STUDY ON AGROMETEOROLOGICAL INSTRUMENTS
Definition Of Meteorology :
Meteorology is the scientific study of the earth’s atmosphere and its changes, used especially in forecasting the weather.
Definition of Agro meteorology :
Agro meteorology puts the science of meteorology to the service of agriculture, in its various forms and facts, to help the sensible use of land, accelerated production of food and to avoid the irreversible abuse of land resources.
Practical Utility of Agro meteorological Study :
The science of agro meteorology has great practical utility in protection against, or avoidance of adverse climate risks (crop losses due to drough or floods). Weather elements which influence agricultural operations and crop production can be forecast for different time spans; hail, tornados, and flash flood can be forecast up to 12 hours in advance. Based on the forecasts of these elements, decisions can be made in advance in agricultural operations and planning so as to make the best use of favorable weather conditions.
However, agro-meteorological information can be used in efficient land use planning; determining suitable crops for a region; risk analysis of climate hazards and profit calculations in farming; production and harvest forecasts; and in adoption of farming methods and choice of farm machinery.
A. Maximum and Minimum Thermometer :
It is an instrument which shows the maximum and minimum temperature of air of the day. It consists of two horizontally placed thermometers. One is maximum thermometer, placed in above and another is minimum thermometer placed in below. The maximum thermometer is a mercury thermometer with a constriction in the bore near the bulb. The constriction allows the expanding mercury to pass as the temperature rises, but when cooing occurs the column of mercury breaks at the constriction leaving a part in the bore to register the highest has a larger bore and its fluid is colorless alcohol. A tiny dark index in the shape of a long dumbell is placed in the bore below the top of alcohol column. As the alcohol contracts with the decreasing temperature the meniscus (concave surface) of the alcohol pulls the index down. When the meniscus moves up the bore, however, it leaves the index behind to register the lowest temperature.
Function : It is used to measure the maximum and minimum temperature of air of a day.
They are automatic self recording thermometers which mark the prevailing temperature continuously on graph paper wound round a drum operated by clock work mechanism. The drum makes one revolution in a day and the automatically marked chart gives the temperature variations taking place during the day.
Unit of Measurement :
Three different scales (Namely Fahrenheit, Centigrade, and Kelvin scale) are commonly used in meteorological stations for recording the temperature.
B. Rain Gauge :
Rain gauge is a device used for measuring the amount of rainfall. It comprises a funnel with five inches diameter in the mouth, a container to which the funnel is shouldered and finally a metallic cylinder that holds both funnel and container. A measuring flask is used for the measurement of amount of rain water received by container through the funnel. Now-a-days self recording rain gange is used where amount of rainfall is recorded automatically on graph paper.
Unit of measurement :
Rainfall is usually measurement in inches, millimeters or centimeters.
C. Dry and wet Bulb Hydrometer :
This instrument is simply two thermometers mounted on the same backing. One is mounted a little lower than the other and has its bulb covered with a piece of muslin or wicking can be wetted for observation. It is known as wet bulb thermometer. When the instrument is swung freely in the air or is aerated by a fan, the loss of heat required to evaporate water from the wet-bulb will cause it to show a lower temperature reading. The difference between the reading is called the wet-bulb depression. When the dry-bulb temperature, the wet bulb depression, and the atmospheric pressure are known, any of the standard expressions of humidity can be determined from a series of hygrometric tables.
The temperature of dry-bulb thermometer = X0C
The temperature of wet-bulb thermometer = X0C
Wet – bulb depression = (X-Y)0C
By interpreting the dry-bulb temperature and wet-bulb depression against the hygrometric table, the relative humidity of air might be obtained.
It is used to measure the relative humidity of atmosphere.
D. Barometer :
Barometer is a device that indicates the pressure of atmosphere. It consists of a glass tube filled with mercury and a brass scale. The glass tube is kept in a metallic tube. The commonly used barometer in meteorological observatories is fotin’s barometer. The readings taken are corrected for-
Continuous recording of pressure is made with this instrument.
Unit of measurement :
Atmospheric pressure is expressed commonly by the height of the column of mercury in the barometer, either in inches, or millimeters.
E. Wind Vane :
Wind vane is an instrument that indicates the direction of wind. It consists essentially of a broad arrow head placed in ball bearings to enable the arrow to move freely in the horizontal plane. The arrow indicates the direction of wind.
F. Anemometer :
Anemometers are instruments used for the measurement of wind speed. The most common type anemometer is the Robinson Cup Anemometer. Either three or four metal hemispheres are mounted on arms which rotate freely about a vertical axis. A system of gears similar to an automobile speed meter translate the rotation generated by the wind to an indicator or recorder for the speed of wind that has passed the instrument. Now-a-days digital anemometers are also used for the measurement of wind speed. Digital anemometer gives more precise and accurate reading.
G. Sunshine Recorder :
Continuous record of bright sun shine bour is obtained by sun-shine recorder. It consists of a spherical glass mounted on a stand. When the sun rays fall on the glass, a strip of prepared paper held in a grove at the focus length starts burning. When the sun does not shine, the burn point of the paper the sun light hours (duration) of the sun shine can be recorded.
H. Flux meter :
Flux meter is an instrument used for the measurement of intensity of sun-shine / solar radiation.
Evaporation pan is a device which measures the amount of water evaporated in certain time from a surface. It consists of a round reservoir with a diameter of four inches and depth of ten inches. The tank is filled with water up to two and half inches from the top. The decrease by noting the level of water with the help of a vernier scale.