A Partially Supervised Reinforcement Learning Framework for Visual Active Search

Visual active search (VAS) has been proposed as a modeling framework in which visual cues are used to guide exploration, with the goal of identifying regions of interest in a large geospatial area. Its potential applications include identifying hot spots of rare wildlife poaching activity, search-and-rescue scenarios, identifying illegal trafficking of weapons, drugs, or people, and many others. State of the art approaches to VAS include applications of deep reinforcement learning (DRL), which yield end-to-end search policies, and traditional active search, which combines predictions with custom algorithmic approaches. While the DRL framework has been shown to greatly outperform traditional active search in such domains, its end-to-end nature does not make full use of supervised information attained either during training, or during actual search, a significant limitation if search tasks differ significantly from those in the training distribution. We propose an approach that combines the strength of both DRL and conventional active search by decomposing the search policy into a prediction module, which produces a geospatial distribution of regions of interest based on task embedding and search history, and a search module, which takes the predictions and search history as input and outputs the search distribution. We develop a novel meta-learning approach for jointly learning the resulting combined policy that can make effective use of supervised information obtained both at training and decision time. Our extensive experiments demonstrate that the proposed representation and meta-learning frameworks significantly outperform state of the art in visual active search on several problem domains.

Paper

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Peer review

Reviewer mjFZ5/10 · confidence 3/52023-07-05

Summary

This paper introduces a novel Reinforcement Learning (RL) framework for visual active search. In contrast to previous methods, the authors suggest integrating visual supervised signals to enhance performance. Additionally, a meta-learning based approach is proposed to allow the model to adapt to varying test cases. The authors also expand their methodology to support multiple queries. Experimental results demonstrate that the proposed method significantly outperforms both the simple baseline approaches and previous RL-based methods.

Strengths

- The proposed method is both intuitive and technically sound. - The motivation for test-time adaptation and multi-query adaptation is logically sound and well-justified. - A variety of datasets and settings were utilized for the experiments, which substantiate the superior performance of the proposed method compared to other approaches. - The manuscript is well-written and presented, enhancing its clarity and comprehension.

Weaknesses

- Regarding PSVAS, while the concept of simply adding supervised loss is reasonable, it seems more like a straightforward engineering extension to an existing method rather than a novel contribution. - The authors should conduct more ablation studies to provide readers with a deeper understanding of their method. For instance, an ablation study on hyper-parameters and different modules of the proposed method would be valuable. - In the proposed method, the supervised loss is merely a binary classification loss that signifies the presence of a target in the query image patch. I wonder if integrating a more fine-grained supervised loss could enhance the overall performance. For example, would adding a detection or segmentation loss be beneficial? - The paragraph from lines 128 to 140 appears to lack logical consistency. I recommend that the authors restructure this section for improved clarity.

Questions

Comments: Although I don't directly work on this area, I perceive the research problem to be valuable, and the proposed method appears to be sound. However, given my limited expertise, I find it challenging to assess the significance of this paper's technical contributions. Therefore, I've initially rated it as "Borderline Accept". My final rating will depend on feedback from other reviewers, as well as the author's rebuttal.

Rating

5: Borderline accept: Technically solid paper where reasons to accept outweigh reasons to reject, e.g., limited evaluation. Please use sparingly.

Confidence

3: You are fairly confident in your assessment. It is possible that you did not understand some parts of the submission or that you are unfamiliar with some pieces of related work. Math/other details were not carefully checked.

Soundness

3 good

Presentation

3 good

Contribution

3 good

Limitations

N/A

Reviewer 2ixD6/10 · confidence 4/52023-07-06

Summary

This paper proposes a Partially Supervised Reinforcement Learning to search for the objects of interest in geospatial images. The paper uses a meta-learning approach to learn initialization parameters of the prediction module jointly with a search policy. A variant of this approach, MPS-VAS, learns to choose a subset of queries to make in each search iteration. The proposed method outperforms the state-of-the-art and other baselines on xView and DOTA benchmarks.

Strengths

This paper proposes a Partially Supervised Reinforcement Learning to search for the objects of interest in geospatial images. The paper uses a meta-learning approach to learn initialization parameters of the prediction module jointly with a search policy. A variant of this approach, MPS-VAS, learns to choose a subset of queries to make in each search iteration. The proposed method outperforms the state-of-the-art and other baselines on xView and DOTA benchmarks. The results show drastically better results than the state-of-the-art model OnlineTTA.

Weaknesses

While the proposed method is promising and novel, it does limit itself to only two benchmarks on satellite images. It would increase the contribution significantly if it was tested on some traditional vision benchmarks. At least, a discussion on it would be useful.

Questions

1. Can we train on a dataset (xView) and generalize to the classes on another dataset (DOTA)? 2. Can we use the same model for image classification task on the fMoW dataset?

Rating

6: Weak Accept: Technically solid, moderate-to-high impact paper, with no major concerns with respect to evaluation, resources, reproducibility, ethical considerations.

Confidence

4: You are confident in your assessment, but not absolutely certain. It is unlikely, but not impossible, that you did not understand some parts of the submission or that you are unfamiliar with some pieces of related work.

Soundness

3 good

Presentation

3 good

Contribution

3 good

Limitations

This paper proposes a Partially Supervised Reinforcement Learning to search for the objects of interest in geospatial images. The paper uses a meta-learning approach to learn initialization parameters of the prediction module jointly with a search policy. A variant of this approach, MPS-VAS, learns to choose a subset of queries to make in each search iteration. The proposed method outperforms the state-of-the-art and other baselines on xView and DOTA benchmarks. The results show drastically better results than the state-of-the-art model OnlineTTA. However, the method is not tested on traditional vision benchmarks.

Reviewer 6bym6/10 · confidence 4/52023-07-08

Summary

The paper proposes a partially supervised reinforcement learning framework (PSVAS) for visual active search tasks (VAS). Specifically, it decompose previous end-to-end deep RL method for VAS into a task-specific prediction module and a task-agnostic search module. In such way, the prediction module can be supervised with observed ground truth during training or inference time. Further, a meta-learning setting is added to adapt to different tasks quickly. Results on xView and DOTA datasets show the proposed methods and variants outperform previous baselines.

Strengths

The idea to utilize the target-location labels as additional supervision signal besides RL loss is easy to follow and makes sense. The method shows much better adaptation capability when applying to search target that is not trained on, demonstrating the advantages of decomposing the problem into prediction and searching separately. The meta-learning variants and multi-query variants further enhanced the performance. Overall the method is techniquely sound and empirically proved.

Weaknesses

How different balancing factor lambda between RL and BCE loss would affect the performance is worth to investigate in ablation study section.

Questions

Can authors address the weaknesses part.

Rating

6: Weak Accept: Technically solid, moderate-to-high impact paper, with no major concerns with respect to evaluation, resources, reproducibility, ethical considerations.

Confidence

4: You are confident in your assessment, but not absolutely certain. It is unlikely, but not impossible, that you did not understand some parts of the submission or that you are unfamiliar with some pieces of related work.

Soundness

3 good

Presentation

3 good

Contribution

3 good

Limitations

Whether it is possible to apply such method across different datasets is not discusses.

Reviewer yVuL5/10 · confidence 2/52023-07-16

Summary

The paper addresses visual active search problem for geospatial exploration. For an effective adaptation of search policies to out-of-distribution tasks, the paper proposes partially supervised reinforcement learning framework. A meta-learning approach is also proposed that focuses on jointly learning a policy and initialization parameters for the supervised prediction module. Experiments are presented on two datasets.

Strengths

+ Proposed partially supervised reinforcement learning framework allows effective adaptation of search policies to out-of-distribution tasks. + Proposed meta-learning framework focuses on effective learning of supervised prediction module + Experiments show promising results

Weaknesses

-- Not sure of the reproducibility of this work. Also, no code is provided in the supplementary. -- If there is fully labeled training task, why imitation learning (IL) is not adopted? IL and RL loss can be used together for the task. -- It will be good to provide the formulation of L_BCE and L_RL loss in the paper?

Questions

Please see weaknesses.

Rating

5: Borderline accept: Technically solid paper where reasons to accept outweigh reasons to reject, e.g., limited evaluation. Please use sparingly.

Confidence

2: You are willing to defend your assessment, but it is quite likely that you did not understand the central parts of the submission or that you are unfamiliar with some pieces of related work. Math/other details were not carefully checked.

Soundness

3 good

Presentation

2 fair

Contribution

3 good

Limitations

NA

Authorsrebuttal2023-08-16

Dear Reviewer yVuL, With the rebuttal/discussion period nearing a close, please let us know if you have further questions/clarifications.  In particular, please let us know if you have any specific lingering concerns about reproducibility. As we mentioned in the rebuttal, we intend to release all code (including both for training, inference, and evaluation), learned models, and data, along with detailed documentation on github that enable easy reproduction of all the results in the paper, if it is accepted.  Since github is not anonymous, and the supplement has a size limitation, we were unable to provide these materials as a part of the original submission (for example, the learned models themselves are quite large).

Reviewer 6bym2023-08-19

Thanks for the author response

Thank authors for the detailed response regarding the balance weight and generation to other datasets. The provided results have resolved my concerns.

Area Chair e7WP2023-08-20

Thanks for your response -- AC Comment

Dear authors, Thanks for providing your responses to the reviewers' comments. They are comprehensive and answer many of the concerns raised during the initial review phase. While there is still time in the discussion phase, the reviewers can engage for further clarifications. -- Your AC

Program Chairsdecision2023-09-21

Decision

Accept (poster)

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