Tree
Identification
Using GPS
GPS - Global Positioning System
What
is GPS and how does it work?
GPS –
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
Global Positioning System
Developed for use by the
U.S. military at the end
of the cold war to track
ICBM missiles.
Fully operational 1995
(selective availability
turned off May 1, 2000)
Original Manpack developed
for use by military
GPS –
Global Positioning System
 24 satellites orbit 22,200
km from earth, with five to
eight satellites always visible
from any point on earth
 GPS receiver needs to make
contact with signals from
three satellites in order to
find a location on earth
 Contact with a fourth
satellite allows for
determination of elevation
above sea level
GPS –
Global Positioning System
GPS –




Global Positioning System
Cost of GPS receivers from $100 for hand-held unit
(accurate within 10 meters horizontally) to over
$50,000 for research receivers (accurate within 1 cm
horizontally)
Used extensively for marine and air navigation and
mapping. Growing popularity of GPS use by hikers,
hunters, fisherman, and gamers.
Scientific uses include atmospheric studies, plate
tectonics, including mapping of volcanoes, and collection
of coastline data
No cost to use the system
GPS –
Global Positioning System
1.GPS technology relies on the use of satellites.
 2.To locate a satellite, a GPS receiver measures
distance using the travel time of radio signals
 3.To measure travel time, GPS needs very accurate
timing which it achieves with some tricks.

• Along with distance, you need to know exactly where the
satellites are in space.
• False code signals are created, one which the satellite
signals, and one that the GPS matches. When the two
signals “line up”, the time is determined. The GPS emits a
radio frequency, similar to the MHz on your radio, which
increases the accuracy of the GPS.
• Finally you must correct for any delays the signal
experiences as it travels through the atmosphere.
GPS –
Global Positioning System
GPS –
Global Positioning System
How Do You Use a GPS?

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Each brand of GPS is set
up differently.
At the Smith Center, we
use Garmin etrex units.
GPS –
Internal GPS
Antenna
UP Button
DOWN Button
ENTER Button
Global Positioning System
PAGE Button
POWER
Button
LCD Display with
Backlight
GPS –
Global Positioning System
The GPS receiver displays pages with separate
functions.

There are four main pages that you will be using to
navigate:
GPS –
Global Positioning System
Let’s Get Started!

All GPS receivers operate on information gathered from
satellites. In order to receive the satellite signals,
you must be outside, away from any objects such as
trees or overhangs that might block the signal. You
need a clear view of the sky.
GPS –
Global Positioning System
Step 1: Push and hold
down the POWER
BUTTON to turn the unit
on. You’ll see the
“Welcome” page for a few
seconds, followed by the
Satellite Page.
GPS –
Global Positioning System
How do I know I’m ready
to go?

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When you see the “Ready to
Navigate” message, you know
the etrex has locked onto
the satellite signal.
This must be displayed
before you can begin using
the GPS to navigate.
Signal strength bar will be
filled in to indicate the GPS
has locked onto signal.
GPS –
Global Positioning System
Satellite Page Basics:

Two display pages:
Normal Skyview that
shows the satellites,
satellite signal strength,
and estimated accuracy.
Advanced Skyview that
shows you the numbered
satellites being used, the
proximity and horizon and
sky overhead.
GPS –
Global Positioning System
What does the MAP
page do?

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The map page shows
where you are and uses
an animated figure to
show where you are
actually going.
Waypoint names and
symbols are also shown.
GPS –
Global Positioning System
Map Page Basics:

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You can change the map
scale by pressing and
holding the UP button to
view a larger area, or
the down button to view
a smaller area.
You can change the scale
from 200 ft to 800 miles
to view your entire trip!
GPS –
Global Positioning System
NAVIGATION PAGE
BASICS

The Navigation Page guides
you to your destination. It
shows you your moving
direction and speed. If you
have a specific destination
entered into the GPS, the
page shows you the name of
the location, the distance
and displays a direction
arrow that is shown in the
compass ring.
GPS –
Global Positioning System
NAVIGATION PAGE BASICS:
We’ll be using LATITUDE and LONGITUDE
coordinates to describe locations.
Latitude measures distances North or South from
the Equator (0°) towards the Poles. (90°)
GPS –
Global Positioning System
NAVIGATION PAGE BASICS:
We’ll be using LATITUDE and LONGITUDE
coordinates to describe locations.
Longitude measures distances West or East from
the Prime Meridian (0° at Greenwich, UK).
GPS –
Global Positioning System
Lines of Longitude
GPS –
Global Positioning System
Lines of Latitude
GPS –
Global Positioning System
Combined!
GPS –
Global Positioning System
The units that we will be
using to measure are:
Degrees (°)
North 39° 06 .582’
West 77° 06 .086’
Minutes ( ‘ )
And . . .
THOUSANDTHS of
Minutes!
GPS –
Global Positioning System
MAIN MENU BASICS:

With the main menu you
can create waypoints,
routes, save and view
your track logs. If you
select MARK, you can
mark your location as a
waypoint.
GPS –
Global Positioning System
GOING TO A WAYPOINT:
 Press the PAGE button and switch
to the MENU Page
 Press UP or DOWN and highlight
WAYPOINTS. Press ENTER..
 Press the UP or DOWN button
and highlight the alphabetical tab
for the waypoint. Press ENTER.
 This will take you to a list of
waypoints.
 Highlight a waypoint, and press
ENTER.
GPS –


Global Positioning System
REVIEW WAYPOINT
page appears. REVIEW
WAYPOINT allows you to
change coordinates,
name, symbols, and
delete waypoints.
On the REVIEW
WAYPOINT page, press
the UP or DOWN button
and highlight GOTO,
press enter.
GPS –
Global Positioning System
Using GPS Technology to
Locate Trees
GPS –
Global Positioning System
GPS technology allows us to identify locations
of specific trees
 Useful in monitoring health of trees over time
 Latitude and longitude coordinates are given for
each tree location

GPS –
Global Positioning System
GOING TO A WAYPOINT
It would be VERY
difficult to use the GPS
Unit by itself to find your
way to your waypoint, so
you will also need to know
how to use. . .
GPS –
Global Positioning System
A Map!
Use the map to look for
landmarks, to stay on
trails, to gauge
distances, and to find
your way back!
GPS –
Global Positioning System
STEPS TO USING THE GPS:

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From the SATELITE page, press the PAGE button until
you come to the MENU page.
Scroll down to WAYPOINTS, press ENTER.
Scroll down to the tree waypoint entered. Press
ENTER.
The REVIEW WAYPOINT screen will appear, select GO
TO, the COMPASS page will appear.
Begin walking. The arrow will reorient in the direction
you should be walking if you could walk a straight line to
your waypoint. You WILL need to adjust your line of
travel to avoid obstacles and to remain on trails.
GPS –
Global Positioning System
STEPS TO LOCATING THE TREE:
Follow the arrow and stay on trails to find
desired coordinates. Remember that the GPS is
only accurate within 10 meters. At this point
you need to begin looking for the tree marker.
 At this point, you will need to spread your
group out and look for the tree marker.

GPS –
Global Positioning System
ONCE YOU’VE FOUND THE TREE:
Use the dichotomous key to identify the tree.
 Check your identification using a field guide to
North Eastern trees.
 Enter the next tree number and coordinates
that you wish to locate as a GPS waypoint.
 Continue to the next tree.

GPS –
Global Positioning System
THINGS TO KEEP IN MIND:
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Do not cross roads (except Meadowside Lane)
Stay on trails. No bushwhacking!
You may need to go around rocks or cross streams.
Stay together – do not leave your group
Use your map and compass in conjunction with the GPS
Respect the park. Take only your memories, leave only
your footprints.
GPS –


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
Global Positioning System
IMPORTANT POINTS:
GPS technology is limited – tree canopy and cloud cover
affect signal strength
Be aware of your direction of travel. Use a map.
Watch the time! Return on time!