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SL2 Viewer: Open Lowrance .sl2 Sonar Logs Online (Beta)

See the 2D sonar, down scan and side scan of a .sl2 log as pictures, with its track and depths, in any browser.

Opens: SL2, SL3, SLG
Saves: JPEG, PNG, GPX, KML, CSV

Open

Sonar log
Choose a file… or drop it here
.sl2, .sl3, .slg · up to 200 MB
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    The .sl2, .sl3 or .slg file the fish finder recorded, copied from its memory card. One log at a time.

    Options
    Colours

    How echo strength is shown, from weak to strong.

    Units

    Automatic uses feet and miles for logs recorded in or near the United States, and metres elsewhere.

    More options
    Picture format

    JPEG pictures are several times smaller; PNG keeps every pixel exactly.

    Contrast

    Automatic stretches each channel's echo strengths over the whole colour scale, so faint fish and structure show. “As recorded” draws the values the unit stored.

    More pings per pixel give shorter pictures and fewer of them; each pixel keeps the strongest echo of its pings. Very long logs are combined anyway, so that each channel fits into 24 pictures.

    Your files are deleted after processing.

    An .sl2 file is the sonar log of a Lowrance, Simrad or B&G fish finder: a recording of every ping the unit sent while logging, with the GPS position, depth, speed and water temperature of each one. The unit can play it back, but on a computer it usually needs Windows software. Here it opens in the browser.

    How to view an SL2 log

    1. Take the memory card out of the fish finder and copy the .sl2 file to your computer or phone. Logs have names such as Sonar0001.sl2 or Chart 05_11_2018 [0].sl2.
    2. Upload it and press Open. A log of a few hundred megabytes takes seconds.
    3. Look at the first sonar picture straight away on the page, and download the pictures, the GPX track and the other files.

    What you see

    An SL2 log holds up to four kinds of sonar at once, and each becomes its own set of pictures:

    • 2D sonar, the classic view with fish arches, often logged twice at two settings.
    • Down scan, the sharper picture of what lies right below the boat.
    • Side scan, to the left and right of the boat, with the boat's path down the middle.

    Every picture has a depth or range scale and marks for the time and the distance travelled. The summary lists the channels and their frequencies, when the log was recorded, how long and how far the boat went, and the depth and temperature range.

    Good to know

    • The pictures show what the unit recorded at its own settings. If the range was set to 20 feet in 40 feet of water, the bottom isn't in the log either.
    • Some units log two 2D channels, the primary and the secondary one. Depending on the unit's settings they hold the same or different frequencies; both get their own pictures.
    • Logs from units whose clock was set store the date and time (in UTC). Others only count the time since logging started, and the pictures mark minutes into the log instead.
    • A log cut off when the unit was switched off is fine: only the last, incomplete ping is lost.

    More about what this tool reads and writes: Sonar Log Viewer.

    More with Sonar Log Viewer