GPS Protocol
Contents
1. me me DEL 06 mm 0 0 08 008 D D O12 08L deja uoneun3q JHSUSEIA DUOM EECH GPS Protocols 5 GLOBE 2003 GLOBE 2003 Protocols 6 GPS Compass True North The magnetic needle in a compass is attracted by the magnetism of the Earth and that is why it always points North However there are really two North Poles on the Earth One is the True North Pole which is located geographically at the top of the earth at 90 North latitude and the other is the Magnetic North Pole an area of highly magnetic rock under central Canada Maps and directions are based on True North while the compass needle points to Magnetic North Magnetic declination is the angle between True North and Magnetic North lts size and direction depends on where you are on the Earth It is necessary to determine the declination to take accurate compass bearings Compasses either have a mechanism to set the angle of declination or a scale to determine declination Because compasses are attracted to metal objects they will give incorrect readings if the user is close to or wearing metal objects including watches keys etc Three Basic Parts of the Compass 1 The magnetic needle See A in the Figure GPS P 5 is attracted by the magnetic North Pole of the earth The magnetic end red always points to magnetic north 2 The graduated dial B is used to set the desired bearing The bearing is read in degrees at t2. gravitational field is known as the geoid This surface is not smooth because of the irregular distribution of Earth gravity field GPS receivers must also use a reference for determining elevation Unfortunately the geoid is very complicated and too large to fit in the internal memory of most GPS receivers Instead they contain a simplified shape for a smooth surface known as the reference ellipsoid All GPS elevation measurements are made against the reference ellipsoid See Figure GPS P 3 While the geoid and reference ellipsoid may overlap in some areas in others they may differ by more than 100 meters Because of this the elevation of your location measured with a GPS receiver may be significantly different from the elevation determined by other methods for example topographic maps The GLOBE server will automatically make the geoid correction to your elevation once you have entered your GPS measurements for latitude longitude and elevation for your site Magnetic Variation On Earth the magnetic North and South poles do not line up exactly with the true North and South poles along our planets rotation axis Earth s magnetic north pole is slowly moving and is currently located in Canada s Northwest Territories about 11 degrees from the North Pole Additionally the magnetic properties of Earths composition vary slightly among locations As a result there is a unique distortion to Earth s magnetic field at any give
3. Average all five latitudes longitudes and elevations 8 Confirm for yourself that your results make sense You should be able to get a rough estimate of your latitude and longitude by looking at a globe or local map 9 Copy and submit all GPS readings as your site location to the GLOBE Student Data Archive 10 Follow this protocol at each site you need to determine its latitude longitude and elevation GLOBE 2003 Protocols 9 GPS Offset GPS Protocol Field Guide Task Measure the latitude and longitude of your school or a GLOBE study site when a GPS receiver is unable to make an accurate measurement What You Need O GPS receiver O Watch O Magnetic compass O Pencil or pen O Tape measure O Offset GPS Data Work Sheet In the Field 1 Determine the direction of true North at your location using Figure GPS P 4 Go to your desired site and mark it with a flag or other obvious marker Follow the GPS Field Guide to confirm that good GPS reception is not possible Sum Use the compass to determine true North Move either North or South to reach the nearest open area in which you can successfully follow the GPS Field Guide This is your offset location 6 Follow the GPS Field Guide and record your latitude and longitude Mark this as the offset location 7 Record whether the offset location is North or South of your site 8 Measure the distance between the offset location and your site in meters and record it on th
4. convert the latitude and longitude readings to decimal degrees before reporting them to GLOBE To do so use the formula and follow the example given below R Ir Converting from Degrees and Decimal Minutes to Decimal Degrees 1 degree 60 minutes Reading in decimal degrees degrees decimal minutes 60 minutes degree Example A latitude reading is given as 15 degrees and 39 03 minutes N Latitude in decimal degrees 15 degrees 39 03 minutes 60 minutes degree 15 degrees 0 6505 degrees 15 6505 degrees Site GPS Measurement Location School Main entrance Atmosphere study site Instrument shelter location Hydrology study site Surface water sampling location Soil study sites Soil Characterization site Soil Moisture site Soil profile location Soil Temperature Center of the soil moisture star pattern Soil Moisture or Atmosphere site locations ya Land Cover sample sites Center of 90 m x 90 m homogeneous area Phenology Location of the tree shrub or one meter square grass area used for the Green Up and Green Down measurements Some GLOBE study sites should provide clear views of the sky and thus good satellite reception e g Q the Offset GPS Protocol Field Guide Atmosphere study site Others especially the Land Cover and Phenology sites may offer poor GPS reception due to heavy canopy cover The school location is to be determi
5. latitude At any location it is also possible to further specify ones position by measuring the elevation or height of the location above or below the average sea level By reporting their latitude longitude and elevation each GLOBE school may be individually located For you the GLOBE student the hand held GPS receiver provides a simple and accurate way to measure your latitude longitude and when corrected elevation These instruments are sufficiently accurate to distinguish the two ends ofa classroom or to determine your location well within an area the size of a single pixel 30 m X 30 m of a LandSat image Besides the location GPS instruments also provide the time as well as additional measurements such as the speed of travel between two points and distance and direction between any two locations Insights into the GPS system as a whole provide an understanding of the measurements it produces and howa simple measurement relies on a sophisticated science and technology infrastructure Offset What if you cannot make a GPS latitude and longitude measurement at a study or sample site because the GPS satellite signals are obscured by thick foliage or a building See Figure GPS P 2 You can move from your site to a nearby location where the GPS receiver can receive the satellite signals This is known as an offset location You can then determine the location of your desired site by measuring the compass direction and distance be
6. GPS Measurement Protocol Purpose To determine the latitude longitude and elevation of your school and of all your GLOBE sites Overview The GPS receiver will be used to determine the latitude longitude and elevation of your school or of your GLOBE sites Student Outcomes Science Concepts Earth and Space Sciences Earth materials have different physical properties magnetism Physical Science Position of an object can be described by locating it relative to another object Materials have measurable properties magnetism Magnets attract and repel each other Geography Tools and technologies have distinct characteristics and capabilities Use appropriate geographic tools Latitude and longitude may be displayed on maps Scientific Inquiry Abilities Using a GPS receiver to determine latitude and longitude Using a compass to determine true north and south Identify answerable questions Design and conduct scientific investigations Use appropriate mathematics to analyze data Time 15 minutes to 60 minutes per site Level DI Frequency Once per site Materials and Tools GPS receiver Magnetic compass Tape measure Pencil or pen GPS Protocol Data Sheet Offset GPS Work Sheet Preparation Determine locations to be visited Bring GPS unit data sheets and pen or pencil to field sites Identify sites where GPS location measurement is not possible because the signal is blocked For there sites compass measu
7. e Offset GPS Data Work Sheet 9 Divide this distance by 0 0011 meters per degree to determine the latitude difference in ten thousandths of a degree between the offset location and your site 10 Depending on the direction of your offset location Ifyou moved to the north of your site subtract this value from the latitude of the offset location to determine the latitude of your site Ifmoved to the south of your site add this value to the latitude of the offset location to determine the latitude of your site 11 The longitude of your site is the same as that of the offset location 12 Determine the elevation of your site by using a topographic map GLOBE 2003 Protocols 10 GPS Frequently Asked Questions 1 How long does it take for a GPS receiver to determine latitude longitude and elevation The GPS receiver may require anywhere from several seconds to several minutes to acquire a sufficient number of satellites after it has been activated This depends on the availability of GPS satellites overhead at the time of your measurement on the presence of obstructions and on the energy level of your receiver s batteries If it takes more than five minutes to get a satellite lock change your batteries and try again 2 The receiver is not displaying latitude or longitude Why The receiver has many functions available on various display screens besides the Location screen that usually appears first when the un
8. he sighting arrow C at the top of the compass The dial is graduated in 2 degree increments from 0 to 360 degrees The cardinal directions are at 0 or 360 90 degrees 180 degrees and 270 degrees which correspond to North East South and West 3 The base plate D has an orienting arrow E and a sighting arrow C Some models also have mirror sights attached These components are used to line up the magnetic needle and point out the line of travel Setting Compass Bearings Step 1 Set the dial B to the desired degree reading the direction in which you want to travel so that the correct compass bearing lines up with the sighting arrow C Figure GPS P 5 Compass Example OIM au Step 2 While holding the compass level turn your body until the red end of the magnetic needle A lines up with the red orienting arrow E Put the red sighing in the shed is a useful saying to help students Anow remember what to do The red orienting arrow is considered the shed Step 3 Your direction or objective will now lie straight ahead in the direction you are holding the compass E orienting Age the direction in which the sighting arrow points de Needle Be sure to choose an object ahead of you in line with your compass bearing and walk toward it B Graduated This allows you to walk without looking down at y Base Dial your compass Every few paces stop and check Piate that you are still tra
9. it is powered up Please read the manual and familiarize yourself with these other functions of your GPS receiver 5 Ys 3 The receiver displays Insufficient S Satellites Poor Signal Reception or similar message What should we do Do not record data if any such messages appear When the receiver has a good view of the sky waiting or moving slightly will usually cause these messages to disappear Standing close to the receiver or a group of people hovering around the receiver may block the receivers view to the satellites and may cause intermittent signal losses which will prompt the messages to appear Stand back or hold the receiver high In thick foliage or heavy canopy the receiver may be unable to lock to the requisite four satellites Because the satellites move in the sky trying again at a later time may provide better results If problems persist due to obstructions follow the Offset GPS Field Guide GLOBE 2003 Protocols 11 GPs ALO OM AN uopnpounui S1090 04d ag Suen Sar J gt Ki Ki Y P
10. n place Typically a small variation of a few degrees must be added or subtracted from magnetic compass bearings to determine the direction of true North This variation is known as magnetic variation or magnetic declination and its value depends on your location Figure GPS P 4 is a world map of magnetic declination Use this figure to determine true north at your location You may also use a topographic map to determine the magnetic variation and true North at your location You will need use the true North heading for the Measuring Wind Direction Field Guide in the Atmosphere Investigation and for the Offset GPS Field Guide in this Investigation Be sure to adjust your compass to true North according to the following directions Figure GPS P 3 Geoid and Ellipsoid Surfaces GPS Measures Topographic Elevation in Reference Elevation is Measured to the Ellipsoid in Reference to the Geoid Earth s Sure Geoid Ellipsoid GLOBE 2003 Protocols 3 E awoJjam uompnponul S PAMY Super s1020101d xipuaddy GLOBE 2003 Protocols 4 GPS sn 09 suo 14 5050 aans r m apen Rap 0132 wou SU Dem Isur noA aaneBaU St anjea UONCUNIAP MOA J 1P 1IQWOWIL ISA ION geet MO E on ann 01 uonsamp AN stuaso da Insa AL YUON Mauser s 18 p 0192 0 anjea SUYA ppy aAoge deur ap BW uone20 mo 1e uONFUNPaP ae AL UUNI Tote NOK Te YHON INI JO UONIAP IPI aufunap 0I MOH
11. ned at the front or main entrance to the school thus building may block satellite reception to some extent In these cases use GLOBE 2003 Protocols 8 GPS GPS Protocol Field Guide Task Measure the latitude longitude and elevation of your school or a GLOBE study site What You Need DI GPS receiver O GPS Data Sheet O watch O Pen or pencil In the Field 1 Take the GPS receiver to the exact location you would like to determine latitude longitude and elevation 2 Tum on the receiver making sure that you are holding it vertical and you are not blocking the antenna view of the sky In most receivers the antenna is internal and is located at the top of the receiver 3 After an introduction message the receiver will start to search for satellites Some receivers may display the previous latitude longitude and elevation values while it is locking onto satellite signals 4 Wait for the receiver to indicate that at least four satellites have been acquired and that a good measurement is available In most receivers this is indicated by the appearance of a 3 D message 5 At one minute intervals and without moving the receiver more than one meter make five recordings on a copy of the GPS Investigation Data Sheet of all digits and symbols for the following displayed values a Latitude b Longitude c Elevation d Time e Number of satellites 2 D or 3 D status icons 6 Turn off the receiver 7
12. ring tape and Offset GPS Data Work Sheet should be also brought Prerequisites None GLOBE 2003 Protocols 1 GPS S1020 01d GPS Protocol Introduction Have you ever considered how you describe your location or how to give directions to a place When you tell a friend where to meet you will most likely give the location relative to a place or object you re both familiar with For example lets meet outside the main entrance of our school In this case you will both go to the same location because you know the local environment of your school it is a system that is referenced to your own experience However should you plan to meet in a new location unfamiliar to both of you such asa nearby city you will need to find a more general framework of reference For example you could use road systems or topographic references such as rivers or hills If you want to locate all GLOBE schools and their study sites you would have to resort to a more universal reference system The geographic locating system used is a set of lines called latitude and longitude that are mapped like a grid onto the spherical surface of the Earth By convention zero degrees longitude passes through Greenwich England and zero degrees latitude is the Equator Locations are identified as Figure GPS P 1 Diagram of one example of a GPS Receiver being east and west of zero longitude and north and south of zero
13. tween the offset location and your site In general you need to use trigonometric skills to determine the desired location However if you restrict yourselves to moving directly North or South from your site you can determine the latitude and longitude of your site using only arithmetic and some knowledge about our planet Our planet is almost a sphere By dividing Earths longitudinal circumference of 39 941 kilometers by 360 degrees we learn that there are 110 95 kilometers or 110 950 meters in a degree of circumference By dividing this by 10 000 we learn how many kilometers or meters are in one ten thousandth of a degree of circumference 0 0111 GLOBE 2003 Protocols 2 GPS Figure GPS P 2 Clear and Blocked Views to a GPS Satellite km 0 0001 degrees or approximately 11 meters 0 0001 degrees GPS receivers typically present locations to the nearest 0 0001 degrees which is approximately 11 meters of latitude on Earth Knowing the distance north or south between your site and an offset location allows you to determine the difference in their latitudes Elevation All measurements of elevation are made using mean sea level as a point of reference For example Mount Everest has an elevation of 8 850 meters above mean sea level Since sea level fluctuates daily with tides the mean sea level surface is used as the reference The reference surface that passes through the global mean sea level and is shaped by Earth
14. veling in the desired compass direction GLOBE 2003 Protocols 7 GPs 3 2 3 A 8 a a xipuaddy Teacher Support Measurement Logistics 1 Students must determine the latitude longitude and elevation of their school and for all other GLOBE study sites NEN 2 Remember the location and elevation of SS each site must be determined only once YA 3 Ifyou or your school do not own a GPS receiver and you are borrowing one you may want to determine all the sites for which you need to take GPS measurements This would allow you to collect GPS data for all the sites in a short period of time e g a week 4 Locations of GPS measurements degrees Student Preparation The Learning Activities in this Investigation provide additional exercises to help students understand the measurements of time relative and absolute position and angles all the basic elements incorporated in the GPS measurement Helpful Hints Before you use a GPS to receiver make sure that it is set to display the following units Time as Universal Time UT Elevation in meters Latitude and longitude in decimal degrees Ifit does not follow the manufacturer directions or users manual to make these adjustments Please note that some GPS receivers are not able to display latitude and longitude readings in decimal If you are using one of these receivers you should set it to read in degrees and decimal minutes and then
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