Each station within the L1 network continously transmits it's data back to a central computer using a 915 Mhz data stream and Time Delay Multiple Access (TDMA) technology (See the related links page for more information on the radio modem technology that is being used). This transmission method does not currently incorperate error checking. As a result, a fraction of all observation packets are lost. The figures here show what percentage of the total number of observations are actually captured by the main data collection computer.
For each station the total number of actual observations recorded is compared to the maximum number of observations. This is represented in the bottom panel as a percentage of epochs. In the upper panel, the actual number of satellites tracked is compared to the maximum number of satellites in view. Data that are missing because of radio transmission problems affect both the number of epochs and the percentage of satellites tracked. GPS receiver tracking problems appear in only the upper panel.