Deep learning (DL)-based object detection algorithms have gained impressive achievements in natural images and have gradually matured in recent years. However, compared with natural images, remote sensing images are faced with severe challenges due to the complex backgrounds and difficult detection of small objects in dense scenes. To address these problems, a novel one-stage object detection model named MDCT is proposed based on a multi-kernel dilated convolution (MDC) block and transformer block. Firstly, a new feature enhancement module, MDC block, is developed in the one-stage object detection model to enhance small objects’ ontology and adjacent spatial features. Secondly, we integrate a transformer block into the neck network of the one-stage object detection model in order to prevent the loss of object information in complex backgrounds and dense scenes. Finally, a depthwise separable convolution is introduced to each MDC block to reduce the computational cost. We conduct experiments on three datasets: DIOR, DOTA, and NWPU VHR-10. Compared with the YOLOv5, our model improves the object detection accuracy by 2.3%, 0.9%, and 2.9% on the DIOR, DOTA, and NWPU VHR-10 datasets, respectively.

https://www.mdpi.com/2072-4292/15/2/371/pdf?version=1674186599

MDCT: Multi-Kernel Dilated Convolution and Transformer for One-Stage Object Detection of Remote Sensing Images

In this work, a model for the characterization of microalgae cultures based on artificial neural networks has been developed. The characterization of microalgae cultures is essential to guarantee the quality of the biomass, and the objective of this work is to achieve a simple and fast method to address this issue. Data acquisition was performed using FlowCam, a device capable of capturing images of the cells detected in a culture sample, which are used as inputs by the model. The model can distinguish between 6 different genera of microalgae, having been trained with several species of each genus. It was further complemented with a classification threshold to discard unwanted objects while improving the overall accuracy of the model. The model achieved an accuracy of up to 97.27% when classifying a culture. The results demonstrate the effectiveness of the Deep Learning models for the characterization of microalgae cultures, it being a useful tool for the monitoring of microalgae cultures in large-scale production facilities while providing accurate characterization over a wide range of genera.

An artificial intelligence approach for identification of microalgae cultures.

Abstract Planktonic organisms including phyto-, zoo-, and mixoplankton are key components of aquatic ecosystems and respond quickly to changes in the environment, therefore their monitoring is vital to follow and understand these changes. Advances in imaging technology have enabled novel possibilities to study plankton populations, but the manual classification of images is time consuming and expert-based, making such an approach unsuitable for large-scale application and urging for automatic solutions for the analysis, especially recognizing the plankton species from images. Despite the extensive research done on automatic plankton recognition, the latest cutting-edge methods have not been widely adopted for operational use. In this paper, a comprehensive survey on existing solutions for automatic plankton recognition is presented. First, we identify the most notable challenges that make the development of plankton recognition systems difficult and restrict the deployment of these systems for operational use. Then, we provide a detailed description of solutions found in plankton recognition literature. Finally, we propose a workflow to identify the specific challenges in new datasets and the recommended approaches to address them. Many important challenges remain unsolved including the following: (1) the domain shift between the datasets hindering the development of an imaging instrument independent plankton recognition system, (2) the difficulty to identify and process the images of previously unseen classes and non-plankton particles, and (3) the uncertainty in expert annotations that affects the training of the machine learning models. To build harmonized instrument and location agnostic methods for operational purposes these challenges should be addressed in future research. 

pdf/survey-of-automatic-plankton-image-recognition-challenges-2rj028pb1j.pdf

Survey of automatic plankton image recognition: challenges, existing solutions and future perspectives

Object detection in remote sensing images faces the challenges of a complex background, large object size variations, and high inter-class similarity. To address these problems, we propose an adaptive adjacent layer feature fusion (AALFF) method, which is developed on the basis of RTMDet. Specifically, the AALFF method incorporates an adjacent layer feature fusion enhancement (ALFFE) module, designed to capture high-level semantic information and accurately locate object spatial positions. ALFFE also effectively preserves small objects by fusing adjacent layer features and employs involution to aggregate contextual information in a wide spatial range for object essential features extraction in complex backgrounds. Additionally, the adaptive spatial feature fusion (ASFF) module is introduced to guide the network to select and fuse the crucial features to improve the adaptability to objects with different sizes. The proposed method achieves mean average precision (mAP) values of 77.1%, 88.9%, and 95.7% on the DIOR, HRRSD, and NWPU VHR-10 datasets, respectively. Notably, our approach achieves mAP75 values of 60.8% and 79.0% on the DIOR and HRRSD datasets, respectively, surpassing the state-of-the-art performance on the DIOR dataset. 

Adaptive Adjacent Layer Feature Fusion for Object Detection in Remote Sensing Images

Marine plankton classification is important for monitoring marine biological populations and understanding marine ecosystems. However, it is difficult to obtain abundant annotated image data of marine plankton to train classification models of high quality. To classify marine plankton with a small number of image samples, a cross-domain few-shot learning model (CDFM) is proposed. First, CDFM learns knowledge from existing labelled images and then transfers the knowledge to new images. In this process, there is an issue of domain differences between the new images and the existing datasets due to differences in data acquisition time and locations. To address this issue, the authors pre-train a model in the source domain and then use fine-tuning to adapt it to the target domain. Second, the graph neural network is used as a meta-learning module to learn a feature distance metric for marine plankton classification with limited samples. Extensive experiments on four marine plankton image datasets are conducted, including Kaggle Plankton, miniPPlankton, ZooScan and WHOI, and CDFM outperforms existing methods for marine plankton classification. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1049/cvi2.12137

CDFM: A cross-domain few-shot model for marine plankton classification

Object detection in remote sensing is becoming a conspicuous challenge with the rapidly increasing quantity and quality of remote sensing images. Although the application of Deep Learning has obtained remarkable performance in Computer Vision, detecting multi-scale targets in remote sensing images is still an unsolved problem, especially for small instances which possess limited features and intricate backgrounds. In this work, we managed to cope with this problem by designing a neck attention block (NAB), a simple and flexible module which combines the convolutional bottleneck structure and the attention mechanism, different from traditional attention mechanisms that focus on designing complicated attention branches. In addition, Vehicle in High-Resolution Aerial Imagery (VHRAI), a diverse, dense, and challenging dataset, was proposed for studying small object detection. To validate the effectiveness and generalization of NAB, we conducted experiments on a variety of datasets with the improved YOLOv3, YOLOv4-Tiny, and SSD. On VHRAI, the improved YOLOv3 and YOLOv4-Tiny surpassed the original models by 1.98% and 1.89% mAP, respectively. Similarly, they exceeded the original models by 1.12% and 3.72% mAP on TGRS-HRRSD, a large multi-scale dataset. Including SSD, these three models also showed excellent generalizability on PASCAL VOC.

/pdf/improved-one-stage-detectors-with-neck-attention-block-for-27u224yl.pdf

Improved One-Stage Detectors with Neck Attention Block for Object Detection in Remote Sensing

Phytoplankton, as an important component of marine ecosystem, play a key role in understanding marine resources and monitoring marine environment. In this paper, under the suggestion of marine biology professional researcher, we selected six kinds of phytoplankton commonly found in China’s coastal areas and conducted digital holographic microscopic imaging experiments to obtain their holograms. Then, the angular spectrum reconstruction algorithm was used to conduct diffraction reconstruction of the phytoplankton hologram to achieve clear imaging of the algae target. A threshold based image segmentation algorithm is used to segment the phytoplankton target area and obtain image dataset. Finally, transfer learning is used to train on the pre-trained model. Experimental results show that the classification accuracy of the trained network on the test set can reach 95.7%.

Classification of phytoplankton digital holograms using transfer learning

Detecting marine plankton by means of digital holographic microscopy (DHM) has been successfully deployed in recent decades; however, in most previous studies, the identification of the position, shape, and size of plankton has been neglected, which may negate some of the advantages of DHM. Therefore, the procedure of image fusion has been added between the reconstruction of initial holograms and the final identification, which could help present all the images of plankton clearly in a volume of seawater. A new image fusion method called digital holographic microscopy-fully convolutional networks (DHM-FCN) is proposed, which is based on the improved fully convolutional networks (FCN). The DHM-FCN model runs 20 times faster than traditional image fusion methods and suppresses the noise in the holograms. All plankton in a 2 mm thick water body could be clearly represented in the fusion image. The edges of the plankton in the DHM-FCN fusion image are continuous and clear without speckle noise inside. The neural network model, YOLOv4, for plankton identification and localization, was established. A mean average precision (mAP) of 97.69% was obtained for five species, Alexandrium tamarense, Chattonella marina, Mesodinium rubrum, Scrippsiella trochoidea, and Prorocentrum lima. The results of this study could provide a fast image fusion method and a visual method to detect organisms in water.

/pdf/a-plankton-detection-method-based-on-neural-networks-and-1th1j61i.pdf

A Plankton Detection Method Based on Neural Networks and Digital Holographic Imaging

Holographic microimaging technology is widely used in the plankton detection due to its large depth of field and ability to record three-dimensional (3D) information. However, traditional methods involve tedious and time-consuming steps, e.g., region of interest (ROI) extraction, dense reconstruction, focused evaluation, and focused ROI recognition. As a result, traditional methods are difficult to detect in real time. In this paper, we propose a neural network-based 3D detection method, which for the first time uses the holograms to obtain 3D sampling data for algae detection, and innovatively designs a convolutional neural network (DHCNN) to improve the speed and accuracy of detection. A dataset containing 3D samples of eight harmful algae species is established, and the trained DHCNN model achieves a mean average precision of 99.2 % on the test set. We find that accuracy is higher with 3D sampled data, which contains more valid information than with autofocused ROIs. Moreover, detection rate is 99.5 %, which means it could detect attached algae and algae abundance statistics are more accurate. And detection time of the proposed method is only 0.066 s, which is 20 times faster than the traditional method. We believe that the proposed method represents an effective approach for real-time algae monitoring. 

Rapid three-dimensional detection of harmful algae using holographic microimaging

Image fusion combines image data on the same target collected from multi-source channels, which are processed to extract the most favorable information from each channel and finally synthesize a high-quality image. In this study, image fusion is used to aggregate multi-focus plankton into a single-fused image. An unsupervised image weighted fusion method based on fully convolutional networks (FCN) is proposed, which can clearly and intuitively show the presence of plankton in the detected water body. The fused image has a high contrast, continuous and clear plankton edges, and little information loss, thereby laying a foundation for the next phytoplankton identification.

Image Fusion Method for Improving the Accuracy of Ocean Plankton Recognition

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