DIDSON
The DIDSON is an imaging sonar from Sound Metrics in the USA. It is primarily used for counting fish in riverine environments with a fixed transdcuer installation, but may also be used in mobile applications. Echoview is a powerful software package for processing DIDSON data (i.e. DIDSON-capable software) that is widely used. Echoview allows rapid inspection of data, background noise removal, fish detection and fish tracking. Fish objects can be filtered on the basis of length, echo strength, area and other paramaters. Echoview enables the detection and viewing of rare objects such as sturgen ("rare object detection"), without the need to reduce the data using DIDSON CSOT (Convolved Samples Over Threshold) algorithms. Echoview's in-house tests with full DIDSON data files proved 25% faster than manual processing using CSOT files. Consultants such as Aquacoutics in Alaska use Echoview DIDSON software for a wide range of applications. Echoview is used by organisations such as the Alaska Department of Fish and Game and the Pacific Salmon Commission. A tutorial is available, to help you learn about DIDSON processing in Echoview, from this web site and the hydroacoustic users forum (www.fisheriesacoustics.com) has several DIDSON related topics. Echoview also supports Blueview imaging sonars and a range of multibeam echosounders. We maintain a solid working relationship with staff at Sound Metrics so that we can provide a high quality support service to our mutual clients.
Example of Echoview use with DIDSON:
"To make the most of existing software the semi-automated analysis uses a combination of two software packages: DIDSON Control and Display Software (Sound Metrics) and Echoview (Myriax). The DIDSON Control and Display Software executes a pre-processing step that removes the image background and empty frames (frames without fish) from the ddf file. Echoview is used to detect and track the fish images and estimate fish length. Part of the Echoview process has been automated with the Kenai EV Auto Processor which uses a template that has been tailored to Kenai River data." (http://www.aquacoustics.com/proj_Didson-automation.html)
More about DIDSON
"DIDSON records video-quality data and thus can require a lot of disk space (1.8 gigabytes/hour). As a result many features have been developed to allow one to record only the data of importance. In Alaska where fish are counted in the thousands per hour, the timer mode allows the DIDSON to count fish in samples of time at different frequencies and ranges within each hour, or day. The sonar can be left unattended while it collects data in preset patterns and times. Some rivers and streams in other states may have a very small run – maybe a 1000 fish in a two-month period. In this case DIDSON can implement a motion detection algorithm and record data only while a fish or a fish-sized object passes through its field of view. This saves gigabytes of recorded data and makes final processing and counting much, much easier." (www.soundmetrics.com)
"DIDSON (Dual-Frequency Identification Sonar) makes counting fish or understanding their behavior in turbid water a lot easier. DIDSON is simple to use and works in shallow, rock-bottomed rivers and around structures (dams, screens, and entry ways) where other acoustic equipment has been ineffective. There are over 74 DIDSONs used for fisheries applications in over 12 countries around the world. Some have been deployed for over 5 years. DIDSON uses acoustic lens technology which forms acoustic images with greater detail than found in conventional sonars. Some call it an acoustic movie camera. DIDSON mounts off the sides of boats, along river-banks, at dams, or in trawl nets among other places. DIDSON is a rugged, non-invasive, non-destructive sonar that provides an intuitive (almost video-quality) display. Between upstream and downstream movement, assess fish habitat, and do these activities in rivers with high turbidity and debris loads. Features: Auto and manual abundance counts; Background Subtraction for highlighting fish moving over rocky bottom, debris abundant river bottoms; Detection of motion can trigger data recording to catch rare fish passages: Record at preset or random times for specified durations on daily basis for hands-free interval sampling: 30-Watt power consumption: Optional sensor for sonar heading, roll, and pitch; Links to your Laptop via Ethernet Port for DIDSON; data display and control" (www.soundmetrics.com)
"DIDSON may also provide a promising new tool for addressing the issue of species apportionment on the Kenai River. In 2002 feasibility studies were conducted at the Kenai River Chinook Sonar Site to determine whether information on fish size could be derived from the high-resolution images (Figure 9) that would aid in classifying acoustic targets as sockeye or chinook salmon. Information was collected on both free-swimming and tethered fish. We concluded that reasonably good estimates of fish length could be extracted from DIDSON images, but only at relatively short ranges where image resolution is highest. Using the high frequency mode at 1.8 GHz greatly enhances image quality because the image is formed using 96 beams each 0.3o wide compared to 48 beams that are 0.6o wide in low frequency mode. For our application, the effective range at high frequency was approximately 12 m." (http://www.sf.adfg.state.ak.us/region2/sonar/didsize.cfm)
"Chinook salmon in the Snake River basin were listed as threatened under the Endangered Species Act in 1992 (NMFS 1992). The Secesh River represents the only stream in the Snake River basin where natural origin (wild) salmon escapement monitoring occurs at the population level, absent a supplementation program. As such the Secesh River has been identified as a long term salmon escapement and productivity monitoring site by the Nez Perce Tribe Department of Fisheries Resources Management. Salmon managers will use this data for effective population management and evaluation of the effect of conservation actions on a natural origin salmon population. The Secesh River also acts as a reference stream for supplementation program comparison. Dual frequency identification sonar (DIDSON) was used to determine adult spring and summer Chinook salmon escapement in the Secesh River in 2008. DIDSON technology was selected because it provided a non-invasive method for escapement monitoring that avoided listed species trapping and handling incidental mortality, and fish impedance related concerns. The DIDSON monitoring site was operated continuously from June 13 to September 14. The first salmon passage was observed on July 3. DIDSON site total estimated salmon escapement, natural and hatchery fish, was 888 fish {+-} 65 fish (95% confidence interval). Coefficient of variation associated with the escapement estimate was 3.7%. The DIDSON unit was operational 98.1% of the salmon migration period. Adult salmon migration timing in the Secesh River occurred over 74 days from July 3 to September 14, with 5,262 total fish passages observed. The spawning migration had 10%, median, and 90% passage dates of July 8, July 16, and August 12, respectively. The maximum number of net upstream migrating salmon was above the DIDSON monitoring site on August 27. Validation monitoring of DIDSON target counts with underwater optical cameras occurred for species identification. A total of 860 optical camera identified salmon passage observations were identical to DIDSON target counts. However, optical cameras identified eight jack salmon (3 upstream, 5 downstream) less than 55 cm in length that DIDSON did not count as salmon because of the length criteria employed ({ge} 55 cm). Precision of the DIDSON technology was evaluated by comparing estimated net upstream salmon escapement and associated 95% confidence intervals between two DIDSON sonar units operated over a five day period. The DIDSON 1 salmon escapement was 145.7 fish ({+-} 2.3), and the DIDSON 2 escapement estimate was 150.5 fish ({+-} 5). The overlap in the 95% confidence intervals suggested that the two escapement estimates were not significantly different from each other. Known length salmon carcass trials were conducted in 2008 to examine the accuracy of manually measured lengths, obtained using DIDSON software, on high frequency files at a 5 m window length. Linear regression demonstrated a highly significant relationship between known lengths and manually measured salmon carcass lengths (p < 0.0001). A positive bias in manual length measurement of 6.8% to 8% existed among the two observers in the analysis. Total Secesh River salmon escapement (natural origin and hatchery) in 2008 was 912 fish. Natural origin salmon escapement in the entire Secesh River drainage was 847 fish. The estimated natural origin spawner abundance was 836 fish. Salmon spawner abundance in 2008 increased by three fold compared to 2007 abundance levels. The 10 year geometric mean natural origin spawner abundance was 538 salmon and was below the recommended viable population threshold level established by the ICTRT (2007). One additional Snake River basin salmon population was assessed for comparison of natural origin salmon spawner abundance. The Johnson Creek/EFSF Salmon River population had a 10 year geometric mean natural origin spawner abundance of 254 salmon. Salmon spawner abundance levels in both streams were below viable population thresholds. DIDSON technology has been used in the Secesh River to determine salmon escapement over the past five years. The results suggest that DIDSON technology is reliable and can be used to generate accurate and precise estimates of salmon escapement if appropriate methods are used." Abstract of paper "Use of Dual Frequency Identification Sonar to Determine Adult Chinook Salmon (Oncorhynchus tshawytscha) Escapement in the Secesh River, Idaho ; Annual Report, January 2008 – December 2008."
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