Dual-frequency Identification Sonar Research Articles

Assessing a dual-frequency identification sonars’ fish-counting accuracy, precision, and turbid river range capability

Accurately assessing migrating salmon populations in turbid rivers with hydroacoustics is challenging. Using single, dual, or split-beam sonars, difficulties occur fitting acoustic beams between the river's narrow boundaries, distinguishing fish from nonfish echoes, and resolving individual fish at high densities. To address these issues, the fish-counting capability of a dual-frequency identification sonar (DIDSON), which produces high resolution, video-like images, was assessed. In a clear river, fish counts generated from a DIDSON, an echo counter, split-beam sonar, and video were compared to visual counts from a tower, a method frequently used to ground-truth sonars. The DIDSON and tower counts were very similar and showed the strongest agreement and least variability compared to the other methods. In a highly turbid river, the DIDSON's maximum detection range for a 10.16 cm spherical target was 17 m, less than absorption and wave spreading losses predict, and 26 m in clear water. Unlike tower and video methods, the DIDSON was not limited by surface disturbances or turbidity. DIDSON advantages over other sonars include: better target resolution; wider viewing angle; better coverage of the water column; accurate direction of travel; and simpler to aim and operate.

Generating River Bottom Profiles with a Dual‐Frequency Identification Sonar (DIDSON)

AbstractEstimating fish passage in rivers with a side‐looking sonar positioned near shore requires proper alignment of the transducer with the river bottom. To maximize fish detection, we developed a robust aiming protocol using river bottom profiles generated from standard and long‐range dual‐frequency identification sonars (DIDSONs). The DIDSON profiles compared well with those generated from range and depth measures or bathymetry methods when the river bottoms were linear or changed from a steeper slope near shore to a flatter slope offshore. If the offshore slope was steeper, the DIDSON profile displayed shallower depths. The actual differences in depth between the DIDSON profiles and those from other methods were often considerably less than the potential differences from beam‐spreading error. The maximum depth differences between the same DIDSON profiles marked independently multiple times ranged from 0.08 m for the DIDSON's highest frequency to 0.5 m for the lowest. A model of the fish‐counting transducer beam was plotted in the same coordinate system as the river bottom profile. Macros developed for Excel spreadsheets enabled us to “rotate” the beam and determine the optimal tilt angle for each river bottom profile.

The complexity of narrowband echo envelopes as a function of fish side-aspect angle

AbstractBurwen, D. L., Nealson, P. A., Fleischman, S. J., Mulligan, T. J., and Horne, J. K. 2007. The complexity of narrowband echo envelopes as a function of fish side-aspect angle. – ICES Journal of Marine Science, 64: 1066–1074. High-frequency, narrowband acoustic signals may contain more information on fish size and orientation than previously thought. Our observations of dual frequency identification sonar (DIDSON) images of fish orientation paired with split-beam echo envelopes helped clarify why metrics such as echo duration have performed better than target strength measurements when predicting salmon lengths at side aspect. Fish orientation has a pronounced effect on the duration and shape of split-beam echo envelopes from large (80–130 cm) salmon insonified at side aspect. At near-normal aspect angles, echo envelopes are unimodal, symmetrical, and resemble echo envelopes from calibration spheres. With increasing oblique-aspect angle, echo shapes become less symmetrical as the number of peaks increases, and echo duration and amplitude become more variable. Using angle and range coordinates, peaks in an echo envelope can be traced to their origin on a DIDSON image. At oblique-aspect angles, discrete peaks develop that are reflected from regions close to the head and tail. In addition, the distance between peaks increases with increasing aspect angle and is larger than can be explained by swimbladder length.

A lightweight transducer platform for use in stationary shallow water horizontal-aspect acoustic surveys

A robust, remotely controlled transducer platform has been designed for use in stationary shallow water acoustic surveys. The transducer array platform is integrated with a weatherized top-side box allowing for collection of acoustic data at remote stations. The platform allows for vertical placement of the transducer array in the water column and for remotely manipulating the transducer pitch. Both a dual-frequency identification sonar (DIDSON) and a BioSonics split-beam transducer were mounted to the platform for simultaneous data collection over a variety of estuarine habitats. The platform is quickly deployed and retrieved by a single user from a small vessel. Effective water depths for optimal use range from 1 to 3.5 m; however, the equipment can be easily deployed at greater depths. The array platform has been in service for 2 years and the performance level and data quality remain high.

Video and acoustic camera techniques for studying fish under ice: a review and comparison

Researchers attempting to study the presence, abundance, size, and behavior of fish species in northern and arctic climates during winter face many challenges, including the presence of thick ice cover, snow cover, and, sometimes, extremely low temperatures. This paper describes and compares the use of video and acoustic cameras for determining fish presence and behavior in lakes, rivers, and streams with ice cover. Methods are provided for determining fish density and size, identifying species, and measuring swimming speed and successful applications of previous surveys of fish under the ice are described. These include drilling ice holes, selecting batteries and generators, deploying pan and tilt cameras, and using paired colored lasers to determine fish size and habitat associations. We also discuss use of infrared and white light to enhance image-capturing capabilities, deployment of digital recording systems and time-lapse techniques, and the use of imaging software. Data are presented from initial surveys with video and acoustic cameras in the Sagavanirktok River Delta, Alaska, during late winter 2004. These surveys represent the first known successful application of a dual-frequency identification sonar (DIDSONTM) acoustic camera under the ice that achieved fish detection and sizing at camera ranges up to 16 m. Feasibility tests of video and acoustic cameras for determining fish size and density at various turbidity levels are also presented. Comparisons are made of the different techniques in terms of suitability for achieving various fisheries research objectives. This information is intended to assist researchers in choosing the equipment that best meets their study needs.

Accuracy and precision of fish-count data from a “dual-frequency identification sonar” (DIDSON) imaging system

Abstract The reliability of sockeye-salmon (Oncorhynchus nerka) count data collected by a dual-frequency, identification sonar (DIDSON) system is evaluated on the basis of comparisons with visual counts of unconstrained migrating salmon and visual counts of salmon constrained to passing through an enumeration fence. Regressions fitted to the DIDSON count data and the visual count data from the enumeration fence were statistically indistinguishable from a line with slope = 1.0 passing through the origin, which we interpret as agreement in both counts. In contrast, the regressions fitted to the DIDSON count data and the unconstrained visual count data had slopes that were significantly <1.0 (p < 0.001) and are consistent with an interpretation of systematic bias in these data. When counts of both unconstrained and constrained fish from the DIDSON system were ≥50 fish event−1, repeated counts of the DIDSON files were observed to produce the same counts 98–99% of the time, respectively, and based on the coefficient of variation, counts of individual passage events varied <3% on average. Therefore, the DIDSON count data exhibit high precision among different observers. As an enumeration fence provides a complete census of all fish passing through it, we conclude that fish-count data produced by the DIDSON imaging system are as accurate as visual counts of fish passing through an enumeration fence when counts range up to 932 fish event−1, the maximum count recorded during our study, regardless of the observer conducting the count. These conclusions should be applicable to typical riverine applications of the DIDSON system in which the bottom and surface boundaries are suitable for acoustic imaging, the migrating fish are adult salmon, and the transducer is carefully aimed so that the beams ensonify the area through which the salmon are migrating.

Echoview software for tracking and counting fish detected with a dual frequency identification sonar (DIDSON) imaging sonar: A flexible approach to signal enhancement and object detection prior to target tracking

The data from the DIDSON (Dual frequency IDentification SONar) are of startling resolution, and show swimming fish in unprecedented detail. Although the fish objects are visually striking, object detection must be achieved in post processing and is a challenge when compared with conventional split beam systems. Data processing can be applied to automatically remove static objects and noise and to enhance the signal from moving objects in DIDSON data. Moving objects are then detected as targets within individual DIDSON frames and converted to X−Y−Z-time position data suitable for input to a tracking algorithm. The initial data manipulation for noise removal and object detection is achieved through the application of successive modular operators. The results of each operation can be viewed as a ‘‘virtual variable’’ enabling each step to be scrutinized and optimized by the operator. This modular approach to data manipulation, target detection, and fish tracking will enable the rapid development of new techniques and tools. It is a ‘‘future-proof’’ data processing solution.

Salmon enumeration in the Fraser River with the dual-frequency identification sonar (DIDSON) acoustic imaging system

Reliable data on the number of salmon entering tributaries of the Fraser River to spawn (escapement) is needed for Pacific salmon management. Existing escapement techniques are costly and the number of populations requiring assessments has risen because of stock rebuilding efforts. The efficacy of a DIDSON acoustic imaging system for salmon stock assessment was investigated. Sixteen potential sites within the Fraser watershed were surveyed and based on channel morphology, bottom morphology, flow pattern, fish behavior and location relative to spawning grounds, ten sites in six rivers meet the needs of fisheries managers and the DIDSON system for escapement estimates. Fish count data from the DIDSON were compared to data from a counting fence (used as a standard) using regression techniques, resulting in relationships with slopes ranging from 0.98 to 1.02. The precison of DIDSON counts >50 (measured by CV) among three readers was 1.7%. This work supports the conclusion that the DIDSON system can deliver escapement estimates whose accuracy, precision and scientific defensibility is consistent with or better than existing escapment techniques and at a lower operating cost to assessment programs. [Work supported by the Southern Boundary Restoration and Enhancement Fund of the Pacific Salmon Commission.]

Differentiating fish targets from non-fish targets using an imaging sonar and a conventional sonar: Dual frequency identification sonar (DIDSON) versus split-beam sonar

A key requirement in applying acoustic techniques to estimating fish abundance is the removal of non-fish targets from the database. In a riverine environment, debris, entrained air bubbles, bottom objects are common ambient targets which can effectively scatter the probing sound from a fisheries sonar system, and cause strong echoes for the system. A conventional sonar system provides limited and highly simplified information for a detected target, which results in difficulty in separating fish from other targets. Recently developed DIDSON sonar utilizes imaging sonar technology to provide photo-quality images of underwater objects, making possible the visual interpretation of targets. A DIDSON system was deployed in the Fraser River at Mission, British Columbia during the salmon migration in 2004. Data were collected simultaneously from the DIDSON sonar and from a 200-kHz split-beam sonar. These data allow for comparisons of estimates of upstream salmon flux acquired concurrently by the imaging and the split-beam sonar systems.

Survey of dual frequency identification sonar (DIDSON) applications in fisheries assessment and behavioral studies

The Dual Frequency Identification Sonar (DIDSON) is a forward-looking sonar that operates in shallow riverine environments with rocky, uneven substrates and near concrete structures such as dams. This allows a number of fisheries applications in environments previously too hostile for reliable sonar operation. Currently 35 DIDSONs have been obtained by 16 groups to accomplish a variety of fish assessment and behavioral studies. This paper surveys the work of these groups and highlights novel assessments allowed by this new acoustic tool. The groups include Alaska Department of Fish and Game, U.S. Fish and Wildlife Service, NOAA, USGS, Bureau of Reclamation, California Department of Water Resources, Pacific Northwest National Laboratories, Nez Perce Tribal Fisheries, Puyallup Tribal Fisheries, Department of Fisheries and Oceans Canada, and Fisheries Engineering Japan. Assessments include: (1) Counting fish migrating up rivers of various sizes, bottom substrates, turbidity, and velocity; (2) Analysis of fish behavior at (A) prototype fish protection devices on dams, (B) irrigation intakes along muddy rivers, (C) intakes of trawl nets; and (3) Detection and measurement of redds in alluvial riverbeds. [Work for the survey supported by Sound Metrics Corp.]

A retrospective on hydroacoustic assessment of fish passage in Alaskan rivers

The Alaska Department of Fish and Game (ADFG) has enumerated fish stocks in rivers for over 30 years using a variety of acoustic technologies including single-, dual-, and split-beam sonar. Most recently, ADFG has evaluated a relatively new sonar technology at several sites in Alaska to determine its applicability to counting migrating fish in rivers. The new system, called a Dual frequency IDentification SONar (DIDSON), is a high-definition imaging sonar designed and manufactured by the University of Washington’s Applied Physics Lab for military applications such as diver detection and underwater mine identification. Results from experiments conducted in 2002–2004 indicate that DIDSON provides significant improvements in our ability to detect, track, and determine the direction of travel of migrating fish in rivers. One of the most powerful uses of the DIDSON has been to combine its camera-like images of fish swimming behavior with corresponding split-beam data. These linked datasets have allowed us to evaluate the effects of fish orientation and swimming behavior on echo shape parameters that have proven useful in the classification of certain fish species.

Imaging Fall Chinook Salmon Redds in the Columbia River with a Dual-Frequency Identification Sonar

We tested the efficacy of a dual-frequency identification sonar (DIDSON) for imaging and enumeration of fall Chinook salmon Oncorhynchus tshawytscha redds in a spawning area below Bonneville Dam on the Columbia River. The DIDSON uses sound to form near-video-quality images and has the advantages of imaging in zero-visibility water and possessing a greater detection range and field of view than underwater video cameras. We suspected that the large size and distinct morphology of a fall Chinook salmon redd would facilitate acoustic imaging if the DIDSON was towed near the river bottom so as to cast an acoustic shadow from the tailspill over the redd pocket. We tested this idea by observing 22 different redds with an underwater video camera, spatially referencing their locations, and then navigating to them while imaging them with the DIDSON. All 22 redds were successfully imaged with the DIDSON. We subsequently conducted redd searches along transects to compare the number of redds imaged by the DIDSON with the number observed using an underwater video camera. We counted 117 redds with the DIDSON and 81 redds with the underwater video camera. Only one of the redds observed with the underwater video camera was not also documented by the DIDSON. In spite of the DIDSON's high cost, it may serve as a useful tool for enumerating fall Chinook salmon redds in conditions that are not conducive to underwater videography.

Investigations into the application of a new sonar system for assessing fish passage in Alaskan rivers

Over a two-year period (2002–2003) the Alaska Department of Fish and Game (ADFG) has evaluated a relatively new sonar technology at several sites in Alaska to determine its applicability to counting migrating fish in rivers. The new system, called a dual frequency identification sonar (DIDSON), is a high-definition imaging sonar designed and manufactured by the University of Washingtons Applied Physics Lab for military applications such as diver detection and underwater mine identification. Studies conducted in 2002 in a clearwater stream with high fish passage rates (5000 fish/hour) demonstrated that the DIDSON could provide accurate estimates of fish migrating upstream in rivers. Additional studies conducted in 2002 with live tethered fish indicated that size information could be derived from the cameralike images produced by the DIDSON system at ranges up to 12 m. In 2003, ADFG deployed DIDSON systems to assess fish passage in five Alaskan rivers. In each river, the DIDSON system was deployed in the side-looking configuration typically used in riverine sonar applications for estimating fish passage. Preliminary results from experiments in both 2002 and 2003 indicate that the DIDSON provides significant improvements in our ability to detect, track, and determine the direction of travel of migrating fish in rivers.

A fisheries application of a dual-frequency identification sonar acoustic camera

Abstract The uses of an acoustic camera in fish-passage research at hydropower facilities are being explored by the U.S. Army Corps of Engineers. The “Dual-Frequency Identification Sonar” (DIDSON) is a high-definition imaging sonar that obtains near-video quality images for the identification of objects underwater. Developed originally for the U.S. Navy by the University of Washington's Applied Physics Laboratory, it bridges the gap between existing fisheries-assessment sonar and optical systems. The images within 12 m of this acoustic camera are sufficiently clear such that fish can be observed undulating as they swim and their orientation ascertained in otherwise zero-visibility water. In the 1.8 MHz high-frequency mode, this system 96 beams over a 29° field-of-view. The high resolution and fast frame rate provide target visualization in real time. The DIDSON can be used where conventional underwater cameras would be limited by low light levels and high turbidity.