. This page will go through each plot individually, as well as point out which ones may be more useful for day to day operations.
The STAMP measures soil variables at 5, 10, 20, 50, and 100cm depths at three (west, south, east) collocated profile sites. The variables measured at each depth are soil temperature, soil specific water content, loam soil water content, plant water availability, soil conductivity, and real dielectric permittivity. Additional variables recorded include total plant water availability, precipitation, and voltage.
There are three ways to visualize the data. The first is by comparing each depth within the same profile. These plots are helpful for identifying incongruences within a particular profile (e.g., suspicious differences between the 10 and 20cm soil temperature in the east profile). The second is by comparing each profile at the same depth, which is helpful to identify incongruences between different profiles (e.g., differences in the 10cm soil temperature between the east and south profiles). The final way is through 2D color plots which enables a quick comparison between each profile as well as within individual profiles themselves.
Each profile may not compare together overly well, though they should be somewhat close. Even though the profiling sites are very close to each other, soil composition can vary impressively. Moreover, each depth may not compare well with other depths within individual profiles. Soil composition varies not only horizontally across profiles, but with increasing depth as well. As such, it can be difficult to identify problems. However, if you suspect a problem, it is better to note it rather than hope it goes away.
At most extended facilities, the soil water content responds similarly in most profiles, especially if the precipitation is heavier, resulting in the soil water contents in the different profiles looking more similar. However, water often drains out of the profiles and levels at different rates, which results in greater differences between the profiles after a while. This is normal (and quite common).
The STAMP is best conquered by looking at the 2D color plots first, and then looking at the other plots as appropriate when suspicious data are identified. It is most helpful (as described by the mentor) to report only grossly different (such as differences of 20% or more in soil water content), or large changes between profiles or levels that are not associated with either precipitation or the drainage from it afterwards.
¶ Comparing Depths Within Individual Profiles
Soil Temperature
Soil specific water content
Loam soil water content
Plant water availability
Soil conductivity
Real dielectric permittivity
¶ Comparing Profiles among Constant Depths
Soil Temperature
Soil Specific Water Content
Loam Soil Water Content
Plant Water Availability
Soil Conductivity
Real Dielectric Permittivity
¶ 2D Color Plots
STAMP Summary Plot
Individual 2D plots
¶ Other Diagnostic Plots
Total plant water availability
Precipitation
Voltage
¶ Site-Specific Information
The STAMP is located at SGP. Individual SGP facility information below:
SGP E13
- The 100cm measurements in the east and west profiles have been replaced with measurements at 75cm.
SGP E21
- The instrument mentor was only able to bury probes at 5, 10, and 20cm due to bedrock starting at around 25cm. Accordingly, the 35, 50 and 100cm depth measurements are not real.
SGP E31
- The 100cm measurements have been replaced with measurements at 80cm.
¶ Known Issues
¶ Known Behaviors
List of known issues for this instrument that MAY NOT need to be mentioned in your DQA's:
Differences in Precipitation Totals between STAMP and MET
It is typically not necessary to mention differences in precipitation totals between STAMP and MET in your DQAs, unless the difference is 15% or more for two or more consecutive rain events of more than 5 mm.
Below is an example of a difference in precipitation totals that would NOT need to be mentioned in your DQAs. Notice that while the difference is 15%, the precipitation amount is less than 4 mm. This rain total is too small to make a good comparison between MET and STAMP:
An example of a difference in precipitation totals that WOULD need to be mentioned in your DQAs is shown below. The 96% difference between MET and STAMP, combined with the total precipitation amounts large enough to make a good comparison (~18.4 mm), clearly indicate an issue. It is also important to note that the differences in precipitation totals between MET and STAMP had been gradually increasing after each successive rain event in the days prior. In this case, the MET rain gauge was the issue. The tipping bucket was rubbing on the tip sensor.
Negative Plant Water Availability Values
Occasionally, plant water availability values can become negative when the soil freezes. Frozen soil can result in either very low or possibly even negative soil moisture values. Instances where this occurs do not need to be mentioned in your DQAs.
However, we are not in the clear of negative plant water availability values once the weather gets warmer. They can also happen if the soil dries out (think summer months during long periods without rain). So, if you notice negative PWA values during the summer, this may be why. Instances where this occurs also do not need to be mentioned in your DQAs.
This may also happen sometimes with soil specific water content values - they can also become negative during dry conditions since soil specific water content is a calculated measurement.
It is important to keep an eye out for exceptions, however. If you find that the plant water availability values or soil specific water content values continue to remain negative even after a precipitation event (excluding very light ones), or if the drop to negative values is very sudden and drastic, then you should mention it in your DQAs (and issue a DQPR). It's always better to be on the safe side!
Sharp Drops in Data
Sometimes, sharp drops may be present in the data values. This is not always indicative of a problem and MAY not need to be mentioned in your DQAs. In the example below, you can see that the West and South profile data for all variables except soil conductivity in the West profile and soil temperature in the South profile drop sharply at approximately 02:45 UTC on 3/16/2019.
First instinct may tell you that something is wrong. If you look at previous days, however, you can see that it rained almost 14 mm total in 2 hours on 3/13/2019:
Following the rain, the soil began the process of drying out over the next few days. The sharp drop we see on 3/16/2019, in this case, is simply the result of the soil drying-down. By 3/16, the deeper soils had begun to dry out.
¶ Past Problems
List of past problems for this instrument that DO need to be mentioned in your DQA's:
Loose Wires
Lightning Strike
Failed Multiplexer Channel
Sometimes, a multiplexer channel can fail and requires a DQPR. When this happens, it can be very tricky to see, because once the multiplexer channel goes out, it will start reporting data from the previous channel. This can make it appear like the data are okay, but they are, in fact, reporting for the wrong level. For example, in the plots below, the 100cm East probe is not working, but it is reporting soil temperature data from the 50cm channel. Because of this, it appears that the 50 cm channel is missing (note how you can't see a red 50cm line in the east profile plot below), when in fact the 100cm is just overlaid on top (because they are both reporting 50cm data). To help with this, a new QC check has been implemented which flags whenever two depths are reading the same exact value for an entire day. An example of this is shown below. In this case, it was identified that the 100cm soil temperature values were the same as the 50cm soil temperature values. Generally, if two sequential levels match, say 50cm and 100cm, it will be the deeper level that is broken (100cm). If 50 and 20 match, 50 is broken. A DQPR was created to indicate that the 100 cm multiplexer channel (because the 100 cm is the deeper of the two levels involved in this example) may have failed.
