Airmar LB150 - Manual (Page 30)

LB150 WeatherStation Technical Manual revision 0.013
Proprietary and Confidential
PRELIMINARY - DRAFT 27
some reason the contents of a given set are not available, then the entire set
(including commas) may be omitted.
Because there are two versions of the XDR sentence, and because a group of four
fields can be omitted entirely, it is necessary when parsing any XDR sentence to
examine the <ID> field in each set of four fields in order to identify the meaning
of the data in that set.
The XDR(A) sentence may be enabled via the $PAMTC,EN,XDRA command.
The XDR(B) sentence may be enabled via the $PAMTC,EN,XDRB command.
The wind chill temperature is the perceived temperature on a person’s face at
the current wind speed. The calculation assumes that the wind speed measured by
the sensor is the same as the wind speed at the face of an observer. The “relative”
wind chill uses the measured apparent wind speed for this calculation, and the
“theoretical” wind chill uses the calculated true wind speed. The wind chill
temperature is only defined when the air temperature is below 50°F (10°C) and
the wind speed is above 3 mph.
The heat index is the apparent temperature felt by a person's skin when exposed
to air with a high moisture content. Dry air allows evaporative cooling of the
skin's surface. The higher the humidity, the less the skin can cool itself with
evaporative cooling. The heat index is only defined when air temperature is
above 80°F (27°C) and relative humidity is above 40%.
The barometric station pressure is the raw, uncorrected barometric pressure
reading. This is provided here in the XDRA sentence, and is distinct from the
altimeter setting, which is the barometric pressure corrected for altitude, provided
in the MDA sentence.
The reported pitch and roll values are adjusted by the azimuth, pitch, and roll
offsets established with the $PAMTC,ATTOFF command.