Hydrometeorological Observatory
The hydrometeorological observatory was established in the Department of Hydrology with the aim of collecting data on various hydrometeorological parameters and training students on various instruments. The observatory serves as a practical training ground for students to learn about the principles and methodologies of measuring and analyzing various hydrometeorological parameters. By utilizing a wide range of instruments and equipment, students gain hands-on experience in data collection, processing, and analysis. This practical training helps to develop the skills and knowledge required to work in the field of hydrology and meteorology. On a daily basis, the students of the department collects data on several hydrometeorological parameters. These parameters include precipitation, temperature, evaporation, humidity, wind speed and direction, solar radiation, and atmospheric pressure.
Details of the Instruments:
1. Non recording rain gauge (Symon’s type)
Standard non-recording rain gauge prescribed by the IMD is the Symon's rain gauge. The gauge consists of a funnel with a sharp-edged rim of 127 mm diameter, a cylindrical body, a receiver with a narrow neck and handle and a splayed base which is fixed in the ground. The rain gauge is having a narrow-neck and sufficiently protected from radiation to minimize the loss of water from the receiver by evaporation. To prevent rain from splashing in and out, the vertical wall of the sharp-edged rim is made deep enough and the slope of funnel steep enough (at least 45°). The rain falling into the funnel is collected in the receiver kept inside the body and is measured by means of a special measure glass which is graduated in mm. The receiver has a capacity of 1000 mm of rain. The measure glass has a capacity of 25 mm and can be read to nearest 0.1 mm. The gauge is fixed on a concrete foundation of size 60 cm x 60 cm x 60 cm which is sunk into the ground. Into this foundation the base of the gauge is cemented, so that the rim of the gauge is exactly 30 cm above the ground level. The top of the gauge is kept perfectly horizontal.
2. Natural Syphon type recording rain gauge
This type of recording rain gauge is also known as float-type gauge. Here, the rainfall collected by a funnel-shaped collector is led into a float chamber causing a float to rise. As the float rises, a pen attached to the float through a lever system records the elevation of the float on a rotating drum driven by a clockwork mechanism. A syphon arrangement empties the float chamber when the float has reached a preset maximum level. This type of rain gauge is adopted as the standard recording-type rain gauge in India and its details are described in Indian Standard (IS: 5235–1969).
A typical chart from this type of rain gauge is shown in picture below. The vertical lines in the pen-trace correspond to the sudden emptying of the float chamber by syphon action which resets the pen to zero level. It is obvious that the natural syphon-type recording rain gauge gives a plot of the mass curve of rainfall.
3. Automatic Rain Gauge with Data Logger
The automatic rain gauges are of the recording type and contain electronic units to transmit the data on rainfall to a base station both at regular intervals and on interrogation. The tipping-bucket type rain gauge, being ideally suited, is adopted for this purpose. The data logger is connected to the rain gauge to store the rainfall data.
4. Class-A evaporation pan
This pan evaporimeter specified by IS: 5973–1970, also known as modified Class A Pan, consists of a pan 1207 mm in diameter with 250 mm of depth. The pan is made of copper sheet of 0.9 mm thickness, tinned inside and painted white outside. A fixed-point gauge indicates the level of water. A calibrated cylindrical measure is used to add or remove water maintaining the water level of 5 cm from the top. The top of the pan is covered fully with a hexagonal wire netting of galvanised iron to protect the water in the pan from birds. Further, the presence of a wire mesh makes the water temperature more uniform during day and night. The pan is placed over a square wooden platform of 1225 mm width and 100 mm height to enable circulation of air underneath the pan.
This pan, 920 mm square, and 460 mm deep, is made up of unpainted galvanised iron sheet and buried into the ground within 50 mm of the top. The water level in the pan is maintained at about ground level. The chief advantage of the sunken pan is that radiation and aerodynamic characteristics are like those of a lake. The pan coefficient, on an annual basis, is about 0.8.
An instrument for providing a continuous record of temperature, typically air temperature. The recording is done on a graph mounted on a drum, which is rotated by clockwork. Two metals of different alloys are welded together in a coil form. The difference in the coefficient of expansions expands or tightens the coil when subjected to temperature changes. This movement is magnified by a lever system attached to the coil with a pen nib slightly resting on a chart.
7. Dry and wet bulb thermometers
A dry bulb thermometer registers normal air temperature. It is an ordinary mercury-in-glass thermometer ranging from -35°C to +55°C. The temperature of cool air is measured with the help of a wet bulb thermometer. Under the saturated condition, both the dry and wet bulb thermometer readings would be same. But when the air becomes dry, the difference between them would increase. The difference is known as wet bulb depression. The dry and wet bulb temperatures are used for calculating the dew point, vapor pressure and relative humidity. The instrument is protected with Stevenson screen.
8. Sunshine hour recorder
A sunshine recorder is a device that records the amount of sunshine at a given location at any time. This information is useful in meteorology, science, agriculture, tourism, and other fields. It has also been called a heliograph. Inside the recorder's adjustable frame are two important pieces: Paper strip and Glass sphere that can focus the sunlight strongly enough to singe the paper.
It consisted of four hemispherical cups mounted on horizontal arms, which were mounted on a vertical shaft. The flowing air turns the shaft at a rate that is roughly proportional to the wind speed. Counting the turns of the shaft over a set time interval produced a value proportional to the average wind speed.
This instrument tells us about which direction the wind is blowing from. A fin sits on top or hangs below a spindle that allows the fin to rotate on a horizontal plane. The fin itself will generally feature a point on one end and a long and broad shape at the other. This will ensure the fin always points in the direction the wind is originating from.
A barometer is a scientific instrument used to measure atmospheric pressure, also called barometric pressure. Atmospheric pressure is an indicator of weather. Changes in the atmosphere, including changes in air pressure, affect the weather. Meteorologists use barometers to predict short-term changes in the weather.
A Stevenson screen or instrument shelter is a shelter to meteorological instruments against precipitation and direct heat radiation from outside sources, still allows air to circulate freely around them. It forms part of a standard weather station and holds instruments that may include thermometers, a hygrometer, a psychrometer, a dew-cell, a barometer, and a thermograph.
A piezometer is either a device used to measure liquid pressure in a system by measuring the height to which a column of the liquid rises against gravity, or a device which measures the pressure (more precisely, the piezometric head) of groundwater at a specific point. It converts water pressure to a frequency signal via a diaphragm and a tensioned steel wire. A change in pressure on the diaphragm causes a change in tension of the wire.
14. Automatic Weather Station
An Automatic Weather Station (AWS) is a facility that automatically transmits, or records observations obtained from measuring instruments. In an AWS, the measurements of meteorological elements are converted into electrical signals through sensors. The signals are then processed and transformed into meteorological data. The resulting information is finally transmitted the by wire or radio or automatically stored it on a recording medium. The AWS at department of hydrology have components of rain gauge (tipping bucket), temperature sensor, anemometer, and solar radiation.