New Echo Sounder Telemetry System for Set-net Fishery Jianfeng Tong1, Yoshinori Miyamoto1, Keiichi Uchida1, Toyoki Sasakura 2, and Jun Han3 1
Tokyo University of Marine Science and Technology, 4-5-7 Konan Minato-ku, Tokyo 108-8477, Japan 2 Fusion Incorporation, 1-1-1-806 Daiba Minato-ku, Tokyo 135-0091, Japan 3 Zhejiang University, 866 Yuhangtang Road, Hangzhou, Zhejiang Province 310058, China Email:
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[email protected] Abstract—Set-net is a kind of passive fishing gear. In order to achieve efficient fishing operation, it is necessary to know the amount of fish entrapped before set out fishing. Therefore, remote monitoring of the fishing state in set-net is important. Although there was a telemetry echo sounder system called ‘telesounder’ used as a remote monitoring tool in set-net fishery successfully, it has been stopped producing and there is no sign that new similar system will spread in set-net fishery. In recent years, with the rapid development of wireless communication technology, remote monitoring of set-net fishing state via 3rd Generation (3G) Network becomes possible. However, echo data from echo sounders are generally voluminous which make it impractical to transfer all the raw echo data via 3G Network. In order to apply 3G Network in the remote monitoring of set-net fishery smoothly, we developed a new echo sounder telemetry system and proposed a fish echo extraction method base on image processing which can largely reduce the data volume to be sent and show good quality echogram-like displays to fishermen. A sea trial experiment has been conducted to verify the functions and capabilities of the new system. Keywords—echo sounder; mobile network; data acquisition; fish detection; telemetry
I.
INTRODUCTION
Set-net fishery has a long history in Japan which is considered to be environmentally-friendly. In recent years, calling for the shift to responsible fisheries and considering the ecological and economical advantage of set-net, the set-set fishing technology has been transferred to the Southeast Asia [1-3]. However, in traditional set-net fishery, fishermen go to haul up the net in a fixed time every day according to their experience and the time of market operation; most of the cost comes from the cost of catch landing such as fuel and labor cost. If there is no fish or few fish entrapped in the net, the cost may exceed the sales and therefore result in a deficit. There are also some reports that the entrapped fish may escaped if the fishing operation intervals are too long or fish may not be entrapped more if entrapped fish volume exceed the final trap accumulation [4,5]. Since the new fishermen lack of experience, it is hard for them to control the net hauling time and hauling intervals. Therefore, in order to achieve efficient fishing operation and maximize the economical profits, it is important to know the fish entrapped time and the amount of fish entrapped in real time. Since set-net is a kind of passive
fishing gear and placed in the sea, remote monitoring of fish entrapped time and entrapped volume is required. There was an echo sounder telemetry system called ‘telesounder’, which could send echogram from sea to a remote displace at land [6]. This system had been introduced into set-net fishery in Japan successfully since 1970s. However, the system was using Very High Frequency (VHF) radio to transfer echogram, which limited its communication distance. And, the VHF waves are easily interfered and may threat to the safety of coastal navigation. Moreover, the ‘telesounder’ has been stopped producing and there is no sign that new similar system will spread in set-net fishery. In recent years, remote monitoring of set-net fishing state via 3rd Generation (3G) Network becomes possible. There are some remote monitoring systems based on 3G Network be developed and tested for set-net fishery [7,8]. However, these systems are using optical cameras, which fail to work in turbid water or at night time. Thus an echo sounder telemetry system which can use 3G network to transfer data is highly demanded. However, echo data from echo sounders are generally voluminous. It is impractical for transmitting all the raw echo data via 3G network. In order to readily transfer echo data by 3G Network, we contrived a new echo sounder telemetry system which can automatically detect and extract fish echo form mass raw echo data, then send the extracted data only instead of the raw data, therefore can reduce the data volume to be sent via 3G Network significantly. II.
MATERIALS AND METHODS
A. System development The new developed echo sounder telemetry system comprised an echo sounder terminal, a web server and some end-user display terminals. In this system, the echo sounder terminal transmitted acoustic pulses into water toward the sea bottom and automatically detected and extracted fishes from the reflected echoes, then sent the extracted data to the web server. The web server received and analyzed the extracted data then reconstructed them as echogram-like images and show them to fishermen by any devices that can connect to internet such as computers, smartphones and tablets.
The main developent of this system is the hardware and software of the echo sounder terminal and the software of on the web server. There is no need to develpe special end-user display terminals. In this study, the echo sounder terminal was assumed to be easily set up in a set-net for long-term monitoring and not interfere to fishing operation. Thus, all the units were expected to be housed in a small buoy. And, the echo sounder terminal was designed by using a portable analog echo sounder, an analog-to-digital (A/D) converter, a compact personal computer (PC) and a 3G USB data card. These units were built into the buoy with a battery. The structure of echo sounder terminal is shown in Fig.1.
3G Data card Portable echo sounder
A/D Converter
USB
USB Compact PC
Transducer Fig. 2. Connections of parts in the echo sounder terminal.
B. Data Processing The data processing of the new echo sounder telemetry system was carried out according to the flowchart shown in Fig.3. The details are explained as follows. Bottom detection Fish echo extraction Data transmission
Fig. 1. Structure of echo sounder terminal (left: the outlook of the echo sounder terminal; right: inside structrue of the echo sounder terminal).
Since there is not a suitable size echo sounder which have echo signals outputs, a portable echo sounder (NAKI8850, Yachting Electronic Co., LTD) was reformed to induce the echo signals. The beam angle of the transducer is 45 degrees, the frequency of the echo sounder is 190 kHz, and the source level is 194 dB re μPa. In order to simplify the system development, we used a 2channel PicoScope™ (Pico Technology Ltd) as the A/D converter. The PicoScope is USB connected and powered by the PC. The self-developed software in the PC first drove the PicoScope, then waiting for A/D converted data. When a trigger arrived, the PicoScope started to sample and convert echo signals. Considering the resolution and data size, we set the sampling rate at 20 kilo-samples per second (kSPS). The length of the A/D sample was determined by the depth range and set by the software automatically. The A/D converted data were transferred to the PC, and processed by the software to detect sea bottom and extract fish echo. Meanwhile, all the raw data were stored in hard disk of the PC for post processing as Comma Separated Values (CSV) text file format. The PC is connected to the echo sounder by the A/D converter, which is used to detect the sea bottom, extract fish echo from the large amount of raw echo data automatically, and send the extracted data to the web server. The connections of parts in the echo sounder terminal is shown in Fig.2.
Echogram reconstruction Fig. 3. Flowchart of data processing.
First, in this study, the fish echo was expected to be extracted automatically. In some cases, sub-bottom reflection may appear like fish echo and make misjudge of real fish echo. In order to identify the sea bottom in real time, the bottom detection was performed within each ping according to the characteristic that the bottom reflection is almost the strongest within each ping. In order to prevent wrong detection of sea bottom, the new detected water depth was compared with the former detected one. By this method, the bottom line was tracked and finally determined. After the bottom line was detected, fish echo extraction could be conducted correctly in the water column. In a normal echogram, fish echo shown to us with different shapes and color scales in different positions. Therefore, in this study, the information of fish echo to be extracted were considered to be the shape, position and reflection strength. To reduce the data size, the extracted data from the echogram are organized in the form of contours with reflection values. A contour is a list of points that represent an outline of an object. Thus the shape and the position of a fish echo could be calculated from the contour. The fish echo extraction was realized by image processing method. First, an echogram was constructed using raw echo data of 5 minutes. Second, a black and white binary image was obtained by setting a thresh value of the echo data. The black pixels stood for weak reflections as background,
while white pixels stood for reflections of objects. Third, morphological filtering (dilation and erosion) with a 5 × 5 mask was performed to eliminate isolated pixels. After the isolated pixels were eliminated, an inner edge detection method [9] was used to detect the edges of the remaining objects and segment them from the background as independent individuals. After the objects were segmented, the area of the each object was calculated. The noise, the area of which is below a threshold, was removed, and the remaining areas were treated as fish echo. Finally, the average echo strengths, which were defined as the average acoustic energy reflected per pixel of the fish echo, were calculated. In this study, the extracted data should be reconstructed to echograms for easy-reading immediately. If the extracted data was directly send to a display terminal, there may be some requirement of the display terminal to process the data. Thus the extracted data was not directly sent to the end-user terminals. In order to easily show the echogram in different kind of end-user terminals, the data transmission and echogram reconstruction was carried out via a web server. First, the data was sent to a web server when it was extracted immediately. Then, the web server would process the data, if there is some important information, it would send a message to the users. The users then can access the web server and view the echogram which is reconstructed by the web server. Since the extracted data was based on the from of contour points and average reflection values, it is easy to reconstruct the echogram. By this method, any device that can access internet can be used to show the echogram without end-user device system requirement.
Fig.6 shows the result of echogram-like display reconstructed by the web server based on the extracted data. The positions of fish echo can be recovered correctly. The shapes of fish echo are concentrated by eliminating the isolate pixels and removing the noises of small areas and weak reflections, which looks more clearly. The reflection strengths which are base on the average values are close to the original ones. The fish echo near the bottom are merged with the bottom line. Although, the bottom line can be simply removed or derived and reconstructed independently, considering the complexity of the data format, the data size and the display effect, the bottom was retained and calculated with the fishes echoes near it together.
1min
Fig. 4. Example of an echogram constructed from the raw echo data.
C. Experiment In order to verify the capabilities of the developed echo sounder telemetry system, a sea trial experiment was carried out from 17:50 on 7th to 6:30 on 8th in July 2013, about 13 hours in the Tateyama Bay, at the mouth of Tokyo Bay in Japan. First, the system was placed very close to shore where the water depth is about 5 m, however, since the water is too shallow, there was too much noise, no fish was detected around here. Then the system was moved near to an offshore farming aquaculture net cage where the water depth is about 15 m, and placed there about 2 hours. III.
RESULTS AND DISCUSSION
Fig.4 shows an example of a echogram constructed from the recorded echo data. As it is shown, the sea bottom is almost the strongest reflector. The reflections beneath the bottom are also strong, if we do not detect the bottom line and remove the part under the bottom line, after the data binaryzation, these reflectors would be mistaken as targets. Therefore, before the image processing, automatic sea bottom detection and water column data extraction is important. Fig.5 shows the result of automatic bottom detection and water column data extraction. The part beneath the bottom line was removed, and the water column data was extracted for post image processing. In order to illustrate the water depth directly to users, the bottom line was also preserved.
Detected bottom line Fig. 5. Echogram of sea bottom detection and water column extraction.
The total size of the recorded experimental echo data was about 788 MB (827,178,160 bytes). Since no fish has been detected during the first 11 hours, After analyzed the last 2 hours’ echo data, 336 fish or fish school echoes were detected extracted, of which the total size was only 330 kB (338,550 bytes). The data to be sent was highly compressed, where the compression ratio in this experiment was about 2443:1. However, the image quality of the echogram was not lost. In our method, the size of extracted data depends on the quantity and complexity of the fish echo. The more complexity of the
contours of fish echo, and the more amount of fish echo, the more size of the extracted data. In this experiment, fish was not detected during the first 11 hours, but observed continually during the last 2 hours. This situation is similar to the set-net fishery, because fish may not always swim into the se-net. Even if fish is abundant, the date to be sent can also be largely reduced.
IV.
CONCLUSION
By reforming a common portable fishing echo sounder, an echo sounder telemetry system base on 3G Network has been developed. The data transmission method base on the extracted fish echo data from the raw echo data can not only reduce the size of data to be sent considerably but also supply enough information to reconstruct the echogram. By applying a web server in data transmission and echogram reconstruction, users can easily monitor the fishing state including fish entrapped time and the quantity of fish entrapped by any devices that can connect to the server from anywhere. ACKNOWLEDGMENT The authors would like to thank Prof. Toshiharu Kakihara and Dr. Kazuo Amakatu for their valuable suggestions.
REFERENCES [1] Fig. 6. Result of reconstructed echogram-like display by the web server base on the extracted data.
The reconstructed echogram can be displayed by any devices that can connect to the server. Fig.8 illustrates the results of the reconstructed echogram displayed on a smart phone and a PC. Both of the displays showed good image quality.
[2]
[3]
[4]
[5]
[6] a.
Result shown by a smart phone
[7]
[8]
[9]
b.
Result shown by a PC
Fig. 7. Results displayed on end-user display terminals (a: a smart phone; b:a PC ).
A. Muprasit, T. Amornpiyakrit, W. Yingyuad, N. Yasook, T. Srikum, K. Bhuttaruksa, T. Arimoto, O. Baba, K. S. Takeda, and N. Manajit. “SetNet Fishing Technology Transfer for Sustainable Coastal Fisheries Management in Southeast Asia,” 5WFC Satellite Workshop on Sustainable Use of Coastal Fisheries Resources in Southeast Asia, pp.56, 2008. N. Manajit, T. Arimoto, O. Baba, S. Takeda, A. Munprasit, T. Amornpiyakrit, Y. Weerasak, N. Yasook, T. Srikum, and K. Phuttharaksa. “Catch analysis of Japanese-type of set-net introduced to Rayong, Thailand,” 5WFC Satellite Workshop on Sustainable Use of Coastal Fisheries Resources in Southeast Asia, pp.7-8, 2008. T. Arimoto, S. Takeda, O. Baba, H. Sudirman, I. M. A. Hajar, and A. Munprasit. “Technology Transfer of Community-based Set-net for Empowerment of Coastal Fishing Community in South Sulawesi, Indonesia,” 5WFC Satellite Workshop on Sustainable Use of Coastal Fisheries Resources in Southeast Asia, pp.9-10, 2008. S. Akiyama, and S. Kaihara, “Accumulation performance of large-scale set nets in Iwate Prefecture for chum salmon Oncorhynchus keta,” Nippon Suisan Gakkaishi, vol. 72(4), pp. 659-664, 2006. S. Akiyama, and T. Arimoto, “Effects of varied hauling intervals on catch of a set-net,” Bulletin of the Japanese Society of Scientific Fisheries, Vol. 63, pp. 340-344, 1997. T. Hashimoto, and Y. Maniwa, “The trial production of telesounder (wireless remote control fish finding equipment) and its tests on the sea,” Technical report of fishing boat, vol. 19, no. 4, pp. 1-7, October 1964. Y. Ishiguro, M. Gotoh, and K. Akinaka, “Development of transmission system for underwater video camera picture and observation of fish schools in set-net,” Bulletin of the Kanagawa Prefectural Fisheries Research Institute, 2003. S. Akiyama, “Underwater video remote monitoring system by using a 3G mobile phone,” Journal of Fishing Boat and System Engineering Association of Japan, Vol. 7(72), pp. 12-15, 2007. M. Sonka, V. Hlavac, and R. Boyle, Image processing, analysis, and machine vision. 2nd ed., 1999.
