Sonar water-column sounding and bathymetry mapping using fish finders
Summary
This water-body activity introduces students to the concept of a regular survey pattern, series of sonar measurements, and water-column and bottom mapping. The basic concept is to cast or tow a small sonar transducer (echo-locator) in a body of water and use its acoustic waves to map objects in the water column and water-bottom bathymetry. Inexpensive units (such as the Lowrance FishHunter or Lucky FishFinder) with their hand-held recorder and a remote transducer on the water are used for the survey and to create resultant sections and maps. This activity requires some logistics (and care) with respect to the water body and its access plus surveying strategy (casting, towing, shore or vessel). Use of the units' wireless recorders, software analysis, and map creation is required. A wide range of possible water bodies and the sophistication of the software allows room for creative and interesting efforts with professional-level results.
This activity was developed so that students can do the survey themselves with affordable equipment, when the in-person field course could not be held.
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Context
Audience
![[creative commons]](/images/creativecommons_16.png)
Skills and concepts that students must have mastered
It is best if students have an Introduction to Geophysics undergraduate course at the junior level as a prerequisite.
How the activity is situated in the course
This activity is one of half a dozen done during in the several-week geophysics remote field course. It is best situated in the middle or end of the course as it is preferable to have some logistics experience beforehand (getting to sites, use of safety equipment, understanding how to undertake a regularly sampled survey, understanding of how instruments work).
Activity Length
It started with an introductory online lecture (30 minutes) on sonar. Then the students need about two hours of study to understand the instruments and conduct some practice, then about three hours of field surveying and measuring of their actual chosen field site. Working up the results and doing the write-up was several more hours.
Goals
Content/concepts goals for this activity
Students will be able to:
- Apply the basic concepts of acoustic wave generation, propagation, reflection, and recording in water
- Conduct a sonar survey, collecting measurements and recordings
- Apply field logistics and safety, taking into account realistic size, scale, and effort for surveying a given site
- Describe data flow in an equipment system
Higher order thinking skills goals for this activity
- Design a water surface survey using the "fishfinder" equipment to investigate the water column and water bottom
- Produce a bathymetric map of the area of interest from their sonar survey measurements
- Evaluate errors, uncertainties, and overall quality of the survey; articulate reasons for incomplete data sets
- Communicate results through a written report with appropriate figures and a short presentation with a video
Other skills goals for this activity
- Learn to use a sonar device (fish finder)
Description and Teaching Materials
This activity needs selection of an appropriate water body that has a water-bottom bathymetry of interest. Examples could be a large swimming pool with a deep end, a river, pond, lake, or sea. Students need access to the site and a method to undertake traverses on it. The traverses could be from casting the instrument at various locations on the shore and reeling the transducer in, walking on top of a bridge and casting, towing the instrument from a canoe, kayak, or other boat. It is preferable to be able to make about 10 traverses of some 10s of meters so that meaningful map can be generated. Any fish-finder instrument that can generate profiles and maps should be useable. However, we found the Lowrance FishHunter to be user-friendly with quite sophisticated output products.
Getting started
Orient the students to the purpose and applications for sonar studies. Sonar surveys can be used to inform applications such as boating, construction, fishing, dredging, archaeology, stratigraphy, or coastal evolution.
- Presentation: Introduction to sonar surveys with fish finder (PowerPoint 2007 (.pptx) 7.1MB Oct28 20)
Activity
Two versions of the activity are available for the two different types of fish finders used in our course.
- Student sonar survey assignment - Lowrance Fish Hunter version (Microsoft Word 2007 (.docx) 1MB Oct28 20)
- Student sonar survey assignment - Lucky Fish Finder version (Microsoft Word 2007 (.docx) 961kB Oct28 20)
Technology Needs
- The Lowrance FishHunter system uses a wireless transmission and a smartphone and is the recommended unit as it has a sophisticated transducer system, wireless connection, and impressive mapping capability downloaded to one's smartphone. The Lucky FishFinder is our second choice (as tested) and will make manual measurements which can be recorded and input into a mapping program.
- Smartphone with compass and distance apps
- Computer with Google Earth
Teaching Notes and Tips
- Give students some days to determine an appropriate site and get logistics in place (access, boats). This might be happening concurrently with other activities in the course, depending on how the course is structured
- Encourage as large and detailed survey as feasible
- Recommend doing in the survey in a small team or with friends/family
Assessment
The activity can be evaluated by accomplishment of the survey as documented with pictures, video, a report, and data. The quality and completeness of the mapped area can be assessed. Some measure of the level of difficulty, creativity, and usefulness of the survey could be assigned.