University of GuyanaFaculty of TechnologyDepartment of Civil Engineering

CIV3101: Hydrology

Lecturer Mr. VeecockSubmission Date 15th September, 2014

Group Members

Chrysann Clarke 13/0933/1392Eketa Edwards 13/0933/2194Jaikeshan Takchandra 13/0933/1323Jayson Lewis 14/0933/2062Larry Carryl 13/0933/1426Narendra Dewnath

ContentsIntroduction4Anemometer5Wind Vane6Manual Rain Gauge7Measuring Cylinder7Sunshine Recorder9Evaporation Pan10Automatic Rain Gauge (Tipping bucket)11Stevenson Screen (thermometer screen)14Soil Thermometer17Humidity Slide Rule19Barometer20The Mercury Barometer20The Aneroid Barometer20References22

IntroductionThe following is a compilation of information on the varying weather instruments found at the Hydrometeorological Service located in the Botanical Gardens, Georgetown. The students, working in a group of six (6) persons, conducted a guided survey of the equipment laid out in the outside environment as well as those situated in the office of the Meteorological Center. The instruments in the outside environment are laid out in a fence area so as to prevent any hindrances to the various weather data collected and recorded. Information received from the students guide as well as research information on the various instruments were garnered and summarized. This assignment is the result of this research, and aims to create a concise manual on the instruments available at the Hydrometeorological Service. The list of all the equipment shown to the students is as follows. 1. Manual Rain Gauge 2. Automatic Rain Gauge 3. Campbell Stokes Recorder4. Anemometer (2 variations)5. Soil Thermometers6. Evaporation Pan7. Stevenson Screen 8. Mercury Barometer9. Humidity Sliding Rule

Anemometer At the Hydrometeorological Service there are two anemometers within the fenced area. One anemometer is 15 centimeters above the ground while the other is 2 meters above.An anemometer is an instrument that measures wind speed and wind pressure. This is an important tool for meteorologists, who study weather patterns. The most common type of anemometer has three or four cups attached to horizontal arms. The arms are attached to a vertical rod. As the wind blows, the cups rotate, making the rod spin. The stronger the wind blows, the faster the rod spins. The anemometer counts the number of rotations, or turns, which is used to calculate wind speed. Anemometers are used at almost all weather stations, from the frigid Arctic to warm equatorial regions. Wind speed helps indicate a change in weather patterns, such as an approaching storm.

Image 2: 6 inch Anemometer located at the Hydrometeorological Service, Botanical Gardens(Taken: 09/09/2014 by Eketa Edwards)Image 1: 2 meter inch Anemometer located at the Hydrometeorological Service, Botanical Gardens(Taken: 09/09/2014 by Eketa Edwards)

Wind VaneA wind vane is an instrument used to show the direction in which the wind blows. The cardinal points of the compass also are usually shown on weather vanes. Wind vanes should be posted in high locations is to prevent interference and to catch the purest breezes.This instrument is equipped with a central pivoting arrow or pointer which usually is tapered at one end to provide balance and to catch even light winds. The larger end of the pointer acts as a sort of scoop that catches the wind. Once the pointer turns, the larger end will find a balance and line up with the source of the winds.To use a wind vane, you must know where are your cardinal points are. It is important to know the direction in which the wind is coming from because in predicting the weather the wind brings us our weather.

Image 3: Manual Rain Gauge located at the Hydrometeorological Service, Botanical Gardens(Taken: 09/09/2014 by Eketa Edwards)

Manual Rain GaugeA manual rain gauge is a weather instrument used by meteorologists and hydrologists to gather and measure the amount of rainfall over a set period of time. Manual rain gauges need to be read and emptied daily in order to maintain an accurate year-round rainfall record. The manual rain gauge located at Guyanas Hydrometeorological Service is equipped with a receiver which houses a funnel where the rainfall passes through into a storage tank. The storage tank consists of a glass bottle placed in a brass cylindrical tank. In case of heavy rainfall, the glass bottle fills up and the excess water flows into the brass cylindrical tank. The amount of rainfall is measured by opening a latch at the bottom of the storage tank so that the rainfall flows into a measuring cylinder where the measurement is read and recorded. The rain gauge measures the precipitation in millimeters although the level of rainfall is sometimes reported in inches or centimeters.The manual rain gauge located at Guyanas Hydrometeorological Service like all rain gauges is placed in an open area where there are no obstacles, such as buildings or trees, to block the rain. This is also to prevent the water collected on the roofs of buildings or the leaves of trees from dripping into the rain gauge after a rain, resulting in inaccurate readings.

Measuring CylinderThe cylinder is a measuring container, made up of glass or resistive plastic materials with volume units marked on it, along its length. The markings are calibrated according to actual volume measurements, by manufacturers. It is basically a volume measurement vessel with a long and slender cylindrical body and is necessarily transparent, to be able to use it for measurements. They have a stable base below, which allows them to be kept on surfaces, without the need for a stand. Function of the cylinder is to measure liquid volumes accurately. They are purposely designed to be long, with a shorter diameter compared to beakers, to facilitate accurate measurements.

Image 4: Manual Rain Gauge located at the Hydrometeorological Service, Botanical Gardens(Taken: 09/09/2014 by Eketa Edwards)Receiver which houses the funnel

Sunshine RecorderA Campbell- Stokes sunshine recorder is a device used to measure the duration of bright sunshine at a given location. The instrument was invented by John Francis Campbell in 1853 and consisted of a glass sphere within a wooden bowl. In 1879 Sir George Gabriel Stokes modified the design. The modified sunshine recorder instrument comprises a glass sphere that is typically 10cm in diameter mounted on a section of a spherical metal housing. This sphere is used to focus the rays from the sun unto a card that is held in the grooves of the metal housing. The spherical nature of the device allows for the rays to reach the card no matter the position of the sun in the sky. These rays of sunlight burns marks onto the card and these markings are used to measure and converted into duration of time. The sunshine recorder is said to measure the duration of bright sunlight and not the amount of sunshine because the instrument is not able to burn the card when the sun is going down or rising for the day. The sunshine recorder requires direct rays of sunlight and as such it should be place in an open area where there are no trees or structures obstructing the direct path of the rays.

Image 6: Burnt card within the Sunshine Recorder (Taken: 09/09/2014 by Eketa Edwards)Image 5: Campbell-Stokes Sunshine Recorder located at the Hydrometeorological Service, Botanical Gardens(Taken: 09/09/2014 by Eketa Edwards)

Evaporation PanThe evaporation pan is used to measure the quantity of evaporation at a given location. The evaporation pan at the Hydrometeorological Service, Georgetown has the dimensions of a class A evaporation pan. This type of pan is made of stainless steel and is typically 54 mm in height and 1206 mm in diameter.For the evaporation of an area to be measured the evaporation pan must first be placed in an open fenced area to avoid disturbances. The pan must then be filled with a known quantity of water approximately three (3) inches from the top of the pan. The water in the pan is allowed to evaporate and after 24 hours the remaining depth of water is measured. If precipitation occurs during the 24 hour period, the amount of rainfall is taken into account when calculating the evaporation. If the amount precipitation is greater than amount of evaporation then the pans water level will be higher than the initial level so the amount of precipitation should be known and considered when calculating evaporation. The depth of the water is measured using a micrometer placed in a still well within the pan.

Image 8: Micrometer from Stilling Well (Taken: 09/09/2014 by Eketa Edwards)Image 7: Evaporation Pan with stilling well and micrometer located at the Hydrometeorological Service, Botanical Gardens(Taken: 09/09/2014 by Eketa Edwards)

Automatic Rain Gauge (Tipping bucket) Specifications: - Bucket size: 0.2 mm- Catchment area: 200cm2 Construction: - Anodized copper catchment funnel- Self logging drum graph- Self emptying aluminum buckets- Long life lithium battery- Funnel filter into collection barrel

Description:A tipping bucket rain gauge (automatic rain gauge - ARG) is a meteorological device that measures and records the amount of precipitation (primarily rain fall), that has fallen over a given period of time. Hence, it measures rainfall intensity. The device has several components that allow it to accurately measure rainfall. As rain falls, it lands in the funnel of the rain gauge. The rain travels down the funnel and drips into one of two calibrated catchment buckets, balanced on a pivot (like a see-saw). This bucket collects an amount of rainfall (that is pre-set), then tips over to dump the collected water. High intensity rain-fall produces faster dripping rates from the funnel. The bucket is held in place by a magnet and will release its hold, causing the bucket to tip. When the bucket tips, it triggers a reed switch (or sensor), sending an electrical signal that is converted to rainfall information, plotted on a drum-roller graph inside the instrument. The grapher consists of an automatic pen mounted on an arm, attached to a geared wheel that moves once with each signal sent from the collector. In this particular design, the wheel rotates at a constant speed (in relation to a ticking clock inside the instrument) and the pen arm either moves up or down, based on the amount of rain-fall collected over each single unit of time interval (10 minute intervals). The result is a rain-fall graph that outlines the rain-fall pattern for a full 24-hour period. After which the drum graph is replaced and the clockwork motor manually wound to allow it to begin ticking again. The tipping bucket rain gauge discussed is an old-style recording device and is not accurate as even a standard graduated rain gauge, since the rainfall may stop before the lever has tipped. This is because it can take more than two drops to tip the bucket, causing the device to underestimate rainfall. Most modern rain gauges of this nature transmit the electrical signal from the tipping bucket to the hydro-met station, which may then be electronically analysed and stored. The advantage of the tipping bucket rain gauge however, is that the character of the rain (light, medium, heavy) is easily obtained from the graph.

Image 9: Automatic Rain Gauge located at the Hydrometeorological Service, Botanical Gardens(Taken: 09/09/2014 by Eketa Edwards)

Image 10: Internal view of the Automatic Rain Gauge located at the Hydrometeorological Service, Botanical Gardens(Taken: 09/09/2014 by Eketa Edwards)

Stevenson Screen (thermometer screen) Specifications:- Box size: 32"x18"x14" Construction: - Wooden box, painted white (minimized heat optimization)- Double louvered construction (for easy ventilation and protection from UV light- Less than 2m off the ground- Houses thermometers inside

History:The Stevenson screen was designed by Thomas Stevenson (1818-1887), a British civil engineer. He developed a small thermometer screen initially, with double louvered walls, in response for the need of a sheltered instrument house. After comparison with other screens in the UK, Stevenson's original design was modified by Mawley. Modifications included double roof, a floor with slanted boards and also modifications to the double louvers.

Description The Stevenson screen (also known as an instrument shelter) is a meteorological screen to shield instruments against precipitation and direct heat radiation from the outside sources, while still allowing air to circulate freely around it. It forms part of a standard weather station and its primary aim is to provide, as near as possible, a uniform environment in relation to the outside conditions whilst sheltering and protecting the instruments inside.

This particular screen contains four type of measuring thermometers: The dry-bulb thermometer is an ordinary thermometer with a dry bulb; used to measure the air temperature, the dry bulb, has its bulb exposed to the atmosphere. The wet-bulb thermometer is a thermometer with a bulb that is covered with moist muslin; used in a psychrometer to measure humidity. Maximum temperature thermometer (mercury-in-glass thermometer which has a constriction in the neck of the thermometer tube. As the air temperature rises, mercury is forced past the constriction. However, as the temperature falls the constriction prevents the mercury from returning to the bulb of the thermometer. The thermometer resets/rests by gentle shaking Minimum temperature thermometer (alcohol-in-glass thermometer) containing a moveable index, used to manually record minimum temperatures. When the temperature falls, the liquid and index move down the column, but when the temperature rises, the index remains in the lowest position while the liquid expands up the tube. The position index indicates the lowest temperature reached since the last reset- which is achieved by tilting the thermometer bulb end upwards.

Image 11: Stevenson Screen located at the Hydrometeorological Service, Botanical Gardens(Taken: 09/09/2014 by Eketa Edwards)

Soil ThermometerA soil thermometer is a thermometer specifically designed to measure soil temperature. Gardeners find these tools useful for planning plantings and they are also used by climate scientists, farmers, and soil scientists. Soil temperature can provide a great deal of useful information, especially when charted over time.For gardeners and farmers, soil temperature is the key to making planting decisions. Whether planting seeds or seedlings, if the soil is too cold, the plants may die. While people can use guidelines like the date of the most recent frost, the ambient air temperature, and the time of year, soil temperature measurements can be very important for confirming that the soil is ready for the growing season. Likewise, people who monitor climate and soil health use soil thermometers in their work.Soil thermometers include a long probe that allows people to reach deep into the soil. Some must be pulled out for reading, using a traditional mercury bulb thermometer design. Others have a display on the top of the thermometer that may be digital or analog, allowing people to quickly read the soil temperature. Typically the probe is coated to help it resist corrosion. It is advisable to periodically wipe down a soil thermometer to remove soil and any salts that may have adhered, to extend the life of the probe. If the probe is used in a wet environment, it should be wiped clean and dry before being put away for storage. Many soil thermometers come with cases or clips that can be used to protect them for storage while they are not in use.A quick read soil thermometer will take a reading very rapidly and is useful for a quick probe of soil to check on conditions. Other thermometers need to be left in place for a few seconds in order to generate a stable reading. Some are designed specifically to be left in place. In greenhouses and other highly controlled environments, people may leave thermometers in the soil so that they can take regular readings.

Image 12: Soil Thermometers located at the Hydrometeorological Service, Botanical Gardens(Taken: 09/09/2014 by Eketa Edwards)

Humidity Slide RuleSlide rules come in a diverse range of styles and generally appear in a linear or circular form with a standardized set of markings (scales) essential to performing mathematical computations. Slide rules manufactured for specialized fields such as aviation or finance typically feature additional scales that aid in calculations common to that field. A humidity slide rule is however described, from which the dew-point, vapour pressure, and relative humidity of an air sample may be obtained from readings of the dry- and wet-bulb hygrometer. The slide rule can also be used for the solution of various hygrometric problems which arise in connexion with meteorology and air-conditioning.

Image 13: Photo of Humidity Slide Rulehttp://www.hpmuseum.org/powerlog.jpg (Retrieved: 13/09/2014)

BarometerThe barometer is a device used in the measurement of atmospheric pressure, that is, the pressure resulting from the weight of air above a given point. The first barometer was invented by Evangelista Torricelli, and was called the Torricellis Tube. This was created by filling a four-foot long glass tube with mercury and inverting the tube into a dish. The tube exhibited a fluctuation in the level of mercury and the creation of a sustained vacuum, both of which were found to be correlated to the change in atmospheric pressure. [footnoteRef:1] [1: http://inventors.about.com/od/tstartinventors/a/Barometer.htm]

The two forms of barometers in common use are the aneroid barometer and the mercury barometer.

The Mercury BarometerThis consists of an approximately 3 feet long, hollow, glass tube, closed at one end and filled with mercury and a cistern filled with mercury. The mercury column in the tube will drop, until the force exerted on a given area in the cistern is equal to the weight of the mercury remaining in the tube. When the pressure is high, the mercury rises further up the tube, and, conversely, when the pressure is low, the mercury level drops, therefore indicating a corresponding change in the weight of the atmosphere. This weight is assumed to be uniform for that height or elevation, based on the principle of uniform pressure at all horizontal points of a system. The changes are measured using the gradations on the tube. At mean sea level, the average height of the mercurial column is 29.92 inches, translated as 1 atmosphere [1,013 millibars], or 101.3 kilopascals.[footnoteRef:2] [2: http://science.howstuffworks.com/nature/climate-weather/meteorological-instruments/barometer-info.htm]

The Aneroid BarometerThis barometer is not as accurate as the mercury barometer, but boasts a greater ease of transport and a reflection of much smaller changes in atmospheric pressure. Air is partially removed from the device and a cylindrical container with a diaphragm flexes to match a change in atmospheric pressure. Sensitive levers transmit these movements to a rotational pointer which moves across a graduated scale. The aneroid barometer is operated by one or more metal cells and a diaphragm which flexes to match a change in atmospheric pressure. Sensitive levers transmit these movements to a rotational pointer which moves across a graduated scale. Increased air pressure causes the cells to converge. Sensitive levers transmit these movements to a rotational pointer which moves across a graduated scale. [footnoteRef:3] [3: http://www.bom.gov.au/info/aneroid/aneroid.shtml]

Image 14: Barometer located at the Hydrometeorological Service, Botanical Gardens(Taken: 09/09/2014 by Eketa Edwards)

References

HSW. n.d. http://science.howstuffworks.com/nature/climate-weather/meteorological-instruments/barometer-info.htm (accessed September 12, 2014).All-weather Precipitation Gauge . (accessed 2014, 09 09). Retrieved from Environment Canada : https://ec.gc.ca/meteoaloeil-skywatchers/default.asp?lang=En&n=7EF00E34-1Obervation of Air temperature . (2014, 09 10). Retrieved from Austrailian Government Bureau of Meteorology : http://www.bom.gov.au/climate/cdo/about/airtemp-measure.shtmlStevenson Screens (Weather Instrument Shelters). (2014, 09 10). Retrieved from Regional and Mesoscale Meteorology Branch : http://rammb.cira.colostate.edu/dev/hillger/shelters.htmWilson, E. (1990). Engineering Hydrlogy (Vol. Fourth). Palgrave MacMillan.2014. All-weather Precipitation Gauge . 09 09. https://ec.gc.ca/meteoaloeil-skywatchers/default.asp?lang=En&n=7EF00E34-1.n.d. Barometer . Accessed 9 12, 2014. about.com. n.d. http://inventors.about.com/od/tstartinventors/a/Barometer.html.n.d. "Evaporation Pan." KEAN University . Accessed 9 9, 2014. http://www.kean.edu/~csmart/Hydrology/Lectures/Evaporation_pan.pdf .n.d. Evaporation Pan. Accessed 9 9, 2014. http://en.wikipedia.org/wiki/Pan_evaporation#Evaporation_pan .n.d. Guide to rain gauges . Accessed 9 10, 2014. http://weather.thefuntimesguide.com/2008/03/rain_gauges_a_guide_to_the_bes.php .n.d. Humidity slide-rule. Accessed 9 10, 2014. http://www.answers.com/topic/Humiditysliderule.n.d. Humidity slide-rule. Accessed 9 10, 2014. http://www.metcheck.co.uk/acatalog/Humidity_Rule.html.2014. Obervation of Air temperature . 09 10. http://www.bom.gov.au/climate/cdo/about/airtemp-measure.shtml.. "Soil Thermometer ." Horbonyan. Accessed 9 10, 2014. http://www.horbonyan.com/catalog1/Temperature/thermometer-soil.pdf.2014. Stevenson Screens (Weather Instrument Shelters). 09 10. http://rammb.cira.colostate.edu/dev/hillger/shelters.htm.n.d. Stokes Recorder. Accessed 9 9, 2014. http://en.wikipedia.org/wiki/Campbell%E2%80%93Stokes_recorder .n.d. Weather Stations UK. Accessed 9 10, 2014. http://shop.weatherstations.co.uk/cocorahs-manual-rain-gauge-802-p.asp.n.d. Weather Vane. Accessed 9 10, 2014. http://science.howstuffworks.com/nature/climate-weather/meteorological-instruments/weather-vane-info.htm.n.d. Weather Vanes. Accessed 9 10, 2014. http://weather.about.com/od/weatherhistory/ss/weathervanes.htm.n.d. What is a soil thermometer. Accessed 9 10, 2014. http://www.wisegeek.com/what-is-a-soil-thermometer.htm.n.d. What is a sunshine recorder? Accessed 9 9, 2014. http://www.wisegeek.com/what-is-a-sunshine-recorder.htm.n.d. "Wind Vane." ISCO. Accessed 9 10, 2014. http://www.isco.com/pcfiles/PartPDF/SL000004/UP0016AA.pdf.n.d. Wind Vane. Accessed 9 10, 2014. http://en.wikipedia.org/wiki/Wind_vane .

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