Jonghyun Ahn

Erratum to: Enhancement of deep-sea floor images obtained by an underwater vehicle and its evaluation by crab recognition

The underwater robot is one of the most important research tools in deep-sea exploration where the high pressure, extreme darkness, and radio attenuation prevent direct access. In particular, Autonomous Underwater Vehicles (AUVs) are the focus of much attention since they do not have tethered cables and can navigate freely. However, ideally, AUVs should be able to make independent decisions even with limited information using mounted sensors. That is, AUVs need powerful programming and low-power consumption computer systems which enable them to recognize their surroundings and cruise for long distances. Thus, modern computer development makes it possible for AUVs to be one of the most practical solutions for deep-sea exploration and investigations. As a next-generation AUV, we have been developing a Sampling-AUV that can dive into deep-sea regions and bring back samples of marine creatures in order to more fully understand the marine ecosystem. Our mission scenario calls for the Sampling-AUV to transmit deep-sea floor images to scientists on the research ship using acoustic communication. The scientists select the marine creatures to sample, and the AUV is tasked with retrieving them. The AUV then returns to the area where the interesting marine creatures have been observed, and collects and brings back samples. In order to realize this mission scenario, the sea-floor images need to be enhanced to assist the judgment of the scientists as the color red attenuates rapidly and the images become bluish while small differences in AUV altitude to the sea-floor also affect the brightness of the images due to light attenuation. Moreover, although underwater acoustic communication is slow and inaccurate, the AUV is required to select interesting images that include marine life. In this paper, we propose a deep-sea floor image enhancement method based on the Retinex theory and its performance was evaluated using deep-sea floor images taken by an AUV. The performance of the image enhancement was evaluated through crab recognition.

Development of an autonomous underwater vehicle with human-aware robot navigation

AUV Tuna-Sand 2 developed in February 2016 can take photograph of the seafloor with high resolution using a camera and two LED strobe every five second and detect sea creature from it based on color information. If sea creature is detected from taken photograph, the AUV transmit its compressed image to the ship using acoustic modem for image transmission. Operator on the ship can select photographing position that the AUV return it, from received photograph. After instruction by operator using acoustic modem for command, the AUV can return to photographing position in the range of ± 0.3 m. In future work, we will develop visual feedback method and manipulation method for sea creature sampling.

Sea-floor image transmission system for AUV

Autonomous Underwater Vehicle (AUV) has become one of the promising tool for ocean exploration during the last few decades, and, in particular, is the solution for the spatial-temporal investigations in wide areas for a long period. One of the next mission expected from AUV is deep sea specimen sampling, which is currently performed by Remotely Operated Vehicle (ROV) or Human Occupied Vehicle (HOV) where the sampling targets are selected by scientists on-line. In order to establish the similar on-line investigation with AUV system, the sea-floor images have to be transmitted to the scientists on the support vessel by acoustic communication. However, the speed of the acoustic communication is low compared with that of radio communication, and the data can be lost because of the directionality of acoustic modem, the positional relationship between the AUV and the support vessel, attenuation and so on. The robust image transmission system is necessary with acoustic communication for in-situ decision making for sampling by AUV with many tasks. In this paper, we propose a sea-floor image transmission system with image compression, and evaluated by sea trials in Suruga-bay. The image compression method is based on a set of color palettes, where the colors of a color palette are assigned as a set of main colors obtained from the minimum variance quantization, to represents a typical sea-floor image. The colors of the obtained images are replaced by the most similar colors in the color palette. The images compressed by a 16-colors color palette are evaluated by Structural SIMilarity (SSIM) method, and these compressed images have shown the SSIM index of 88.5%. The duration of one image transmission is about 40 seconds in the sea trials and the transmission success rate is 75%.