Environmental Monitoring
& Technology Series
Collect & evaluate
meteorological data
For Technicians
Study module 6
Meteorological measurements
cffet.net/env
Collect & evaluate meteorological data
Study Module 6
Assessment details
Purpose
This subject covers the ability to site and set up basic ‘ground level’ meteorological
equipment and collect and record reliable data. It also includes the ability to assess data
quality, interpret significant data features and use the data to ensure the validity of air and
noise monitoring measurements.
Instructions
◗ Read the theory section to understand the topic.
◗ Complete the Student Declaration below prior to starting.
◗ Attempt to answer the questions and perform any associated tasks.
◗ Email, phone, book appointment or otherwise ask your teacher for help if required.
◗ When completed, submit task by email using rules found on last page.
Student declaration
I have read, agree to comply with and declare that;
◗ I know how to get assistance from my assessor if needed…
☐
◗ I have read and understood the SAG for this subject/unit…
☐
◗ I know the due date for this assessment task…
☐
◗ I understand how to complete this assessment task…
☐
◗ I understand how this assessment task is weighted…
☐
◗ I declare that this work, when submitted, is my own…
☐
Details
Student name
Type your name here
Assessor
Marker’s use only
Class code
CMD
Assessment name
SM6
Due Date
Speak with your assessor
Total Marks Available
34
Marks Gained
Marker’s use only
Final Mark (%)
Marker’s use only
Marker’s Initials
Marker’s use only
Date Marked
Click here to enter a date.
Weighting
This is one of seven formative assessments that make up 20% of
the overall mark for this unit
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 1
Collect & evaluate meteorological data
Study Module 6
Meteorological measurements
This is the chapter that provides the ‘nuts and bolts’ content for the environmental
technician. This unit assumes that you will be gainfully employed as a field technician whose
job it is to acquire the raw data for all aspects of environmental regulation and legislation,
and more often than not, that requires the collection (and analysis) of meteorological data.
Why? After all, it is only wind and the like…how could that be important? Good question! It
turns out that nearly all ambient air analysis and noise measurements (which are two huge
fields under the environmental banner) require good, accurate, micro-scale meteorological
measurements. In fact without these measurements, the air and noise data can be ‘thrown
out of court’ (as you shall find out in a later unit).
Quite often, when we talk about ‘meteorological measurements’ we are describing direct
measurements (such as the air temperature) as well as derived measurements (such as the
dew point temperature), which require calculations based on the direct data you measure.
In this chapter we will look at both types of measures and see how they are related to
particular meteorological phenomena by answering five simple questions for each class of
measure;
◗ What is it?
◗ What measurements are there?
◗ How do we measure it?
◗ What values do we expect to find?
◗ What can go wrong with the measurements?
Exercise 6.1
Complete the glossary of terms (pg 23) before continuing to help understand this chapter.
So what do we commonly measure?
From a meteorological perspective, we only measure a (relatively) few atmospheric
parameters, as most are calculated or derived from the parameters that are measured.
Understand that measurements can be made at ground level, and, via the use of weather
balloons, at various altitudes through a vertical slice of the atmosphere. The most common
measures include temperature(s), pressure, and the speed and direction of the wind, as well
as rainfall rates and humidity, but these days solar information (such as solar flux and
ultraviolet intensity) are common place. It is from these few measurable parameters that we
infer our weather and other specific environmental information.
It must be said again that other parameters are commonly measured, such as rainfall, solar
intensity, snow depth and the like, and it really depends on the reason the meteorological
station is being used; for weather forecasting, air pollution studies or noise studies.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 2
Collect & evaluate meteorological data
Study Module 6
Temperature measurements
What is temperature?
You would know of temperature as the hot and cold of something, but temperature is
actually a property of matter. In fact, temperature is the key to the subject of
thermodynamics. Temperature is something that matter exhibits and can be easily
measured.
On the microscopic scale, temperature is related to the motion of atoms in matter. On the
macroscopic scale, temperature is the unique physical property that determines the
direction of heat flow between two objects placed in thermal contact. If no heat flow
occurs, the two objects have the same temperature; otherwise heat flows from the hotter
object to the colder object. These two basic principles are stated in the zeroth law and
second law of thermodynamics, respectively.
How do we measure temperature?
Temperature is measured with an apparatus called a thermometer that may be calibrated to
any common scale such as Celcius or Kelvin. There are three major classes of thermometer;
physical, mechanical and electrical, and each class can have many types of thermometer.
Note that images of common lab equipment have been used below as modern temperature
sensors in weather stations have been reduced to boring ‘black boxes’.
Physical thermometers
These include the traditional liquid in glass thermometers (alcohol and mercury) which work
because the liquid expands significantly compared to the expansion of the glass containing it
and can be calibrated against a primary thermometric procedure.
Figure 6.1 – Routine glass thermometer
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 3
Collect & evaluate meteorological data
Study Module 6
Infra-red detectors (and laser based equipment) use the properties of blackbody emission
(see chapter 2) and a detector to generate a voltage which is equivalent to the actual
temperature.
Figure 6.2 – Infrared temperature detector (thermographer)
Mechanical thermometers
These include bi-metallic strips which curve with an increase in heat, which inflects a needle
pointing to a calibrated scale.
Figure 6.3 – Bi-metal mechanical thermometer.
Electrical thermometers (transducers)
Thermocouples which use a unique property of metal called the thermoelectric effect to
produce a voltage difference which is equivalent (somehow) to the temperature. Note that
these are not considered to be very precise or accurate. Thermistors are conceptually
similar to thermocouples, but any of these transducers can be used in met stations
Figure 6.4 – Thermocouple thermometer device
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 4
Collect & evaluate meteorological data
Study Module 6
What units of temperature measurements are there?
Direct measures of temperature include;
◗ The dry bulb temperature (T), which measures ambient air temperature, and is usually
measured in the shade, but can be done in direct sun for certain reasons.
◗ The wet bulb temperature (Tw) which is used for determining the relative humidity (RH)
amongst other derived measures. See the moisture section below for uses.
◗ Both the minimum temperature and maximum temperature can be recorded via use of
an old style Six’s thermometer or a computer controlled data system.
◗ The dewpoint temperature (Td) was usually a derived temperature, but modern stations
can employ a cooled mirror which directly measures the Td.
Derived measures of temperature include;
◗ Dewpoint, as mentioned above has historically been determined mathematically.
◗ Virtual temperature (Tv) is calculated to make equal the density of a parcel of both dry
and moist air. Because the density changes with temperature, we ask the question “to
what temperature must we raise the dry air so that its density equals that of a moist
parcel of air?”
◗ Potential temperature (Tp) is calculated to determine the temperature that a parcel of
aloft air would be if it was brought down to the altitude where the pressure is 1000hPa.
What units are involved?
Celsius scale (°C)
The Celsius scale is (and was originally called) a centigrade scale, it was derived from Anders
Celsius thermometer which used the freezing and boiling points of water (0°C and 100°C
respectively) as the calibration points. This unit is used by both scientific and layman in most
countries. You will notice in Figure 6.4 below that 0 K = -273.15°C.
Kelvin scale (K)
The Kelvin, after Lord Kelvin, is the thermodynamic temperature which is just the Celsius
scale shifted downwards so that 0 K = −273.15 °C, or absolute zero. All scientific fields use
the kelvin scale for thermodynamic (physics) calculations. You will notice in Figure 6.5 below
that 0 K = -273.15°C.
Fahrenheit scale (°F)
Fahrenheit is the temperature scale named after its inventor, Daniel Fahrenheit. The
freezing point of water is 32 degrees Fahrenheit (°F) and the boiling point 212 °F (which
gave a difference of 180, which was apparently significant at the time somehow). Absolute
zero is −459.67 °F. You will notice in Figure 6.4 below that 0 K = -459.67°C. The Fahrenheit
scale will not be used at all in these notes.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 5
Collect & evaluate meteorological data
Study Module 6
Unit conversions
Converting between these units is often required. This is not a daunting task at all and you
may have encountered such conversions in other units of study, but we shall go through
them here given the ultimate significance of temperature in both the study and practice of
meteorology.
To convert from Celsius to Fahrenheit;
9
℉= ×℃+32
5
To convert from Fahrenheit to Celsius
℃=
5
× (℉ − 32)
9
To convert from Celsius to kelvin;
𝐾 = ℃ + 273.15
To convert from Kelvin to Celsius;
℃ = 𝐾 − 273.15
To convert Kelvin to Fahrenheit;
℉=
9
× (𝐾 − 273.15) + 32
5
To convert Fahrenheit to Kelvin;
5
𝐾 = [ × (℉ − 32)] + 273.15
9
Figure 6.5 The scales of temperature from 0 K to 330K. Note that Fahrenheit and Celsius are the
same at -40°. Axis are both Kelvin.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 6
Collect & evaluate meteorological data
Study Module 6
What temperature values do we expect to find?
The Australian atmosphere has experienced temperature extremes from ~ -23°C to ~ 51°C.
Industrial applications obviously experience much higher (and lower) temperatures, and you
may encounter some of these if you work as a stationary emission technician (smoke stack
testing).
Rainfall & humidity measurements
How hard could it possibly be to measure the amount of moisture in the air…? Surely it’s a
simple case of …umm…just…Yeah right! So, how could you do it? You could in fact perform a
gravimetric analysis, and draw a sample of air through a desiccating material such as silica,
and then determine how ‘wet’ the desiccant has become. Simple! Except….how exactly did
you calculate the volume? Trust me, it is much easier to calculate the humidity rather than
measure it directly (although there are modern devices that do just that!).
Humidity and water vapor
Because of the difficulty associated with performing direct moisture measurements on air,
scientists have found a number of different ways of expressing the amount of moisture in
the air, and all of them can be calculated from simple measures of temperature, with the
help of one or two scientific constant values to help them along the way. The most common
‘measures’ of atmospheric moisture are;
Absolute humidity (Ha, gH2O/m3)
This is a measure of density, m/V. The water vapor is expressed as the mass of water vapor
contained in a given volume of air. A problem with using absolute humidity is that an air
parcel changes volume as the ambient temperature and pressure change. This means that
the absolute humidity changes when the volume changes. How do you conveniently
measure the mass and the volume?
Specific humidity (q, gH2O/kg-moist air)
This is the vapor content of the air using the mass of the water vapor for a given mass of air.
The kilogram of air measured includes the water vapor present. Unlike absolute humidity,
specific humidity doesn't change as the air parcel expands or is compressed.
Mixing ratio (w, gH2O/kg-dry air)
This measures the mass of water vapor for a given mass of dry air. Since water vapor
comprises only a small percentage of the mass of air, the values for specific humidity and
mixing ratio are very close for a given parcel of air. Mixing ratio is not affected by changes in
pressure and temperature. This is a commonly used measure by meteorologists.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 7
Collect & evaluate meteorological data
Study Module 6
Vapor pressure (e, hPa)
As mentioned in earlier discussions, vapor pressure measures the water vapor content of
the air using the partial pressure of the water vapor in the air. The gases in the atmosphere
exert a certain amount of pressure which we call atmospheric pressure, the average of
which is 1013.25 hPa. Since water vapor is one of the gases in air, it contributes to the total
air pressure, but is obviously variable. The contribution by water vapor is rather small, since
water vapor only makes up a few percent of the total mass of a parcel of air.
Saturation
The term saturation refers to the mass of water vapour per unit mass of air (including the
water vapour). It is another measure of the actual water vapour content of the air, except
that it describes the point at which no more water vapor can exist in the air without
condensing out to form water droplets.
Saturated vapour pressure
The actual water vapour pressure when the air is saturated.
Relative humidity (RH, %)
The term most frequently used to express the amount of moisture in the air is relative
humidity (RH). The relative humidity is the ratio of the actual amount of water vapour in a
sample of air compared to the total amount of water vapour the same sample can hold
before condensation begins (i.e., it becomes saturated with water vapour) at a given
temperature and pressure, but RH only gives us a relative sense of the amount of moisture
in the air, not the actual amount.
How do we measure humidity?
Psychrometer (Wet bulb / dry bulb)
This is a very traditional way of finding the relative humidity. It is very simple, and
reasonably accurate. Two liquid in glass thermometers are used in this technique where one
is dry and measures the ambient (or dry) temperature of the air and the other has a cloth
material (can be glass fibre, muslin or cotton etc) wrapped around the glass bulb that
houses the liquid (alcohol or mercury) that is moistened with water (not saturated). The dry
thermometer measures the dry temperature (T) and the wet thermometer measures the
wet bulb temperature (Tw) in whatever units the thermometers are scaled in.
There are two common varieties of the technique. The most common for the layman is the
wall mounted type where the two thermometers are positioned in a housing mounted on a
wall with the wet bulb material connected via a wick to a store of water. The other type is
called a sling psychrometer and is the same as for the wall mounted type, except it is
designed to be twirled around in the air for a few minutes which ensures the liquid levels in
the thermometer are not falsely positive, and enhances a maximum evaporation rate,
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 8
Collect & evaluate meteorological data
Study Module 6
leading to a ‘truer’ value than the wall mounted type which is prone to variable evaporation
rates due to variable wind speed.
Psychrometers work by determining the wet bulb depression, which is simply the difference
between the dry bulb and wet bulb temperatures. It is called a depression, because the wet
bulb temperature will always be cooler than the dry bulb temperature if there is moisture in
the air (if the air is saturated with water vapor, then both thermometers will read the same
temperature). Why is it cooler? Because of the latent and sensible heat used up in the
evaporation of the water (which changes from a liquid to a gas), thus lowering the
temperature as a result.
Figure 6.6 – Left - Simple psychrometer [source]. Right - Sling psychrometer. [source]
Once you have established the wet bulb depression value (T – Tw), you then look up a
psychometric table (or humidity table, Appendix A or MetExplore spreadsheet) where you
will find the dry bulb temperature in the rows and the wet bulb depression in the columns.
The value that you arrive at is the relative humidity. It is that simple!
Hair Hygrometer
These things sound a little bit disturbing at first, but are actually quite ingenious. It turns out
that hair – yes the stuff on your head (actually horse hair) - gets longer and shorter
depending on the humidity, and this can be used to measure it by attaching a calibrated hair
system to a needle or pen which writes against a scaled paper roll– in much the same way
that the mechanical barometer works in the barograph – and produce a hydrograph, or a
continuous plot of humidity.
Figure 6.7 – Hair hydrograph showing the use of hair connected to a mechanical drum with scaled
paper and an ink trace recording the change in humidity over time. [source]
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 9
Collect & evaluate meteorological data
Study Module 6
Transducers
This is the modern day ‘small black magic box’ approach where electronics perform all the
work. Transducers simply (in a very complex manner) transform one measured (or sensed)
parameter, in this case water vapour, into an electrical signal, which is then turned into the
relative humidity reading (or other reading) by calculation.
This is the most common form of measuring technique for humidity in met stations today as
they allow for continuous measurements and do not require personnel to monitor.
Figure 6.8 – Modern solid state humidity transducer (as with most modern day equipment it is an
unimpressive ‘small black magic box’. http://customer.honeywell.com
Remote Sensing
Satellites can use infrared technology to view the humidity of the Earth from space. See
image below;
Figure 6.9 – Example of a remote sensing image. Atmospheric water vapour from NOAA/NASA.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 10
Collect & evaluate meteorological data
Study Module 6
Calculated values
Humidity and water vapour information can be calculated from a variety of sources, but it is
usually from Dewpoint temperature readings taken from condenser mirrors (which you
don’t need to worry about).
Rainfall
The concept of rainfall seems pretty simple at first, but there are certain aspects of it that
can cause confusion. Meteorological stations measure rate of rainfall, as in mm/hr, and this
information is related against other values (typically in software) to give hydrological
estimates of floods and other information pertinent to users.
Rain gauge
The standard rain gauge works by providing a wide mouthed vessel which collects rain as it
falls and directs the rain to a measuring cylinder which has been specifically calibrated to
report the level of rain in millimetres of water. The disadvantages of this technique is that it
does not provide information about the rate of rainfall (only on a per day basis unless you
observe it over a different time period). Also, it needs to be manually emptied and read
each day by an observer. The advantage is that rain gauges do deliver a very accurate
measure of the amount for rainfall that has fallen in one day.
Figure 6.10 – Typical rain gauge used to monitor rainfall.
Generally speaking, these older style rain gauges are not to be used for regulatory
monitoring and as such are not used in any standard. As a side note, the manufacture of
these gauges requires a very simple formula to calibrate the opening size to the measured
volume which is simply a ratio of 10:1. The area of the funnel will always be 10 times greater
than the cross sectional area of the measuring cylinder. This means that the volume
collected is ‘magnified’ by ten, and that the true volume is one tenth of the actual volume
collected.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 11
Collect & evaluate meteorological data
Study Module 6
Tipping bucket gauge
This is currently the most popular choice for compliance monitoring situations and is the
main consideration of the Australian Standard and other regulatory documents.
With reference to the image below, the tipping bucket gauge uses two small buckets which
receive rain conducted through the rain collector. The two small measuring buckets are on a
pivot, so that one bucket is always raised to collect rain, and when it fills up it tips over and
expels the rain water to a drain. The tipping process raises the other measuring bucket into
the receiving position which fills and empties and the process repeats endlessly. Each time
the measuring buckets tip, a magnet activates a reed switch which registers a tipping event
on the computer and an exact amount of rainfall is recorded.
Figure 6.11 – Typical tipping bucket rain gauge. The tipper buckets are the two silver scoops. This
model has a USB data logger to collect data. The black rain collector sits over the whole tipper.
The advantages of this type of instrument is that they are accurate and can record the rate
of rainfall over a variety of time frames. The disadvantage is the requirement for power to
run the process (typically solar though), the mechanical parts which can break, and the poor
precision involved as it can only count volume to the nearest tipped bucket.
The tipping bucket is the method most commonly employed, but there are other methods
for detecting rain including;
◗ Capacitance or pressure transducers,
◗ Optical and acoustic sensors, and
◗ Radar based technology
If your workplace uses these types of devices, then your focus should be on learning these.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 12
Collect & evaluate meteorological data
Study Module 6
Atmospheric Pressure
What is pressure?
The concept of atmospheric pressure is often a hard one to grasp but it is simply defined as
force (F) per unit of area (A), i.e., P=F/A, unfortunately, it is difficult to think of the
atmosphere as having mass because we generally do not notice its weight pressing on our
body.
Pressure is not only due to the mass of the molecules, but also the motion of the molecules
bombarding our body. If you want to feel how much pressure your body is actually under
from the force of the atmosphere, simply go to a diving pool and touch the bottom. Being
ten meters under water applies the equivalent pressure as one atmosphere!
What pressure measurements and units are there?
Although pressure can be difficult to sense, the measurements are very easy. Atmospheric
pressure is measured as both the true pressure, and as corrected to a ‘standard’ pressure.
Standard Pressure
The standard for pressure is called sea level (or more accurately, the Mean Sea Level
Pressure (MSLP), and has a value of 101.325 kPa. But what is sea level? It is the average
height (or imaginary line) of the ocean measured over about 2 years for a specific place (see
the navigation unit for a full explanation).
True/real/actual pressure
This is simply a raw pressure reading at any point or altitude prior to the value being
corrected to the MSLP (if it is corrected at all). This is what you will measure if you use an
aneroid or mercury barometer, as most modern instruments will use an algorithm to
correct, unless they offer both raw and corrected readings.
The unit problem
The problem with pressure is not the number of measures that are available; it is with the
number of units that have been invented, so we shall provide a comprehensive overview of
atmospheric pressure units here that will help you ‘cope’ with the ‘problem’.
The international system of units (SI) stipulates that the standard unit of pressure is the
Pascal (Pa), which is called a derived unit, as the Pascal exhibits the base units of kg/ms2, or
Newtons/m2. The use of the Pascal leads to large cumbersome numbers, so we often
employ the use of a metric prefix such as kilo (kPa) or hecto (hPa). Other units of pressure
include;
◗ mmHg (Torr)
◗ atmosphere
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 13
Collect & evaluate meteorological data
Study Module 6
◗ bar
◗ psi
◗ dyne/cm2
Unit Conversions
If you ever need to convert between units, then tables such as the one below from the SI
Chemical Data Handbook are invaluable tools to get the job done. Your teacher will explain
to you how to use it. These days, most search engines have converters (such as Google).
Pascal
atm
mmHg
bar
dyne/cm2
psi
1
9.87x10-6
7.5x10-3
10-5
10
1.45x10-4
1.013x105
1
760
1.013
1.013x106
14.7
133.3
1.32x10-3
1
1.33x10-3
1333
1.93x10-2
bar
105
0.9869
750.1
1
106
14.5
dyne/cm2
10-1
9.87x10-7
7.5x10-4
10-6
1
1.45x10-5
psi
6895
6.8x10-2
51.71
6.89x10-2
6.89x104
1
Pascal
atm
mmHg
Table 6.1 – Pressure unit conversion table. To convert, find the unit you want to convert from in the
left column, and multiply your value by the conversion factor in the corresponding row.
How do we measure atmospheric pressure?
Pressure at the surface and aloft is measured with a barometer. While there are many types
of barometers, the most commonly used barometers for meteorological purposes are the
aneroid and mercury barometers, but there are many others. Pressure measurements at
higher altitudes (such as on a plane or weather balloon can be measured with either a
barometer, transducer or via a simple mechanical ‘Pitot tube’ set up which measures
pressure by comparing the static and absolute pressure.
A simple water barometer
History suggests that the first barometer was invented by Evangelista Torricelli (whom the
pressure unit Torr is named after). This invention was water based vessel with a narrow
spout, and as the atmospheric pressure changed, the water in the narrow spout moved up
and down, indicating high and low pressure. From this simple device, the prediction of
stormy weather could be made, and hence such devices were known as ‘storm’ or ‘thunder’
glasses. These are no more than home decorations these days, but do provide an
opportunity for students to make their own barometer using a beaker filled with coloured
water and a capillary tube!
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 14
Collect & evaluate meteorological data
Study Module 6
The mercury barometer
A properly calibrated mercury barometer is extremely accurate. These barometers consist
of a glass tube filled with liquid mercury and closed on one end. The tube stands on end
with the closed end up and the open end submerged in a reservoir of mercury that is
exposed to the air. As the air pressure rises, it pushes on the liquid in the reservoir. The level
of the mercury rises in the glass tube to compensate for the additional pressure exerted on
the exposed reservoir.
Figure 6.12– Mercury barometer. Not shown is the scale from which the pressure is read in mmHg. A
properly calibrated mercury barometer is very accurate, but must be corrected for temperature and
latitude
The aneroid barometer
An aneroid barometer is a mechanical device which used a specially constructed chamber
that is partially evacuated. As the atmospheric pressure changes, it either ‘pushes’ or ‘pulls’
the wall of the chamber which is connected to a needle and scale, thus providing a measure
of pressure. They are calibrated against a known pressure and as such can be quite
accurate. Aneroid barometers needles can be connected to pens rather than scales, and
record changes in pressure over time, in which case the instrument is called a barograph.
Figure 6.13- The aneroid barometer consists of a closed capsule with flexible sides. Any change in
pressure alters the thickness of the capsule. Levers magnify these changes and cause a pointer to
move on a dial, or numbers to change on a digital readout.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 15
Collect & evaluate meteorological data
Study Module 6
Modern instruments…
In this day and age, there have been several instruments made in order to acquire accurate
pressure reading which need to meet modern requirements such as wireless recording and
electronic data storage. These devices are varied and the transducers are complex in design
and as with the humidity transducers, are visually disappointing, and often appearing as
little black boxes hidden away inside a casing. You will often need to refer to the
manufacturer’s handbook to find out exactly how your modern barometer will work.
What pressure values do we expect to find?
To answer this you must remember the how pressure changes around the Earth, with
temperature and with altitude. Other considerations include corrected pressures and raw
data. The lowest ever recorded mean sea level pressure (MSLP) was 870 hPa during
Typhoon Tip and the highest value is about 1080 hPa (debatable), which is an approximate
variation of 210 hPa. Standard pressure also changes with altitude where the average MSLP
= 1013.25 hPa, whereas on top of Mount Everest it is approximately 320 hPa.
In Australia, the pressure variation will obviously not be as dramatic, but we are not far off
these extremes. Our highest mainland peak is ‘hill’ Kosciusko at a meagre 2228 meters,
where the pressure is approximately 780 hPa.
Wind Measurements
What is wind?
Wind is the horizontal movement of air which results from the presence of a pressure
gradient and creation of the horizontal pressure gradient force between areas of high and
low pressure. The pressure differences results from the heating of the Earth from the Sun
which creates convective lifting or air, creating a low pressure system relative to the air
around it. This process starts a chain reaction of high and low pressure systems which occur
on all the scales from global to micro – the result of which is wind.
What wind measurements and units are there?
Measurements
Two important measurements of the wind are the direction and speed of the wind.
Wind speed obviously refers to the velocity of wind. Wind direction obviously refers to the
direction in which the wind is blowing, but is not given in reference to the direction in which
they are blowing, but rather the direction from which the wind comes from. A westerly wind
blows from west to east. A northerly wind blows from north to south.
Units of measure
Wind direction is obviously measured via either compass points (i.e. North, South etcetera)
or by degrees bearing (i.e. 335°N).
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 16
Collect & evaluate meteorological data
Study Module 6
Wind speed on the other hand has a variety of units that can be employed, the most
important being the SI derived unit, which is m/s or other metric prefix such as km/hr. Other
common units include;
◗ Miles per hour (mph)
◗ Knots (nautical miles per hour)
◗ Unit conversions
◗ 1 m/s = 3.6 km/h
◗ 1 mph = 1.609 km/h
◗ 1 knot = 1.852 km/h = 0.514 ms-1
How do we measure wind?
Wind speeds and directions at the surface and aloft help meteorologists to predict where
and how fast weather systems will move and pollutants will be transported. The most
common way to measure the wind direction and speed at the earth's surface is with wind
cups and vanes. The vane gives the direction (in conjunction with a compass of some sort)
while the cup catches the wind and rotates giving an indication of speed. Any device that
measures the wind speed is called an anemometer, of which there are many types. There
are many types of anemometer available;
◗ Cup
◗ Windmill
◗ Hot wire
◗ Sonic
◗ Laser Doppler
◗ Even a manometer can be used
and even measure winds. Satellites can collect, compile, and transmit data from remote
surface stations making data collection and organization an easier task.
Figure 6.14 – Typical commercial style wind cup anemometer and vane.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 17
Collect & evaluate meteorological data
Study Module 6
Solar measurements
Solar measurements measure specific aspects of the Sun’s energy. The two most common
are Solar Flux and Ultra-violet (UV) radiation intensity.
The information from solar measures can be used for a variety of reasons, and with the
advent (or requirement) of sustainability measuring, the need has increased ‘exponentially’.
Solar flux
You may remember from chapter/study module 2 that sunlight is energy. The energy from
the Sun comes in the form of electromagnetic radiation which is best expressed to you in
the form of a Planck Curve, as seen below;
Figure 6.15 – Planck Curves for Earth’s atmosphere. Red line is theoretical, blue is observed at top of
atmosphere. Green is observed at Earth’s surface. The green line represents the energy available to
the Earth. From Planck’s-curve.xlsx interactive spreadsheet.
The term flux refers to the rate of flow of energy per unit area (m2), and for us the standard
unit is Watt’s per meter squared; W/m2 or W.m-2, where a Watt is 1 Joule per second (J/s or
J.s-1).
It is the unit of W.m-2 that is specified in the Australian Standard AS 3580.14 – 2011
Methods for sampling and analysis of Ambient Air – Meteorological Monitoring for Ambient
Air Quality Monitoring Applications.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 18
Collect & evaluate meteorological data
Study Module 6
Solar flux sensor
Most solar flux sensors are transducers in the form of a silicon photovoltaic detector (a
simple solar panel to you and I) which takes the light energy and transforms it into an
electric signal which gives a value on the display. Solar flux sensors can have filters to
exclude various parts of the electromagnetic spectrum, but are usually unfiltered to count
all of the Sun’s energy. From sunrise to sunset, the angle of the light that hits the sensor will
vary, so all of these types of sensor have a built in correction to allow for that (called a
‘cosine correction’).
Figure 6.16 – Example of a solar flux sensor. Only the opaque acrylic diffuser (little white disk)
receives light for the sensor. [source]
Ultraviolet radiation
Ultraviolet radiation is part of the electromagnetic spectrum that ranges from about 10 nm
to approximately 350-400 nm. the UV spectrum is almost split in half, with half being of such
high energy (10 to 120 nm) that it is calle1,mk4d ‘ionising radiation’ as it can ionise gaseous
atoms such as nitrogen and oxygen, whereas the other half (120 to 350 nm) is non-ionising.
Although only half of the UV light spectrum is considered ionising radiation, all UV light can
be considered as biologically ionising radiation as all UV light has enough energy to alter
some key biochemical molecules.
Ultraviolet light is measured due to the harm it can cause humans through skin damage, and
many countries including Australia report the strength of UV intensity through common and
social media by using arithmetically manipulated values of UV light intensity called indexes
(or indices).
UV Sensors
UV radiation sensors are typically solar flux sensors that have been filtered to ensure that
only certain parts of the spectrum get through to the detector.
UV is not part of the Australian Standard for ambient air but is becoming an important
parameter for WHS monitoring reasons.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 19
Collect & evaluate meteorological data
Study Module 6
Where and How We Take Measurements
While the parameters we have discussed so far can be directly measured, there are many
others that can be used such as solar flux, UV intensity, rainfall, and snow depth to name a
few. Furthermore, we can calculate even more parameters from the few mentioned which
provide us with even greater detail of the atmosphere.
In order to map the atmosphere we need measurements at many points along the surface
and at different heights in the atmosphere. The remainder of this session will focus on
where we take our measurements and the technology we use to get them.
What ‘meteorologists’ measure
The BoM use staff and volunteers to gather data from all of Australia and its territories so
that it can produce the forecasts that it delivers. This requires a substantive network of
communication gathering, even with today’s modern equipment. While it is simple enough
to obtain data from the surface, it is a bit more difficult to get readings from high up in the
atmosphere.
Surface measurements
A weather station is a facility with instruments and equipment to make observations of
atmospheric conditions in order to provide information to make weather forecasts and to
study the weather and climate. The measurements taken include temperature, barometric
pressure, humidity, wind speed, wind direction, and precipitation amounts. Wind
measurements are taken as free of other obstructions as possible, while temperature and
humidity measurements are kept free from direct solar radiation, or insolation. Manual
observations are taken at least once daily, while automated observations are taken at least
once an hour.
Figure 6.17 – Example of a typical surface (2 m) meteorological data collection station. This particular
model is both wireless and portable so it can be used in multiple locations for compliance monitoring
purposes.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 20
Collect & evaluate meteorological data
Study Module 6
Automated weather stations are also frequently used to gather data remotely. These consist
of metal masts which can be 2, 10 or 30 meters tall. Attached to the masts are all of the
required sensors, as well as solar panels to provide a source of electricity and well as
telephony and data storage.
Higher altitude measurements
Planes and weather balloons are used to make high altitude measurements, however,
planes are limited in the heights they can fly. Commercial planes fly at heights of around
10000 meters, and meteorologists require readings as high up as 30 km, especially if they
are looking at ozone levels.
A weather balloon is a helium (or hydrogen) filled balloon used to provide vertical profiles of
the atmosphere (and make Americans believe in UFO’s).
Figure 6.18 – Deployment of a weather balloon showing the major components.
The balloon is just the vehicle, attached to the balloon is a device called a radio sonde,
which is group of small black magic boxes that act as a mobile weather station and take
measurements (including temperature, pressure humidity and so on) which are transmitted
data back to receivers on the ground at pre-determined time intervals.
The BoM uses its own radar system to track the radio sonde’s position so that wind speeds
and directions can be determined as well as the height of the balloon for each measurement
taken. A computer takes this data and constructs a profile of the atmosphere for each
location at which a balloon is released
Ground Based Remote Sensing Devices
You would be very familiar with the concept of weather radar images. Radar, which stands
for Radio Detection and Ranging, is the most common of several ground based remote
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 21
Collect & evaluate meteorological data
Study Module 6
sensing profiling techniques in use today. Ground based devices are categorized by the
wavelength of the electromagnetic signal they emit. Radars emit a signal in the radio
frequency but there are many more ground based devises including;
◗ Sodar (Sound Detection and Ranging) devices, emit signal in the audible spectrum.
◗ Lidar (Light Detection and Ranging) devices emit signals of visible wavelengths.
The BoM has several radar stations which it uses to monitor the weather;
Satellites
While radar technology can provide us with a view of a localized cross section of the
atmosphere, satellites in orbit above the earth can beam down photos of the entire globe.
Satellites have become an invaluable tool for forecasting the weather. Not only can
satellites take photographs, they also function as sensing devices. Satellites can measure
radiation from the earth's surface and atmosphere which can help us make determinations
about the earth-atmosphere heat budget.
Figure 6.19 - The BoM’s radar system covers the major population centres of Australia with two major
types of radar (with most moving towards being Doppler image collectors).
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 22
Collect & evaluate meteorological data
Study Module 6
Assessment Task
After reading the theory above, answer the questions below. Note that;

Marks are allocated to each question.

Keep answers to short paragraphs only, no essays.

Make sure you have access to the references (last page)

If a question is not referenced, use the supplied notes for answers
Complete the following table of important terms. 0 mk
Term
Definition
Ambient air
Type your answer here.
Direct / derived measures
Type your answer here.
Dry/wet bulb temperatures Type your answer here.
Dewpoint temperature
Type your answer here.
Mixing ratio
Type your answer here.
Relative humidity
Type your answer here.
Saturation
Type your answer here.
Psychrometer
Type your answer here.
Hygrometer
Type your answer here.
Transducer
Type your answer here.
Barometer
Type your answer here.
Remote sensing
Type your answer here.
Anemometer
Type your answer here.
Radiosonde
Type your answer here.
Meteorological station
Type your answer here.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 23
Collect & evaluate meteorological data
Study Module 6
Answer the following questions
a) List and describe the three common types of thermometer. 6 mk
Type your answer here
Leave blank for assessor feedback
b) Which type of these thermometers are used in modern met stations. 1 mk.
Type your answer here
Leave blank for assessor feedback
c) What is the most reportable unit used for temperature for met work? 1 mk
Type your answer here
Leave blank for assessor feedback
d) Describe humidity and water vapour in general. 2 mk
Type your answer here
Leave blank for assessor feedback
e) What is the most common measure of humidity? 1 mk
Type your answer here
Leave blank for assessor feedback
f) How is it measured in modern met stations? 1 mk
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 24
Collect & evaluate meteorological data
Study Module 6
Type your answer here
Leave blank for assessor feedback
g) In which unit is relative humidity reported? 1 mk
Type your answer here
Leave blank for assessor feedback
h) How is the unit of relative humidity derived (what is it a ratio of)? 3 mk
Type your answer here
Leave blank for assessor feedback
i) Define ‘rainfall rate’. 2 mk
Type your answer here
Leave blank for assessor feedback
j) By what technique is the rainfall volume and rate most commonly measured on modern
met stations? 2 mk
Type your answer here
Leave blank for assessor feedback
k) State one advantage and one disadvantage of a tipping rain bucket. 2 mk
Type your answer here
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 25
Collect & evaluate meteorological data
Study Module 6
Leave blank for assessor feedback
l) Define the likely range of pressure values in Australia both vertically and horizontally. 2
mk
Type your answer here
Leave blank for assessor feedback
m) A wind vane has a flat blade on one end, and a pointy weight on the other. Which end
faces the wind, and what information is it telling us? 3 mk
Type your answer here
Leave blank for assessor feedback
n) What is the most common technique for measuring wind speed? 1 mk
Type your answer here
Leave blank for assessor feedback
o) What is the most common reportable unit for wind speed in Australia? 1 mk
Type your answer here
Leave blank for assessor feedback
p) Define the term ‘solar flux’. 2 mk
Type your answer here
Leave blank for assessor feedback
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 26
Collect & evaluate meteorological data
Study Module 6
q) What is the most common unit of measure for solar flux in Australia? 1 mk
Type your answer here
Leave blank for assessor feedback
r) Briefly describe how a solar flux sensor works. 2 mk
Type your answer here
Leave blank for assessor feedback
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 27
Collect & evaluate meteorological data
Study Module 6
Assessment & submission rules
Answers
◗ Attempt all questions and tasks
◗ Write answers in the text-fields provided
Submission
◗ Use the documents ‘Save As…’ function to save the document to your computer using
the file name format of;
name-classcode-assessmentname
Note that class code and assessment code are on Page 1 of this document.
◗ email the document back to your teacher
Penalties
◗ If this assessment task is received greater than seven (7) days after the due date (located
on the cover page), it may not be considered for marking without justification.
Results
◗ Your submitted work will be returned to you within 3 weeks of submission by email fully
graded with feedback.
◗ You have the right to appeal your results within 3 weeks of receipt of the marked work.
Problems?
If you are having study related or technical problems with this document, make sure you
contact your assessor at the earliest convenience to get the problem resolved. The name of
your assessor is located on Page 1, and the contact details can be found at;
www.cffet.net/env/contacts
Resources & references
References
Sturman, A.P, Tapper, N.J., (2000). The weather and climate of Australia and New Zealand.
Oxford University Press. Melbourne. Australia.
National Environment Protection (Ambient Air) Measure Technical Paper No. 6 –
Meteorological Measurements 2001
Australian Standard AS 3580.14 – 2011: Methods for sampling and analysis of ambient air.
Part 14: Meteorological monitoring for ambient air quality monitoring applications.
Standards Australia. SAI Global Limited.
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 28
Collect & evaluate meteorological data
Study Module 6
Further reading & online aids
www.bom.gov.au
http://www.desktopaero.com/appliedaero/appendices/stdatm.html
http://www.engineeringtoolbox.com/international-standard-atmosphere-d_985.html
http://www.aeromech.usyd.edu.au/aero/atmos/stdatm.html
http://www.bom.gov.au/info/ftweather/page_15.shtml
The following website was used for most calculations;
http://www.srh.noaa.gov/epz/wxcalc/formulas/
ISO 2533:1975
Hunter TAFE - Chemical, Forensic, Food & Environmental Technology [cffet.net]
Course Notes for delivery of MSS11 Sustainability Training Package
Page | 29