2101FEATS1010ASSIGN3

2101FEATS1010ASSIGN3 - Name:_Lab. Session:_Student #_ YORK...

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Name:____________________________ Lab. Session: ________Student #_______________ EATS 1010 3.0 2010 Laboratory Exercise #3 SPACE GEODESY You will need to bring a calculator to the laboratory. Dress warmly , as you will be spending time outside (rain or shine). SECTION 1. Introduction - GPS Signals The NAVSTAR GPS is a global positioning system making use of radio signals transmitted from a man-made constellation of 24 satellites orbiting Earth at a height of 20,200 km. These signals are detected, recognized and interpreted by GPS receivers to determine the precise geographic coordinates (latitude and longitude) and elevation of the GPS receiver. Professional quality receivers can obtain a location, or “fix”, with an accuracy of a few centimetres at a cost of approximately $20,000. However, for many purposes location accuracy of a few metres is quite adequate. This may be achieved with inexpensive hand held GPS receivers at a cost of slightly less than $200. The transmitted signal from each satellite is encoded onto a radio wave, known as the carrier wave, which is transmitted at a frequency of ~1.575 GHz or ~1.575 billion cycles per second. Thus, each oscillation of the carrier signal wave takes 0.6349 x 10 -9 seconds to complete. After about 154 of these perfectly regular oscillations, [i.e., approximately every 10 -7 seconds] the carrier wave is “modulated” by multiplying its amplitude by either +1.0 or -1.0, in a Pseudo Random Number (or PRN) sequence of ±1's which is unique to each satellite. By cross- correlating a satellite generated PRN sequence arriving at the receiver with an identical PRN sequence which is generated in the receiver, the time of flight, Δ t, of the radio signal from the satellite to the receiver can be determined. The accuracy of this determination is limited by the precision of the timing of the modulations of the carrier signal. If we assume that this precision allows us to specify the timing of carrier signal modulations with an uncertainty corresponding to a small fraction of one cycle of oscillation of the carrier signal, we can compute the corresponding uncertainty in distance measurement from this cause alone. Suppose the timing of carrier signal modulations is accurate to within 1% of the duration of a single cycle of the carrier wave. What is the corresponding uncertainty, or error, in our determination of distance from the satellite. [Use 3.0 x 10 10 cm/sec as the speed of light.] Other errors in measuring the time of flight will add to this ideal limit. Uncertainty in distance: __________________________________________ SECTION 2. Properties of a handheld GPS receiver In this part of the Laboratory exercise you will use the “etrex Personal Navigator” a handheld GPS receiver, made by Garmin. You will pair up with one or two other students and will be provided with (and responsible for the care of) an etrex
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2101FEATS1010ASSIGN3 - Name:_Lab. Session:_Student #_ YORK...

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