Campbell UT30 Installation Manual

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Campbell UT30 Installation Manual Manual pdf 10 page image

SECTION 1. PREPARATION AND SITING1-51.4 DETERMINING TRUE NORTH FORWIND VANE ORIENTATIONMagnetic declination, or other methods to find TrueNorth, should be determined prior to installing theweather station. True North is usually found byreading a magnetic compass and applying thecorrection for magnetic declination*; wheremagnetic declination is the number of degreesbetween True North and Magnetic North. Magneticdeclination for a specific site can be obtained from aUSFA map, local airport, or through an internetservice called NSSDC CGM (Section 1.4.1). Ageneral map showing magnetic declination for thecontiguous United States is shown in Figure 1.4-1.Declination angles east of True North areconsidered negative, and are subtracted from 0degrees to get True North as shown Figure 1.4-2.Declination angles west of True North are con-sidered positive, and are added to 0 degrees to getTrue North as shown in Figure 1.4-3. Forexample, the declination for Logan, Utah is 14.5°East. True North is 360° - 14.5°, or 345.5° as readon a compass.* Other methods employ observations usingthe North Star or the sun, and arediscussed in the Quality AssuranceHandbook for Air Pollution MeasurementSystems, Volume IV - MeteorologicalMeasurements 4.Subtract declination from 360° Add declination to 0°22 E18 E16 E14 E12 E10 E 8 E 6 E 4 E 2 E02 W4 W6 W8 W10 W14 W12 W16 W18 W20 W20 EFIGURE 1.4-1. Magnetic Declination for the Contiguous United States