Lecture 24 - Global Positioning Systems

Introduction to Coordinate Systems in Wildlife Management

• Global Positioning Systems (GPS) are ubiquitous in daily life, but their implementation in wildlife management requires a specific understanding of coordinate systems and environmental limitations.

• The lecture focuses on how we define a position on the Earth's surface and the transition from human-centric address systems to coordinate-based systems suitable for wilderness.

Human Address Systems vs. Natural Landscapes

• Human Settlement Mechanisms: In human environments, location is defined by a clear sequence of anthropogenic markers:

  • Country (Australia)

  • State (Victoria)

  • City (Melbourne)

  • Suburb (Burwood)

  • Street Address ($221 \text{ Burwood Highway}$)

  • Specifics (Building T, Level 3, Room $T 3.12$)

• The Problem in Natural Environments: Places like the Avon Wilderness Area in Victoria lack roads, walking paths, or street addresses.

• The Role of GPS: GPS provides a coordinate system that specifies locations irrespective of any human construction or anthropogenic markers. These systems are classified into two main types: Geographical Coordinate Systems and Projected Coordinate Systems.

Geographical Coordinate Systems (GSC)

• Concept: These systems treat the Earth as a sphere or a rounded three-dimensional object.

• Coordinates Used:

  • Latitude: Specifies how far North or South a point is from the equator.

  • Longitude: Specifies how far East or West a point is from the Prime Meridian.

• Melbourne Example: The rough location for Melbourne in this system is approximately $37^{\circ} 47' 49'' S$ and $144^{\circ} 57' 22'' E$.

• Benefits: Ideal for quantifying locations in mapping space and scaling phenomena exactly to the size of the Earth.

• Limitations (The Distance Problem):

  • Grid cells in a geographical system are of varying sizes and shapes.

  • Cells near the equator are quite large, while they become much smaller as they approach the poles.

  • This irregularity makes it mathematically difficult to logistically quantify distances like the length of a walking trail or a driving distance (e.g., $200 \text{ km}$).

Projected Coordinate Systems (PCS)

• Concept: This involves taking the spherical Earth and projecting it onto a flat, two-dimensional surface.

• Universal Transverse Mercator (UTM): One of the most common projected systems. It generates a grid with equally sized cells.

• Example Placement: In this system, Melbourne is located in Zone $55 H$.

• Components: Within a zone, location is specified by numerical values known as Eastings and Northings, which can reach a resolution of a $1 \text{ meter}^2$ square.

• Benefits: Allows for accurate calculations of distance (e.g., from Melbourne to Cape Conran) because the grid is uniform.

• Distortion Factor: Flattening a sphere inevitably distorts some part of the map.

  • Example: On many flat maps, Antarctica appears larger than Africa.

  • Real Scale: Antarctica is approximately $14,000,000 \text{ km}^2$, whereas Africa is $30,000,000 \text{ km}^2$ (roughly double the size of Antarctica).

Projection Methods and Cylindrical Systems

• Cylindrical Projection: Imagine a cylinder wrapped around the Earth sphere. Where the cylinder touches the Earth (usually the equator), distortion is minimal. The further the projection extends toward the poles, the more the surface is stretched.

• Variations in Projections: There are many ways to project surface data, leading to different systems used worldwide (at least 81 listed systems):

  • Cylinder placed around the Equator.

  • Cylinder placed around the Prime Meridian.

  • Planar Projection: Projecting a flat surface onto the edge of the Earth.

  • Conic Projection: Placing a cone over half of the Earth and flattening it.

Australian Coordinate Datums and Tectonic Movement

• Geodetic Datum of Australia 1994 (GDA94): The most common system in Australia. It is a cylindrical UTM system where the cylinder's contact point is largely over Australia based on its position on January 1, 1994.

• Geocentric Datum of Australia 2020 (GDA2020): A newer update reflecting Australia's position as of January 1, 2020.

• Tectonic Drift: Australia moves slightly North each year due to tectonic plate movement. Over a 26-year period (1994 to 2020), this movement causes the old system to become inaccurate.

• Practical Application: While GDA2020 is modern, many tools still use GDA94 because hardware/software hasn't been updated. The instructor notes they still use GDA94 in the current unit.

• World Geodetic System (WGS): A broadly applicable system used globally, often by countries without their own specific national datum.

The Mechanics of Global Positioning Systems (GPS)

• Signal Nature: A GPS unit never sends signals; it only receives them from satellites.

• Satellite Constellations:

  • Navstar: The first system, developed by America, consisting of approximately $24$ plus satellites.

  • GLONASS: Russian global navigation system.

  • Galileo: European global navigation system.

• Trilateration Process:

  • The GPS receives a signal that identifies which satellite sent it and how far away that satellite is.

  • 1 Satellite: You know you are at a specific distance from that point, but not your direction.

  • 2 Satellites: Narrows the location down to an intersection area.

  • 3 Satellites: Narrows it down to two potential points on the Earth's surface.

  • 4 Satellites: Confirms the exact location through 3D trilateration. This is the minimum requirement for an accurate reading.

Practical Risks and Signal Obstruction

• Importance of Correct Settings: GPS units must be preset to the correct datum (e.g., GDA94).

  • Case Study: A PhD student recorded data in AGD66 (Australian Geodetic Datum 1966) instead of GDA94. The discrepancy between these two datums is approximately $200 \text{ meters}$, making the recorded tree locations scientifically inaccurate.

• Zone Transitions: Moving across a state can change your zone (e.g., from Zone $55$ in Melbourne to Zone $54$ in the Grampians National Park).

• Signal Interference in Natural Environments:

  • Gullies: Walking through steep mountain ranges or gullies can block the line of sight to satellites, reducing visibility to below the required 4 satellites.

  • Vegetation: Extremely dense forest canopies can impair signal strength.

  • Atmospheric Conditions: Thick cloud cover, storms, or heavy rain can reduce accuracy.

  • Urban Environments: Large buildings can block signals similarly to mountain ranges.

Applications in Wildlife Management

• Navigation: Moving through landscapes without getting lost and generating precise track maps.

• Animal Tracking: Advances in technology have shrunk GPS units, allowing them to be attached to wildlife for fine-scale data collection.

• Benefits of GPS over Radio Tracking:

  • Provides more detailed movement data without requiring the researcher to constantly manually relocate the animal.

  • Identifies preferred habitat types and movement corridors.

  • Tracks the impact of anthropogenic factors like roads or housing estates.

• Examples of Tracking Today:

  • Powerful Owls: Tracked in urban Melbourne.

  • Swamp Wallabies: Tracked via collars.

  • Domestic Cats: Commercial GPS trackers (approx. $\$30$) allow owners to see if their pets are roaming in natural environments, encouraging containment policies.

• Conservation Strategies: GPS data helps implement strategies like placing culverts under roads in the exact locations where animals frequently cross, reducing roadkill.

Questions & Discussion

• Before the lecture, the following questions were posed for self-testing knowledge:

  • How do we define where we are on the Earth's surface at any point in time?

  • Why is it important to select the correct coordinate system?

  • What is the difference between GCS and PCS?

• At the end of the session, students are encouraged to consider the broader applications and potential issues of GPS in their specific field of study and complete the quiz on the unit site.