Lecture and lab schedule. Lecture: GPS, remote sensing, spatial analysis and applications Labs: 1. GPS/RS lab 2. Fire Fuel Mapping and Modeling in a Forested Environment 3. Your lab. Why GPS. GPS basics. Figure out where you are and where you’re going
1. GPS/RS lab
2. Fire Fuel Mapping and Modeling in a Forested Environment
3. Your lab
What is GPS?
GPS stands for Global Positioning System which measures 3-D locations on Earth surface with the aid of satellites
• Created and Maintained by the US Dept. of Defense and the US Air
• System as a whole consists of three segments
satellites (space segment)
receivers (user segment)
ground stations (control segment)
Note: Russia and a European consortium are implementing similar systems.
2. Distance measure
3. Getting perfect timing
4. Satellite position
Start by determining distance between a GPS satellite and your position
Adding more distance measurements to satellites narrows down your possible positions
Three distances = two points
Ground Stations (control segment)
Map from P. Dana, The Geographer\'s Craft Project, Dept. of Geography, U. Texas-Austin.
Any errors in a GPS signal are likely to be the same among all receivers within 300 miles of each other.
Reference Receiver sits over
Precisely surveyed point
Note: differential correction can be applied in "real time" or after the fact (post-processing)
Base station (known location)
Rover receiverGPS - Differential Correction
How it works:
• use a base stationat a known position base station calculate
its own position & compares to its known position
• determines correction factors that can be applied to
Differential correction will reduce horizontal position Error to 1 - 3 meters with standard receiver
much GPS fieldwork for GIS/mapping purposes will require differential correction!
National Differential GPS Network (NDGPS) being created
Example: Base Station File
Datums, or so called “reference globe” in map projections, need to be defined for GPS.
The WGS 84 is defined and maintained by the US National Imagery and Mapping Agency (NIMA) as a global geodetic datum. It is the datum to which all GPS positioning information is referred by virtue of being the reference system of the broadcast GPS satellite ephemerides.
Garmin’s Forerunner 201: A watch that uses GPS to determine current speed, average speed, exact distance traveled, etc. ( ) Basic features also available in the Forerunner 101 ($115).
Garmin’s iQue 3600 PDA:
Etrex Legend C ($375)
“Along with the Etrex Vista C, is one of Garmin\'s smallest, least expensive products to combine a color TFT display and advanced GPS routing capabilities in a waterproof design.”
--is WAAS enabled
--has USB port for downloading maps from Garmin’s MapSource CD library
Etrex Vista C ($430)
--has a TFT (thin-film transistor, with 1-4 tranistors controlling each pixel; it is the highest-definition flat-panel technique) display
--has USB port for downloading maps from Garmin’s MapSource library
The 2000 Receiver Survey in the GPS World magazine lists 495 receivers from 58 manufactures (GPS World, January 2001). Why are there so many GPS receivers on the market?
12XL from Garmin –
City point database, $309.07 , area calculation
Etrex from Garmin – 500 points, $145.71
(2)GIS/Mapping receivers - Receivers used for mapping and GIS data Collection typically requires a positioning accuracy in the range of sub-meter to a few meters.
Both (1) and (2) are single-frequency units, designed to operate in real-time. (2) are distinguished from (1) by having both a LCD display/command unit through which instructions and user-centered data is input, and a Differential GPS (DGPS) signal decoder.
(3) Dual-frequency receiver, collecting data for post-processing, has the highest accuracy, and are often used for surveying/geodetic-type applications. These are typically the most expensive class of GPS receiver.