ARGN Data Quality/Availability Descriptions

Australian Regional GPS Network

This document describes the ARGN data quality/availability information that is generated daily by Geodesy for each site. This information is based on Rinex data provided by the ARGN. There are five separate data quality/availability sections:

• Delay
• Data Percentage
• Cycle Slips
• Multipath MP1
• Multipath MP2

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This information has been derived from programs developed within the National Mapping Division and also from software which has been developed by UNAVCO for quality checking static GPS dual-frequency phase and pseudorange data from a single site - TEQC.

TEQC is used to process all available daily Rinex files from each ARGN site, some of the results of this processing are then used to generate data quality statistics for each site. TEQC also requires certain parameters to be preset before processing, as the values of these parameters can influence the results obtained, it is important to detail the parameters used. They are:

1. Elevation cut-off angle 15 degrees
2. Minimum gap in data to be detected 2 minutes
3. Maximum L2-Ionospheric time-rate of change 800cm/minute

It is important to recognize that when analysing the quality statistics shown for each site, they should be viewed in relation to the whole time series rather than isolating a single daily value. This time series of data quality is to allow variations in receiver performance to be highlighted and also to enable data quality comparisons with other ARGN sites.

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Delay/Latency

This graph indicates the delay between the last time tag in the file (normally 23 59 30 UT) and the availability of the data on National Mapping Division’s FTP site. The vertical scale of this graph is shown in hours. Any site that has a delay of over 48 hours has been assigned a maximum delay of 48 hours for convenience of display. If there is no point given for a particular day this indicates that data for that day is not available.

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Data Percentage/Quantity

The data percentage component shows the data availability for each day, there are two percentage values shown. The percentage indicated by the red bar graph, highlights the size of the Rinex data file available for that day. The value of this percentage is determined by dividing the size of the particular Rinex file (in terms of file size, not epochs) by the nominal size of a Rinex file containing a total of 24 hours data.

The second percentage, shown by the black circles, are the result of TEQC processing of each Rinex file. This percentage indicates the data collection percentage, which is the ratio of complete observations within the Rinex file as calculated by TEQC against the number of possible observations above the elevation mask (15 degrees) for the observing period. For an observation from a GPS SV to be "complete", it must have:

1. P1 or C/A code data
2. P2 code data
3. L1 and L2 code data
4. SV elevation at or above the elevation mask (15 degrees)

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Cycle Slips

The cycle slips graph indicates the number of cycle slip detected by TEQC in a single day’s file. In order for a slip to be qualified both MP1 and MP2 must slip (though not necessarily by the same amount) at the same epoch for a particular SV.

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Multipath MP1 and MP2

The final two graphs show daily RMS values of L1 and L2 pseudorange multipath for P-code observations. The daily RMS values are computed by forming a linear combination of the GPS carrier and phase data. For both MP1 and MP2 the final daily multipath RMS value is the average of the RMS values for all SV’s.

Although the term multipath is used to describe these derived values, other factors are also influencing the results as well as multipath. They include things such as receiver noise and residual ionospheric delay that has not been completely removed from the formed linear combination.

More information regarding the derivation of both MP1 and MP2 can be found on UNAVCO’s website.

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