Sunshine Recording Equipment and Equipment for Measuring Evaporation

AN ASSIGNMENT

ON

SUNSHINE RECORDING EQUIPMENT AND EQUIPMENT FOR MEASURING EVAPORATION.

BY

AYEJUYONI BABATUNDEARC/05/5598

AKINOLA OLUJIDE FRANCIS ARC/05/5590

ADANIKIN OLUMIDEARC/05/5570

SUBMITTED TO

PROF. OGUNSOTE O.

DEPARTMENT OF ARCHITECTURE FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE

MARCH 2008

TABLE OF CONTENT

1.0INTRODUCTION

2.0EVAPORATION PAN

2.1 INSTALLATION

2.2 MAINTENANCE

2.2.1CONTROL OF ALGAE

2.2.2FIXED POINT GAGE

2.3MEASURING THE AMOUNT OF EVAPORATION

2.4WATER STORAGE TANK

2.5DETERMINING EVAPOTRANSPIRATION WITH EVAPORATION PANS

2.6TYPES OF PAN

2.7LOCATION OF PAN

3.0SUNSHINE RECORDERS

3.1CAMPBELL STROKE SUNSHINE RECORDER

3.2HELIOGRAPH

REFERENCES

1.0INTRODUCTION

Sunshine and evaporation data are very important in building climatology to determine the level of convenience that would be experienced by the inhabitant of the buildings. These are necessary in carrying out very important researches in metrological stations. Evaporation level and the degree of sunshine in a particular zone are very important data’s in building climatology. This write up tends to help bring about the better understanding of these equipments, their functions, their capabilities, their usage and their component parts.

The primary source of information for this assignment is from the internet since most of these equipments are not readily available in most meteorological stations in Nigeria.

2.0EVAPORATION PAN

The pan is circular, 10 inches deep, and 47.5 inches in diameter (inside diameter). It is constructed ofmonel metal.

Plate 1 showing evaporation pan

2.1 INSTALLATION

The pan must be centred on supports resting on levelled ground. Take care to locate the pan in an areathat is free from flooding even in heavy rains, or where runoff could wash away the support. If fill dirt isrequired to level the ground, it should be tamped firmly. The top of the support should be .5 inch abovethe dirt. This will leave an air space between the bottom of the pan and the fill dirt to simplify inspectingthe pan for leaks.

2.2MAINTENANCE

Carefully inspect the pan for leaks at least once a month (leaks make measurements useless). Report any leaks immediately, Record the date the leak was discovered and the date the

pan was repaired or replaced.

Clean the pan as often as necessary to keep it free from any substance that will alter the evaporation rate,such as sediment, SCUM algae, and oil films. Oil films greatly reduce evaporation.

The pan should never be painted. This would alter the evaporation characteristics. In order to comparemeasurements between sites, all pans must have identical characteristics.

Under no circumstances should the pan be lifted and emptied with a significant amount of liquid in it, assuch action can split or bend the pan. Most of the water should be siphoned or dipped out first.During months when freezing conditions are likely, empty, clean, and store the pan, preferably indoors. Ifleft in the fenced enclosure, it should be turned upside down and secured to the support with a strong rope.

2.2.1 CONTROL OF ALGAE

A small amount of copper sulphate may be added to the water to discourage algae growth. If algae are already present, they must be removed by

Thoroughly cleaning the pan

2.2.2FIXED POINT GAGE

The fixed point gage consists of a pointed rod mounted in a tube called the stilling well. It is placed insidethe evaporation pan, one foot from the north edge. The stilling well makes readings more precise byeliminating wind-caused surges in the water level and ripples.

The stilling well is 2.5 to 3.5 inches in diameter and 10 inches tall, and is attached to a base. All parts aremade of non-corrosive metal. The base must be heavy enough to resist being moved by the wind. Thestilling well has two small openings, 1/8 inch in diameter, located opposite each other near the base. Theypermit the flow of water in and out of the stilling well.

The pointed rod is 1/8 inch in diameter. It is attached to the centre of the base inside the well. The point is7.5 inches above the bottom of the evaporation pan when in position.

Evaporated water must be replaced. This is done by using the transparent measuring tube, shown besidesthe stilling well in exhibit 5.4. It is 15 inches deep with an inside diameter of 4-3/4 inches, which isone-hundredth of the surface area of the evaporation pan. The tube is graduated at one-inch intervals,with the zero mark at the top. One inch of water in the measuring tube is equivalent to .01 inch in theevaporation pan.

Plate 2: Stilling Well, Fixed Point Gage, and Measuring Tube

2.3MEASURING THE AMOUNT OF EVAPORATION

Evaporation is measured by determining the amount of water required to bring the water level in thestilling well exactly to the tip of the pointed rod. Use the transparent measuring tube to add or removewater from, the evaporation pan. Mien water must be added, fill the measuring tube to the zero mark (thetop mark on the tube), then pour (slowly) exactly enough water into the evaporation pan (not in the stillingwell) to bring the water level to the tip of the fixed point. Next, read the level of water remaining in themeasuring tube. If this reading is closest to the 12 mark, for example, 0.12 inches of water has evaporated(or else evaporation has exceeded precipitation by 0.12 inches).

Plate 3 Evaporation measurement

If precipitation has occurred since the previous observation, the water level may be above the tip of thefixed point. In this case, remove water by filling the measuring tube up to the zero level with water fromthe evaporation pan as many times as necessary to bring the water level to the fixed point. Be sure to keeptrack of the number of times the tube is filled. Each filling represents 0.15 inches of water. When enoughwater has been removed to bring the water level below the fixed point, fill the measuring tube with waterfrom the storage tank (subsection 5.3.3) to the zero level, and pour enough water back into the pan tobring the level to the tip of the fixed point. Deduct this amount from the total removed.An alternative to bringing the water level below the fixed point is to remove enough water from the paninto the measuring tube to bring the water exactly to the fixed point, measuring the amount in the tube, and subtracting this from 0.15 inch. For example, if the tube is filled to the "5" level (0.05 inch), subtract0.05 from 0.15. The amount removed by dipping is thus 0.10 inch. This is added to the amount removed(if any) by filling the tube from the pan as described in the previous paragraph.

For recording purposes, water added is positive and water removed is negative. For example, if 0.24inches of water mist be added, record this as +0.24. On the other hand, if rain has fallen and the measuringtube must be filled three times to bring the level below the fixed point, 0.45 inches is deducted. If 0.06 inchof water is then added to bring the level back to the fixed point, enter the sum of -0.45 and +0.06, or -0.39,on the recording form

2.4WATER STORAGE TANK

If clean water is not available at the site, a storage tank should be located there. The tank should be placedwhere it will not shade or reduce wind flow over the pan. It should be thoroughly cleansed at the beginning ofthe evaporation measuring season. The water must be completely free of oil.

2.5DETERMINING EVAPOTRANSPIRATIONWITH EVAPORATION PANS

Irrigation scheduling using climatic data requires the use of evapotranspiration (ET) data. Evapotranspiration data can be calculated using various weather parameters obtained from a weather station or obtained directly from anevaporation pan. Guidance on how to set up, locate, maintain and operate an evaporation pan is provided in this factsheet.

Types of Evaporation Pans

Two types of pans are commonly used. Class A pan is the standard one used by research facilities and climate stations where a standard method of measurement is essential. Galvanized washtubs are often used in situations where a simpler and less expensive method of collecting ET data is desired.

Class 'A' Pan

The Class A evaporation pan (Figure 1) is a universally used standard-sizedpan with a diameter of 1.2 m and a depth of 250 mm. When installed, it is elevated 150 mm off the ground. The operating water level is 175 – 200 mmdeep; therefore, the water level in the pan is kept 50 – 75 mm from the rim.

A stilling well located on the side of a Class A pan has a level sensor which isused to record water depths. The measurements can be taken automatically.

This pan can be purchased with an automatic refill that fills the pan back to the200-mm depth when necessary.

Plate 4: Galvanized Washtub

The galvanized washtub (Figure 2) is approximately 0.50 m in diameter and 0.25 – 0.30 m in depth. A tub with thisdepth is most desired. Since the tub is located in the field, a wire cage is placed over the tub to keep away birds andanimals.

A ruler is attached to the tub to measure the water level. It is important tomeasure the water depth at the same place in the tub every time. This is toensure the differences in water depths in the tub are due to evaporation andrainfall, not irregularities at the bottom of the tub. Mark the inside of the tubto indicate where the measurements are to be made.

The water depth in the tub should be maintained between 50 – 75 mm fromthe rim of the tub. The maximum water depths should be marked on the sideof the tub. After each irrigation or if the water level reaches the minimum

prior to the next irrigation, the tub should be refilled to the full mark.

Plate 4: Galvanized Washtub

Rain Gauges

Rain gauges are required to monitor the amount of precipitation that falls in the evaporation pan and on the irrigated field. The measured rainfall is subtracted from the water level reading in the pan to determine the amount of moisture evaporated.

Rain gauges can be automated (Figure 3) or manual (Figure 4). The automated type measures rainfall automatically using a tipping bucket. These rain gauges require a datalogger to keep track of the rainfall, and are used at the packaged climate stations. It is most often used with an automated Class A pan. The manual type is simpler and less expensive than the automated one, and is usually used with the washtub evaporation pan. The manual rain gauge should be read and emptied after every rainfall event. To prevent the water from evaporating before a reading is taken, the gauge should be seeded with a few drops of light mineral oil. The mineral oil will create a floating layer on the surface of the rainwater.

2.6LOCATION OF EVAPORATION PAN

The location of an evaporation pan is very important for reliable estimates of

evaporation. The tub should be placed near the field, but not on bare ground or next toareas with gravel or black top. These areas increase evaporation due to temperaturesthat are above normal. The pan should be raised 150 mm above the ground, levelled andfirmly supported.Moreover, the pan should not be placed under trees or near buildings where it will beshaded for part of the day. Vegetations within a 10-m radius of the tub should be keptmowed. An ideal location is a grassed area next to the irrigated area. The irrigationsystem should not add water to the pan. The conditions should be representative of what

the crop is experiencing, taking into account wind, sunlight and temperature.

Plate 6: Shows a pan and a rain gauge located 30 m from the edge of an orchard.

3.0SUNSHINE RECORDERS

Sunshine Recorders are used to indicate the amount of sunshine at a given location. The results are used to help provide information on the climate of an area and some of the fields it is of importance to are science, agriculture and tourism.

Traditionally, sunshine recorders are divided into two groups. In the first group the time of the occurrence of the event is provided by the sun itself and in the second a clock type device is used to provide the time scale.

The older type of recorders required the interpretation of the results by an observer and these may have differed from one person to another. Today, with the use of electronics and computers it is possible to record the sunshine duration that does not rely on an observer’s interpretation. At the same time the newer recorders can also measure the global and diffuse radiation.

There are various types of sunshine recorders these include:

• Campbell-Stokes recorder
• Heliograph

3.1Campbell-Stokes recorder

The Campbell-Stokes recorder (sometimes called a Stokes sphere) is a kind of sunshine recorder. It was invented by John Francis Campbell in 1853 and later modified in 1879 by Sir George Gabriel Stokes. The original design by Campbell consisted of a glass sphere set into a wooden bowl with the sun burning a trace on the bowl. Stokes's refinement was to make the housing out of metal and to have a card holder set behind the sphere.

This basic unit is still in use today with very little change. It is probably the most common sunshine recorder in use today, outside of the United States where the Marvin sunshine recorder is the instrument generally used by the National Weather Service.

The unit is designed to record the hours of bright sunshine which will burn a hole through the card. However, at sunrise and sunset the sun is lower in the sky and will tend to leave a scorch mark on the card which may at the extreme end be difficult to see.

The glass sphere - typically 10 cm (4 inches) in diameter - is designed to focus the rays from the sun onto a card mounted at the back and is set on a stand. The card is held in place by grooves of which there are three overlapping sets, to allow for the height of the sun during different seasons of the year. In the northern hemisphere the winter card is used from the 15th of October to the 29th of February, the equinox card from the 01st March to the 11th of April and the 03rd of September to 14th of October. The summer card is therefore used from the 12th of April to 02 of September. Each card is marked as to the hour, with local noon being in the centre, and is read in 10th's. The unit is set in a stand facing south to enable the maximum amount of sun to be recorded. Of course it is of great importance to set the unit in an area where the sun will not be blocked by buildings, trees or flagpoles.

A modification to the standard unit for Polar regions is the addition of a second, north facing, sphere and card, to record the sunlight during the summer when it remains in the sky for 24 hours.

Advantages

The major advantage of this type of recorder is its simplicity and ease of use. There are no moving parts and it thus requires very little maintenance. The unit can be used anywhere in the world with little or no modification and is relatively inexpensive

Disadvantages

When the sun is low in the sky it may not have enough strength to properly burn the card and thus can only measure the amount of bright sunshine as opposed to visible sunshine. Rain may cause the card to be torn when removing it and thus making it difficult to read. In areas of high frost and during periods of freezing rain the sphere may be difficult to clean and may not be removed before the sun is shining again. However, the single biggest problem is in the reading of the cards. As the sun is covered and exposed by clouds the amount of burn on the card may be the same for 30 seconds as for 5 minutes. Thus, the reading of the card may differ from one observer to another.

A Campbell-Stokes recorder adapted for use in polar regions (The right sphere is facing south)

Close up of a summer sunshine card for the Campbell-Stokes recorder. The amount of sunshine is recorded in 10th's of an hour.

3.2Heliograph

Signaling with heliograph, 1910

A heliograph uses a mirror to reflect sunlight to a distant observer. By moving the mirror, flashes of light can be used to send Morse code. The heliograph was a simple but highly effective instrument for instantaneous optical communication over 80km or more in the 19th century. Its major uses were for military and survey work. It was still in use till at least 1935.

Description

Heliograph equipment varied somewhat from country to country. The U.S. Army heliograph had two mirrors mounted on a tripod. A shutter for interrupting the flashes was mounted on another tripod. If the sun was in front of the sender, its rays were reflected directly from a mirror to the receiving station. The sender used the sighting rod to align the flash with the receiver. If the sun was behind the sender, its rays were reflected from one mirror to another, to send the beam on to the target receiver. The British army version had a single mirror with a small sighting hole in the middle and a keying mechanisms that tilted the mirror up a few degrees at the push of a lever at the back of the instrument. Auxiliary mirrors mounted on separate tripods were used to redirect the sunlight if it were not coming from a favorable angle.

The heliograph had some powerful advantages. It allowed long distance communication without a fixed infrastructure, though it could also be linked to make a fixed network extending over hundreds of miles, as in the fort-to-fort network used in the Geronimo campaign. It was highly portable, required no power source, and was relatively secure since it was invisible to those not near the axis of operation. However, anyone with the correct knowledge could, in theory, intercept signals without being detected.