From the beginning of Argos service, locations have been classified according to the following criteria:
For each location for which at least four messages are received during a satellite pass, an estimated error is calculated. The error is assumed to be isotropic and hence characterized by a single number called the radius of error. It corresponds to one standard deviation (sigma) of the estimated location error. The location class is attributed based on the radius of error. The location class and associated error is sufficient for many applications.
Still, the location error is not strictly isotropic and hence is better approximated by an ellipse than by a circle. Users wishing to use an improved description of the location error, for example to assimilate positions into an animal movement model, will now have access to this information (see Chapters 3.6 and 3.7). Note however, that the classical error description based on location class and radius of error will remain available to all users.
|
Class |
Type |
Estimated error* |
Number of messages received per satellite pass |
|
G |
GPS |
< 100m |
1 message or more |
|
3 |
Argos |
< 250m |
4 messages or more |
|
2 |
Argos |
250m < < 500m |
4 messages or more |
|
1 |
Argos |
500m < < 1500m |
4 messages or more |
|
0* |
Argos |
> 1500m |
4 messages or more |
|
A |
Argos |
No accuracy estimation |
3 messages |
|
B |
Argos |
No accuracy estimation |
2 messages |
|
Z |
Argos |
Invalid location (available only for Service Plus/Auxiliary Location Processing) |
|
* Class 0 locations are available by request only.
This value-added service provides users with complementary information about transmitter performance. It also distributes non-standard locations, including locations calculated with less than four messages (Locations classes A, B, and Z) and locations that fail plausability tests. This service is very useful in certain cases, and is thus activated by default for a number of applications, including animal tracking.