By Shane Beilue
April 15, 2011
Getting the Most from Side Imaging Sonar
One of the great qualities of using a Humminbird side imaging sonar unit is the ease of use in operating the equipment right “out of the box”. The factory default settings allow you the ability to simply turn the unit on and start enjoying the underwater images that appear on screen. That being said, every good photographer understands how to adjust his camera based on different light conditions. Similarly, we can further enhance the image on the sonar screen based upon certain conditions. This month, we’ll examine a few small tweaks that can optimize image quality and maximize the return on your investment.
Humminbird Pro-Staffer Doug Vahrenberg believes the first adjustment every side imaging owner should make is to match the chart speed to the current boat speed. For example, if you’re idling over structure at 3 mph (which will be displayed on screen based upon GPS tracking) set the chart speed on your side imaging screen to “3”. This allows the data to be displayed without streaks or gaps in the image, which will result if the chart speed is moving too fast.
For Humminbird users, scroll speed can be accessed by pressing the “Menu” button once to open the “Xpress Menu”. Scroll down to “Chart Speed” to adjust as needed with the directional key pad.
Matching scroll speed to boat speed is the first step to providing crisp, clean images that are free of distortion.
Minor adjustments in sensitivity can pay dividends for optimum screen images depending upon the depth of water and type of bottom composition you encounter. For example, many of the lakes I fish in western and southern Texas have a lot of rocky bottoms which provide very strong signal returns; therefore, the rocks show up as very vivid, bright images on the sonar screen. To prevent the strong returns from washing out the screen, I find adjusting the sensitivity down to around “8” works well for me (Humminbird has a sensitivity range from “1-20”). You may find a setting of “10” or higher suits you better, depending upon your circumstances. To find the optimal sensitivity setting, I suggest turning up the sensitivity until the screen image washes out, then start backing off until you get the desired image.
Humminbird has a nice feature that allows quick access to fine tuning the screen image via a menu setting called “SI Enhance”. Accessible by one touch of the menu button in the “Xpress menu”, SI Enhance allows for quick adjustments in Sensitivity, Contrast and Sharpness. Increasing the sharpness is beneficial when looking specifically for fish, as detailed by the image comparisons (courtesy of Doug Vahrenberg) below. As you see, increasing the sharpness causes the rest of the image to appear grainy; however, the upside is the way the fish will pop out on the sonar screen, in this case, over the sunken creek channel.
Contrast adjustment is self-explanatory: it will affect the degree to which light and dark images appear on the screen and should also be set according to personal preference. Shades of light and dark are useful for determining the slope of bottom contours, as bottom terrain that is rising (i.e. the top of an underwater hump) will appear lighter, while descending contours appear darker.
A final note about “SI Enhance”: with the latest software download from Humminbird, users can access “Contour Mode” in the “SI Enhance” menu. “Contour Mode” removes the dark water column directly underneath the boat by merging the two halves of the SI screen image. This gives a true bird’s eye view as though you were looking directly down upon the lake bottom below. You may or may not find this mode useful - it’s another option for viewing underwater images according to your personal preference.
Area of Coverage
One major advantage to side imaging is the ability to quickly search a tremendous amount of bottom structure and water column – even as much as 240’ from both sides of the boat. This amount of search coverage is great when looking for a large object, such as a bridge; however, it can have its down side when looking for small detail such as fish or sparse cover. Searching with the maximum area of coverage compresses the data considerably; therefore, smaller objects may be difficult to see clearly. By decreasing the area of coverage to 100’ or less for each side of the boat, the image will enlarge dramatically and small detail will become more noticeable on the screen.
Side imaging sonar utilizes a much higher frequency signal than traditional 2-D sonar, allowing much sharper screen detail. With side imaging, you can select 455 kHz or 800 kHz as your frequency of choice. The 455 kHz frequency is suitable for most situations; however, 800 kHz is useful in providing the finest level of screen detail when desired. The only sacrifice to the 800 kHz setting is it provides less area of coverage than the 455 kHz frequency. I find this is an acceptable trade-off when trying to separate subtle detail, such as fish, on deep structure.
Adjusting the frequency setting on a Humminbird is easily accomplished by pressing the “Menu” button twice to access the “Sonar” tab, then scrolling down to “Side View Frequency”.