confined spaces where cups or propellers cannot rotate, such as within crop canopy.
These devices are more suitable for measuring the total air velocity than their
components.
Wind direction sensors (pinwheels) are second-order sensors, coupled with air
velocity measuring devices, capable of detecting variations in wind direction, at
speeds of the order of 0.6 ms
−1 , with a precision of ± 2º. Modern dataloggers for
data acquisition, already allow the necessary connections with sensors with complex
electronic circuitry.
A1.7 Precipitation Measurement
Precipitation is another important micrometeorological variable, necessary for
accounting for water inputs and comparison with evapotranspiration. Its
measurement is performed with buckets (Fig. A1.12), with water collection areas
ranging from 200 cm
2 to 500 cm
2 (Foken 2017). A possible operating option is the
filling and emptying of the bucket, a rain gauge, and the consequent generation of
electrical impulses, which are counted by an appropriate data acquisition device.
A1.8 Data Acquisition Devices
Many sensors are designed for spot and real-time measurements of physical
quantities, and the readings of these measures are adapted to the intended purposes.
A multimeter is a particular case of an independent reader, prepared to measure
only electrical quantities. Independent readings of quantities such as air temperature
and humidity or soil respiration are portable solutions in which the measurement
processes, signal conversion, possible memory storage with the indication of the
measurement time, and reading are integrated, for possible real-time usage. The
Fig. A1.12 Precipitation measuring device
Annex A1: Instrumentation in Environmental Physics
331
These devices are more suitable for measuring the total air velocity than their
components.
Wind direction sensors (pinwheels) are second-order sensors, coupled with air
velocity measuring devices, capable of detecting variations in wind direction, at
speeds of the order of 0.6 ms
−1 , with a precision of ± 2º. Modern dataloggers for
data acquisition, already allow the necessary connections with sensors with complex
electronic circuitry.
A1.7 Precipitation Measurement
Precipitation is another important micrometeorological variable, necessary for
accounting for water inputs and comparison with evapotranspiration. Its
measurement is performed with buckets (Fig. A1.12), with water collection areas
ranging from 200 cm
2 to 500 cm
2 (Foken 2017). A possible operating option is the
filling and emptying of the bucket, a rain gauge, and the consequent generation of
electrical impulses, which are counted by an appropriate data acquisition device.
A1.8 Data Acquisition Devices
Many sensors are designed for spot and real-time measurements of physical
quantities, and the readings of these measures are adapted to the intended purposes.
A multimeter is a particular case of an independent reader, prepared to measure
only electrical quantities. Independent readings of quantities such as air temperature
and humidity or soil respiration are portable solutions in which the measurement
processes, signal conversion, possible memory storage with the indication of the
measurement time, and reading are integrated, for possible real-time usage. The
Fig. A1.12 Precipitation measuring device
Annex A1: Instrumentation in Environmental Physics
331