Echosounder Operation FAQ

Below is a list of commonly asked questions about operating a Knudsen 320 Series echosounder. Most of the questions are applicable only to users that control their sounder via the EchoControl program. Many thanks to Seth Mogk of Scripps Institution of Oceanography, for helping us with this list.

1. I can't seem to get the Autophase to track the bottom.
2. What does the Sensitivity button do?
3. I am seeing spurious depths reported - what is going on?
4. There is a significant difference between the multibeam depth and the 320 Series depth - why is that?
5. The pink line is showing on the recorder paper. What do I do to put in a fresh roll?
6. I'm trying to start the echosounding program (EchoControl), but nothing seems to be happening.
7. I've been testing the 320 Series echosounder and everything works fine except for one thing: although the bottom graphs clearly, 0.00m remains in the depth display window. Am I missing something?
8. I'm recording SEGY and I don't see any bottom in the recorded data, what's going on?

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1) I can't seem to get the Autophase to track the bottom.

If you are having trouble getting the autophase to work, be sure to check the Tracking Gate, under the Setup menu. The system sets up initially with a 10 m gate width, which is fine for shallow water, rapid pinging, but nowhere near enough for offshore. With up to 8 seconds between pings and any kind of topography to produce side-echo's and multi-path returns, the difference from one ping to the next can easily be more than 10 m. But any signal observed by the system outside of the gate width from last depth while in autophase will be disregarded. So open it up to 50 or even 100 m. Also, normally use max chirp width, 12 m/sec., unless in quite shallow water.

2) What does the Sensitivity button do?

The way the system picks the bottom depth normally (sensitivity off) is to take the time of the peak signal and convert that to depth. Sometimes the signal comes up in such a way that it will print on the screen well before the peak is reached. That is why sometimes the digitized depth is below what appears to be the first return on the screen. For our purposes over normally hard but sloping bottom, the peak gives the best result. What sensitivity does is use a threshold signal level prior to peak; the higher the sensitivity, the lower the threshold. The reason it was included was for people who work where there is a soft layer over a hard layer--without sensitivity, the system would report the depth of the hard layer (remember, the Knudsen was originally a hydrographic system). But for deep-water use, you normally want to have it off.

3) I am seeing spurious depths reported-what is going on?

If the autophase max limit, or the maximum depth shown in manual mode, is less than the actual depth, the system will report a spurious depth. This is because the system has been forced to start a new cycle before the return arrives. When it does arrive, the new cycle is already in progress and the system uses that as the depth. So if you don't know the depth, always start with the system wide open, like 0 to 5000 m. Another check is if you think you have the bottom, change ranges; the digital depth should stay the same. If it jumps radically, like from 960 to 225 for example, then you have to open up and start looking for the bottom from scratch.

4) There is a significant difference between the multibeam depth and the Knudsen 320 Series depth-why is that?

There are two main causes for the discrepancy. First, we use a standard sound velocity of 1500 meters per second with the Knudsen, while for the multibeam we use a measured sound velocity curve. Second, the multibeam depth is from the vertical beam, of 2 degrees in angle, while the Knudsen's LF array has a beam pattern of about 30 degrees; they both report the depth at the signal peak from all the ensonified area, but the Knudsen obviously has much more variability within its footprint.

5) The pink line is showing on the recorder paper. What do I do to put in a fresh roll?

First off, don't just shut off the recorder-it will crash the system. To perform the task gracefully: 1, turn off the Hardcopy; 2, under the File menu, select Recorder Setup, then replace the recorder with None; 3, now you can shut off the recorder, put in the new paper and turn it back on; 4, go back to Recorder Setup and put in the recorder again; 5, finally, select Hardcopy and you are back in business.

6) I'm trying to start the echosounding program (EchoControl), but nothing seems to be happening.

Very occasionally we have seen the Echo Control program get into a mode in which it has no open window, although it does appear as running under the Task Manager. The better way to deal with this is to invoke (double-click) a registry backup file. To make this file, use the Regedit program to create an entry for Echo Control (under HKEY_CURRENT_USER\Software\SounderSuite). If this file has not yet been created, deleting that same key will allow the program to come up again using default values. Be very careful when using the Regedit program, you can cause the computer to be unusable.

7) I've been testing the 320 Series echosounder and everything works fine except for one thing: although the bottom graphs clearly, 0.00m remains in the depth display window. Am I missing something?

This condition is certainly possible. Maybe it's choppy, getting some bubble entrainment across the transducer face. Or the power is set low in deep water so the return doesn't stand out well from the water noise. Make sure the tracking gate (under Setup) is wide enough, say 50 m. And the Autophase maximum and minimum are appropriately set to include the return. And make sure the Tx Blank is high enough, say 50 or even 75 if you are in deep water using moderate to high power--this feature keeps the system from locking onto the reverberation of the transducer. Keep the Sensitivity on 0/off, it is only appropriate over flat, fluffy bottoms. I favor using AGC and Autophase if possible. Presumably you're using the LF, if so setting the TVG to 20LogR helps the image (but won't affect depth reporting).

8) I'm recording SEGY and I don't see any bottom in the recorded data, what's going on?

When recording in SEGY format, it is particularly important that the bottom be acquired, not reporting 0.0m. This is because this format can store a limited number of samples to form a window around the bottom return; this window must be started based on an accurate digitized depth. If the depth is showing 0, all you're going to record is a bunch of water noise. For experienced seismic SEGY users, a couple notes: some settings you may be used to having control over (such as sample interval, recording window, anti-alias filter settings) are hard-wired into the code on this system. Correct values appear in the appropriate places in the file and shot headers, but there is no user control over these parameters.