HYDRA-LAB - A LOW COST, MICROPROCESSOR BASED SENSOR SYSTEM FOR THE ACQUISITION OF HYDROLOGIC AND METEOROLOGIC DATA

Understanding of the hydrologic cycle is fundamental for geoscientists, environmental and agricultural scientists; however, actual training in long-term field observations of hydrologic phenomena is often limited, due to time constraints and equipment costs. We have developed a low cost microprocessor and sensor system - the HYDRA-LAB (Hydrologic Acquisition Laboratory), which can collect measurements for most major parameters used to model the flux of water at the earth's surface.

The HYDRA-LAB uses a BX-24 (Net Media) microprocessor with 16 I/O lines, eight of which can access a 10-bit analog to digital converter. The BX-24 can perform floating point math and access a 32KB EEPROM. This allows the system to function as a data logging device. Sensor systems use a voltage regulator that can be shut down when the sensors are not in use. The housings for HYDRA-LAB and the sensor systems are constructed of PVC pipe and connectors. The assembly of the laboratory is simple and can be accomplished by students as part of laboratory training. The HYDRA-LAB can be utilized as a research-grade system by using higher-grade instrumentation or by rigorous characterization and calibration of the regular sensor package.

The HYDRA-LAB meteorological system consists of a Dallas 1-Wire weather station (excluding a pressure sensor). Evapotranspiration can be estimated from meteorological data or it can measured using a reduced scale evaporation pan and a pair of ultrasonic rangers. One ranger monitors a fixed target to provide corrections for variations in sound velocity produced by changing temperature and humidity. The second ranger measures the change in water height in the evaporation pan. Addition of water to the pan from precipitation is measured by a rain gauge. The ultrasonic ranging system can also be used to measure water levels in steams, ponds and lakes. Infiltration rates are measured using an IR distance sensor to monitor water levels in a Mariotte siphon connected to a dual ring infiltrometer. Alternatively, water levels are monitored by the IR system directly at the ring, which is supplied with monitored water volumes supplied by a peristaltic pump. Water temperatures of surface water and soils are measured using a LM35 analog thermometer. Soil moisture can be estimated by the AC resistance in a gypsum granular matrix sensor.