Ping Average function
The acoustic Doppler current profiler (ADCP) works by transmitting constant frequency pings into the water. The velocity of the water current is calculated by measuring the time it takes for the echoes to be returned and the changes
in the frequency caused by the Doppler effect. Using only single pings for these calculations may result in velocity errors that are too large to meet the measurement requirements. For this reason, the average measurements from multiple pings are used. The average values are determined using a selected number of pings and the sliding average principle. Use the Ping Average function to specify how many pings you want to use.
How to open
You open this function from the Active menu.
Description
The first average value is obtained by calculating the average information from the chosen number of pings. The next average value is calculated after the next ping. The "oldest" ping from the previous average is then discarded, and replaced with the "newest" ping. In this way each average value is calculated based on the latest ping plus the remaining number of "old" pings.
The sliding average principle smooths out short-term fluctuations in the ADCP measurements, and identifies longer-term trends in the views.
We recommended that you average over several pings as this will to reduce random noise. The random noise from a single-ping measurement is typically too high for high qualiy measurements. The averaging operation reduces the ensemble noise of a a factor of approximately √N, where N is number of averaged pings.
Tip
The question is whether to use a large or small value for Ping Average. By selecting a high value, you get a steady average value for the water flow in the area. The local variations are filtered
out, but you get a long response time. If you choose a small value, however, you will more easily see local variations, and
you will have a faster response time. If you have disturbances in the data, such as objects in the water column or interference,
these may more easily affect the measurement data if you have selected a lower value. The speed of the vessel will also affect
your measurements. High speed and high value give low response and an average value for a large geographical area. In the
same way, low speed and a low value will give a high response and an average value for a small geographical area.
To change the setting, move the cursor to either side of the button. Select the left side of the button to decrease the value. Select the right side of the button to increase the value. Select the middle of the button to open it.