This resource delineates the different rainfall measurement technologies with each weather station model available from Columbia Weather Systems.
Tipping Bucket Rain Gauge Technology: The tipping bucket gauge consists of a collector funnel with a knife edge that diverts water to a tipping bucket mechanism. The mechanism is so designed that one alternate tip of the bucket occurs for each 0.01 inch of rainfall accumulation. A magnet is attached to the tipping bucket, which, as the bucket tips, actuates a magnetic switch to signal the accumulation to the data logger.
Pros: Tipping buckets are the most widely used rain sensors in the world. The technology has been around for a long time and the mechanism is simple and mechanical.
This sensor is low cost and very reliable.
Cons: The accuracy of the tipping bucket sensor is based on a specific rainfall rate. Higher rainfall rates tend to introduce more error in readings.
Susceptible to error due to evaporation, splashing, and high wind.
For accurate readings, the sensor must be level with no vibration.
Sensor should be checked regularly to make sure it is not clogged with debris.
Applications: Best used when rainfall accumulation is compared to other tipping bucket sensors.
Weather Station: The tipping bucket gauge is used with the Capricorn FLX and also interfaces with the digital channel on the Weather MicroServer for use with any other model. See below for the Pulsar 601 with Tipping Bucket Raingauge.
Capricorn FLX Tipping Bucket Raingauge Specifications:
Accuracy: ±1% at 2 in./hr or less
Collection Diameter: 6”
Heating option is available to measure snowfall as rain accumulation.
Pulsar 601 Tipping Bucket Raingauge Specifications:
Maximum intensity: 144 mm/hr
Impact Sensor (Orion) Technology: The rainfall measurement is based on an impact sensor, which detects the impact of individual rain drops. The signals exerting from the impacts are proportional to the volume of the drops. Hence, the signal from each drop can be converted directly to the accumulated rainfall. Due to the measurement method, flooding, clogging as well as wetting and evaporation losses in rain measurement are eliminated.
Pros: Requires no maintenance. Accurate under heavy rainfall rates. Is not affected by clogging and evaporation.
Able to detect hail.
High resolution output.
Cons: Under reports under misty and light rainfall conditions.
Applications: Ideal for weather station installation that has low maintenance requirements.
Weather Station: This sensor is available with the Orion weather station.
Collection Area: 60 cm2 Accuracy: ±5% (spatial variations may exist) Resolution 0.001 in. (0.0254 mm)
Doppler Radar Sensor (Pulsar 100, 600, 700, 800) Technology: Precipitation is measured by a 24 GHz Doppler radar which measures the drop speed of an individual drop of rain or snow. Precipitation quantity and intensity are calculated from the correlation between drop size and speed. The Doppler radar sensor is able to sense (measure) rain drops size between 0.3 mm and 5.0 mm.
Pros: The sensor is fast responding with a resolution of 0.0004 inches (0.01 mm).
Able to differentiate between snow and rain.
Cons: The accuracy decreases when drop size is outside of the measurement range.
Applications: The sensor is ideal for applications that require high resolution in order to report start of rainfall. For example, the tipping bucket rain gauge will not report rainfall until it reaches 0.01” accumulation. The Doppler radar sensor will report rainfall when accumulation reaches 0.0004”.
Weather Station: This sensor is available with the Pulsar 600 weather station.
Measuring Range: Drop size 0.3 – 5mm Resolution: 0.0004” (0.01 mm) Reproducibility: typ>90% Type: Rain / Snow
Optical Sensor (Magellan MX600) Technology: An integrated optical rain gauge that automatically senses water hitting its outside surface and provides measurements based on the size and number of drops. Algorithms interpret this data and simulate the output of a tipping bucket rain gauge.
Pros: Provides rain measurement for systems that require a transmitter with GPS and electronics compass.
The optical rain gauge has no moving parts associated with tipping bucket gauges. It is mostly used in applications where rain accumulation accuracy is not critical.
Cons: Low accuracy and resolution.
Applications: Best used for mobile and portable applications for general monitoring such as recording precipitation event and duration. Application such as vehicle track testing, power transmission line monitoring, and aircraft testing.
Weather Station: This sensor is available with the Magellan MX600 weather station with GPS.
Resolution: 0.01inch Range: 0 to >12 inches/hr Repeatability: 3%
Contact Columbia Weather Systems for information about which technology is best for your precipitation monitoring application.