6 Atmospheric Measurements

Transcription

1 6 Atmospheric Measurements Introduction 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? 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. 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. 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 70

2 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 a 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 thermometeric procedure. Figure 6.1 Routine glass thermometer Infra-red detectors (and laser based equipment) use the properties of balckbody 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. a) b) Figure 6.3 a) Bi-metal mechanical thermometer. b) Thermocouple Electrical thermometers 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. 71

3 Figure 6.4 Thermocouple thermometer device 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 (T w ) 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 (T d ) was usually a derived temperature, but modern stations can employ a cooled mirror which directly measures the T d. Derived measures of temperature include; Dewpoint, as mentioned above has historically been determined mathematically. Virtual temperature (T v ) 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 (T p ) 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? Celcius scale ( C) The Celcius scale is (and was originally called) a centigrade scale, it was derived from Anders Celcius 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 leyman in most countries. You will notice in Figure 6.4 below that 0 K = 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 = 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 = C. Fahrenheit scale ( F) 72

4 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 F. You will notice in Figure 6.4 below that 0 K = C. The fahrenheit scale will not be used at all in these notes. 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 celcius to fahrenheit; 9 F = C To convert from fahrenheit to celcius 5 C = F 9 ( 32) To convert from celcius to kelvin; K = C To convert from Kelvin to Celcius; C = K To convert Kelvin to Fahrenheit; 9 F = K 5 ( ) + 32 To convert Fahrenheit to Kelvin; 5 K = F 9 ( 32) Celcius, Kelvin and Fahrenheit Scales

5 Figure 6.5 The sclaes of temperature from 0 K to 330K. Note that Fahrenheit and Celcius are the same at -40. Axis are both Kelvin. What 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). MOISTURE MEASUREMENTS (WATER VAPOR) 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!). What is Humidity? 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 (H a, g H2O /m 3 ) 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, g H2O /kg moistair ) 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, g H2O /kg dryair ) 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. 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 hpa. Since water vapor is one of the gases in air, it contributes to the total air 74

6 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 (T w ) 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, 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. 75

7 a) b) Figure 6.5 a) Simple psychrometer b) Sling psychrometer. Once you have established the wet bulb depression value (T T w ), you then look up a psychometric table (or humidity table) 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 - 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 6.6 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. 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. 76

8 Figure 6.7 Modern solid state humidity transducer (as with most modern day equipment it is an unimpressive small black magic box. Remote Sensing Satellites can use infrared technology to view the humidity of the Earth from space. See image below Calculated Usually from Dewpoint temperature readings 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 force as one atmosphere! What pressure measurements and units are there? Although pressure can be difficult to comprehend, the measurements are few are far between. Atmospheric pressure is measured as both the true pressure, and as corrected 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 kpa. But what is sea level? It is the average height (or imaginary line) of the ocean measured over about 19 years for a specific place. 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. 77

9 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/ms 2, or Newtons/m 2. 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 bar psi dyne/cm 2 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. pascal atm mmhg bar dyne/cm 2 psi Pascal x x x10-4 atm 1.013x x mmhg x x x10-2 bar dyne/cm x x x10-5 psi x x x 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 there own barometer using a beaker filled with coloured water and a capillary tube! 78

10 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 6.8 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 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. 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. 79

11 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 = 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). 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 = km/h 1 knot = km/h = ms-1 80

12 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 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. Automated weather stations are also freuqently used to gather data remotly. 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. 81

13 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 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). The balloon is just the vehicle, attached to the balloon is a device called a radiosonde, 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. a) b) Figure 6.10 a) The hydrogen filled balloon prior to launch, and b) the radiosonde (small black magic box) which takes the measurements. The BoM uses its own radar system to track the radiosonde'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 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. 82

14 The Newcastle radar has a range of 128 km and 256km (the user has a choice). 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 earthatmosphere heat budget. They can measure water vapour content in the air and even measure winds. Satellites can collect, compile, and transmit data from remote surface stations making data collection and organization an easier task. 83

15 WHAT ENVIRONMENTAL TECHNICIANS MEASURE As an environmental technician, you will be expected to perform the following tasks; Perform a checklist on the portable meteorological unit Undertake pre-site testing of all equipment Load and transport the equipment to site Set up equipment as per manufacturers instructions and appropriate standards Test on-site application of equipment (quality control) Set equipment to perform required tasks for set timeframe Perform post-application checks (quality control) Capture, record or load data from data logger to computer (or setup other technique) Pack up and transport equipment back to source. Transfer data to appropriate data storage device (data base or other) Perform simple data manipulations such as summary/descriptive statistics Provide simple reports based on summarised data. 84

16 So what does this unit that you will more than likely use look like? Outlined below is an image that would reflect a great many environmental met stations. Obviously, each individual application will determine what parameters are measured (air and noise studies may have different sensors to what is used for forecasting). In the picture below we are using basic weather sensors. 85

17 BEFORE USING THE EQUIPMENT You will need to become familiar with your equipment to ensure competency in the field where you may largely be unsupervised. Obviously you will receive some training on the equipment from a workplace mentor (or in our case, your teacher), but familiarisation of the equipment is an essential task to perform. The types of tasks you would perform prior to the field set up could include; Perform a checklist on the portable meteorological unit Checking to see if all of the equipment is accounted for Looking for obvious damage to casings, cables and other hardware Locating all user manuals, logbooks and manufacturer s literature Undertake pre-site testing of all equipment Determining power supplies are operational or suitable for use on site. Performing diagnostic tests for each sensor and data handling / storage devices Some quality procedures (if any) may be incorporated at this point Powering down all equipment ready for transportation and use Load and transport the equipment to site Using appropriate packaging to safely store the equipment for transport Performing checklists These tasks would involve not much more than following the manufacturer s instructions (which will vary according to each manufacturer). ONSITE USE OF THE MET STATION Once onsite, you will need to set up the equipment in accordance with the manufacturer s specifications and all appropriate standards. This requires some amount of double checking to ensure everything will work fine while when you are absent. Set up equipment as per manufacturers instructions and appropriate standards Checking that the site location is accurate is the first step Unpacking equipment Setting up the met station and attaching sensors, loggers etcetera Ensuring stability of equipment for duration of test Test on-site application of equipment (quality control) You may be required to perform some quality control testing of the equipment Testing any telecommunications, logger or wireless connection Testing power supplies Set equipment to perform required tasks for set timeframe Start up all equipment to run for the required timeframe as per manual 86

18 Perform post-application checks (quality control) Once the equipment has run its course, you need to stop the operation and perform any required testing of data capture or sensor operation May require testing power supply is still functional Capture, record or load data from data logger to computer (or setup other technique) May require immediate transfer of data to computer drives or elsewhere POST-SITE MAINTENANCE OF MET STATION Once the measurements are all performed, we can pack up and prepare for another job. Tasks associated with this stage could include; Pack up and transport equipment back to source. This is simply the reverse of the unpacking procedure Transfer data to appropriate data storage device (data base or other) The data transfer may occur at this stage Perform simple data manipulations such as summary/descriptive statistics Once the data is on a useful computer, statistical analysis or summarising can occur including averages, standard deviations and other descriptive statistical analysis. Provide simple reports based on summarised data. If you are truly unlucky, your employer (or teacher) may make you write a report other such document using the data you summarised earlier. IN CONCLUSION Although the tasks sound many, varied and potentially complex (especially when stated in the expanded bullet points you read above), meteorological stations are surprisingly simple things to setup and operate. In this age of really impressive gadgetry, it won t be long before all met stations simply unfold like plastic Christmas trees, and all you have to do is plant it in the ground! It was mentioned in the introduction that this chapter contained the nuts and bolts of meteorology for environmental technicians. This can not be stated clearly enough, but as usual, you will need to incorporate the skills and knowledge from other units in order to be truly competent. For example, the navigation unit will provide you with the skills to get you to your location, the OH&S unit will make sure you do things safely, and many other units will contribute to the overall success in the field of meteorology! 87

19 What you need WHAT YOU NEED TO BE ABLE TO DO List and describe the commonly measured meteorological parameters List and describe the equipment used to measure defined parameters Use and convert commonly applied units of measure Understand the expected values for the purposes of problem solving and quality Understand what can go wrong with the measures (calibration, calibration!) Check, set up, use and maintain standard meteorological equipment Acquire and analyse meteorological data REFERENCES 1. Sturman, A.P, Tapper, N.J., (2000). The weather and climate of Australia and New Zealand. Oxford University Press. Melbourne. Australia was used for most calculations 3. ISO 2533: National Environment Protection (Ambient Air) Measure Technical Paper No. 6 Meteorological Measurements FURTHER READING & ONLINE LEARNING AIDS The MetExplore spreadsheet contains a full set of interactive computations under the Ch6 tab 88

20 IMPORTANT TERMS Regulation / legislation Ambient air Direct / derived measures Dry / wet bulb temperatures Dewpoint temperature Mixing ratio Relative humidity Saturation Psychrometer Hygrometer Transducer Barometer Wet bulb depression Remote sensing Anemometer Radiosonde Meteorological station 89

21 REVISION QUESTIONS 1. Why is environmental legislation and regulation important to environmental technicians? 2. List and describe the common measures of the atmosphere 3. What is meant by the term ambient air? 4. How do we measure temperature? 5. How do we measure water vapor? 6. How can we measure atmospheric pressure? 7. How do we measure wind speed and direction? 8. How do meteorologists perform the measures from above at high altitudes? 90