Record your sonar data to map your favorite lakes

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Which map would YOU rather use? Insight Genesis created the detailed map on the right.

Success in most endeavors requires a good map. Successful fishing, however, takes a great map.

Modern sonar and cloud-computing (web-based) technologies are giving you, the angler, virtual eyes underwater; empowering you to create your own maps at the level of detail you need to successfully locate and catch fish. Simply by logging your sonar from your .sl2 compatible Lowrance or Simrad unit while deliberately covering water, or passively while you fish, you have the raw ingredients to create your own custom map.  The process of creating your own map involves 3 easy steps (Record, Upload, Download) that you can review at your leisure at Lowrance’s Insight Store or YouTube (search “Lowrance Insight Genesis.”)

This blog focuses on how maps are created in Insight Genesis and points you toward some strategies for creating the best map for your needs.

How Maps Are Created with Quality Assurance

With default Lowrance or Simrad settings, your transducer is sending 20 signals per second. The GPS location of those signals is determined about every 1-2 seconds. The quality of every signal is evaluated immediately by an algorithm upon upload. If you lose signal, drive too fast (> 20 mph (32 km/h) for depth, >12 mph (19 km/h)for vegetation, and now >10 mph (16 km/h) for composition), or your transducer signal is blocked or too weak, these signals are thrown out by the software and not considered for mapping. Quality signals are automatically sent on to be processed to turn the image you see on your Sonar screen into a series of data points. Each data point conveys information on depth, vegetation height, and bottom composition or hardness. It is generally not feasible to cover every inch of water with the downlooking 200 kHz signal (the signal primarily analyzed for contours, vegetation, and composition), so Insight Genesis uses a third process that estimates structure between actual data collection locations and creates smooth map layers.  It all sounds pretty complicated but the Genesis software does all the work to automatically create a map for you.

Depth data points automatically recorded from the 200 kHz signal. Point spacing depends on your boat speed. In this instance, boat travel was approximately 2 mph (3.2 km/h) and points were spaced 1 – 6 ft apart (0.3 – 1.8 m). These data points are sent to a third algorithm that estimates depth between actual sample locations and creates the smooth bluescale map that Insight Genesis users are familiar with.

Because mapping algorithms estimate data between boat tracks to predict depth where you didn’t drive, map accuracy declines the farther you move from an actual sampled location. Accordingly, Insight Genesis creates a map “buffer” around your trip path. By default, this is 25 meters and you may find blank areas in your map if boat paths are greater than 50 m apart.  As you can imagine, maps on the market today could have been created with large distances between survey paths resulting in a lot of estimating.

Default contour map created after a merge of several trips. Areas >25 m from the nearest boat path are “blanked” to prevent inaccurate map outputs.

You have two solutions for creating a complete map. First, you can choose to return to the lake and map those blank areas and merge all your trips together. Or you can select a higher buffer with your merge. By increasing the buffer, you fill in blank spots and also generalize the map output.

Increasing the buffer for merged trips will fill in unmapped areas as well as generalize or “smooth” the map output. Buffer was increased from the default 25m to 50m for the merged trip on the right. Some blank (black) areas still remain. Merges can be deleted, and the buffer increased again until you reach a desirable completeness and level of detail.

You Control the Detail

Do you need a highly detailed map of small holes, humps, points, or patches? Or, do you need to cover water and map out the general “lay of the land” (or better put: water)? Your speed and back and forth coverage control these outcomes. Go slow (trolling speed up to 3 mph or 4.8 km/h) and close in a back and forth and crossways pattern over known structure for a highly detailed map. Go faster (3-6 mph or 4.8-9.7 km/h) and spread your back and forth tracks wider (130-160 ft or 40 – 50 m) to cover water faster. With 20 transducer signals per second and GPS location reports at least every second; even at 6 mph (9.7 km/h), you are still getting a data point for mapping every 9 feet (3 m) or so. The result is a map that is still far more accurate and detailed than purchased maps or the vintage scanned paper maps from most public natural resource agencies (see below).

Left: an example of a lake map that you may find available from your public natural resource agency (this example is from 1961). Right: the result of 3 hrs of mapping with Lowrance and Insight Genesis (lake is 119 acres)

If you are a professional or recreational tournament angler “pre-fishing” a lake prior to the tournament is an important task for finding areas that are likely to hold fish. Prior to Insight Genesis, recording waypoint “dots” on your chartplotter was the likely extent of mapping detail that you had at your disposal. Now with Insight Genesis, you can “pre-map” tournament waters to locate structure that should hold fish. If areas of interest show up on StructureMap or your Sonar while doing a rapid pre-mapping excursion, simply slow your boat down, turn around and drive all around that interesting spot you located. No need to worry about precise placement of those waypoints, all the critical location and bottom information is being recorded automatically. You can land your boat, go to the coffee shop with your SD card and laptop, upload your data to Insight Genesis and generate your .AT5 map in time to hit the evening bite (keep in mind upload and processing times depend on your internet connection speed and file size.) Multiple small files upload and process quicker and then can be merged together.

Area rapidly mapped while searching for potential largemouth bass haunts (Left). Map of prominent structure (previously hidden by the ancient map on the right) now conveyed after a 1-hr mapping excursion and upload to Insight Genesis. Angler successfully worked this point with a Texas Rig.

You Are Empowered!

You don’t have to have an advanced degree to create a professional-quality map. Computers automate the process of creating maps. You determine what you want mapped, upload a sonar log and the map will be available in minutes. Do you want to map just your local fishing spots, or do you want a full lake map? You decide! Solving a problem starts with measuring it. Success in any aspect in life requires a good map. Go Get One!

2 thoughts on “Record your sonar data to map your favorite lakes

  1. Hi Steve:

    Because the system estimates points from your GPS position, the beam angle/cone size conveys information about the size of the bottom “footprint” that is integrated into each point estimate. For maximum precision below your track, and perhaps better penetration through dense vegetation, a narrower beam angle is best. For the best overall picture of bottom, a wider angle is better. In testing, we haven’t found a great deal of difference with vegetation detection with the 12-deg 200 khz and the 20-deg 200 khz and they are likely to produce similar bottom contour and composition outputs as well. For most waterbodies, you get a pretty good map (for both fishing and research purposes) with 130-ft (40-m transects), and I expect that to be pretty similar even across different traditional beam angles.

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