In the 8+ years BioBase has been in service, we’ve seen our share of sonar logs and maps (both good and bad). We’ve learned some things and improved back-end processes that have resulted in you getting better maps processed faster. But we’ve also learned from you, our users, about strategies and techniques that result in better outcomes, and what to avoid. Here are eight of those lessons learned:
1. Good transducer installation is critical
You could be the most experienced hydrographer in the world and execute the perfect survey design, but your map will be mostly worthless if your transducer is not securely attached to your boat or is slanted at an angle. We’ve devoted a fair amount to this topic in previous blogs, so we won’t dwell on it here. The two key take aways are: 1) ensure the transducer is installed straight in all directions keeping in mind the slant of the hull in the water fully loaded. Replicate that tilt with your tongue jack when installing your transducer. 2) Install the transducer where the flow of water is smooth and laminar over the transducer face at all speeds. If you lose your transducer signal as the boat speeds up, you probably have an issue with cavitation (water turbulence) around the transducer face. Adjust the transducer height (sometimes only a very small amount) or move it away from rivets or anything else near the hull that could cause cavitation. One of the benefits of working with consumer devices like Lowrance and Simrad is that there is a wealth of online self-help resources and service centers that can help you install your transducer correctly. A simple Google Search “Lowrance Transducer Installation” will turn up all the resources you need. This one from Lowrance is one of our favorites. If you have multiple survey boats and want to make your unit portable, I strongly recommend purchasing and installing multiple transducers on all of your boats rather than a portable transducer bracket. In the grand scheme of things, consumer-sonar transducers are cheap and the consistent results you will get from a firmly mounted transducer is worth it!
2. Watch your sonar screen when you are recording
When I say “sonar,” I mean the traditional broadband channel (Figure 2). At the minimum, view the sonar along with your GPS chart. A frequent mistake by users is not monitoring the sonar signal while mapping. More than once, we have encountered cases where the user logged data for hours without knowing their sonar wasn’t connected or wasn’t receiving a consistent bottom signal. If you encounter areas where the sonar loses bottom, stop the boat and wait for the signal to return. If the signal takes longer than 1 minute to return, stop logging and reboot the unit. For best bottom tracking through vegetation, select the 200 kHz sonar frequency.
3. Lowrance HDS and Simrad NSS product lines are the highest performing, most durable devices for extended use.
When it comes to hardware, BioBase is only compatible with Navico brands Lowrance and Simrad. Lowrance is the most common brand for inland use and Simrad is more commonly used on coastal vessels. Both utilize the same acoustic algorithms and share many of the same accessories. They are NMEA 2000 compatible which is the marine industry data networking protocol. The Lowrance HDS and Simrad NSS product lines generally have upgraded processors, components, and features compared with lower price point models (e.g., Elite Ti, Hook, Go, Cruise) and are recommend for users who are putting a lot of hours on the water. Lowrance Elite Ti is a good buy for users who need a high performing unit but don’t expect to put a ton of hours into mapping. Screen size in all product lines drive price points as well. A 9-inch screen represents the “Goldilocks” screen size. Large enough to have a 3 or 4 way screen split and still be able to see detail while keeping you within a limited budget.
4. Get familiar with your device
Although consumer sonar devices are moving in the direction of smart mobile technology, the marine electronics industry is no where near the size of the mobile technology industry. Unlike your iPhone, your Lowrance will not read your mind, anticipate what you want to do, and perform flawlessly without much more of a press of an easy button. Give it a few years! In the meantime, read up on your quick start guides, search blogs, FAQ’s, and YouTube videos for tips and tricks. Get to know where various functions are and what they do. Heck, you may even find something useful in a historic document called a manual (which before the internet was the single source of truth for learning how to operate computers and machinery). Lastly, stay on top of software updates. Although Lowrance and Simrad are wireless capable, they aren’t always on and connected to a hotspot where cloud magic can automatically download updates. Rather, users need to periodically hook their device up to wireless and search for updates. Or browse the Lowrance Update web page.
5. Ensure your GPS signal is aligned with your transducer.
Out of the box, your GPS signal (X and Y positions) come from your display. Bottom (Z position) comes from your transducer. These need to be aligned. To get maximum precision, network a Lowrance Point-1 or 3rd party NMEA compatible GPS/GNSS device. Place the GPS receiver directly over the transducer and ensure your Lowrance or Simrad is pulling positions from the correct source. Modest separation between the GPS Source and transducer will result in artificially wavy contours.
6. For the best bathymetric maps, map early in spring.
Although BioBase is the industry-leading technology for mapping aquatic plants in lakes, sometimes aquatic plant growth can interfere with bottom tracking. Generally speaking, this is worse at the height of summer or early fall when plant biomass begins to scenesce, or die, and fall out of the water column (Figure 3). Horizontal interlacing stems and decaying mats of vegetation will often create false bottoms leading to artificial contours (Figure 4). Waiting until spring after most decomposition has taken place (but before new growth) is the best time to map bathymetry. See the difference in a pond mapped in fall when dense decaying vegetation was present (Figure 4) versus the following spring (Figure 5).
7. For best vegetation maps, map in early to mid summer.
Although BioBase creates robust vegetation maps any time of the year, if you wish to schedule surveys during an optimal window of plant growth, do so during the times of year when plants have fully elongated but have not hit peak biomass (Figure 6). This is related to the issue of depth loss in dense vegetation described above. Aquatic vegetation in most regions typically elongates vertically as the water warms in spring. As water temperatures reach seasonal maximums, aquatic vegetation accumulates biomass and proliferates in multiple directions and often “tops out” at the water surface. This growth can be a challenge for any sonar technology since plant canopies in these situations often appear very acoustically similar to bottom. Still, biovolume that displays 100% (Red as in Figure 7) should be accurate regardless if the depth is inaccurate.
8. Approach transect design like painting: execute a design that will ensure the best coverage in the least amount of time.
Are you mapping bathymetry in a large shallow bowl? Then spread your transects out wide and drive fast, up to 17 knots. Adjust the buffer in BioBase as wide as necessary to get the coverage you need. This is akin to buying a big paint roller and rolling on a coat of paint over a large flat wall.
Alternatively, maybe you are focused on mapping detail in a dammed reservoir with a convoluted shoreline. Or mapping patchy growing vegetation in a small lake or pond? In these cases, you need to put the roller away and switch to a small detailing brush and take your time. Use “strokes” that best covers what needs to be covered and don’t be locked into a “back and forth” or “up and down” style. In other words, drive the boat over any structure that needs to be mapped in any way that efficiently covers the water. In many cases, a concentric circle transect design may be the best option (Figure 8). I generally recommend against a waffle grid patterns or laying down a plate of spaghetti tracks where it’s difficult to retrace your steps if there are anomalies in the map. Ok, enough with the painting and food analogies (but hopefully they help you visualize the concept). If you want to dig deeper into transect mapping strategies, consult this blog.