Code and Documentation
written by Dick Kreisberg
Table of Contents
With the advent of ocean observatories, it is now possible to observe and record acoustical data in real-time. This presents numerous advantages for upward looking echosounders. Time-sensitive data for brief events can be gathered and evaluated in a timely fashion. Severe weather, sudden temperature and salinity changes, and biological blooms are examples of sudden, short events which may be evaluated quickly for future investigation.
Echogram Online is a Flash-based software capable of displaying acoustical information shortly after it has been collected. In this initial demonstration, data from the MARS ocean observatory can be viewed. The software is platform agnostic (Windows, Macintosh, Linux compatible) and can be accessed from any Internet connected device in the world. The only software requirements are a web browser with Adobe Flash plugin installed.
The following guide will assist you in operating Echogram Online. Please visit www.acoustics.washington.edu for more information on Fisheries Acoustics.
Echogram Online Display Components
Far be it from me to try to explain the data displayed in an echogram. I am but a humble programmer. For my part, I'll say that the axes are still in development. Trust the Data Tip more than the axes for depth and time/ping.
The Data Tip is a popup that appears when the cursor is held over valid data on the echogram display. This is a very useful little tool for investigating individual data points within the display. For a given data point in a particular ping (row and column), the tip displays the time of day, the depth, and the backscatter (Sv) value. Nifty!
The backscatter colormap displays the range of Sv values over which the data values are differentiated. It serves as a quick reference for the echogram display. It changes as the values in the colormap toolbar are adjusted.
Using Echogram Online
Loading Data Sets
Data sets can be loaded by EO. The list is located on the right hand side of the Echogram display. It consists of a data column and a button.
A data set is loaded by simply clicking the mouse cursor on the desired data set name, followed by pressing the button below it. Note that loading a data set does not currently reset the viewing position of the data. This behavior is purposely implented.
Data sets are stored remotely on a server. Currently the data set size averages about 630KB. Time stamps are also transferred and contribute an additional 7KB of information. Currently, this results in a reasonable 2-8 second download time.
Navigating Echogram Data
Viewing and manipulating echogram data is straightforward. After the user selects and loads the correct data set, they can then begin to navigate it. The most useful feature in this case is the horizontal slider bar, located in the Echogram Navigation Toolbar (see Echogram Online Display Components). The slider bar consists of a draggable thumb (the black rectangle) and a bar along which the thumb is dragged. The position of thumb in relation to the length of the bar determines the position of the data on the echogram display.
The buttons labeled Rev and Fwd move the data one ping backwards or forwards, respectively. Finally, the data can be set directly to the first ping using the lefthand button with the left facing arrows on the toolbar. This has the same effect as dragging the thumb of the slider bar to the far left.
Play & Framerate
EO provides the unique ability to "play" echograms through a web browser. This can be used either to simulate a real-world data gathering experience or to understand the nature of the data as it was seen at the time of collection.
The Play button activates the echogram movie feature. While the "Play" mode is active, the button's beahvior changes to a Stop button. The "Play" mode can be deactivated either by pressing the Stop button or allowing the echogram to reach the last frame. The framerate is currently limited to a minimum of 0.1 frames per second (fps). The maximum is 10 fps. The arrows will increment the framerate by 0.5 fps. The value is not accepted until a different component is selected (or the mouse is clicked in another area.)
Backscatter Threshold & Step Size
The Echogram display can be adjusted in several useful ways by selecting parameters from the Backscatter Controls toolbar. The toolbar offers both thresholding and step size control. The effects can be noted on the Backscatter colormap (as shown on right.)
Noise is a constant obstacle in analyzing acoustical data. It can be generated by waves, bubbles, uneven seafloors, passing ships, and other echosounders in the water. Often, the signal-to-noise ratio is large (30-40dB). Thus, the signal can be isolated by use of simple thresholding. Advanced techniques can be used as well.
Another concern is distributing the maximum and minimum signal level across the designated colormap. In other words, we'd like to use the full colormap to tell us as much about the data as possible. This includes matching the maximum backscatter of interest to the maximum backscatter value of the colormap. The same is true of the minimum. Another concern is that the step size be of an easily understood nature. In this case, -3dB is equivalent to a loss of half of the backscatter strength. This step size provides a straightforward display of the logrithmic scale (decibels) data.
The toolbar controls operate in an obvious way, excepting their inter-relation. By that, I mean that changing the Step Size will automatically change the Maximum threshold to a valid value. Alternatively, changing the minimum or maximum threshold does not affect the step size, but rather the other threshold. The step size remains constant when the thresholds are changed.
The values of the controls are internally limited to valid values. The maximum threshold value is -1dB. The minimum threshold value is -120dB. The step size is limited to integer values between -1 and -6. The value can be input either directly by selecting the text area or by using the arrows next to each textfield. The value is not accepted until a different component is selected (or the mouse is clicked in another area.)
The Colormap Settings toolbar simply allows the user to select the color scheme used in displaying echogram data. EK60 refers to the colormap used with Simrad products. Heat refers to a standard heatmap.
A useful feature is the Default Settings button located at the bottom right of the application. This button returns the application to the initial settings displayed when it was begun. As more features are added, this feature can extended.