1 (Introduction To The Global Positioning System)

Explain how a GPS device in your hands is capable of determining your exact latitude/longitude. Be specific and detailed as you explain the entire process. 

1. Find Satlites 
2. Figure D = RxT 
3. Finds trilateration 
4. Repeat 

How can a satellite tell where you are within the precision ag system?  Explain the importance of time in precision ag. 

1. Figure D = RxT 
2. Better accuracy requires better clocks: Atomic clocks 

What role does the atomic clock play in precision ag? 

Better accuracy requires better clocks: Atomic clocks 
Limiting factor for the science of positioning 

The technological revolution produced 3 key developments that enabled the precision Ag system to be developed. What are these developments? 

• Atomic clocks (1949) 
• Satellites (1957) 
• Microchips and calculators (1958) 

The GPS system went live in what year? 

1994

Who designed/built the GPS system? 

First satellites built by Rockwell in Cedar Rapids, Iowa 

Satellites orbit at what speed and how far from earth? 

2.42 miles per second 
Altitude: 12,427 miles

How long does it take for a signal to move from a satellite to your satellite receiver on earth? 

Speed of Light 

What role does a base station play in the precision farming system? 

“Reference point on earth”  

“Sends signals to satellite”  

“Satellite calculates location”  

“Location does not change on earth”  

“Location Surveyed precisely” 
"**Located one in every County***

Who operates the base stations utilized in the precision farming system? 

Operated by US Space Force

What role does a GPS receiver play in a precision farming system? 

Tells precise location 

What roles does GIS play in a precision farming system? 

Software that creates, edits, and uses data

How does trilateration work? 

“D = R x T” 

How is the concept of trilateration utilized to determine your specific location on the earth’s surface? 

One you have distance, its ‘easy

How many satellites are required by modern GPS receivers to calculate position? 

4

List 3 limitations of GPS. 

1. “Must be able to ‘see’ the satellites”  

2. “Requires power”  

3. “Multiple sources of error” 

For each of the 6 sources of error in GPS be able to list the source and how it impacts the positioning calculation of the GPS receiver. 

“Multipathing (bouncing signals - ex - buildings, rock, water)”  

“Atmospheric Delays (clouds, dust, rain)”  

“PDOP (spread of satellites)”  

“Clocks”
  

“Orbits (is it really where it says it is?)”  

“Receiver electronics (quality—John Deere tractor vs your cell phone)” 

Explain the difference in GPS quality between a John Deere Firestar GPS system and your Iphone. 

Receiver electronics 

What does “error” mean in GPS terms? 

For each correction source be able to list the expected maximum error rate when utilizing the correction signal. 

“WAAS 8–10 ft”  

“DGPS 3–9 ft”  

“RTK <1 cm to 5 cm (subscription-based)”  

“IaRTN 1–2 cm 

What is the difference between temporal and pass-to-pass in precision ag