• 1 watt = 1 joule/second
• CGS unit of solar radiation is Calories/cm2/min
• 697.93 W/m2 = 1 cal/cm2/min
• Lux is oldest unit of solar radiation
• 10,000 lux = 3.47 Mega Joules
• Photosynthetic active radiation (PAR) is measured in Einstein units.
• 1 Einstein unit = 1 mole of photons
• Total incoming radiation measured by pyranometer.
• Diffused radiation measured by shading pyranometer.
• Reflected radiation is measured by albedometer.
• Net radiation is measured by net radiometer.
• Photosynthetically active radiation is measured by quantum sensor.
• Direct solar radiation is measured by pyrheliometers.
• Pyrgeometer is used to measure terrestrial radiation.
• Sunshine hours recorded by sunshine recorder.
• Height of sunshine recorder from ground surface is 3.08 m.
• Cambell stokes sunshine recorder is used to measure sunshine hours in India.
• Height of Stevenson screen from ground surface is 1.22 m.
• Duration of the day and night are equal all over the earth on March 21 which is called vernal or spring equinox.
• From March 21, the day length increases gradually in the northern hemisphere till June 21, which is called the summer solstice.
• From June 21 onwards, day length decreases in the northern hemisphere till September 23, which is called the autumn equinox.
• Day and night are equal all over the world, with the sun right over the equator.
• From September 23, sun moves southward and and the days continue to get shorter and shorter in the northern hemisphere till December 21, which is called the winter solstice.
• Solar radiation in narrow wave bands is measured by Spectroradiometer.
• Infrared thermometer measures temperature of canopy without contact.
• Infrared thermometer senses radiation in the range of 8-14 micro meters wave band (infrared region).
• Infrared thermometer is used to estimate water status of plants and also to schedule irrigation.
• Temperature is the degree of hotness or coldness of a substance determined by its molecular activity.
• Temperature is measured by thermometer.
• Depth of water table is measured by Piezometer.
• Conduction is transfer of heat by molecular activity.
• Convection is process of heat transfer within liquids and gases resulting from the motion of fluid.
• Convection is faster than conduction.
• Radiation is transfer of energy by electromagnetic waves moving at the speed of light.
• Conduction and convection requires medium, whereas radiation does not require medium.
• X-rays are short.
• Radio waves are long.
• On an average cloudy day 43% solar radiation absorbed by earth, 22% by atmosphere and 35% reflected into space from earth.
• Reflected solar radiation is unchanged in character.
• Solar radiation absorbed by earth or atmosphere is converted into thermal energy.
• Solar radiation is more at 12 noon, whereas highest temperature is noticed after 2 P.M.
• At equator seasonal temperature variation is less.
• Seasonal variation in temperature is more at higher latitudes.
• Isotherms are the lines that connect points of equal temperature.
• Vertical temperature variations influence cloud formation, condensation and precipitation.
• Lapse rate is vertical temperature decrease or gradient.
• Normal lapse rate is 6.5oC per km or 3.5oF per 1000 feet.
• Adiabatic lapse rate is rate at which temperature changes as air rises or falls.
• Dry adiabatic lapse rate is 10oC per km.
• At some altitudes there is abrupt increase instead of fall of temperature is called inversion. This occurs when air near ground cools off faster than above air.
• Thermal conductivity is the quantity of heat flowing in unit time through a unit cross section of soil in response to a specified temperature gradient.
• Unit of thermal conductivity is Watts/m depth of soil/oK temperature gradient.
• Thermal conductivity depends on texture, moisture and organic matter content of soil.
• Thermal conductivity decreases with increase in porosity.
• When soil is ploughed, it increases soil porosity and reduces thermal conductivity.
• Thermal conductivity increases with increase in moisture content.
• Soil organic matter lowers thermal conductivity.
• Thermal conductivity higher in sandy soils than clay soils due to less porosity in sandy soils compared to clay soils.
• Temperature is measured in Celsius, Fahrenheit or Kelvin scales.
• In Fahrenheit scale melting point of water is 32°F.
• In Fahrenheit scale boiling point of water is 210°F.
• In Celsius scale melting point of water is 0°C.
• In Celsius scale boiling point of water is 100°C.
• Absolute temperature is measured by Kelvin scale.
• Absolute zero means 0°K.
• At absolute zero (0°K) there will be no activity of molecules in a substance.
• Melting point of water in Kelvin scale is 273°K.
• Formulae for conversion of different temperature scales
C = (F-32)5/9
F = (9C/5) + 32
K = C + 273
• Maximum thermometer is used to measure highest temperature of a day.
• Maximum thermometer is set in the morning time.
• Minimum thermometer is used to measure lowest temperature of a day.
• Minimum thermometer is set in the evening time.
• Thermocouple is used to measure soil temperature.
• Thermograph is used to record air temperature continuously.
• Aneroid barometer and barograph are used for measuring atmospheric pressure.
• Standard international unit of pressure is Pascal.
• One Pascal is equal to force of one Newton m-2.
• Ten bars is equivalent to the S.I. unit Mega Pascal (MPa).
• Wind velocity is measured by anemometer.
• Density of gases is measured by aerometer.
• Specific gravity of liquids is measured by hydrometer.
• Pycnometer is used to measure specific gravity of liquids.
• Direction from which wind blows is called windward side.
• Direction towards which wind blows is called leeward side.
• Wind direction is measured by windvane.
• Absolute humidity is the absolute or actual quantity of water vapour by weight present in a given volume of air. Absolute humidity = Weight of water vapour (g) Volume of air
• Unit of absolute humidity is g/m3.
• Specific humidity is the weight of water vapour per unit weight of air (including water vapour). Specific humidity = Weight of water vapour (g) Weight of the air including water vapour (kg)
• Unit of specific humidity is g/kg.
• Absolute and specific humidity are difficult to measure.
• Absolute humidity changes with change in temperature.
• Absolute and specific humidity have less effect on crop growth.
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