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The difference is known as the drift, and can be determined by the wind triangle. At least seven ways to measure the heading of a vehicle have been described. [1] Heading is typically based on cardinal directions, so 0° (or 360°) indicates a direction toward true north, 90° true east, 180° true south, and 270° true west. [1]
A drift meter consists of a small telescope extended vertically through the bottom of the aircraft with the eyepiece inside the fuselage at the navigator's station. A reticle, typically consisting of spaced parallel lines, is rotated until objects on the ground are seen to be moving parallel to the vertical lines.
Because water currents or wind can cause a craft to drift off course, a navigator sets a course to steer that compensates for drift. The helmsman or pilot points the craft on a heading that corresponds to the course to steer. If the predicted drift is correct, then the craft's track will correspond to the planned course to the next waypoint.
The drift angle is marked in red. While dead reckoning can give the best available information on the present position with little math or analysis, it is subject to significant errors of approximation. For precise positional information, both speed and direction must be accurately known at all times during travel.
Step 5. Measure length of course by using speed of 8.8 knots and converting into nautical miles via the time, speed, and distance scale; Step 6. Connect the two ends of the vectors from the current course to the course made good. Thus creating your set and drift vector; Step 7. Using the navigational triangle, place on set and drift vector.
A salinity sensor (specifically, a highly accurate pair of conductivity and temperature sensors) is used to measure sea surface salinity at the base of the surface float. This can also be done deeper on the tether between the float and the drogue. [15] Wind. A sonic anemometer and a wind vane are used to measure wind speed and wind direction. [15]
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A feature's orientation can also be represented by dip and dip direction, using the azimuth of the dip rather than the strike value. Linear features are similarly measured with trend and plunge , where "trend" is analogous to dip direction and "plunge" is the dip angle.