# Presentation: 567808

##  Introduction

** ****Introduction**

## Summary of Topics

**-  GPS**
**-  WAAS**
**-  Coordinate Systems**
**-  Datums**

## 1973 – U.S. Air Force tasked with initial development
1980’s – First civilian use
1995 – GPS declared “Fully Operational”
2000 – “Selective Availability” suspended
Today – Wide variety of products and services utilize GPS technology, and the European Union builds its own GPS

**1980’s – First civilian use**
**1995 – GPS declared “Fully Operational”**
**2000 – “Selective Availability” suspended**
**Today – Wide variety of products and services utilize GPS technology, and the European Union builds its own GPS**

**A Brief History Of GPS**

**Notes:**
1973 – U.S. Department of Defense directed the Air Force to develop the Defense Navigation Satellite System (DNSS), which evolved into the Navigation Satellite Timing and Ranging Global Positioning System, or NAVSTARGPS.  The purpose of this system was to provide world-wide force navigation and weapons guidance without dependence on ground-based navigation aids.

1980’s - Civilian scientists began using GPS for non-military purposes.

1995 – GPS was declared to have met the requirements for “Full Operational Capability”, at a cost of $14 billion.

2000 – Selective Availability (intentional “dithering” of the civilian GPS signal) is suspended.

Today – GPS has proved so successful and useful that many companies now provide a wide variety of products and services utilizing GPS technology.  The European Union is developing its own global navigation satellite system, to be called Galileo.

## Apply GPS To Fire Situations

**Report a fire’s location**
**Navigate to a fire’s reported location**
**Map a fire’s point of origin, or its perimeter**
**Locate a safety zone, helispot, pump, water source, or other point of interest**
**Map roads or trails to be used for access**
**Map resources or improvements to be protected**
**Map dozer line to be rehabilitated**
**Document search, rescue, or recovery efforts**

**Notes:**
How many other ways can you think of that GPS could be applied to fire or ICS situations?

## How does GPS work?

**Notes:**
There are currently 30 satellites launched by USAF

## The Global Positioning System 

**The Global Positioning System **

**Control Segment**

**Space Segment**

**User Segment**

**Notes:**
3 segments. Perhaps start with Control, then User, and lastly Space because there are several slides that follow about the space segment.
	1.  Control segment manages the satellites – there are no more slides about this segment
	2.  The space segment is the satellites – more slides
	3.  User segment
By January 17, 1994,  a complete constellation of 24 satellites was in orbit. 
July 17, 1995, reached Full Operational Capability

## Control Segment

**Kwajalein Atoll**

**US Space Command**

**Control Segment**

**Hawaii**

**Ascension Is.**

**Diego Garcia**

**Cape Canaveral**

**Notes:**
Control Segment
	The Master Control Station, or MCS (also known as the Consolidated Satellite Operations Center) is located at the US Air Force Space Command Center at Schriever Air Force Base (formerly Falcon AFB) in Colorado Springs, Colorado. It's responsible for satellite control and overall system operations. The Control segment is made up of a Master Control Station (MCS), five monitor stations, and three ground antennas (plus a reserve antenna at Cape Canaveral used primarily for pre-launch satellite testing) used to uplink data to the satellites. Monitor Stations continuously receive GPS satellite transmissions, and relay this information in real time to the Master Control Station in Colorado. The user segment also receives these same transmissions.
The MCS uplinks data to GPS satellites which includes:
-Clock-correction factors for each satellite; necessary to insure that all satellites are operating at the same precise time 
-Almanac, which is a log of all GPS satellite positions and their health, and allows a GPS receiver to identify which satellites are in its hemisphere, and at what times. 
-Ephemeris data is unique to each satellite, and provides highly accurate satellite position (orbit) information for only that GPS satellite. It doesn’t include information about the GPS constellation as a whole. Ephemeris information is also transmitted as a part of each satellite’s time signal. 

## The Space Segment

**24 or more satellites in Earth orbit that transmit:**
**PRN code**
**Ephemeris data**
**Atmospheric data**
**Clock information**
**An almanac**

**Notes:**
The Space Segment consists of 24 or more GPS satellites circling the Earth in six orbital planes inclined at 55 degrees to the equator.  Satellites orbit the Earth at an altitude of about 12,000 miles and complete an Earth orbit every twelve hours.  With an orbital speed of about 1.8 miles per second, they make a horizon-to-horizon transit in about 2 hours.

GPS satellites transmit on two frequencies.  Frequency “L1” is used by consumer-grade GPS units, and “L2” serves Precise Positioning Service (PPS) receivers.

The signal broadcast to GPS receivers on L1 includes:
PRN code (a complex code unique to each satellite) permits receivers to calculate their distance from each satellite.
Ephemeris data provide extremely accurate orbital information unique to each satellite.
Atmospheric data help receivers account for some portion of signal delay caused by the atmosphere.
Clock information defines the exact time of satellite signal transmission.
An almanac is a constellation-wide schedule of GPS satellite positions, and their states of health.  Receivers automatically download, and store, a fresh almanac whenever receiving a signal.  The stored almanac permits rapid signal acquisition at next use because the receiver will already “know” the scheduled location and health of GPS satellites.  An almanac may become obsolete if a receiver isn’t used for 30 days, or is moved more than 300 miles while not receiving a signal.

## JTrack

**JTrack**

- http://liftoff.msfc.nasa.gov/RealTime/JTrack/3D/JTrack3D.html

_**Altitude**_
**20,200 km **
**10,900 nm**

**Notes:**
Here’s one satellite going around the earth.  This provides a sense of the satellites orbit.

Invite students to go visit this site outside of class.  All the dots are satellites.  Click on one and the orbit and name appears.  It’s real time.  Can twist and turn the globe around for perspective that matches your location.  

Web address ok as of 2/5/08

satellites are about 12,500 statute miles  12,000
earth’s diameter 8,000 miles

10,988 nautical miles (12,645 statute miles)

## Earth in a Cage of Satellites                                                        

**	****Current:****	****Satellites 1 - 32**
**	****Max:****	****32 Satellites**

## Military
Search and rescue
Disaster relief
Surveying
Marine, aeronautical and terrestrial navigation
Remote controlled vehicle and robot guidance
Satellite positioning and tracking
Shipping
Geographic Information Systems (GIS)
Recreation

**Search and rescue**
**Disaster relief**
**Surveying**
**Marine, aeronautical and terrestrial navigation**
**Remote controlled vehicle and robot guidance**
**Satellite positioning and tracking**
**Shipping**
**Geographic Information Systems (GIS)**
**Recreation**

**User Segment**

## How to Calculate a Position

**Measure the Distance to the Satellites**

**Notes:**
The question is what is the minimum number of satellites required for the GPS receiver to calculate its location in terms of latitude, longitude and elevation.  

Remember how the receiver determines its location - it measures the distance to a number of satellites.  There’s only one place we can be based on all of these measurements.   

## How to Calculate Distance

**How to Calculate Distance**

**Speed of Light **
_**x   Travel Time**_** **
**Distance**

**Time signal left satellite**

**Time current**

**Notes:**
However, the distance is not measured directly, it’s also calculated.  That calculation is based on measuring time.  

Clocks inside the GPS receiver are very inaccurate compared to the clocks inside the satellite.  So essentially we have another unknown.  

All together we have 4 unknowns:  time, latitude, longitude and elevation.  

In 1 microsecond the signal travels about 300 meters.  

## Minimum # of Satellites Required-Algebra Problem

_**Unknown**__** **_
**time**
**latitude**
**longitude**
**elevation**

**4  ****Unknowns     **_**We Need**_**      4    Satellites**** **

_**Equation**__** **_
**satellite location **

**Notes:**
Now, think of solving for all of these unknowns as an algebra problem.  In other words we need one equation to solve for one unknown, 2 equations for 2 unknowns, etc.  So if you think of each satellite as providing an equation, then that means we need a minimum of 4 satellites to calculate the latitude, longitude and elevation of our position.  

Please note that I use 1st, 2nd, 3rd as a way of counting satellites.  I do not mean that if you had only 2 satellites you would at least have determined your latitude.  

## Minimum # of Satellites Required-Trilateration

**1 satellite – somewhere on a sphere **

**Notes:**
An alternative way of looking at this is triangulation – actually in our case it’s trilateration   

## Minimum # of Satellites Required-Trilateration

**2 satellites – somewhere on a circle **

## Minimum # of Satellites Required-Trilateration

**3 satellites – one of two points **

## Minimum # of Satellites Required-Trilateration

**Note:  with 3 satellites, one point is on the earth’s surface and one is nowhere near.  However, we still need the 4****th**** satellite because receiver clocks are inaccurate.**

**4 satellites – one point**
**3D GPS Location**

**Notes:**
So in order to calculate a position, the receiver needs a minimum of ________satellites. 

This is also called a 3D position because the receiver has calculated the lat, long, and elevation.  On the GPS receiver it displays 3D GPS Location.    

## When There are Only 3 Satellites

**2D GPS Location**
**Elevation - last known**
**2-5 X Error Rule**

**Notes:**
Garmin calls it 2D GPS Location, elevation cannot be calculated, but elevation must be part of the equation, therefore, receiver uses the last value it had for elevation. 

2-5x rule:  for every unit of error in the vertical, there is a 2-5x error in the horizontal.  

Example:  if the vertical is off by 10 feet, then the horizontal could be off by 20-50 feet.  

## Garmin Estimated Accuracy

**-****	****Want index as low as possible**

**Garmin Estimated Accuracy**

**Relies on Dilution of Precision**

**Notes:**
Now, we know we need at least 4 satellites.  Does it matter where the satellites are in the sky?  Yes.  
There are lots of DOPs.  In this case we are using PDOP as a measure of how spread out the satellites are.  
	If I measure the distance to student A over and over, I will end up with a very accurate distance, but I won’t know if I’m a little to the right or a little to the left.  If I measure my distance to Student B at the same time I measure the distance to Student A.  Then that will help determine if I’m a little to the left or a little to the right.  However, it doesn’t take care of whether I’m a little high or a little low.  
	If all my satellites are clumped together, there’s nothing to offset the error in another direction.  So ideally, I want 1 satellite overhead and 3 arranged around the horizon about 120 degrees apart.  
	There are no satellites under the earth to offset the error that’s in the direction of all the satellites above the earth.  So rule of thumb is vertical error is 1.5 to 2 times the error of the horizontal error.  

## Ideal Satellite Geometry

**Ideal Satellite Geometry**

**N**

**S**

**W**

**E**

**Notes:**
	In the diagram above the outer ring of the circle represents the Earth’s horizon. The center of the cross hair represents the sky directly above the GPS receiver. The satellite configuration shown is considered optimal for providing the best 3D positioning because any horizontal error from one direction will be offset by the opposing satellites. The fourth satellite directly overhead improves vertical accuracy.

## Good Satellite Geometry

**Good Satellite Geometry**

**Notes:**
Good Satellite Geometry (cont.)
	The best satellite configuration for optimum receiver positioning is one satellite directly above the receiver, and three or more satellites equally spaced around the horizon (as shown in the previous diagram). In this configuration satellite geometry is very good since distance measurements are from all directions. The area where all four calculated pseudo-ranges intersect will be much smaller, providing a more precise position (as shown above). The farther apart the satellites are from each other the smaller the smaller area of position uncertainty will be (shown by the diamond be in this diagram), resulting in low PDOP.
	If at all possible a GPS receiver will choose four satellites spread out across the sky rather than four satellites bunched close together in one quadrant of the sky. But it should be noted that many receiver types (Garmin included) always try to provide a position, even a poor position, regardless of satellite geometry. The reasoning is that any GPS position information provided by the receiver is better than no position information. 
	Most GPS receivers provide some means of determining satellite geometry, either graphically (as in Garmin receivers), or through satellite position information (as in Trimble receivers). Garmin receivers use a sky view display to show the locations of GPS satellites above the receiver. A user can visually check satellite geometry, as well as the strength of the satellite signals, using the receiver’s information page. Other brands of receivers may use a similar or different method of displaying satellite geometry and signal strength. When using Trimble brand receivers, the best way to verify good satellite geometry is through the displayed PDOP value.

## Poor  Satellite Geometry

**Poor  Satellite Geometry**

**N**

**S**

**W**

**E**

**Notes:**
Poor Satellite Geometry
	The locations of satellites in relation to each other in space at any given time can affect the quality of a GPS receiver’s position fix. Spaced low on the horizon, with no satellite directly above the receiver, can result in high a PDOP. Similarly, if all satellites acquired by a receiver are bunched closely together in one quadrant of the sky can also result in poor triangulation measurements (and a high PDOP). Topography on the ground also affects satellite geometry. A receiver inside a vehicle, near tall buildings, under dense canopy, or in mountainous terrain can be affected by blocked signals. GPS receivers require clear line of sight to every satellite or else signal will be lost.

## Poor Satellite Geometry

**Poor Satellite Geometry**

**Notes:**
Satellite Geometry (cont)
	Most of the time there are more satellites available than a GPS receiver needs to triangulate a good position fix, so the receiver can pick satellites which will provide the best geometry to provide a precise position. However, if a receiver happens to acquire satellites that are spaced closely together in the sky will result is a larger area of position uncertainty around the receiver. Add several more satellites with the same tight pattern, and the resulting position error will be very high.

## Positions Recorded by Stationary GPS Receiver

**Positions Recorded by Stationary GPS Receiver**

**Garmin GPSmap76S**** **
**1 position/second**
**10 minutes**
**WAAS Disabled**

**3.6 meters**

**3.1 meters**

**Notes:**
The positions illustrated above were captured by a stationary GPS receiver.  The receiver never moved, but the positions it reported during a 10-minute period had a maximum spread of over 4.4 meters (on the diagonal).  Furthermore, repeating the process would result in a different set of positions.

GPS positions aren’t absolute.  Even when a receiver is stationary, its calculated position will fluctuate as a result of:
Constantly shifting satellite arrangement (DOP);
Sophistication of the receiver’s antenna design, electro-magnetic shielding, and position processing firmware; and
Consistency of local conditions, like multi-path and sky obstructions.

Since GPS positions aren’t absolute, a receiver may have difficulty navigating back to the exact position of a previously established waypoint.  It should, however, get you pretty close.  Furthermore, even though Garmin receivers may report coordinates to the nearest meter (UTM) or tenth of a second (Latitude/Longitude), they usually aren’t technically capable of that level of accuracy.

## Errors(tens of meters)

**Ionosphere**
**Troposphere**
**Satellite Clock Errors **
**Satellite Ephemeris Errors**
**Multipath **
**Receiver Noise**

**Notes:**
Anything that affects the length of time it takes the signal to reach the GPS antenna will add to the error in the location of a position.  We know there are charged particles in the ionosphere and weather in the troposphere.  We know that the satellites keep precise time, only the earth doesn’t (like the leap seconds that are added routinely), and the satellites’ locations need to be updated.  Then there’s the bouncing around of multipath and how well the GPS is engineered to reduce noise.  Error Sources:

Selective Availability
  SA essentially consists of two different components, known as dither and epsilon. Dither is an intentional manipulation of the satellite clock frequency resulting in the generation of the carrier waves and the codes with varying wavelengths. In other words, under SA, the distance between each C/A code chip will be variable, and no longer the designed 293m. The replica code generated within the receiver will still assume the chip length to be 293m and pseudorange measurements are based on this. Typical pseudorange errors for satellites with SA imposed are +/-100m - see SPS.
GPS pseudorange errors - an example time series 

The epsilon component of SA refers to errors imposed within the description of the satellite orbit in the ephemeris data sent in the broadcast message. For positioning purposes, the coordinates of the satellites are derived using this incorrect information, and errors in these coordinates propagate into the position of the receiver.
Anti-spoofing
AS further alters the GPS signal by changing the characteristics of the P code by mixing it with a so-called W code resulting in the Y code. It is the latter that is modulated onto the carriers and is thus designed to prevent the ability of the receiver to make P code measurements. Many receiver manufacturers have already developed techniques to still make P code measurements with only a small addition in added noise (cross correlation techniques), see for instance Talbot (1992)or Ashjaee and Lorenz (1992).
Cross correlation
 Satellite Errors
Further unintentional errors within the space system still exist and will propagate into a position solution. These include errors in the modeling of the satellite clock offset and drift using a second order polynomial, and also errors that exist within the Keplerian representation of the satellite ephemeris information. The cause of these errors is primarily due to the manner in which the satellite ephemeris and clock is monitored. Tracking data for all observed satellites recorded at the GPS Monitor Stations is sent to the Master Control Station which then uses this data to predict the parameters for the future. These predictions are then returned to the uplink stations where they are transmitted to the satellites. The latency of the tracking data and the prediction routines used at the Air Force Base therefore directly effect the satellite system errors. Although similar to the SA errors, these are much smaller in magnitude.
Atmospheric Propagation Errors
The satellite signals propagate through atmospheric layers as they travel from the satellite to the receiver. Two layers are generally considered when dealing with GPS: the ionosphere which extends from a height of 70 to 1000 km above the Earth, and the troposphere which from the ground level to 70 km (Gu et al, 1993).
Multipath
Mutipath is the phenomena by which the GPS signal is reflected by some object or surface before being detected by the antenna. The signal can be reflected off a part of the satellite (for instance the solar panels) although this is usually ignored as there is nothing that can be done by the user to prevent this. Mutipath is more commonly considered to be the reflections due to surfaces surrounding the antenna and can cause range errors as high as 15 cm for the L1 carrier and of the order of 15-20 m for the pseudoranges (Rodgers, 1992). The surface most prone to multipath is water, whilst sandy soil is the least (abid.).
Receiver Noise
Errors which are due to the measurement processes used within the receiver are typically grouped together as receiver noise. These are dependent on the design of the antenna, the method used for the analogue to digital conversion, the correlation processes, and the tracking loops and bandwidths (Pratt, 1992). Noise within the pseudorange measurements can be reduced by a factor of 50% by combining with the more precise carrier phase observations (Goad, 1990).

## Real Time Differential GPS

**True coordinates =  *****x*****+0, *****y*****+0 **
**Correction = *****x*****-5, *****y*****+3**

**DGPS correction =***** x*****+(30-5) and *****y*****+(60+3)**
**True coordinates = *****x*****+25, *****y*****+63**

**Real Time Differential GPS**

**Notes:**
Real Time Differential GPS
	(This is an example of real time DGPS, and not a representation of differential correction done in the office on a computer using software such as Trimble’s Pathfinder Office.)
	Real-time DGPS employs a second, stationary GPS receiver at a precisely measured spot (usually established through traditional survey methods). This receiver can correct many errors found in the GPS signals, including atmospheric distortion, orbital anomalies, Selective Availability (if it’s activated), and other errors. A DGPS station is able to do this because its processor already knows its precise location, and can easily determine the amount of error provided by the GPS signals by comparing its known location with the erroneous position data provided by the GPS.
DGPS corrects or reduces the effects of:
	- Orbital errors
	- Atmospheric distortion
	- Selective Availability
	- Satellite clock errors
	- Receiver clock errors
	DGPS cannot correct for GPS receiver noise in the user’s receiver, multipath interference, and user mistakes.
	In order for DGPS to work properly, both the user’s receiver and the DGPS station receiver must be accessing the same satellite signals at the same time. This requires that the user’s receiver not be more than 300 miles from the DGPS station (100 miles or less is considered optimum). In the example, the DGPS station receives GPS signals telling the station that its location is x+5, y-3. But the station already knows that its true location is x+0, and y+0. So it calculates a correction of x-5, y+3, and transmits this correction out to the field on its own frequency. The DGPS receiver in the field uses this correction factor to update the same GPS radio signals its receiving. Here the GPS receiver triangulates its position with GPS as x+30, and y+60. The DGPS receiver provides the correction factor to the GPS receiver’s processor, which calculates its correct position at x+25, y+63. The user can generally get accurate position fixes within a few meters or less using DGPS technology.

## Wide Area Augmentation System

**WAAS satellites**

**GPS Constellation**

**WAAS Control Station****(Position known)**

**GPS receiver****(Position with errors)**

**Wide Area Augmentation System**

**25 Reference Stations (Position known)**

**Notes:**
The Wide Area Augmentation System (WAAS) is designed to enhance GPS positioning over the United States, as well as portions of Mexico and Canada.  Unlike GPS, which is funded and maintained by the Department of Defense, WAAS is funded by the Department of Transportation.

There are 25 Wide Area Reference Stations positioned across the United States (including three in southern Alaska, and one each in Puerto Rico and Hawaii) that monitor GPS satellite signals.  These stations continuously receive and calculate GPS satellite timing corrections, just like a DGPS site does.  Each reference station then transmits those timing corrections to one of two WAAS Control Stations located on the Pacific and Atlantic coasts of the U.S.  The control stations, in turn, transmit timing corrections to two geosynchronous WAAS satellites for re-broadcast to GPS receivers in the field.

WAAS is available to any GPS receiver capable of receiving the WAAS signal.  WAAS limitations include signal blockage by vegetation and terrain, poor coverage over portions of the northern U.S., and very slow signal acquisition time.

WAAS works on the same principle as DGPS, except that timing corrections are broadcast to geosynchronous WAAS satellites for re-broadcast to GPS receivers in the field.

## WAAS

**WAAS**

**Wide Area Augmentation System**

**WAAS Satellite**

**Notes:**
GPS signals are received by Reference Stations.  The reference stations calculate the error, and send it to the Master Stations.  The Master Stations forward the corrections to the uplink stations.  The uplink stations transmit the corrections to the WAAS satellites. The WAAS satellites send signals containing the corrections back to earth.  GPS receivers calculate their location based on the GPS signals, and apply corrections to that calculation based on the corrections in the WAAS signal.     

There are 2 WAAS satellites. 

One satellite is Galaxy 15 at 133.0°W(LyngSat SatTracker) which is seen as 48 on Garmin receivers. The other satellite is Anik F1R at 107.3°W (LyngSat SatTracker) which is seen as 51 on Garmin receivers. Both are much higher in sky than the previous WAAS satellites (which were 27° vs 6° at a location in Canada).  

Note that there are two numerical designations for each WAAS satellite. PRN numbers identify the code transmitted by the satellite while the NMEA designation is simply the PRN minus 87. Garmin uses the NMEA number. The current WAAS satellites servicing Canada are summarized in the table below and in this GoogleMap showing elevations and azimuths to the satellites from cities across Canada

WAAS Geostationary SatellitesWAAS/NMEA# 48, PRN# 135, Latitude 133 W, Galaxy 15
WAAS/NMEA# 51, PRN# 138, 107.3 W, Anik FIR

## 	 Errors Reduced by WAAS Correction(multi-meter)

**Ionosphere**
**Troposphere**
**Satellite Clock Errors **
**Satellite Ephemeris Errors**
**Multipath **
**Receiver Noise**

**Notes:**
Error Sources
Single receiver GPS positioning is capable of horizontal accuracies of 20 meters (or better), 95% of the time simply due to the effect of hardware, environmental and atmospheric error sources. 
Satellite Errors
Further unintentional errors within the space system still exist and will propagate into a position solution. These include errors in the modeling of the satellite clock offset and drift using a second order polynomial, and also errors that exist within the Keplerian representation of the satellite ephemeris information. The cause of these errors is primarily due to the manner in which the satellite ephemeris and clock is monitored. Tracking data for all observed satellites recorded at the GPS Monitor Stations is sent to the Master Control Station which then uses this data to predict the parameters for the future. These predictions are then returned to the uplink stations where they are transmitted to the satellites. The latency of the tracking data and the prediction routines used at the Air Force Base therefore directly effect the satellite system errors. Although similar to the SA errors, these are much smaller in magnitude.
Atmospheric Propagation Errors
The satellite signals propagate through atmospheric layers as they travel from the satellite to the receiver. Two layers are generally considered when dealing with GPS: the ionosphere which extends from a height of 70 to 1000 km above the Earth, and the troposphere which from the ground level to 70 km (Gu et al, 1993).
Multipath
Mutipath is the phenomena by which the GPS signal is reflected by some object or surface before being detected by the antenna. The signal can be reflected off a part of the satellite (for instance the solar panels) although this is usually ignored as there is nothing that can be done by the user to prevent this. Mutipath is more commonly considered to be the reflections due to surfaces surrounding the antenna and can cause range errors as high as 15 cm for the L1 carrier and of the order of 15-20 m for the pseudoranges (Rodgers, 1992). The surface most prone to multipath is water, whilst sandy soil is the least (abid.).
Receiver Noise
Errors which are due to the measurement processes used within the receiver are typically grouped together as receiver noise. These are dependent on the design of the antenna, the method used for the analogue to digital conversion, the correlation processes, and the tracking loops and bandwidths (Pratt, 1992). Noise within the pseudorange measurements can be reduced by a factor of 50% by combining with the more precise carrier phase observations (Goad, 1990).

## Receiving WAAS Correction

**If WAAS signal intermittent- **
**   **

**WAAS correction for SV 19**
**No WAAS correction for SV 11**

## Caution!

**If WAAS Enabled – **
**	****- 2D WAAS chosen over 3D uncorrected**
**	****- WAAS chosen over DOP**

**Recommendation**

**If WAAS signal intermittent **
**	****(example: under canopy) - **
**   ****disable WAAS**

## Signal Disruption

**Signal Disruption**

**Ionosphere**

**Solid**** ****Structures**

**Metal**

**Electro-magnetic Fields**

**Notes:**
Sources of Signal Interference (cont.)

## Good Data Collection Techniques

**External Antenna**
**	****Map76S more accurate under canopy **
**Sleeve Mounts**
**Vehicle Brackets **
**	**

**Notes:**
Other GPS error can be “managed” because human error factors in.
User mistakes account for most GPS errors on the ground. Incorrect datum and typographic errors when inputting coordinates into a GPS receiver can result in errors up to many kilometers. Unknowingly relying on a 2D position instead of a 3D position can also result in substantial errors on the ground. A GPS receiver has no way to identify and correct user mistakes.
The human body can cause signal interference. Holding a GPS receiver close to the body can block some satellite signals and hinder accurate positioning. If a GPS receiver must be hand held without benefit of an external antenna, facing to the south can help to alleviate some signal blockage because the majority of GPS satellites are oriented more in the southern sky.
Errors in GPS are cumulative, and are compounded by position dilution of precision (PDOP) (covered later). It is the user’s responsibility to insure the accuracy of the data being collected with the GPS.

## Map Projections & Coordinate Systems

## Projecting a Sphere Onto a Plane

**Three-dimensional sphere to two-dimensional flat map.**

**Notes:**
Projecting a Sphere Onto a Plane
The earth is a three-dimensional sphere that can be portrayed on two-dimensional paper maps using a process called “projection.” To project something literally means to “throw forward” (as in projecting a movie from a camera onto a wall – hence the name “projector”). Whenever a three-dimensional object (such as a sphere) is projected onto a flat surface a certain amount of distortion occurs. This is because displaying three-dimensional objects in two-dimensional form is very difficult to do without introducing some distortion.
	To demonstrate this, try peeling an orange, keeping the rind in one piece. Then press the rind onto a flat surface. Notice how the rind “splays” outward when pressed flat? It loses its original shape and dimensions. The same thing occurs when projecting the earth onto flat maps. This is one reason why map projections generally tend to be regional in scope, and cover only a portion of the earth’s surface. In the example above, the earth is projected using the Mollweide projection, which is a common “global” projection. In the graphic example above it’s easy to see that with the Mollweide projection, areas near the Equator are shaped and sized most realistically. But nearer the poles, the size of land masses is dramatically increased. Hence the Mollweide projection distorts shape and area.
	Every projection presents some form of distortion. Map distortion can affect shape, area, distance, and direction. Any one form of distortion, or a combination of all four, may be present in a map projection. Mapmakers over the years have created many different projections to suit their particular cartographic needs. For example, a mapmaker creating an road map will probably not want to select a projection that distorts distance and direction.
The next slide shows examples of distortion among several projections.

## Examples of Several Projections

**Depending on the projection, a certain amount of distortion occurs when portraying the earth on paper.**

**Notes:**
Examples of Several Projections

Each projection incorporates its own unique distortion. Forms of map distortion include shape, area, distance, and direction. 
Using the peeled orange analogy again, with virtually all projections distortion increases the further away from the projection’s point of origin. If the peeled orange is pressed flat, the center of the peel will exhibit the least amount of shape and linear distortion, while the outer edges will exhibit the greatest distortion. The same is true for map projections. 

## Coordinate Systems (Projections)

_**We Use – **_
**2 Coordinate Systems**
**	****Latitude / Longitude**
**	****Universal Transverse Mercator (UTM)**

_**Garmin**_** -**_** **_
**29 Location Formats**

**Notes:**
A coordinate system is a way of describing a location. 
Although it’s true that some folks use State Plane, maybe MGRS, I suggest we don’t mention these because we don’t want the students’s heads to explode. So use words to fuzzy what’s on the slide a little, like “Basically, we use only 2 coordinate systems....” or “in this class we only use 2 coordinate systems”.  If a student asks about State Plane, we can point out that State Plane is not available on the GPSmap76.  

Garmin doesn’t list coordinate systems – they list Location Formats, which is a combination of different coordinate systems and different ways of expressing one coordinate system.   
	Coordinate systems assign a unique “address” to every point on Earth.
	Coordinates are expressed relative to a datum.

## Latitude & Longitude

**Latitude & Longitude**

**Notes:**
Latitude & Longitude 
My recommendation is to move through this slide, not belabour it.  Use it as the introduction to the next group of slides.  

	The point of origin for latitude and longitude on the Earth’s surface is where the Prime Meridian and the equator intersect. Geographically that point is just west of Africa in the South Atlantic Ocean. Lines of latitude (known as “parallels”) slice through the Earth horizontally. Lines of longitude (known as “meridians”) slice through the Earth vertically. 

## Parallels of Latitude

- 10o

- 10o

- 10o

- 690 miles

- 690 miles

- 690 miles

- 10o S

- 0o N

- 10o N

- 20o N

**Notes:**
Parallels of Latitude

	The distance between each degree of latitude does not change, regardless of where it lies in relation to the equator. This differs from longitude where lines converge as they approach the North and South Poles. 

## Meridians of Longitude

- 10o

- 10o

- 110o W

- 120o W

- 690 miles

- 460 miles

- 240 mi

- 10o

- Equator

- To North Pole

- To South Pole

**Notes:**
Meridians of Longitude

Very important to understand error difference in different locations.  People work all over the country on fires.  They may have been told in Montana not to record decimal places for the longitude and then assume it’s OK to do the same thing in Florida.  

Longitude lines (meridians) run north to south, but partition the Earth into east and west halves. Unlike latitude, the distance between each degree of longitude narrows as the distance away from the equator increases. 

## Three Ways To Express Latitude / Longitudeon a Garmin

## Three Ways To Express Latitude / Longitude(for the Same Location)

**hddd****°**** mm’ ss.s”**
**Degrees-Minutes-Seconds (*****Decimal Seconds*****)****N 43****°**** ****40’ 55.8”,  W 116****°**** ****17’ 14.1”**

**hddd****°**** mm.mmm’**
**Degrees-Minutes (*****Decimal Minutes*****)****N 43****° ****40.930’,  W 116****° ****17.235’**

**hddd.ddddd****°**
**Degrees (*****Decimal Degrees*****)**
**N 43.68216****°,  ****W 116.28725****°**

**Notes:**
Here’s what we mean by formats

Latitude and longitude can be expressed in three different formats.  Though their formats differ, these coordinates are equivalent.

The conversion works like this:
To convert seconds to decimal minutes, divide the seconds by 60 to get decimal minutes.
To convert minutes to decimal degrees, divide the minutes by 60 to get decimal degrees.

## Coordinate Systems

**hddd****0**** mm’ ss.s”: N 43****0 ****40’  **_**55.8”**_**  X  W 116****0 ****17’ 14.1”**
**(**_**55.8”**_** ****/ 60 =**** ****.93****’****)**

**Different coordinates representing the same location:**

**UTM/UPS:****	****	****11T  0557442m E     4836621m N**

**Notes:**
Coordinate Systems

	Think of coordinate systems as just another way of expressing a geographic location. For example, the intersection of Fifth Avenue and Main Street might also be described as “the corner where Floyd’s Barber Shop is located.” These are merely two different ways of describing the same location. Similarly, that same geographic location can be identified using a variety of geographic coordinates, such as the UTM coordinates 17S 0345678E 4123678N. Or, using latitude and longitude, Floyd’s Barber Shop might be: N 40° 23’ 45”   W 98° 12’ 06” (expressed in degrees, minutes and seconds).
	As for latitude and longitude, there are three ways to describe coordinates:
	degrees, minutes and seconds:		 N 40° 23’ 45”   W 98° 12’ 06”
	degrees and decimal minutes:		 N 40° 23.75’   W 98° 12.1’
	decimal degrees:				 N 40.395°   W 98.201°
Each of the above sets of coordinates represents the same location.
	To convert seconds to decimal minutes, simply divide the seconds by 60 to get decimal minutes.
To convert decimal minutes to decimal degrees, divide the decimal minutes only by 60 to get decimal degrees.
	Universal Transverse Mercator (UTM) is another way of expressing the location of a point on a map, or on the ground. The “UPS” included with UTM in GPS receivers stands for “Universal Polar Stereographic”, a coordinate system that is a variation of UTM and is used in place of UTM in polar regions. 

## Example:  Error in Latitude

**35° 24 ́ 45 ̋ N**
**35° 24.450’ N**

**1/3 of a mile**

**Notes:**
These two latitudes are not the same, although someone might carelessly place a decimal thinking it’s the same.  

## Lat / Long Shortcomings

**Lat / Long Shortcomings**

**1 minute**

**?**

**?**

- +

- +

- +

**?**

**Notes:**
However, it’s hard for me to relate to a distance in terms of degrees, minutes and seconds.  I have a sense of what a foot or meter means.  I don’t have a sense of what a minute is (By the way, it’s 1.2 statute mile).  

Furthermore the distance covered by 1 degree of latitude is the same as the distance covered by 1 degree of longitude only at the equator.   

And it’s really hard to pack a globe with you when you need a map.  

## Universal Transverse Mercator

**   ****measured in meters**
**   ****located in zones (1 - 60)**
**   ****include northing and easting**
**   ****are positive**

_**Coordinates**_

**Zone**

**Easting**

**Northing**

**Latitude Band**

**Notes:**
Talking Points
 We’re start the discussion with an example of a UTM coordinate

UTM uses meters – something we understand (on the screen point to the numbers and say “these are meters – 3 hundred fifty-one thousand, eight hundred seventy-nine meters and this is 6 million, seven hundred seventy-six thousand, five hundred eighty-five meters”

UTM provides a way of taking the 3-dimensional sphere that’s inconvenient for traveling and flattening it onto a 2-dimensional piece of paper that travels well.  When a sphere is flattened there is distortion.  
1.  UTM minimizes the distortion by creating 60 zones (longitudinally).  In our example the zone number is 6 (point to the screen).  
2.  Remember how on the globe, 1 degree of latitude does not cover the same distance on the earth as 1 degree of longitude when you are away from the equator?  The same thing happens when you look at longitude on paper – 1 degree of latitude will not cover the same distance on the paper as 1 degree of longitude.  Well, on the UTM grid we can measure 1 meter and it will cover the same distance on the paper no matter what direction in which you chose to measure.
The coordinates are called easting and northing (point to the screen), because they are only to the east of a starting point and only to the north of a starting point which means  ....all the coordinate values are only positive.  In the GIS world of lat/long, north is positive and south is negative, east is positive, west is negative.  In the UTM world we aren’t negative.   

## UTM Zones in the Lower 48 

**Notes:**
UTM Zones Covering the Contiguous U.S.

The continental United States lies within ten UTM zones. 

Additional information:
Universal Transverse Mercator (UTM) is a Cartesian coordinate system (also known as rectangular or planar) whose zones are based on latitude and longitude.

Earth is divided into 60 UTM zones extending between 84° N latitude and 80° S latitude.  Polar areas are covered by the Universal Polar Stereographic (UPS) coordinate system.
UTM zones are 6° wide, 3° to either side of a Central Meridian of longitude.  This narrow shape permits UTM zones to be projected from Earth’s spherical surface to a flat map with minimal distortion.
Each UTM zone’s Central Meridian coincides exactly with a line of longitude.
UTM zones get narrower with distance from the Equator because their boundaries are defined by meridians of longitude that converge at North and South Poles.
The Equator serves as the “x axis” for all UTM zones.
Each UTM zones has its own “y axis” known as the Origin of False Easting, an imaginary line 500,000 meters west of, and parallel to, the Central Meridian.
UTM coordinates are composed of a Northing and an Easting.
A Northing is the distance (in meters) north of the Equator.
An Easting is the distance (in meters) east of that UTM zone’s Origin Of False Easting.
Let’s address the latitude band (point to the screen)... on the next slide 

## UTM Grid Overlay

**1**

**60**

**UTM Grid Overlay**

**60 Zones, and 20 Latitude Bands**

**Zones**

- Equator

**Notes:**
Universal Transverse Mercator

Note: The grid shown in the example is not drawn to scale.
	There are sixty UTM zones, running north-south, cover all of the earth, beginning with zone 1 located at 180o W longitude. Twenty latitude bands, running east-west, cover most of the earth from 80o S latitude to 84o N latitude. The polar regions are covered by the Universal Polar Stereographic coordinate system, which is based on the UTM system. Notice that the letters “I” and “O” are not used to designate a latitude band. This is to prevent confusion with the numbers 1 and 0. The Equator separates latitude bands N (north of the Equator), and M (south of the Equator). If a GPS receiver is showing a position with a latitude band letter of C through M, then it thinks it’s in the southern hemisphere If the latitude band letter shown on a GPS receiver display is N through X then the receiver thinks it’s position is in the northern hemisphere. Either hemisphere could have exactly the same easting and northing coordinates representing two different locations (one in each hemisphere) within the same zone.
	Zones and latitude bands make up 1,200 unique grid rectangles in the UTM grid system. A UTM zone is 6° wide (remember, it’s based on longitude) and extends from 80° south latitude to 84° north latitude. By knowing the correct zone number and latitude band letter, you can narrow your location from the entire surface of the earth down to a rectangle 6° x 8°, as shown in the example above with “21T.” The easting and northing numbers refine the position to a single point somewhere inside that rectangle. 
Try this test with your GPS receiver. Set your receiver coordinate system to UTM. Get a UTM position where you live, and save it as a waypoint. Note the UTM zone number. Now change the coordinate system in the receiver to latitude and longitude (it doesn't matter which format you select). Then edit the waypoint in lat/long by changing just the longitude to a new value. For example, if the original waypoint longitude shows 115° 10' 30", change the degrees from 115° to 90°. Save the modified waypoint, and change the lat/long coordinate system back to UTM in the receiver's setup page. Now look at the saved waypoint once again in UTM. Notice how the UTM zone number has changed to match the edited longitude. Try the same test again, only this time leave the coordinates in UTM. Edit the northing coordinate by a large amount and notice how the latitude band changes automatically the moment you save the edited waypoint. 

## UTM Latitude Band

** ****UTM bands**
**	****Bands C - M, southern hemisphere**
**	****Bands N - X, northern hemisphere**

**UTM Latitude Band**

**Latitude Band**

_**We Use – **_
**2 GIS choices**
**	****UTM Zone _ North**
**	****UTM Zone _ South**

**no “I”**
**no “O”**

**Notes:**
In the GIS world each UTM zone comes as a north or south choice.  

Gamin displays the UTM latitude band

## If You Don’t Know Zone, Latitude Band... 

_**Entering Waypoints**_
**	****Zone – look up**
**	****Band – enter any letter C – M for ****	****	****	****	****northern hemisphere, receiver ****	****	****	****will display correct one**

_**Collecting Waypoints**_
**	****Receiver figures it out!**

**Notes:**
If you don’t know the UTM zone and latitude band, then there are 2 situations – one when you need to enter the coordinates on the receiver and the other when you are collecting a waypoint in the field.

When you need to enter the coordinates, if you don’t know the zone, then you’ll have to look it up.  If you don’t know the latitude band, but you do know the hemisphere, then let the receiver figure it out for you.  If you’re in the northern hemisphere, the band will be a letter between N and X, so enter any letter between N and X (not O),  and when your done with the northing/easting, the receiver will automatically display the correct band based on the northing value.  Same holds true for the southern hemisphere, C-M (not I).  

## UTM Location Format  on a Garmin

**Notes:**
UTM is Universal Transverse Mercator
UPS is Universal Polar Stereographic

Actually, they are 2 separate systems.  UPS covers the North and South Pole areas, and UTM covers everything else.  

Garmin, of course, handles it their own way and combines them on the tab.  

## What is a datum?

**Notes:**
NAD 27 is a local datum for North America and has it’s origin in Kansas
NAD 83 & WGS 84 are earth centered datum’s and use satellite measurements for surface determination.

## Datums

**WGS 84****	****         NAD 83****	****                          NAD 27**

_**Garmin**_** -**_** **_
**>100 Map Datums**

_**We Use – **_
**3 Datums**

**1 meter**

**10 - 120 meters**

## Example:  Datum Shift in Arizona

**Example:  Datum Shift in Arizona**

**NAD83**
**N34.555****o****, W111.195****o**

**NAD27**
**N34.555****o****, W111.195****o**

**210 meters**

**Notes:**
Unrecognized datum shift may have consequences if the mis-applied coordinates refer to a safety zone, drop point, medevac point, helispot, or other critical feature.

To alleviate potential datum mis-match issues, GPS users should follow these guidelines:
Verify which datum and coordinate system are officially sanctioned, and use them.
When receiving coordinates provided by another, always verify which datum those coordinates are referenced to, and use that datum.
When plotting coordinates from a map, use the map’s legend to determine which datum the map’s coordinates are referenced to.
When passing GPS coordinates on to other users, always provide them with the datum those coordinates are referenced to.
When manually entering coordinates on a GPS receiver, set the receiver’s map datum and location format to match those of the coordinates.

## Lat, Long

**Lat, Long**
**WGS-84**
**UTC**

**Lat, Long**
**NAD27**
**-8 GMT**

**UTM**
**NAD83**
**UTC**

**Lat, Long**
**WGS84**
**-9 GMT**

**Lat, Long**
**NAD27**
**-8 GMT**

**UTM**
**NAD83**
**GMT**

**Lat, Long**
**WGS84**
**UTC**

**Display doesn’t matter**

**Notes:**
		Not all receivers store in WGS 84

## Coordinate System?

**Coordinate System?**
**Datum?**

**Notes:**
Remember,  if it’s lat/long, which format and IF UTM, what zone
NAD83/WGS84, Fed Stand is NAD83, Pilots work in WGS84.  

If we had to break the Datum shift issue into two areas where it matters most, its in the Field and in the GIS.
	In the field when communicating between GPS users and when communicating or transferring data between GPS and paper maps.  The classic example here is the dispatcher is in one datum and you, the user is in another datum.  
	In the GIS, after the data is stored and transferred into a Geographic Information system like arcView.

Projecting data on top of GIS data based in a different datum and/or coordinate system.  The data is shifted relative to the base layers.  This is a very common occurrence and can prove disastrous when the map is printed out the next day with the fire depicted on the wrong side of the road or the safety zone is in the wrong place.  The GISS making the map never had the chance to visit the site, so confirmation of the data was impossible.

## Review of Topics

**-  GPS**
**-  WAAS**
**-  Coordinate Systems**
**-  Datums**

## Slide 59