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Lecture 3 – Automated Data Collection

Lecture 3 – Automated Data Collection. Distance Calculation – How? 2 dimensional using sound travel: An accurate timepiece The ability to pick up distant sound signals A map showing the coast and the locations of any soundhouses Knowledge about sound travel (750 miles/hour, or 20 Km/minute).

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Lecture 3 – Automated Data Collection

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  1. Lecture 3 – Automated Data Collection Distance Calculation – How? 2 dimensional using sound travel: • An accurate timepiece • The ability to pick up distant sound signals • A map showing the coast and the locations of any soundhouses • Knowledge about sound travel (750 miles/hour, or 20 Km/minute)

  2. Suppose: • S1 has a sound house • Sound house emits a blast each minute • Objective – To determine the distance of your vessel at V.

  3. How it works Measuring Distance By Measuring Time • Known locations of GPS satellites • Knowledge of signal travel speed (300000 Km/Sec) • Accurate clocks on GPS satellites and GPS receivers Then distances from GPS receiver to several satellites can be calculated and can be used to compute receiver’s position

  4. Soundhouse VS NAVSTAR • 3D VS 2D • Dynamic VS Static • Radio Waves VS Sound • Auto VS Manual

  5. From 2D to 3D La From one satellite (a), we could compute the circle where x locates.

  6. From 2D to 3D (cont.) Candidate 1 for x La Circle Candidate 2 for x Lb Circle

  7. Factors Affecting When and How to Collect Data Major factors that relate to the accuracy of GPS measurements are: • satellite clock errors • ephemeris errors • receiver errors • ionosphere errors • troposphere errors • multipath errors

  8. Dilution of Precision (DOP) • High DOP values can magnify the other errors • DOP values can be monitored during data collection and excessive DOP values can be masked out • DOP values can be predicated • Differential correction can not help with data collected with inappropriate DOP values

  9. Position Accuracy and DOP The quality (accuracy) of fix is depend on a number of factors, including • the number of satellites in view, and • their geometry, or arrangement, in the sky.

  10. How DOP can affect accuracy? Figure 2-7. Area in which “x” might reside, given satellite positions “a” and “b.” The shaded figure indicates the area that contains the actual location sought.

  11. Too close, too far, or just about right

  12. Actually, what is DOP? DOP – sometimes referred to as GDOP (Geometric Dilution of Precision), is a number which is a measure of the quality you might expect from a position measurement of the GPS system based solely on the geometric arrangement of the satellites and the receiver being used for the measurement.

  13. Different DOPs • GDOP (Geometric Dilution Of Precision); Overall-accuracy; 3D-coordinates and time • PDOP (Positional Dilution Of Precision) ; Position accuracy; 3D-coordinates • HDOP (Horizontal Dilution Of Precision); horizontal accuracy; 2D-coordinates • VDOP (Vertical Dilution Of Precision); vertical accuracy; height • TDOP (Time Dilution Of Precision); time accuracy; time

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