If testing uses independent measurements of speed, this instrumentation shall meet specification limits of at least ฑ0.2 km/h.1
1.1.3. Meteorological instrumentation
The meteorological instrumentation used to monitor the environmental conditions during the test shall meet the following specifications:
ฑ1 ฐC or less for a temperature measuring device;
ฑ1.0 m/s for a wind speed measuring device;
ฑ5 hPa for a barometric pressure measuring device;
ฑ5 percent for a relative humidity measuring device.
1.2. Acoustical environment, meteorological conditions and background noise
1.2.1. Test site
The test site shall consist of a central acceleration section surrounded by a substantially level test area. The acceleration section shall be level; its surface shall be dry and so designed that rolling noise remains low.
On the test site the variations in the free sound field between the sound
source at the centre of the acceleration section and the microphone shall be
maintained to within 1 dB(A). This condition will be deemed to be met if
there are no large objects which reflect sound, such as fences, rocks, bridges
or buildings, within 50 m of the centre of the acceleration section. The road
surface covering of the test site shall conform to the requirements of
Annex 4.
The microphone shall not be obstructed in any way which could affect the sound field, and no person may stand between the microphone and the sound source. The observer carrying out the measurements shall take up position so as not to affect the readings of the measuring instrument.
1.2.2. Meteorological conditions
The meteorological instrumentation shall deliver data representative of the test site, and shall be positioned adjacent to the test area at a height representative of the height of the measuring microphone.
The measurements shall be made when the ambient air temperature is within the range from 5 ฐC to 45 ฐC. The tests shall not be carried out if the wind speed, including gusts, at microphone height exceeds 5 m/s, during the noise measurement interval.
A value representative of temperature, wind speed and direction, relative humidity and barometric pressure shall be recorded during the noise measurement interval.
1 Independent measurements of speed are when two or more separate devices will determine the values
of vAA', vBB' and vPP'. A continuous measuring device such as radar will determine all required speed
information with one device.