A broadband chirp with 100 kHz of bandwidth can separate two echoes about 0.75 cm apart, while a classic single-frequency pulse of 1.024 ms smears them over about 76 cm, roughly a hundredfold difference (76 / 0.75 is about 101) in how finely a fish finder can split targets (Lavery et al., ICES Journal of Marine Science 2017). That gap explains why CHIRP (a pulse that sweeps through a band of frequencies) now sits in everything from scientific echosounders to consumer transducers. In tank tests, fast-ramped broadband pulses resolved two calibration spheres just 5 cm apart (ICES Cooperative Research Report No. 336, 2017). Physics still sets the depth limit: seawater absorbs about 50 dB/km at 200 kHz against about 10 dB/km at 38 kHz (Simrad EQ60 manual), and near 333 kHz field measurements found 15 dB/km more loss than the standard formulas predict (Macaulay, Chu and Ona, JASA 2020). We aggregated data from ICES, NOAA Fisheries and NCEI, peer-reviewed papers in the ICES Journal of Marine Science, JASA, Fisheries Research and Scientific Reports, and manufacturer documentation from Garmin, Simrad and Airmar (labelled as vendor claims). For the wider picture of sound in the ocean, see our underwater acoustics and ocean sonar statistics.
TL;DR
- A 100 kHz broadband chirp gives about 0.75 cm range resolution vs about 76 cm for a 1.024 ms single-frequency pulse (Lavery et al., ICES Journal of Marine Science 2017).
- Fast-ramped broadband pulses resolved two spheres 5 cm apart on the 70, 120 and 200 kHz channels (ICES CRR No. 336, 2017).
- Seawater absorbs about 10 dB/km at 38 kHz and about 50 dB/km at 200 kHz (Simrad EQ60 manual).
- Near 333 kHz, measured absorption was 15 dB/km higher than existing formulas (Macaulay, Chu and Ona, JASA 2020).
- A random forest separated whitefish from sticklebacks with 73.4% accuracy using a 90 to 170 kHz chirp (Gugele et al., Scientific Reports 2021).
- Two classifiers reached about 89% accuracy for cod, polar cod and shrimp with a single 200 kHz broadband transducer (Dunn et al., Fisheries Research 2025).
- Broadband echo-counting estimated 12% more Atlantic cod than echo-integration in a Greenland fjord (Gardella et al., Fisheries Research 2026).
- Broadband and single-frequency volume backscattering were statistically equivalent at 38, 70, 120 and 200 kHz with frequency-domain processing (Levine, Bassett and De Robertis, ICES Journal of Marine Science 2025).
- 80% of intercepted boat anglers and 79% of ice anglers used imaging technology such as sonar, against 3.9% of shore anglers (Kerkhove et al., Fisheries 2024).
- 16% of anglers on a Florida lake used forward-facing sonar, rising to 28% among largemouth bass anglers (Henry et al., North American Journal of Fisheries Management 2025).
- Harbour porpoise detections fell 65 to 79% during echosounder pinging at 13 North Sea sites (Hubert et al., Environmental Pollution 2025).
1. Range Resolution: CHIRP vs Single-Frequency Pulses
Range resolution is the smallest distance along the beam at which two targets still show up as two separate echoes. For a single-frequency (CW, continuous wave) pulse it is fixed by the pulse length; for a chirp it is fixed by the bandwidth after pulse compression, a matched-filter step that squeezes the long sweep back into a sharp spike. That is why a 100 kHz chirp resolves about 0.75 cm while a 1.024 ms CW pulse resolves about 76 cm (Lavery et al., ICES Journal of Marine Science 2017).
The practical message is that wider transducer bands, not longer pulses, buy separation. The same paper notes that above 70 kHz a CW pulse would have to be shorter than about 100 µs just to match a tapered chirp, and such short pulses sacrifice much of their frequency content. Bats solved the same trade-off with frequency-modulated calls, as our microbat echolocation statistics show.
| Metric | Value | Source |
|---|---|---|
| Range resolution of a 1.024 ms single-frequency (CW) pulse vs a broadband pulse with 100 kHz bandwidth after pulse compression | about 76 cm vs about 0.75 cm | Lavery et al., ICES Journal of Marine Science 2017 |
| EK80 theoretical range resolution: 18 kHz channel (band 15 to 25 kHz) vs 38 kHz channel (band 25 to 45 kHz) | 7.5 cm vs 3.75 cm | Lavery et al., ICES Journal of Marine Science 2017 |
| EK80 theoretical range resolution: 120 kHz channel (band 95 to 160 kHz) vs 333 kHz channel (band 260 to 400 kHz) | 1.15 cm vs 0.54 cm | Lavery et al., ICES Journal of Marine Science 2017 |
| Maximum CW pulse length that would match a tapered chirp on transducers above 70 kHz | shorter than about 100 µs | Lavery et al., ICES Journal of Marine Science 2017 |
| Range resolution of a towed broadband system spanning 1.7 to 100 kHz, lower vs upper frequencies | about 20 cm vs 3 cm | Stanton et al., ICES Journal of Marine Science 2010 |
Context: the EK80 values are theoretical (speed of sound divided by twice the bandwidth). Real systems lose some of this to tapering, the smoothing of the pulse edges used to suppress side lobes (false echoes beside the main one). Most recent available data: the 2017 tank study above and Stanton et al. 2010, which remain the reference measurements.
2. Target Separation in Practice: Spheres, Walls and the Seabed
Theory says centimetres; tank tests show what survives real processing. In the 2016 USA-Norway workshop, fast-ramped broadband pulses resolved two spheres only 5 cm apart on all three tested channels (70, 120 and 200 kHz), while slow-ramped pulses did so only on the 200 kHz channel (ICES CRR No. 336, workshop report 2017). The taper choice alone decides whether a fish hugging another fish is one blob or two.
Boundaries are harder than open water. A fish near the bottom competes with a far stronger seabed echo, and the side lobes of that echo can hide it. That is the real-world meaning of target separation for a skipper looking for groundfish.
| Metric | Value | Source |
|---|---|---|
| Two spheres 5 cm apart resolved: fast-ramped vs slow-ramped broadband pulses (70, 120 and 200 kHz channels tested) | all three channels vs 200 kHz channel only | ICES CRR No. 336, 2017 |
| Closest a 38.1 mm sphere could be detected to a tank wall, EK80 slow taper vs custom Gaussian-tapered signal | 20 cm vs 10 cm | Lavery et al., ICES Journal of Marine Science 2017 |
| Target strength of the sphere relative to the wall echo peak (120 kHz channel, 1.5 m from the wall) | 40 dB lower | Lavery et al., ICES Journal of Marine Science 2017 |
| Closest separation of individual fish above the bottom with a low-Q (wide-band) transducer | 1 inch (vendor claim) | Airmar CHIRP seminar slides 2015 (vendor’s own claim) |
| Q factor of CHIRP-designed transducers vs competitor narrowband transducers | 3 or less vs 25 to 35 (vendor claim) | Airmar CHIRP seminar slides 2015 (vendor’s own claim) |
Context: Q factor measures how long a transducer keeps ringing after it is driven; low Q means a wider usable band and a shorter ring. The Airmar figures are marketing claims from a 2015 Airmar seminar deck and have not been independently measured. Most recent available data for these tank tests: 2017.
3. Depth Penetration: Frequency vs Absorption in Seawater
Every fish finder trades detail for reach. Higher frequencies give narrower beams and finer resolution, but seawater soaks them up: about 50 dB/km at 200 kHz against about 10 dB/km at 38 kHz, and in fresh water the same frequencies lose only about 10 and 0.5 dB/km (Simrad EQ60 manual, page 6). Because the echo travels down and back, those losses double over the two-way path, which is why offshore units still carry 38 to 50 kHz channels.
The standard absorption formulas hold up below about 200 kHz but break down above it. Field measurements found absorption roughly 15 dB/km higher than predicted near 333 kHz, enough to cut usable range at that frequency to about 55 m in the test conditions (Macaulay, Chu and Ona, JASA 2020). The same frequency-versus-range trade-off governs data links, as our underwater acoustic modem statistics show.
| Metric | Value | Source |
|---|---|---|
| Sound absorption at 38 kHz, seawater vs fresh water | about 10 dB/km vs 0.5 dB/km | Simrad EQ60 manual (manufacturer documentation) |
| Sound absorption at 200 kHz, seawater vs fresh water | about 50 dB/km vs 10 dB/km | Simrad EQ60 manual (manufacturer documentation) |
| Measured absorption minus the Francois and Garrison formula: at 38 / 120 / 200 kHz vs at 333 kHz | 0.73 / 1.31 / 1.21 dB/km vs 15.24 dB/km | Macaulay, Chu and Ona, JASA 2020 |
| Variability of the absorption measurements, all frequencies | about 2 dB/km | Macaulay, Chu and Ona, JASA 2020 |
| Formula contributions at 333 kHz (typical conditions): pure water vs magnesium sulphate vs boric acid | 39.0 vs 36.7 vs 0.1 dB/km | Macaulay, Chu and Ona, JASA 2020 |
| Usable range at 333 kHz vs lower frequencies in the field tests | about 55 m vs beyond 60 m | Macaulay, Chu and Ona, JASA 2020 |
| Change in a 38 kHz deep-water biomass estimate after revising the absorption equation | 17% lower | Doonan et al. 2003, as cited by Macaulay, Chu and Ona, JASA 2020 |
Context: the 2020 estimates come from 20 measurements at 4 locations over 3 years, in water around 7 C, 33 PSU (practical salinity units) and the equivalent of 10 m depth. Absorption rises with temperature and salinity, so tropical results differ. Most recent available field data: 2020.
4. Commercial, Scientific and Recreational Hardware Compared
The gap between a survey echosounder and a boat-show fish finder is less about frequency than about calibration, power control and logging. NOAA’s walleye pollock surveys run five EK80 channels at 18, 38, 70, 120 and 200 kHz and analyse echoes from 16 m below the surface to within 0.5 m of the seabed, as deep as 1,000 m (NOAA Fisheries, InPort record for the 2024 Eastern Bering Sea survey). Consumer units cover similar frequencies but quote best-case depth figures without calibration data.
Cost tells the rest of the story. Equipping a single research ship with the wideband system was estimated at US$260,000 to 300,000 in 2017, while consumer CHIRP transducers are sold as boat accessories.
| Metric | Value | Source |
|---|---|---|
| EK80 channels on the NOAA 2024 Eastern Bering Sea acoustic-trawl survey | 18, 38, 70, 120 and 200 kHz | NOAA Fisheries InPort 2024 |
| 2024 Eastern Bering Sea survey dates | June 11 to July 20, 2024 | NOAA Fisheries InPort 2024 |
| EK80 settable pulse duration range | 64 to 8,192 µs | ICES CRR No. 336, 2017 |
| Cost to convert one research ship to EK80 (2017), including five or six transceivers at about US$40,000 each | about US$260,000 to 300,000 | ICES CRR No. 336, 2017 |
| Garmin ECHOMAP UHD traditional sonar frequencies vs CHIRP ClearVu frequencies | 50, 77, 83 or 200 kHz vs 260, 455 or 800 kHz (vendor spec) | Garmin ECHOMAP UHD manual (vendor’s own claim) |
| Garmin ECHOMAP UHD maximum sonar depth and transmit power | 701 m at 77 kHz, 500 W RMS (vendor spec) | Garmin ECHOMAP UHD manual (vendor’s own claim) |
| Airmar CHIRP transducer operating span and largest single-transducer bandwidth | 28 to 210 kHz, over 117 kHz (vendor claim) | Airmar CHIRP seminar slides 2015 (vendor’s own claim) |
Context: Garmin’s sonar specification page states that depth depends on the transducer, water salinity and bottom type. Vendor depth figures are best-case and not comparable with calibrated survey ranges. Most recent available cost data: 2017.
5. Species Classification With Broadband Echoes
A chirp returns not just one echo strength but a whole spectrum, the frequency response of each fish, and that spectrum carries clues about swim bladder size and shape. Classifiers trained on these spectra now reach about 89% accuracy for Atlantic cod, polar cod and northern shrimp using a single 200 kHz transducer in broadband mode (Dunn et al., Fisheries Research 2025). The catch: that result, like most in this section, comes from mesocosms (large in-water net pens, here holding one species at a time), not open-sea surveys.
Similar-sized swim-bladder fish remain the hard case. Small whitefish and sticklebacks (mean lengths 7.0 cm and 5.1 cm) were separated with 73.4% accuracy, and the useful information concentrated in a narrow 140 to 155 kHz slice of the 90 to 170 kHz chirp (Gugele et al., Scientific Reports 2021).
| Metric | Value | Source |
|---|---|---|
| Classification accuracy, cod vs polar cod vs northern shrimp, single 200 kHz broadband transducer (LightGBM and support vector machine) | about 89% | Dunn et al., Fisheries Research 2025 |
| Test accuracy separating whitefish from sticklebacks: frequency response curves vs numerical feature descriptors | 73.4% vs 66.6% | Gugele et al., Scientific Reports 2021 |
| Chirp band used in the whitefish and stickleback test, and the band carrying most classification importance | 90 to 170 kHz; 140 to 155 kHz | Gugele et al., Scientific Reports 2021 |
| Fish targets with extracted frequency responses: sticklebacks vs whitefish | 101 vs 86 | Gugele et al., Scientific Reports 2021 |
| Individual-fish echo detection accuracy and false recognition rate in simulated aquaculture cages (PDIM method) | 78.34% and 1.32% | Yang et al., Fishes 2025 |
| Reduction in positive skew of mesopelagic fish target strength after filtering anomalous broadband echoes | up to 35% | Chawarski, Coté and Geoffroy, JASA 2025 |
Context: the aquaculture result (Yang et al., Fishes 2025) measures how well single-fish echoes are picked out of dense cages, not species identity. The mesopelagic study (Chawarski et al., JASA 2025) shows that cleaning broadband data matters as much as the classifier. Scientific Reports 2021 is the most recent available two-species mesocosm accuracy figure.
6. Survey Continuity, Data Volume and Calibration
Fisheries agencies cannot simply swap in broadband and break decades of abundance indices. The good news from 2025: when broadband echoes are averaged in the frequency domain, volume backscattering is statistically equivalent to the old single-frequency values at 38, 70, 120 and 200 kHz (Levine, Bassett and De Robertis, ICES Journal of Marine Science 2025). That clears the path for broadband in stock surveys without restarting time series.
The cost is data. Broadband files are far larger, and configuration errors once produced offsets as big as the signals being measured. The shift is from a hardware question to a data-management one, and NOAA’s public archive already holds more than 170 TB of water column sonar (NOAA NCEI, Water Column Sonar Data).
| Metric | Value | Source |
|---|---|---|
| Broadband (FM) vs single-frequency (CW) volume backscattering at 38, 70, 120 and 200 kHz, frequency-domain processing | statistically equivalent | Levine, Bassett and De Robertis, ICES Journal of Marine Science 2025 |
| Data collected by an EK80 compared with an EK60 | 1 to 2 orders of magnitude more | ICES CRR No. 336, 2017 |
| Offsets between EK60 and EK80 echo-integration results before vs after fixing configuration errors | up to 6 dB vs under 0.5 dB | ICES CRR No. 336, 2017 |
| Water column sonar data held in the NOAA NCEI archive | more than 170 TB | NOAA NCEI, Water Column Sonar Data (read October 2026) |
| Broadband echo-counting vs echo-integration estimate of Atlantic cod in the Nuuk fjord, Greenland | 12% more | Gardella et al., Fisheries Research 2026 |
| Broadband echo-counting vs the SAM stock assessment model, same cod stock | 6.3% more | Gardella et al., Fisheries Research 2026 |
Context: echo-counting counts individual fish tracks, which broadband makes reliable because single targets separate better; echo-integration sums the total backscattered energy. Gardella et al. (Fisheries Research 2026) recommend echo-integration only in dense patches where the Sawada index (a measure of how many fish share one sampling volume) exceeds 0.04. The data-volume and offset figures come from the 2017 EK80 workshop and are the most recent available.
7. Recreational Sonar Use and Wildlife Side Effects
Fish-finding sonar is no longer a niche tool on recreational boats. In a dual intercept creel survey (interviews of anglers on the water), 80% of boat anglers and 79% of ice anglers used imaging technology such as sonar or cameras, against 3.9% of shore anglers, yet technology had no effect on actual catch (Kerkhove et al., Fisheries 2024). Forward-facing sonar, which shows live images ahead of the boat, is the newest flashpoint: on Florida’s Lake Talquin, users caught 1.32 largemouth bass per hour against 0.51 for non-users (Henry et al., North American Journal of Fisheries Management 2025).
The ocean side of the ledger is the sound itself. Fish-detection echosounders at 70 kHz and 185 to 255 kHz drove harbour porpoise detections down by 65 to 79% at 13 North Sea moorings (Hubert et al., Environmental Pollution 2025). Ship noise is a separate pressure covered in our propeller cavitation noise statistics.
| Metric | Value | Source |
|---|---|---|
| Use of imaging technology (sonar, cameras): boat anglers vs ice anglers vs shore anglers | 80% vs 79% vs 3.9% | Kerkhove et al., Fisheries 2024 |
| Share of anglers using forward-facing sonar on Lake Talquin, Florida: all anglers vs black crappie vs largemouth bass anglers | 16% vs 26% vs 28% | Henry et al., North American Journal of Fisheries Management 2025 |
| Largemouth bass catch rate, forward-facing sonar users vs non-users | 1.32 vs 0.51 fish per hour | Henry et al., North American Journal of Fisheries Management 2025 |
| Catch rate of largemouth bass 406 mm or longer, forward-facing sonar users vs non-users | 0.49 vs 0.09 fish per hour | Henry et al., North American Journal of Fisheries Management 2025 |
| Drop in harbour porpoise detections during echosounder pinging, 13 North Sea sites | 65% to 79% | Hubert et al., Environmental Pollution 2025 |
| Time for porpoise detections to return to normal after pinging stopped | about 30 minutes | Hubert et al., Environmental Pollution 2025 |
| Distance at which a porpoise deterrent effect was still observed | 2.5 km | Hubert et al., Environmental Pollution 2025 |
Context: the porpoise study found no habituation over six weeks of hourly exposure, with echosounders active on average 51 days per mooring. Forward-facing sonar is a scanning imaging sonar rather than a downward CHIRP sounder, but it shows how fast better target separation changes behaviour on the water.
Summary: Commercial Fish Finder CHIRP Sonar by the Numbers
| Metric | Value | Source |
|---|---|---|
| Range resolution, 100 kHz broadband chirp vs 1.024 ms single-frequency pulse | about 0.75 cm vs about 76 cm | Lavery et al., ICES Journal of Marine Science 2017 |
| Towed broadband system range resolution, lower vs upper frequencies | about 20 cm vs 3 cm | Stanton et al., ICES Journal of Marine Science 2010 |
| Smallest sphere separation resolved with fast-ramped broadband pulses | 5 cm | ICES CRR No. 336, 2017 |
| Seawater absorption, 38 kHz vs 200 kHz | about 10 vs 50 dB/km | Simrad EQ60 manual (manufacturer documentation) |
| Excess absorption over the standard formula at 333 kHz | 15.24 dB/km | Macaulay, Chu and Ona, JASA 2020 |
| Biomass change at 38 kHz after revising the absorption equation | 17% lower | Doonan et al. 2003, as cited by Macaulay, Chu and Ona, JASA 2020 |
| Garmin ECHOMAP UHD maximum sonar depth | 701 m at 77 kHz (vendor spec) | Garmin ECHOMAP UHD manual (vendor’s own claim) |
| Species classification accuracy, single 200 kHz broadband transducer | about 89% | Dunn et al., Fisheries Research 2025 |
| Whitefish vs stickleback classification accuracy | 73.4% | Gugele et al., Scientific Reports 2021 |
| Broadband vs CW volume backscattering, frequency-domain processing | statistically equivalent | Levine, Bassett and De Robertis, ICES Journal of Marine Science 2025 |
| EK80 data volume vs EK60 | 1 to 2 orders of magnitude more | ICES CRR No. 336, 2017 |
| NOAA NCEI water column sonar archive | more than 170 TB | NOAA NCEI, Water Column Sonar Data (read October 2026) |
| Echo-counting vs echo-integration cod estimate | 12% more | Gardella et al., Fisheries Research 2026 |
| Imaging technology use, boat anglers | 80% | Kerkhove et al., Fisheries 2024 |
| Harbour porpoise detection drop during echosounder pinging | 65% to 79% | Hubert et al., Environmental Pollution 2025 |
Methodology and Sources
- Lavery, Bassett, Lawson and Jech, Exploiting signal processing approaches for broadband echosounders, ICES Journal of Marine Science 2017: NOAA Institutional Repository
- Demer et al., 2016 USA-Norway EK80 Workshop Report, ICES Cooperative Research Report No. 336, 2017: full report (NOAA SWFSC) and ICES news release
- Stanton, Chu, Jech and Irish, New broadband methods for resonance classification and high-resolution imagery of fish with swimbladders, ICES Journal of Marine Science 2010: DOI
- Macaulay, Chu and Ona, Field measurements of acoustic absorption in seawater from 38 to 360 kHz, JASA 2020: NOAA Institutional Repository
- Simrad EQ60 user manual, environment and absorption section (manufacturer documentation): manual page
- NOAA Fisheries, Results of 2024 Eastern Bering Sea acoustic-trawl survey (DY2408): InPort record
- NOAA NCEI, Water Column Sonar Data archive: product page
- Garmin ECHOMAP UHD owner’s manual, sonar specifications (vendor’s own claims): specification page
- Airmar, CHIRP in Detail seminar slides 2015 (vendor’s own claims): PDF
- Dunn et al., Broadband acoustic classification of Atlantic cod, polar cod, and northern shrimp in in situ mesocosm experiments, Fisheries Research 2025: DOI
- Gugele et al., Differentiation of two swim bladdered fish species using next generation wideband hydroacoustics, Scientific Reports 2021: DOI
- Yang et al., Individual Fish Broadband Echo Recognition Method and Performance Analysis Oriented to Aquaculture Scenarios, Fishes 2025: DOI
- Chawarski, Coté and Geoffroy, Unsupervised classification increases precision in acoustic broadband target strength measurements of mesopelagic fish, JASA 2025: DOI
- Levine, Bassett and De Robertis, Broadband and narrowband echosounder signals produce comparable estimates of volume backscattering, ICES Journal of Marine Science 2025: DOI
- Gardella et al., Towards the inclusion of broadband acoustic methods in the assessment of benthopelagic fish stocks, Fisheries Research 2026: DOI
- Kerkhove et al., Understanding the Role of Recreational Angling Technology in Angler Expectations of Catch, Trip Catch, and Angler Satisfaction, Fisheries 2024: DOI
- Henry, Strickland and Winstead, Differences in catch rates of Black Crappie and Largemouth Bass anglers using forward-facing sonar in Lake Talquin, Florida, North American Journal of Fisheries Management 2025: DOI
- Hubert et al., Echosounders for fish detection disturb harbour porpoises, Environmental Pollution 2025: DOI
- Data watch: the core range-resolution and tank-separation measurements (2010 and 2017) and the absorption field data (2020) are older than three years and remain the most recent available. Range resolution figures are theoretical (c/2B) and degrade in practice with tapering. The 2020 absorption paper gives the 333 kHz usable range as about 55 m in one passage and says the signal-to-noise limit was reached at about 60 m in another; we report 55 m. Species accuracies (73.4%, about 89%, 78.34%) come from mesocosm or cage experiments with two or three species and should not be read as open-sea survey performance; the 2017 EK80 workshop reported no classification accuracy and called for standard wideband classification procedures. The Simrad EQ60 manual page is undated. Absorption values from the Simrad manual are rounded manufacturer figures; real values vary with temperature, salinity and depth. Vendor figures from Garmin and Airmar are best-case marketing claims, and Airmar’s own slides are inconsistent (5x vs 5 to 10x resolution gains), so we did not use those multipliers. The Doonan et al. 2003 biomass change is reported here as cited in the 2020 absorption paper; we could not open the original. The NCEI archive size carries no date on the page and was read in October 2026.
- Last updated: October 27, 2026. We update this roundup quarterly, and the next refresh is expected when ICES WGFAST (Working Group on Fisheries Acoustics, Science and Technology) publishes its 2026 report and NOAA releases its 2026 acoustic-trawl survey results.