Echogram editor

The echogram editor is the most powerful tool in Hydromagic to remove sounding errors by using an echogram. Because an echogram is displayed, which shows the relation between time and depth, you can easily see which data does not make sense and take appropriate actions.

In the echogram editor you have the following tools to clean the echo sounder data:

• Range filter - similar to the one in the filter tool
• Data selection and remove - select data to remove using the mouse;
• Median filter - use a "median filter" to filter out small spikes and smooth the data;
• Mean filter - use a mean filter to filter out small spikes and smooth the data;

The example below shows an echogram before filtering. In this example we will first filtered out the zero values using the range filter, then the largest spikes will be removed using the mouse and finally the median filter will be applied to smooth the data.

Example of an echogram with lots of spikes and noise.

View an echogram data processing demo on our YouTube channel (and please subscribe!)

Range Filter

When you didn't apply this filter by using the filter tool, you can filter out of range data from within the echogram editor as well, otherwise you can skip this step and proceed to the removing of the spikes using your mouse.

Looking at the example above, as you can see there are spikes starting at 0.00 meters, which are obviously measurement errors (the echo sounder couldn't detect the bottom so it returned zero depth instead). To filter the data by range, click the small arrow next to the left-most button and select the first "Range Filter..." option, or the second to apply the filter to all selected raw data files.

Use the range filter tool to filter out spikes starting at zero.

Now enter the minimum and maximum allowed depths. Especially the minimum depth is important here: For the minimum depth value it is recommended to set the static draft (echo sounder offset) plus approximately 0.3 meter (or 1 feet), since most echo sounders are unlikely to report (accurate) depths below this value. For instance, when the distance between the transducer and the waterline is 0.60 meter, add 0.90 meter as lowest possible value.

Select the minimum and maximum allowed depth values.

Click "OK" to apply the filter. Changes should be visible in the echogram immediately:

Spikes starting at the water surface are now removed thanks to the range filter.

Removing the remaining spikes by hand

The remaining spikes can be removed by hand. Just remove spikes which are larger then a couple of millimeters on the screen: small spikes will be smoothed out when applying the median filter after this step. When using a dual frequency echo sounder, it is recommended to remove the spikes for one channel at a time. You can switch between "Low Frequency", "High Frequency" and "Dual Frequency" by clicking the boxes at the bottom of the window. When dual frequency is selected, you can select both low and high frequency spikes or data for deletion, when working on a single channel, only the data selection for this channel will be deleted.

When you accidentally removed too much data, just click the "Undo" button or press "Control"+"Z" on your keyboard to undo the last step. In the unlikely scenario that everything has been lost beyond repair, just go to the file selection page and choose the "Start editing from original raw data" option to start from the original raw data.

To remove a single or a collection of spikes, click and hold the right mouse button and draw a rectangle around the 'peaks' of the spikes. To make thinks easier, you can use the scroll wheel on your mouse to zoom in and out on the data, so you can select with more accuracy.

When the selection seems okay, just press the "DEL" key on your keyboard to remove the data, or click the second left-most button in the echogram editor's tool bar. Repeat this step until you are satisfied with the result.

The example echogram as shown above, but after finishing the manual spike removal. Only small spikes remain visible

Median and Mean filters

The median and mean filters can be used to further smooth the data which also suppressed the latest small spikes that were left behind after the manual spike removal process. To apply the median filter, click the small arrow next to the left-most button and select the first "Median Filter..." option, or the second to apply the filter to all selected raw data files.

Use the median filter tool to further smooth the data after manual spike removal.

You can apply the median filter multiple times until the desired smoothing level has been reached. When there are still spikes, you can remove them by hand and then apply the median filter again. The mean filter can also be used to smooth the data, although we recommend to use the median filter since it leaves the data more intact. When we applied smoothing we should end up with a smooth, filtered echogram like the one below:

Same echogram as the first example on this page, but after filtering, spike removal and smoothing.

Echogram editor tool bar

(a) - Remove Selection

To remove spikes and zero value, you can select the data by clicking and holding the right mouse button.
When the invalid data has been selected, click this button to remove it from the data file.

(b) - Filter echogram (remove spikes!)

Use one of the built in data smoothing and filtering to remove spikes and noise from the data.
Supported filter algorithms include median and mean filtering.

(c) - Reload echogram

Reload the echogram from disk

(d) - Undo operation

Use this button when you removed data by accident. This button undoes the last operation.

(e) - Redo operation

Redo an operation which has been undone.

(f) - Scroll to begin

Scroll to the beginning of the echogram, only available when zoomed in.

(g) - Scroll back

Scroll back one screen, only available when zoomed in.

(h) - Scroll forward

Scroll forward one screen, only available when zoomed in.

(i) - Scroll to end

Scroll to the end of the echogram, only available when zoomed in.

(j) - Select the previous data file

Select to the previous raw data file in the collection of files you are currently editing

(k) - Select the next data file

Select to the next raw data file in the collection of files you are currently editing

(l) - Zoom In

Zoom in on the data which is currently visible

(m) - Zoom Out

Zoom out on the data which is currently visible

(n) - Zoom All

Reset all zoom operations, shows all data in the file

(o) - Print echogram

Send the current echogram view to a printer or plotter