The backscatter average time,
BS_Av_Tim
e, is the period over which the laser is firing and
taking measurements.
The measurement period is the time interval between the start of backscatter average time (
BS_
Av_Time
), during which the laser fires, and the start of the next measurement period. The
measurement period must be long enough to include the backscatter average time and some
processing time. The minimum measurement period is 2 seconds, which assumes the backscatter
average time is 1 second. The measurement period can be set between 2 to 600 s (default is 10 s).
If it is set to 0, then measurements must be polled.
The rolling average (1 to 29, default ) is the number of periods used to calculate each scatter
value that is either used in a profile message or in a calculation of cloud height.
The message interval chosen may affect measurement parameters allowed within the
BS
command, which can be used to set non-standard measurement parameters) as follows:
If message interval = measurement period = 2 (the lowest values allowed), then the backscatter
average time (BS_Av_Time) must equal 1 and the rolling average must equal 1.
If the message interval is between 3 and 9 s, then the measurement period must be the same as
the message interval.
In the following examples, yellow means laser firing.
To comply with the requirements for Sky Condition the total measurement period for rolling
averages should not exceed 30 seconds.
In this case, the SkyVUE 8M sends a message every 2 seconds based on one measurement
averaged over 1 second. Therefore, each message is based on a single 1 second period of
backscatter average data.
Laser firing (yellow)
(
BS_AV_Time
) = 1 s
1 s
Measurement Period = 2 s 2 s
Message Interval = 2 s
2 s
In this case, with the rolling average set to 1, the SkyVUE 8M sends a message every 30 seconds. It
takes three, 2 second, measurements at 10 second intervals. Only the last measurement is used in
the output message but all three are used for calculating sky condition. Therefore, each message
is based on a single 2 second period of backscatter average data.
SkyVUE™8M Tactical LIDAR Ceilometer
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