Development of a Low-Cost Citizen Science Soil Moisture Sensor

Soil moisture (SM) is identified as an Essential Climate Variable and it exerts a strong influence on agriculture, hydrology and land-atmosphere interaction. The project goal is to develop an affordable (low-cost), durable, and user-friendly, sensor and an associated mobile app to measure in-situ soil moisture by the citizen scientists or any K9-K12 students. The sensor essentially uses the electrical resistance or frequency domain reflectometry between two metallic rods to measure SM based on soil specific calibration equations. The sensor is controlled by a Programmable Circuit Board (PCB) and a mobile app (available both for iOS and Android) developed at Jet Propulsion Laboratory (JPL), NASA. The phone app reads the observation from the PCB converts it into SM for the soil type selected by the user. Extensive laboratory tests were conducted to standardize the sensor and to calibrate the sensor for various soil types. The sensor was also be tested during field campaigns and recalibrated for field conditions. The prototype beta version of the low-cost soil moisture sensor is now ready and being tested by the Citizen Scientists. In addition to the development of the low-cost sensor and the mobile app, supporting documentation and videos are also being developed that show the step-by-step process of building the sensor from scratch and measurement protocols. Initial laboratory calibration and validation of the prototype suggested that the sensor can satisfactorily measure SM for all the soil types except for the soil with very high organic content. The affordable and simple sensor will help citizen scientists to understand the dynamics of SM at their site and the in-situ data will further be utilized for validation of the satellite observations such as from the SMAP mission. The additional observation of soil temperature, air temperature, relative humidity, solar radiation will also help to compute evapotranspiration (ET). The ET measurements are critical for crop/plant health monitoring and can help farmers for agricultural applications such as determination of the water demand i.e., the amount of water required for irrigation to meet the evapotranspiration needs of the crop/plant.