Average Data Throughput Table
Argos System, Pass Frequency, and Pass Duration
Service Argos data transceivers are aboard two of NOAA’s sun-
synchronous, polar-orbiting satellites. The polar orbits allow a
single satellite to provide coverage of the entire Earth’s surface as
it rotates through the plane of the orbit.
The satellite can receive and decode data from several PTTs
simultaneously, removing the timing constraints associated with
GOES transmissions. In applications where the PTT is mobile (e.g.,
drifting oceanographic buoys), Argos can use Doppler shift data
gleaned from several received transmissions to locate a PTT to
within 150 m. The satellites’ relatively low orbit of 850 km permits
the PTT to operate with a small antenna and power supply.
The Service Argos transceiver receives messages from the PTT
when passing overhead. Pass duration is 10 minutes on average.
The orbital period for each satellite is 1 hour, 42 minutes; passes
per day vary from six at the Equator to 28 at the poles. Typical
transmissions occur in under 1 second and are spaced at 200
second intervals (±6 seconds).
The ST-21 transmitter supports up to eight Argos ID codes, allow-
ing transmission of seven unique data sets per expected satel-
lite pass. Because the PTT does not “know” when the satellite is
overhead, messages are repeated to ensure reception. Each data
transmission includes up to 32 bytes.
Our CR800, CR850, CR1000 and CR3000 dataloggers can format
the data as bits per data point, allowing the user to select the
resolution used for each data point.
Assuming a repetition period of 200 seconds, and two 32 byte
buffers are used with one 20 bit ID number, the average data
throughput by latitude is provided below.
Message repeat intervals, Argos ID numbers, and duty cycles are
changed at Campbell Scientific or by using the datalogger. Data
must be decoded by the user, or by Service Argos. The datalog-
ger’s CS I/O port provides power and I/O connections to the
transmitter using the standard SC12 cable.
Site Latitude
Cumulative Visibil-
ity Over 24 hrs
Minimum Number
of Passes Per 24 hrs
Mean Number of
Passes Per 24 hrs
Maximum Number
of Passes Per 24 hrs
Average Bytes Per
24 hrs
0°
80 minute
6
7
8
448
15°
88 minute
8
8
9
512
30°
100 minute
8
8
12
576
45°
128 minute
10
11
12
704
55°
170 minute
16
16
18
1024
65°
246 minute
21
22
23
1408
75°
322 minute
28
28
28
1792
90°
384 minute
28
28
28
1792
