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KHL Sanjeewa
Content
1. Introduction……………………….…………………………………………………….
1.1. Climatology…………………………………...…………………………………..
1.2. Meteorology…………………………………...………………………………….
1.3. Agro meteorology…………………………..…………………………………….
1.4. Agro climatology…………………………..……………………………………..
2. Meteorological parameters……………………………………..……………………….
2.1. Sun shine…………………………………………………..……………………..
2.1.1. Effect of sunshine on agriculture………………………………………....
2.2. Precipitation…………………………………………………………………..…..
2.2.1. Effect of precipitation on agriculture..........................................................
2.3. Wind speed……………………………………………………………………......
2.3.1. Effect of wind speed on agriculture…........................................................
2.4. Temperature…………………………………………………………...………….
2.4.1. Air temperature……………………………………………….…………..
2.4.2. Effect of air temperature for agriculture………………………………….
2.4.3. Soil temperature…………………………………………………………..
2.4.4. Effect of Soil temperature for agriculture………………………………...
2.5. Evaporation………………………………………………………….....................
2.6. Relative humidity…………………………………………………………………
2.6.1. Dry Bulb Temperature …………………………………………………...
2.6.2. Wet Bulb Temperature …………………………………………………..
2.6.3. Dew Point Temperature………………………………………………….
2.7. Air pressure………………………………………………………………………
3. Measuring of meteorological variables…………………………………………………
3.1. Sunshine………………………………………………………………………….
3.2. Precipitation………………………………………………………………………
3.3. Wind speed & direction…………………………………………………………..
3.4. Temperatures……...................................................................................................
3.5. Evaporation……………………………………………………………………….
3.6. Air pressure……………………………………………………………………….
4. Selection of suitable site for weather station……………………………………………
5. Installation of equipments in the site……………………………………………………
6. Data observation………………………………………………………………………...
6.1. Method of data observation………………………………………………………
6.2. Data recording procedure…………………………………………………………
1. Introduction
1.1. Climatology
Climatology is a study of the climate of a place or region on the basis of weather records
accumulated over long periods of time. The average values of meteorological parameters
derived from a data base that extends over several decades are called climatological
normals. Different regions of the world have different characteristic climates. However, it
is now recognized that climate is not static and issues such as climate change and global
warming are receiving increasing attention.
1.2. Meteorology
Meteorology is the science of weather. It is essentially an inter-disciplinary science because
the atmosphere, land and ocean constitute an integrated system. The three basic aspects of
meteorology are observation, understanding and prediction of weather. There are many
kinds of routine meteorological observations. Some of them are made with simple
instruments like the thermometer, anemometer. The observing techniques have become
increasingly complex in recent years and satellites have now made it possible to monitor
the weather globally. Countries around the world exchange the weather observations
through fast telecommunications channels. These are plotted on weather charts and
analyzed by professional meteorologists at forecasting centers. Weather forecasts are then
made with the help of modern computers and supercomputers. Weather information and
forecasts are of vital importance to many activities like agriculture, aviation, shipping,
fisheries, tourism, defense, industrial projects, water management and disaster mitigation.
Recent advances in satellite and computer technology have led to significant progress in
meteorology.
1.3. Agro meteorology
In simple terms, agricultural meteorology is the application of meteorological information
and data for the enhancement of crop yields and reduction of crop losses because of
adverse weather. This has linkages with forestry, horticulture and animal husbandry. The
agro meteorologist requires not only a sound knowledge of meteorology, but also of
agronomy, plant physiology and plant and animal pathology, in addition to common
agricultural practices. This branch of meteorology is of particular relevance to the areas
high dependence of agriculture on monsoon rainfall. A branch of meteorology that
examines the effects and impacts of weather and climate on crops, rangeland, livestock,
and various agricultural operations.
2. Meteorological parameters
Sun shine
Precipitation
Wind speed
Temperature
Evaporation
Relative humidity
Atmospheric pressure
2.1. Sun shine
The term sunshine is associated with the brightness of the solar disk exceeding the
background of diffuse sky light, or — better observable by the human eyes — with the
appearance of shadows behind illuminated objects. As such, the term is related more too
visual radiation than to energy radiated at other wavelengths, although both aspects are
inseparable. In practice, however, the first definition was established directly by the
relatively simple Campbell-Stokes sunshine recorder. The units used are seconds or hours.
For climatological purposes, derived terms such as “hours per day” or “daily sunshine
hours” are used, as well as percentage quantities, such as “relative daily sunshine
duration”.
2.1.1. Effect of sunshine on agriculture
Correct light intensity quality and duration helps for normal growth and development of
every organism on earth. In rice and other germinate plants production of tillers mostly
influence by sunshine, the three broad spectrum at solar energy are significant to plant life.
Correct light intensity, quality and duration are essential to normal plant development.
According to response of sunshine crops are divided in to 3 categories
Short day plants
Long day plants
Day neutral plants
2.2. Precipitation
Precipitation is defined as the liquid or solid products of the condensation of water vapor
falling from clouds or deposited from air on the ground. It includes rain, hail, snow, dew,
rime, hoar frost and fog precipitation. The total amount of precipitation which reaches the
ground in a stated period is expressed in terms of the vertical depth of water to which it
would cover a horizontal projection of the Earth’s surface. Snowfall is also expressed by
the depth of fresh, newly-fallen, snow covering an even horizontal surface. It does not
discuss measurements either which attempt to define the structure and character of
precipitation, or which require specialized instrumentation, which are not standard
teorological observations (such as drop size distribution).
2.2.1. Effect of precipitation on agriculture
Precipitation, especially rain, has a dramatic effect on agriculture. All plants need at least
some water to survive; therefore rain is important to agriculture. While a regular rain
pattern is usually vital to healthy plants, too much or too little rainfall can be harmful, even
devastating to crops. Drought can kill crops and increase erosion, while overly wet weather
can cause harmful fungus growth. Plants need varying amounts of rainfall to survive. For
example, certain cacti require small amounts of water, while tropical plants may need up to
hundreds of inches of rain per year to survive. In areas with wet and dry seasons, soil
nutrients diminish and erosion increases during the wet season. Animals have adaptation
and survival strategies for the wetter regime. The previous dry season leads to food
shortages into the wet season, as the crops have yet to mature.
2.3. Wind speed.
Wind speed is the speed of wind, the movement of air or other gases in an atmosphere. It is
a scalar quantity, the magnitude of the vector of motion. Wind speed has always meant the
movement of air in an outside environment, but the speed of air movement inside is
important in many areas, including weather forecasting, aircraft and maritime operations,
building and civil engineering. High wind speeds can cause unpleasant side effects, and
strong winds often have special names, including gales, hurricanes, and typhoons. There
are also links to be found between wind speed and wind direction, notably with the
pressure gradient and surfaces over which the air is found.
2.3.1. Effect of Wind speed on agriculture
Normally high windy conditions are not suitable for crop production, because wind speed
is more than 7.2 Kmh-1 is harmful. It retarded the growth plant. A slight wind replenishes
CO2 in the vicinity of the plant. This is more important during rapid growth of plants.
Excessive wind cause to high evapotranspiration and result in high moisture losses of
plants. Also can cause to damage to irrigation systems.(ex:- sprinkler irrigation)and falling
of the trees & branches, damage to the pollination process, application of the fertilizer &
chemicals to the crops can be affected by wind speed & direction.
2.4. Temperature
WMO (1992) defines temperature as a physical quantity characterizing the mean
random motion of molecules in a physical body. Temperature is characterized by the
behavior that two bodies in thermal contact tend to an equal temperature. The current
International Temperature Scale is called ITS-902 and its temperature is indicated by T90.
For the meteorological range (-80 – +60°C) this scale is based on a linear relationship with
the electrical resistance of platinum and the triple point of water, defined as 273.16 Kelvin.
For meteorological purposes temperatures are measured for a number of media. The most
common variable that is measured is air temperature (at various heights). Other variables
are ground, soil, grass minimum and seawater temperature. WMO (1992) defines air
temperature as “the temperature indicated by a thermometer exposed to the air in a place
sheltered from direct solar radiation”. Although this definition cannot be used as the
definition of the thermodynamic quantity itself it is suitable for most applications.
2.4.1. Air temperature
Temperature is a measure of the level of sensible heat of matter, whether it is gaseous (air),
liquid (water), or solid (rock or dry soil).Air temperature is the intensity aspect of sun's
energy that strikes the earth's surface. Because the amount of energy from the sun reaching
the earth varies from day to day, from season to season, and from latitude to latitude,
temperatures also vary. The earth as a whole receives a constant flow of radiant short-wave
energy from the sun. The earth also radiates long-wave energy to space. During the day,
the flow of short-wave radiation absorbed exceeds long -wave energy emitted, and the
surface temperature increases.
2.4.2. Effect of air temperature for agriculture
Temperature, an approximate measurement of the heat energy available from solar
radiation, is a significant factor because both low and high temperatures limit plant growth.
Most plant biological activity and growth occur within only a narrow range of
temperatures, between 32F (0C) and 122F (50C).Months with mean monthly temperatures
below 32.0F (0.0C) are too cold for active plant growth. Low temperatures define the
growing season for perennial plants, which is generally from mid April to mid October (6.0
months). Perennial grassland plants are capable of growing for longer than the frost-free
period, but to continue active growth, they require temperatures above the level that freezes
water in plant tissue and soil. Winter dormancy in perennial plants is not total inactivity but
reduced activity.
2.4.3. Soil temperature
It has been determined that biological and chemical activities are an energy expression and
that these changes will not continue with the right intensity unless certain temperatures are
maintained The most favorable limit of temperature are 80 to 90 degrees Fahrenheit as
nitrification does not begin until the soil reaches around 40 degrees Fahrenheit.
2.4.4. Effect of soil temperature for agriculture
Seed germination and plant growth highly varies with soil temperature. The soil gets its
energy for normal activity from the sun. Another important factor in the temperature of the
soil is determined if the soil is bare or covered with vegetation as this affects the amount of
insulation that is received. A field of grass doesn't have much effect on temperature
fluctuations but a forest does. Bare soils will warm more quickly and cool off more rapidly
that those covered with vegetation or even with mulches. During the winter, frost
penetration is considerably greater in non insulated land. Mineral soils will not only vary in
respect to the energy necessary to raise their temperature but also that this variation is
largely in proportion to the amounts of water present. Moisture is one of the major factors
in respect to the heat capacity of a soil, and hence, has much to do with its rate both of
warming up and cooling off.
2.5. Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid.
The other type of vaporization is boiling, that instead occurs on the entire mass of the
liquid. Evaporation is also part of the water cycle. Water vapor that has evaporated and
disappeared from hot tea condenses into visible droplets called vapor. Gaseous water is
invisible, but the clouds of water droplets are evidence of evaporation followed by
condensation Evaporation is a type of phase transition; it is the process by which molecules
in a liquid state (e.g. water) spontaneously become gaseous .Generally, evaporation can be
seen by the gradual disappearance of a liquid from a substance when exposed to a
significant volume of gas. Vaporization and evaporation however, are not entirely the same
processes.
2.6. Relative humidity
Relative humidity represents the extent to which air is saturated with moisture at a given
temperature. The Dry Bulb, Wet Bulb and Dew Point temperatures are important to
determine the state of humid air. The knowledge of only two of these values is enough to
determine the state - including the content of water vapor and the sensible and latent energy
(enthalpy).Relative humidity can be measured by using,
Wet & dry bulb thermometer
Sling psychrometer
Thermohydrograph
2.6.1. Dry Bulb Temperature - Tdb
The Dry Bulb temperature, usually referred to as air temperature, is the air property that is
most common used. When people refer to the temperature of the air, they are normally
referring to its dry bulb temperature.
2.6.2. Wet Bulb Temperature - Twb
The Wet Bulb temperature is the temperature of adiabatic saturation. This is the
temperature indicated by a moistened thermometer bulb exposed to the air flow. Wet Bulb
temperature can be measured by using a thermometer with the bulb wrapped in wet muslin.
The adiabatic evaporation of water from the thermometer and the cooling effect is
indicated by a "wet bulb temperature" lower than the "dry bulb temperature" in the air.
2.6.3. Dew Point Temperature – Tdp
The Dew Point is the temperature at which water vapor starts to condense out of the air, the
temperature at which air becomes completely saturated. Above this temperature the
moisture will stay in the air. If the dew-point temperature is close to the air temperature,
the relative humidity is high, and if the dew point is well below the air temperature, the
relative humidity is low.
2.7. Air pressure
A column of air one square inch in cross-section, measured from sea level to the top of the
atmosphere, would weigh approximately 14.7 lbf (65 N). Atmospheric pressure is the force
per unit area exerted against a surface by the weight of air above that surface in the Earth's
atmosphere. In most circumstances atmospheric pressure is closely approximated by the
hydrostatic pressure caused by the weight of air above the measurement point. Low
pressure areas have less atmospheric mass above their location, whereas high pressure
areas have more atmospheric mass above their location. Similarly, as elevation increases
there is less overlying atmospheric mass, so that pressure decreases with increasing
elevation.
3. Measuring of meteorological variables
3.1. Sun shine
Universal Sunshine recorder
This instrument consist of a solid glass globe of about 10 cm in diameter, mounted
within a section of a hallow useful bowl. No electrical sunshine duration meter, the
Campbell stock sunshine recorder. When sunlight is sufficiently strong, the globe acts as
magnifying glass, focusing the beam onto a special recording paper. A trace is burned on
this paper as the sun moves through the sky. The trace indicates the duration of bright
sunlight. The depth of the burn is also a rough intensity of the intensity of the sunshine.
Campbell-stocks sunshine recorder Sun shine cards
3.2. Precipitation
Rain gauges
Precipitation gauges (or rain gauges if only liquid precipitation can be measured) are the
most common instruments used to measure precipitation. Generally an open receptacle
with vertical sides is used, usually in the form of a right cylinder, and with a funnel if its
main purpose is to measure rain. Various sizes and shapes of orifice and gauge height are
used in different countries, so the measurements are not strictly comparable (WMO,
1989a). The volume or weight of the catch is measured, the latter in particular for solid
precipitation. The gauge orifice may be at one of many specified heights above the ground
or it can be at the same level as the surrounding ground. The orifice must be placed above
the maximum expected depth of snow cover, and above the height of significant potential
in-splashing from the ground. For solid precipitation measurement, the orifice is above the
ground and an artificial shield is placed around it. The most used elevation height in more
than 100 countries varies between 0.5 and 1.5m (WMO, 1989a).
Rain gauges can b classified in to 3 main categories
Recording type rain gauges
Non recording type rain gauges
Automatic radio recording rain gauges
(Different shapes of
standard precipitation
gauges. Solid line
shows streamlines and
dashed line the
trajectories of
precipitation particles.
The 1st gauge shows
the largest wind field
deformation above the
gauge orifice and the
last gauge the
smallest.
Consequently, the
wind induced error
for the first gauge is
larger than for the last
gauge.)
Recording type rain gauges
These types of rain gauges provide information about onset duration and intensity of rain
fall. These gauges can be divided into 3, such as,
• Weighing type rain gauge
• Tipping bucket rain gauge
• Float type rain gauge
Weighing type rain gauge
This rain gauge operates when a certain weight of rain fall precipitates on a bucket
connected with a spring lever balance arrangement. The total weight of the bucket and the
collected rain fall actuated a pen. The movement of the pen proportions to the total weight
of rain fall received is recorded on a chart wrapped round clock driven drum. This plots the
curve of total rain fall with respect to time.
Tipping bucket rain gauge
This instrument have cylindrical receiver of 30 cm diameter at the bottom at which it is
attached a funnel. Just below the funnel a Pair of small tipping buckets is installed. When
any bucket receives a rain fall of 0.5mm, it tips and empties its water in to a tank or ground
the other bucket. Then this tipping is recorded in graph.
Float type rain gauge
This rain gauge the rain enters the float chamber accommodation a float. As the level of
water collected in to float moves up and with a connecting rod is also actuated. The
movement of the pen is marked on chart wrapped round a revolving drum. When the float
chamber fills up automatically its water content is siphoned out through an interconnected
siphon mechanism.
Non- recording type rain gauges
That observes manually and gives total amount of rainfall at the rain gauge station, during
the Measuring period.
3.3. Wind speed & direction
Anemometers
An anemometer is used for measuring wind speed, and is a common weather station
instrument. Anemometers can be divided into two classes: those that measure the wind's
speed, and those that measure the wind's pressure; but as there is a close connection
between the pressure and the speed, an anemometer designed for one will give information
about both. A simple type of anemometer is the cup anemometer. It consisted of four
hemispherical cups each mounted on one end of four horizontal arms, which in turn were
mounted at equal angles to each other on a vertical shaft.
The air flow past the cups in any horizontal direction turned
the cups in a manner that was proportional to the wind
speed. Therefore, counting the turns of the cups over a set
time period produced the average wind speed for a wide
range of speeds.
On an anemometer with four cups it is easy to see that since
the cups are arranged symmetrically on the end of the arms,
the wind always has the hollow of one cup presented to it
and is blowing on the back of the cup on the opposite end of
the cross.
3.4. Thermometer
3.4.1. Maximum thermometers
The recommended type is mercury -in-glass thermometer with a constriction in the bore
between the bulb and the beginning of the scale. This constriction prevents the mercury
column from receding with falling temperature. However, the thermometer can be reset
intentionally by the observer by holding it firmly, bulb-end downwards, and swinging the
arm until the mercury column is reunited. The maximum thermometer should be mounted
at an angle of about two degrees from the horizontal with the bulb at the lower end to
ensure that the mercury column rests against the constriction without gravity forcing it to
pass. It is desirable to have a widening of the bore at the top of the stem to enable parts of
the column which have become separated to be easily united.
3.4.2. Minimum thermometers
The most common instrument is a spirit thermometer with a dark glass index, about 2 cm
long, immersed in the spirit. Since some air is left in the tube of a spirit thermometer, a
safety chamber should be provided at the upper end and it should be large enough to allow
the instrument to withstand a temperature of 50°C without damage. Minimum
thermometers should be supported in a similar manner to maximum thermometers, in a
near-horizontal position. Various liquids can be used in minimum thermometers, such as
ethyl alcohol, pentane and toluol. It is important that the liquid should be as pure as
possible since the presence of certain impurities increases the tendency of the liquid to
polymerize with exposure to light and after the passage of time; such polymerization
causes a change in the calibration. In the case of ethyl alcohol, for example, the alcohol
should be completely free of acetone. Minimum thermometers are also exposed to obtain
grass minimum temperature.
3.4.3. Wet bulb thermometer
Wet bulb thermometer is used to determine the relative humidity. The Wet Bulb
temperature is the temperature of adiabatic saturation. This is the temperature indicated by
a moistened thermometer bulb exposed to the air flow. Wet Bulb temperature can be
measured by using a thermometer with the bulb wrapped in wet muslin. The adiabatic
evaporation of water from the thermometer and the cooling effect is indicated by a "wet
bulb temperature" lower than the "dry bulb temperature" in the air. The rate of evaporation
from the wet bandage on the bulb, and the temperature difference between the dry bulb and
wet bulb, depends on the humidity of the air. The evaporation is reduced when the air
contains more water vapor
3.4.4. Dry bulb thermometer
This is use to measure dry bulb temperature. The Dry Bulb Temperature refers
basically to the ambient air temperature. It is called "Dry Bulb" because the air
temperature is indicated by a thermometer not affected by the moisture of the
air. Dry-bulb temperature can be measured using a normal thermometer freely
exposed to the air but shielded from radiation and moisture. The temperature is
usually given in degrees Celsius (oC) or degrees Fahrenheit (oF). The SI unit is
Kelvin (K). Zero Kelvin equals to -273oC.The dry-bulb temperature is an
indicator of heat content and is shown along the bottom axis of the
psychometric chart. Constant dry bulb temperatures appear as vertical lines in
the psychometric chart.
3.4.5. Soil thermometers
For measuring soil temperatures at depths of 20 cm or less, mercury-in-glass thermometers,
with their stems bent at right angles, or any other suitable angle, below the lowest
graduation, are in common use. The thermometer bulb is sunk into the ground to the
required depth, and the scale is read with the thermometer in situ. These thermometers are
graduated for immersion up to the measuring depth. Since the remainder of the
thermometer is kept at air temperature, a safety chamber should be provided at the end of
the stem for the expansion of the mercury. For measuring temperature at depths of over 20
cm, mercury-in-glass thermometers, mounted on wooden, glass or plastic tubes with their
bulbs embedded in wax or metallic paint, are recommended. The thermometer-tube
assemblies are then suspended or slipped in thin-walled metal or plastic
tubes sunk into the ground to the required depth. In cold climates, the tops
of the outer tubes should extend above the ground to a height greater than
the expected depth of snow cover. The technique of using vertical steel
tubes is unsuitable for the measurement of the diurnal variation of soil
temperature, particularly in dry soil, and calculations of soil thermal
properties based on such measurements could be significantly in error
because they will conduct heat from the surface layer. The large time
constant due to the increased heat capacity enables the thermometers to be
removed from the outer tubes and read before their temperature has had
time to change appreciably from the soil temperature.
3.5. Evaporation
Pan evaporimeter
Piche evaporimeter
United States Class “A” pan
The United States Class A pan is of cylindrical design, 25.4 cm deep and 120.7 cm in
diameter. The bottom of the pan is supported 3 to 5cm above the ground level on an open -
frame wooden platform that permits air to circulate under the pan, keeps the bottom of the
pan above the level of water on the ground during rainy weather, and enables the base of
the pan to be inspected without difficulty. The pan itself is constructed of galvanized iron
0.8 mm thick, copper or monel metal, and is normally left unpainted. The pan is filled to 5
cm below the rim (which is known as the reference level). The water level is measured by
means of either a hook gauge or a fixed-point gauge. The hook gauge consists of a movable
scale and vernier fitted with a hook, the point of which touches the water surface when the
gauge is correctly set. A stilling well, about 10 cm
across and about 30 cm deep, with a small hole at the
bottom, breaks any ripples that may be present in the
tank, and serves as a support for the hook gauge during
an observation. The pan is refilled whenever the water
level, as indicated by the gauge, drops by more than 2.5
cm from the reference level.
There are some other pans also.
Pitcher evaporimeter
This consists of an inverted test tube 20 to30cm long and closed at its base by a disk of
blotting paper. The area of the evaporating surface is about 10 cm 2. The tube is directly
graduated from the top in lengths of millimeters of water evaporated.
3.6. Air pressure
The atmospheric pressure on a given surface is the force per unit area exerted by virtue of
the weight of the atmosphere above. The pressure is thus equal to the weight of a vertical
column of air above a horizontal projection of the surface, extending to the outer limit of
the atmosphere. The basic unit for atmospheric pressure measurements is the Pascal (Pa).
Normally Mercury barometers used to measure the atmospheric pressure. The basic
principle of a mercury barometer is that the pressure of the atmosphere is balanced against
the weight of a column of mercury. In some barometers, the mercury column is weighed on
a balance, but for normal meteorological purposes, the length of the mercury column is
measured against a scale graduated in units of pressure. Following instruments are also
using for measurement of air pressure.
Electronic barometers
Aneroid barometers
Barographs
Bourdon tube barometers
4. Selection of site for establish weather station
Factors that should consider before establishing weather station,
Ground is covered with grasses.
There should be a fence around the site (to protect the equipments from
animals) the distance between the rain gauges and this fence should be about
twice of the height of fence.
The place should be open area with uniform flat land.
There should not be any barriers such as trees, building…etc, within m
distance from the place of measuring of rainfall. . Even small obstruction
may cause a significant change in measurements.
Away from the other objects about tenth of their height.
It should be a representative location for the area, should not place closer to
water bodies
Place sufficiently comparable with natural or regional studies.
The place selection should not be steeply slope or hollow.
Outdoor instrument should have placed on a ground that is 7m*10m with
short grass. It should be surrounded by open fence.
Sunshine recorder rain gauge, Anemometer must be on site with exposure to
satisfy their requirements.
The area should be satisfied for most meteorological instrument.
The site should be uniform & horizontal in all directions.
The enclosure may not be best pace from which to estimate the wind
The enclosure should be in close proximity to the meteorological Office for
convenience of access. But it should be more then 300m down ward (with
respect to the prevailing wind, of any area used for running aircraft engines
&should be more then 100m in any direction From any such area)
In selecting site the future should be considered as well as the present. A
good site can become a bad one because of the growth of tree &
establishment of buildings at adjacent plot.
Sketch of a weather station
5. Installation of equipment in the site.
There are 3 types of equipments we can identify.
I. Onsite Equipments
Eg: Recording / Non recording type rain gauges.
II. Equipment in the Stevenson screen
Eg: Wet and dry bulb thermometer
Minimum and maximum thermometers
Air thermometer
III. Offsite Equipments
Eg: Barometer
Rain Gauge Installation
− Site should be level and surrounding ground should be uniform.
− Ground should be preferably grassed of loose earth
− Objects such as other instruments should not be in the site, trees or buildings should not
be closer than 4 times of their height.
− Very exposed site such as on the top of a hill should be avoided.
− The rain gauge should be firmly mounted on a concrete base (30cm above the ground)
− The rim of the rain gauge must be horizontal.
− In very open situation the each of the gauge may be seriously reduced by the addles set
up the gauge itself when the wind is strong. In such situation it’s necessary to set up a
turf wall round the gauge.
Sunshine recorder installation
− Sunshine recorder installed place should not interfere to the solar radiation.
− Recorder should install on a bricks or concrete pillar.
Anemometer installation
− Any obstruction near the place of Anemometer installed should not disturb to the
Anemometer function.
− Anemometer needs to be at a height H+10 (H-height of the tallest of the various
obstacles) Therefore when installing has to make detailed site plan showing the height
and extend of all obstacles within 300cm.
− Cup Anemometers must be used in the horizontal position only.
Stevenson screen installation
− Place the screen on the stand with its door opening towards north, and then screw it in
to position.
− The legs may have to be get in individual blocks of concrete at windy sites when finally
installed the base of the screen should be 1.1m above the ground.
Class `A` evaporimeter
− The pan is painted in white
− Put on a wooden frame height of 1.5 cm from the ground in order to get better air
circulation.
− Water is filled to depth of 30 cm
− Water is added each day to bring the water level constant.
− This must be install horizontal to the ground surface & constructed place where no any
interference.
Soil Thermometer installation
For depths 30cm or more
− Thermometers (soil) installed in steel tubes of required depth driven vertically in to the
ground. Upper end of the steel tube is closed by polythene cap to prevent entrance of
rain water and dirt.
− Land surface should not have disturbances.
For depth less than 30cm
− Soil should free from weeds and any other disturbance.
− Surface soil temperature, 5cm… depth are measured by installing thermometer directly
in glass tubes, it prevent breaking of thermometer.
Barometer installation
− Barometer is off-site equipment.
− It should not expose to direct sun light.
− Barometer should not (site) expose to extreme temperature variation.
− This should be installed in an air conditioned or normal room.
− Barometer should be mounted on a wall by means of mounting plate or bench or shelf
mounted.
6. Data observation
6.1. Method of data observation
Time schedule
Air Temperature Wet & Dry bulb Temp. Air RH%
Evaporation
8 12 16 pressure
Rain fall
8 12 16 Max Min D W D W D W 8 12 16 8 12 16
Date
Soil Temperature Anem.
Wind sp.
Surface 5cm 10cm 20cm 30cm 60cm Read.
Sun hr
Date
8 12 16 8 12 16 8 12 16 8 12 16 8 12 16 8 12 16 8 12 16
6.2. Data recording procedure
Rainfall
Reading was taken at 8.00am only. That reading is included to the previous day
Temperature
Soil temperature
Four thermometers were used to measure the soil temperature in 5cm, 20cm,
30cm, 60cm. sheathed thermometers are used to measuring temperature at 30cm
and 60cm. Readings are taken at 8.00am, 12.00am, 16.00pm in the day.
Air temperature
It was measured by thermometer in the Stevenson screen. The data is taken at
8.00am, 12.00am, and 16.00pm in the day.
Wet and Dry bulb temperature
The data was taken at 8.00am, 12.00am, and 16.00pm in the day.
Maximum and Minimum temperature
Readings were taken at 8.00am, 12.00am, and 16.00pm in the day.
Wind speed
Readings were taken at 8.00am, 12.00am, and 16.00pm in the day by using
anemometer.
Evaporation
It was measured by pan evaporimeter. Reading was taken at 8.00am only. That
reading was belongs to the previous day.
Air pressure
Mercury barometer is used to measure the pressure. Readings are taken at 8.00am,
12.00am, and 16.00pm in the day