Specifications

RAWS-F Remote Automated Weather Station for Fire Weather

8.2 Siting References

General guidelines for site selection are listed below.

EPA, (1987): On-Site Meteorological Program Guidance for Regulatory

Modeling Applications, EPA-450/4-87-013, Office of Air Quality

Planning and Standards, Research Triangle Park, NC, 27711.

WMO, (1983): Guide to Meteorological Instruments and Methods of

Observation, World Meteorological Organization, No. 8, 5th edition,

Geneva, Switzerland.

The State Climatologist, (1985): Publication of the American Association of

State Climatologists: Height and Exposure Standards, for Sensors on

Automated Weather Stations, vol. 9, No. 4.

EPA, (1989): Quality Assurance Handbook for Air Pollution Measurement

Systems, EPA Office of Research and Development, Research Triangle

Park, North Carolina 27711.

8.3 RAWS Orientation

8.3.1 Determining True North and Sensor Orientation

Orientation of the wind direction sensor is done after the datalogger has been

programmed and the location of True North has been determined. True North

is usually found by reading a magnetic compass and applying the site-specific

correction for magnetic declination; where the magnetic declination is the

number of degrees between True North and Magnetic North. Magnetic

declination for a specific site can be obtained from a USGS map, local airport,

or through the web calculator offered by the USGS (Section 8.3.2). A general

map showing magnetic declination for the contiguous United States is shown

in Figure 8.3-1.

Declination angles are always subtracted from the compass reading to find

True North. A declination angle east of True North is reported as positive a

value and is subtracted from 360 (0) degrees to find True North as shown

Figure 8.3-2. A declination angle west of True North is reported as a negative

value and is also subtracted from 0 (360) degrees to find True North as shown

in Figure 8.3-3. Note that when a negative number is subtracted from a

positive number, the resulting arithmetic operation is addition.

For example, the declination for Longmont, CO is 10.1°, thus True North is

360° - 10.1°, or 349.9° as read on a compass. Likewise, the declination for Mc

Henry, IL is -2.6°, and True North is 0° - (-2.6°), or 2.6° as read on a compass.