When depth measurement is recorded by ultrasound, the meter head is usually attached to the chamber wall. The ultrasonic signal transmitted by the measuring device is reflected from the surface of the water in the shaft chamber and received at the meter. It is therefore necessary that the minimum operating distance between the instrument head and the maximum expected water level in the chamber be maintained at all times. This distance is specified by the device manufacturer. Ultrasonic measuring instruments may therefore not be suitable for use in wells where surface flooding or high surcharges are to be expected. The field calibration device developed at the University of Genoa consists of a water tank equipped with a series of air intakes and water outlet nozzles. Different combinations of these inputs and nozzles make it possible to generate different flow rates. The device is equipped with an electronic system capable of detecting the drain time of the amount of water, and the capacity of the instrument is calibrated in the laboratory to serve as a reference. An example image of how this device works in the field is shown in Fig. 4.9. An optical rain gauge consists of a laser/infrared diode and a light-sensitive sensor located in enclosed spaces on opposite sides and under a series of funnels that receive precipitation. 2. During the use of the instrument, the silt (silt, dust, leaves, insects and other debris) must be regularly dredged according to the actual local conditions, the water channels checked and dredged, and the ring and inner surface of the rain receiver must be wiped to ensure an unblocked flow of water.
The rain gauge must be outside for a long time and the environment of use is very harsh. Therefore, the surface of the instrument should be kept clean and often wiped with a soft cloth. The device should be cleaned once a month for long-term operation and once every three months. If more than one verification time is taken into account, the N of the above sums is extended over all verification periods, taking into account all available pairs (oi, yi). On the basis of pairs of observed and predicted values, it is possible to define the dichotomous contingency table (Table A21.1) for a precipitation threshold: storage meters are the simplest rain gauges and only require a calibration of the storage volume. This is done by pouring a known volume of water into the meter and checking the corresponding water level in the container. If automatic sensors are used to record the level of water collected in the storage tank, an appropriate calibration of the sensor (float, acoustic or pressure level probe) is required. The operation of a tipping bucket rain gauge differs significantly from that of the standard measuring device. The reception funnel leads to one of the two small buckets. The filling of a bucket is done to the hundredth of an inch. The result is an “inclination” of the liquid in the outer shell of the meter, as a result of which the second bucket takes its place.
The process is then repeated, allowing the intensity and amount of precipitation to be accurately measured. This meter has become the standard for wireless weather stations. Fig. 2.4. Stevens tilts the bucket with rain gauge holder. To evaluate the performance of TBR at different levels of precipitation, a dynamic calibration procedure in accordance with EN 17277:2019 is required. The tests shall be carried out under stationary conditions different from the intensity of the reference equivalent precipitation and the relative difference between the measured precipitation intensity and the intensity of the reference precipitation shall be calculated. This rain gauge is also commonly called an integrator rain gauge because it records cumulative precipitation. Errors in the measurement of precipitation are given below: the naturalist Gilbert White took measurements to determine the average amount of precipitation from 1779 to 1786, although it was his brother-in-law Thomas Barker who made regular and careful measurements for 59 years, recording temperature, wind, atmospheric pressure, precipitation and clouds.
Its meteorological archives are a valuable source for knowledge of the British climate of the 18th century. He was able to show that the average amount of precipitation varied considerably from year to year and showed few recognizable trends. [11] where RImeas is the precipitation intensity for liquids measured by the meter and RIref is the equivalent reference precipitation intensity specified by the calibration device. Place the standard rain gauge on a fixed shelf in the observation area. The mouth of the organ is held horizontally, 70 cm above the ground. In areas of deep snow in winter, a backup shelf should be installed nearby, which can reach the height of the rain gauge 1.0-1.2 meters above the ground. If the snow depth exceeds 30 cm, the instrument must be brought to the emergency shelf for observation. Ciach and Krajewski (1999) divide radar-derived average surface precipitation into two terms: for instrument error (deviations between radar and measurement measurements at measurement points) and for representativeness error (differences between local measurements of measuring bands and the actual average of the area).
The first of these contributions is easy to characterize, using earlier datasets for radar-derived precipitation at Raingage sites. The second paper is much more difficult to calculate without data from a very dense Raingage network, although a model-based estimate can be derived by assuming the characteristics of the spatial correlation structure of precipitation fields. The results of this study showed that the representativeness error component was most important on the shortest time scales, but that even for 4-day precipitation accumulations, it remained a significant contribution to the whole.