2.8 Recommendations

Wind Speed

Light weight three cup anemometers (Section 2.1.1) or propeller anemometers (Section 2.1.2) should be used for measuring wind speed. Sensors with high accuracy at low wind speeds and a low starting threshold should be used (see Section 5). Light weight, low friction systems which meet the performance specifications given in Section 5.0 should be used. Heaters should be employed to protect against icing in cold climates. Sonic anenometers and hot wire panenometers may be used with the approval of the reviewing authority. These instruments are especially suited for use in direct measurements of turbulence. 

Wind Direction

Wind direction should be measured directly using a wind vane (Section 2.2.1) or may be derived from measurements of wind speed components (Section 2.2.2). Light weight, low friction systems which meet the performance specifications given in Section 5.0 should be used. Heaters should be employed to protect against icing in cold climates. Bivanes are regarded as research grade instruments and are not generally suited for routine monitoring. Data from bivanes may be used on a case by case basis with the approval of the reviewing authority. 

Temperature

Temperature and temperature difference should be measured using resistance temperature devices which meet the performance specifications of Section 5.0. Thermoelectric sensors (thermocouples) are not recommended because of their limited accuracy and complex circuitry.

Humidity

Humidity should be measured using a dew point, lithium chloride, or thin-film capacitorhygrometer. The hygrometer should meets the performance specifications in Section 5.0.

Precipitation

Precipitation should be measured with a weighing or tipping bucket rain gauge. In cold climates, the gauge should be equipped with a heater and a wind shield.

Pressure

Atmospheric pressure should be measured with an aneroid barometer which meets the performance specifications given in Section 5.0

Solar Radiation

First class or second class pyranometers should normally be used for measuring global solar radiation, depending on the application. If the solar radiation data are to be used in procedures for estimating stability (Section 6.4) then second class (photovoltaic) pyranometers are acceptable. For most other applications, first class or secondary standard pyranometers should be used. Applications requiring ultraviolet (UV) radiation data should not employ photovoltaic measurements as these instruments are not sensitive to UV radiation.

2. PRIMARY METEOROLOGICAL VARIABLES 
 2.1 Wind Speed
      2.1.1 Cup Anemometers
      2.1.2 Vane-oriented and Fixed-mount Propeller Anemometers 
      2.1.3 Wind Speed Transducers 
  2.2 Wind Direction 
      2.2.1 Wind Vanes  
      2.2.2 U-V and UVW Systems  
      2.2.3 Wind Direction Transducers 
      2.2.4 Standard Deviation and Turbulence Data  
  2.3 Temperature and Temperature Difference 
      2.3.1 Classes of Temperature Sensors  
      2.3.2 Response Characteristics  
      2.3.3 Temperature Difference 
      2.3.4 Sources of Error 
  2.4 Humidity  
      2.4.1 Humidity Variables  
      2.4.2 Types of Instrumentation  
  2.5 Precipitation 
  2.6 Pressure  
  2.7 Radiation  
  2.8 Recommendations

Recommended performance specifications for the primary meteorological variables are provided in Table 5-1