Developing a Ruggedized Soil Moisture Sensor for 10+ Year Climate Observatories.

The establishment of long term climate observatories is becoming a priority in many countries around the world.  It is generally acknowledged that, although many parameters can be measured effectively at a few distributed sites, soil moisture requires a much wider and more intensively sampled distribution.  However, researchers are still left with a difficult choice.  Low cost sensors can be distributed in this manner but do not have an expected >10 year life expectancy.  Sensors with better performance are available but are expensive.  In addition, all of these sensors are difficult to install.  The goal of this project was to develop, calibrate, and characterize a sensor that would have a >10 year life expectancy and simplified installation but maintain a low price point so it would not be cost prohibitive to heavily sample an area.  Several prototype sensors were constructed and optimized for accurate soil moisture response in the soil.  The sensors were subjected to extensive accelerated durability tests to assess long term weaknesses.  In addition, calibration and characterization determined the response of the sensor to soil moisture and other confounding factors such as % clay, soil salinity, and temperature.  Results showed excellent survival rate in the accelerated testing and consistent calibration with soil type and salinity.  Temperature effects were observed at similar levels as other, similar soil moisture sensors.  These results indicate it may be possible make a lower cost, rugged, long lasting soil moisture sensor available for climate observatory sites and other applications.