Measuring Temperature using an Analogue
Thermometer (Alcohol/ Mercury in-glass Thermometer)
1.
The temperature should be
recorded over a grassy/dirt surface. (Concrete surfaces tend to radiate more
heat which may affect data collected).
2.
Hold the analogue/digital
thermometer away from the body so that it does not pick up body
heat. Also ensure that the thermometer is held at the tip and not at the bulb.
3.
The thermometer should also be
placed at a height of around 1.5m away from the ground to ensure
that data collected is not affected by heat radiating from the ground.
4.
Also ensure that there is no
direct sunlight heating up the bulb of the thermometer.
5.
Keep the thermometer at the position for 2
minutes before reading off the markings on the thermometer and taking down the
temperature.
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Evaluation of process of measurement
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Reading the thermometer
inaccurately due to parallax error.
·
Holding the thermometer too
close to the body/ ground, thus allowing heat radiated from these surfaces to
affect the reading of air temperature
·
Swinging the thermometer
while taking measurements may also affect the results
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Measuring Diurnal Temperature Using a Maximum
and Minimum Thermometer
1.
Ensure that the maximum and minimum thermometer
is calibrated and that the two metal indexes within the instrument are sitting
on top of the mercury/alcohol.
2.
Place the maximum and minimum thermometer in a
Stevenson’s screen where it is kept out of direct sunlight and is elevated off
the ground.
3.
Ideally, the instrument should be placed during
solar noon (where sun is at its highest elevation in the sky [may not be 12
noon]). The instrument will be placed for 24 hours.
4.
After 24 hours, read the thermometer by looking
at the lowest point of the metal index which indicates the temperature.
5.
Subtract the temperatures read from the maximum
thermometer with that from the minimum thermometer to record the diurnal
temperatures recorded for that day.
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Evaluation of process of measurement
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Read “Measuring
Temperatures”
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Measuring Precipitation Using a Rain Gauge
1.
Position the rain gauge in an open area where
there is no obstructions from buildings or vegetation. Also ensure that the
area is uniformly protected from the wind in all directions to ensure that
there will not be underestimation of rainfall due to wind turbulence.
2.
Sink
the rain gauge into the ground with 30 cm of the equipment protruding above the
ground to ensure that the equipment does not topple over.
3.
Record
the time at which the rainfall events start and end. (The time where the rain
gauge is placed at the location depends on the investigation you are conducting
[can be one rainfall event or total rainfall in one day)
4.
Pour
out the rain collected in the rain gauge and measure the amount with a
measuring cylinder.
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Evaluation of process of measurement
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·
Reading of measuring
cylinder inaccurately due to parallax error
·
Setting up rain gauge at
unsuitable locations (e.g. under a tree/ on top of a building [too much wind
turbulence])
·
Not ensuring that glass
bottle within rain gauge is completely empty before placing equipment at
location
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Measuring Relative Humidity Using a Sling
Psychrometer
1.
Before
collecting data on the field, thoroughly saturate the wick of the wet bulb
thermometer with water.
2.
Swing
the sling psychrometer at a steady and comfortable pace of about 2 seconds per
turn for one minute. Ensure that the equipment is swung away from the
body so that it does not pick up body heat.
3.
After
one minute, read and record the temperature on the wet bulb thermometer.
4.
Swing
the psychrometer for another minute and ensure that reading for the wet bulb
temperature is the same. Repeat this step until a constant reading is achieved.
Then, read and record the temperature on the dry bulb thermometer.
5. Calculate the wet bulb
depression and refer to the conversion table to determine the relative
humidity.
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Evaluation of process of measurement
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Psychrometer is swung too
quickly, causing more evaporation to occur on the wick which would result in
lower temperatures for the wet bulb.
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Psychrometer is swung too
close to the body, resulting in the body heat affecting the readings.
·
Moving/Walking around while
taking the readings can also result in inaccurate data since rate of
evaporation may be altered.
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Measuring Wind Speed using an Anemometer
1. Identify an open area where
wind flows freely.
2. Hold up the anemometer and
ensure that there is no obstruction of wind by any objects.
3. Read the wind speed off the
display on the anemometer found above the handle (readings are either in m/s or
Beauforts)
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Evaluation of process of measurement
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·
Obstruction of wind, for
example, holding the equipment in front of the body (torso)
·
Human intervention such as
turning on a fan when data was collected leading to data recorded to be
inaccurate
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Moving/ walking around when
data is collected, resulting in the speed of movement to be added to the wind
speed
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Measuring Wind Direction using a Wind Vane
1. Identify an open area where
wind flows freely.
2. Use a compass to determine
the cardinal directions of a location and align the wind vane to the compass
directions
3. Hold up the wind vane and
ensure that there is no obstruction of wind by any objects.
4. Record the direction the wind
vane points to (the direction the wind is blowing from)
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Evaluation of process of measurement
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·
Misaligning wind vane with
compass directions, resulting in wrong directions recorded
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Obstruction of wind, for
example, holding the equipment in front of the body (torso)
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Measuring Air Pressure using an (Aneroid)
Barometer
1.
Set
up the barometer by manually calibrating it. Turn the moveable pointer to match
the current barometric pressure in your location. You may want to verify the
current barometric pressure reading with an online source such as the NEA
(National Environment Agency) website.
2. The time where the barometer
is placed depends on the investigation you are conducting (can be a few hours
to one day).
3. The measuring hand moves
according to the air pressure. If the measuring hand moves to the left of the
moveable pointer, it shows that pressure has decreased and if the hands moves
to the right of the moveable pointer, it shows that pressure has increased.
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Evaluation of process of measurement
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Barometer was not
calibrated beforehand thus resulting in inaccurate readings
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