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🧠 Submission to TGRS 2026:Curriculum-Aided Synergistic Self-Training for Source-Free Unsupervised Domain Adaptation of Remote Sensing Image Segmentation

🧠 Full source code will be released after the paper is accepted.

👓Abstract

Source-free unsupervised domain adaptation (SFUDA) is a promising approach for remote sensing image (RSI) segmentation, as it transfers knowledge from a well-trained source network to an unlabeled target domain without requiring access to the source data. Most existing SFUDA methods rely on self-training to guide the transfer process. However, when applied to RSI segmentation, they still suffer from three unresolved challenges. First, due to large cross-domain discrepancies in RSIs, pseudo labels are often structuredly unreliable, making it difficult to distinguish trustworthy supervision from misleading predictions. Second, preserving representation diversity is difficult because reliability-oriented selection tends to discard informative hard regions and rare classes, resulting in insufficient target-domain coverage. Third, target samples exhibit significantly different adaptation difficulty, yet most methods optimize them with nearly uniform training strength, which often leads to unstable adaptation in the early stage. To address these challenges, we propose a Curriculum-aided Synergistic Self-training (CSS) framework, which performs selective pseudo-label learning in an easy-to-hard manner. Specifically, a Synergistic Self-Training (SST) strategy is proposed to achieve effective knowledge transfer by jointly modeling reliability and diversity. SST consists of two complementary paradigms: lazy learning and hungry learning. Lazy learning suppresses noise propagation by selecting pseudo labels with both high confidence and low uncertainty, while hungry learning improves target-domain representation coverage through global-wise and class-wise ordered label selection. Moreover, a Curriculum Information Propagation (CIP) strategy is proposed to stabilize the transfer process by progressively propagating domain-invariant information from easy samples to hard samples according to sample entropy. In this way, CSS establishes a unified adaptation mechanism that simultaneously addresses reliability, diversity, and stability. We further provide a theoretical analysis showing that CSS reduces the generalization error bound. Extensive experiments on satellite and aerial benchmarks demonstrate that CSS significantly outperforms state-of-the-art SFUDA methods and can be effectively extended to the black-box scenario.

✨Highlight

  • We propose the CSS framework for SFUDA semantic segmentation of RSIs, which explicitly addresses three unresolved challenges in remote sensing SFUDA: unreliable pseudo supervision, insufficient target representation diversity, and unstable adaptation across samples with different difficulty.
  • We propose the SST strategy to achieve effective knowledge transfer. Unlike previous self-training methods that mainly emphasize either reliability filtering or broader pseudo-label utilization, SST unifies lazy learning for reliable feature learning and hungry learning for diverse feature learning in a complementary manner.
  • We propose the CIP strategy to achieve stable knowledge transfer, which facilitates easy-to-hard information propagation by adaptively adjusting the supervision strength of lazy learning and hungry learning according to sample entropy.
  • We provide theoretical proof that CSS narrows the domain gap by effectively reducing the generalization error bound. Extensive experimental results show that CSS outperforms state-of-the-art SFUDA methods on both satellite and aerial benchmarks. Moreover, CSS also exhibits competitive performance in the black-box scenario, where only the source network's predictions are available.

💡Method Overview

图片描述

👀Visualization

👀Ablation visualization on the ISPRS datasets.

图片描述

👀Ablation visualization on the CASID dataset.

图片描述

📦Usage

📦Datasets

All datasets including ISPRS dataset and CASID dataset.

🚀Training

To train the source-only model:

CUDA_VISIBLE_DEVICES=0 python so_run.py

To train the adaptation model:

CUDA_VISIBLE_DEVICES=0 python run.py

🚀Evaluation

python eval.py

📊 Results

📊Results on the ISPRS dataset

Domain Method SF Surf Bldg Vegt Tree Car Bkgd mIoU Domain Surf Bldg Vegt Tree Car Bkgd mIoU
P2V Source only - 28.4 54.0 21.9 50.8 28.0 2.0 30.9 PRGB2V 26.4 54.0 12.3 13.4 27.5 1.0 22.5
AdaptSeg 54.4 63.1 29.0 52.7 6.4 4.6 35.0 51.3 60.7 12.8 51.6 10.3 3.0 31.6
CBST 61.3 67.3 26.4 60.8 35.3 3.4 42.4 56.6 55.6 16.2 52.8 38.0 2.9 37.0
ProDA 62.5 71.6 34.5 56.3 39.2 4.0 44.7 49.0 68.9 32.4 49.1 31.6 2.4 38.9
DualGAN 49.4 62.3 38.9 57.7 34.3 29.7 45.4 46.2 65.4 27.9 55.8 40.3 3.9 40.0
CCDA 67.7 76.8 47.0 55.0 44.9 20.7 52.0 64.5 76.9 38.4 52.8 43.4 12.4 48.1
ProCA 64.6 76.5 41.8 64.0 30.8 8.3 47.7 54.2 64.2 17.7 65.2 36.5 4.1 40.3
LD 54.1 50.9 34.7 44.1 19.8 5.5 33.8 49.4 43.7 23.0 32.4 15.0 3.5 28.0
DTAC 52.9 52.5 32.7 42.5 20.0 5.8 33.4 48.5 42.3 19.0 32.2 15.2 3.8 26.8
SND 54.5 53.3 34.4 43.3 21.5 6.9 34.7 49.6 44.0 20.0 31.0 17.4 3.8 27.8
CROTS 53.8 51.1 34.3 43.9 20.3 5.6 33.9 49.7 44.9 21.2 32.1 17.6 3.9 28.1
ATP 55.7 53.2 36.0 45.6 22.4 7.5 35.8 46.1 42.4 28.1 33.7 22.9 5.0 29.7
SFDA-DE 54.4 53.0 34.3 43.9 21.6 6.9 34.7 50.9 43.9 22.9 32.3 19.6 4.2 29.0
SFDA* 52.3 52.1 32.9 42.7 19.4 5.2 33.0 43.6 41.5 18.9 28.5 13.9 3.4 25.0
HCL* 53.2 51.5 33.8 43.4 20.1 5.7 33.5 47.5 41.2 19.6 30.1 14.7 3.4 26.1
CSS(Ours)* 56.0 48.3 33.5 44.5 21.4 6.7 35.1 51.1 46.3 22.2 32.9 18.2 3.9 29.1
CSS(Ours) 55.3 51.1 36.0 42.4 25.1 6.1 36.0 50.4 43.1 24.2 35.2 24.7 3.9 30.2
V2P Source only - 51.3 47.3 33.9 19.2 46.0 13.1 35.1 V2PRGB 44.9 42.4 17.3 4.9 40.5 6.1 26.0
AdaptSeg 49.6 48.0 34.4 22.6 41.0 8.4 34.0 37.7 54.3 15.1 30.7 42.3 6.1 31.0
CBST 49.9 33.2 40.6 3.1 49.6 2.2 29.8 43.5 19.9 0.0 0.0 48.4 3.7 19.3
ProDA 44.7 56.9 40.1 31.6 46.8 10.6 38.4 44.8 46.4 35.8 30.6 41.2 11.1 35.0
DualGAN 51.0 53.4 36.5 35.0 48.5 11.5 39.3 46.0 59.0 41.7 25.8 39.7 13.6 37.6
CCDA 64.4 66.4 47.2 37.6 59.4 12.3 47.9 57.7 65.4 29.8 35.9 57.0 13.3 43.2
ProCA 57.4 40.6 45.6 12.3 63.1 4.8 37.3 40.1 27.1 5.8 2.7 58.0 7.1 23.5
LD 44.3 49.0 30.7 37.0 50.8 8.9 36.8 37.4 38.6 15.5 29.9 42.6 2.9 27.8
DTAC 39.0 45.6 30.6 35.0 45.2 7.8 33.9 30.9 36.1 14.9 28.1 37.3 2.2 24.9
SND 43.8 48.5 31.6 36.3 50.4 8.2 36.5 33.3 39.4 22.9 35.4 44.5 2.2 29.6
CROTS 43.2 47.0 34.5 37.2 47.6 7.8 36.2 33.1 34.5 16.1 28.1 38.4 1.8 25.4
ATP 45.9 49.1 33.4 37.0 52.3 9.1 37.8 37.7 38.5 16.0 29.2 46.2 3.2 28.5
SFDA-DE 39.6 47.9 30.8 36.9 46.2 9.6 35.2 36.0 36.1 18.6 30.9 34.0 5.2 26.6
SFDA* 44.9 46.3 31.4 36.6 43.4 6.3 34.8 33.3 35.1 15.7 28.8 34.8 2.3 25.0
HCL* 42.3 47.0 32.2 36.3 42.1 6.5 34.4 31.1 37.8 18.3 32.3 39.0 2.1 26.7
CSS(Ours)* 46.0 46.5 35.4 30.2 49.1 7.0 35.7 35.4 38.0 16.2 30.2 41.4 4.4 27.6
CSS(Ours) 50.3 48.9 31.9 35.2 53.4 7.7 37.9 43.8 38.8 14.9 29.9 50.3 2.5 30.0

📊Results on the CASID dataset

Domain Method SF Bkgd Bldg Forest Road Water mIoU Domain Bkgd Bldg Forest Road Water mIoU
SubMs2TroMs AdaptSeg 71.3 55.5 81.1 10.6 72.4 58.2 SubMs2TroRf 26.2 70.5 91.3 11.0 21.1 44.0
CBST 72.1 54.0 82.0 16.5 68.7 58.7 24.6 71.6 92.2 25.4 20.4 46.8
CLAN 72.3 56.3 81.2 13.6 67.0 58.1 26.1 71.6 93.2 14.7 34.8 48.1
PyCDA 70.8 29.1 70.2 1.2 52.7 44.8 3.9 17.5 45.7 1.5 9.7 15.6
FADA 72.5 50.1 80.6 7.9 46.5 51.6 20.0 65.7 90.5 12.5 28.0 43.3
ASA 56.6 30.4 67.1 0.3 16.7 34.2 12.5 50.1 87.0 0.5 11.9 32.4
LD 63.2 25.3 66.8 14.7 29.3 39.9 11.9 14.9 72.1 5.5 9.8 22.8
DTAC 62.2 24.3 66.7 14.7 25.3 38.6 10.7 16.2 72.5 4.4 9.9 22.7
SND 62.6 23.5 66.4 15.7 26.8 39.0 11.3 18.2 72.5 4.9 8.4 23.1
CROTS 62.1 23.1 65.9 15.3 22.7 37.8 12.6 16.7 75.7 5.4 11.0 24.3
ATP 63.2 28.2 69.6 15.9 26.5 40.7 11.8 15.6 72.6 5.4 9.7 23.0
SFDA-DE 62.8 26.0 67.9 14.2 25.8 39.3 11.0 13.3 68.8 4.6 8.7 21.2
SFDA* 62.3 22.6 64.6 15.9 24.6 38.0 10.6 16.2 70.7 4.9 8.5 21.9
HCL* 62.2 21.1 63.0 14.5 25.9 37.3 11.9 14.9 72.0 5.8 9.7 22.9
CSS(Ours)* 62.6 24.8 66.7 15.5 26.2 39.2 12.1 16.4 74.4 4.8 9.9 23.6
CSS(Ours) 63.3 30.3 70.9 15.4 27.9 41.6 12.3 17.7 75.9 5.9 11.0 24.6
TemMs2TroMs AdaptSeg 59.5 53.1 75.7 2.9 36.6 45.6 TemMs2TroRf 7.5 66.2 83.3 5.7 14.5 35.4
CBST 70.1 53.2 81.0 2.3 39.5 49.2 6.5 66.0 58.1 18.7 5.6 31.0
CLAN 64.0 56.2 81.9 3.5 42.6 49.7 8.6 64.3 81.5 8.9 28.0 38.2
PyCDA 59.5 20.3 47.8 0.6 19.1 29.5 4.8 31.4 46.8 0.8 4.9 17.8
FADA 62.5 48.8 75.4 4.5 29.8 44.2 7.1 48.0 67.4 8.1 11.4 28.4
ASA 50.9 19.8 70.3 0.5 51.7 38.6 7.6 29.8 83.0 1.8 0.1 24.5
LD 53.3 46.7 71.1 14.2 23.5 41.7 6.3 23.8 69.6 4.0 7.5 22.3
DTAC 51.9 45.2 71.0 12.9 21.4 39.8 7.0 32.5 74.3 5.2 6.9 25.1
SND 53.0 44.4 72.7 13.4 26.6 42.0 6.9 29.8 70.6 4.6 6.9 23.9
CROTS 52.6 46.1 71.7 13.6 21.6 41.1 6.9 30.0 72.6 4.5 6.2 24.6
ATP 53.8 46.9 72.3 13.0 23.9 41.6 6.8 33.9 71.9 4.7 6.4 24.7
SFDA-DE 54.4 45.8 72.1 12.7 22.4 41.5 6.6 30.1 70.8 4.5 6.2 23.7
SFDA* 51.1 46.0 71.2 13.8 19.1 40.3 6.4 34.1 70.9 5.0 7.2 24.8
HCL* 51.1 45.1 71.5 12.4 20.5 40.1 7.0 26.6 77.0 4.9 7.5 24.6
CSS(Ours)* 52.7 47.0 71.9 13.9 21.4 41.4 6.5 34.8 72.5 5.7 7.4 25.4
CSS(Ours) 53.5 46.4 73.1 14.6 26.2 42.8 7.4 35.4 78.3 5.5 8.1 26.9
TroRf2TroMs AdaptSeg 65.7 56.1 79.2 7.0 74.8 56.5 TroMs2TroRf 17.9 58.2 85.0 18.2 29.1 41.7
CBST 66.3 61.2 78.9 6.8 68.9 56.4 17.1 56.9 85.1 22.1 22.0 40.6
CLAN 66.3 56.7 78.7 5.4 76.6 56.8 18.2 69.9 85.4 20.3 29.0 44.6
PyCDA 64.0 16.6 46.6 0.4 57.4 37.0 4.6 18.6 53.6 1.5 17.2 19.1
FADA 52.0 42.9 73.6 6.5 69.2 48.8 19.0 65.2 87.4 19.9 22.3 42.8
ASA 52.5 28.2 66.1 5.0 33.5 36.1 9.1 50.4 81.5 2.6 23.8 33.5
LD 45.3 42.0 72.9 9.8 35.8 41.3 11.4 16.1 71.2 5.6 20.3 24.9
DTAC 46.6 42.2 72.6 9.2 38.4 41.8 10.9 15.4 70.1 4.6 20.6 24.5
SND 45.3 40.0 73.0 9.0 37.3 41.0 10.5 13.0 71.4 4.2 18.5 24.2
CROTS 43.2 41.7 72.5 9.2 36.3 40.6 11.0 16.1 72.0 4.6 19.4 25.0
ATP 47.9 42.2 73.3 8.9 39.8 42.4 11.5 15.7 74.0 4.9 21.8 26.4
SFDA-DE 46.0 42.8 73.7 9.2 34.1 42.0 10.9 15.9 73.7 5.4 21.2 26.0
SFDA* 45.3 40.3 72.7 9.0 31.7 39.8 10.3 13.0 71.9 4.6 18.1 23.0
HCL* 45.3 42.1 72.8 9.2 35.2 41.1 10.9 15.4 70.0 4.5 20.5 23.3
CSS(Ours)* 47.1 42.7 73.3 10.3 36.1 41.9 10.9 16.6 74.8 5.3 21.2 26.7
CSS(Ours) 49.0 43.0 72.9 9.9 42.5 43.5 12.1 23.1 78.1 5.4 23.4 28.4
SubMs2TemMs AdaptSeg 44.4 60.2 45.3 21.9 6.4 35.7 TemMs2SubMs 40.3 76.6 74.8 22.5 51.7 53.2
CBST 37.7 54.0 23.8 27.7 4.3 29.5 40.9 75.7 66.3 25.8 29.7 47.7
CLAN 41.1 59.7 36.0 22.6 7.2 33.3 45.5 76.9 77.4 23.5 39.7 52.6
PyCDA 37.3 32.3 22.8 7.2 0.3 20.0 13.3 57.5 44.0 4.4 17.9 27.4
FADA 48.4 60.1 59.8 19.5 5.0 38.6 40.0 75.6 70.9 21.9 49.1 51.5
ASA 34.2 28.2 60.0 9.9 4.9 27.4 24.2 53.0 62.6 66.0 13.7 30.8
LD 38.3 30.0 37.3 7.5 2.0 23.0 32.7 65.4 62.2 14.6 21.4 39.3
DTAC 32.3 29.0 41.2 4.7 2.2 21.9 31.8 60.5 61.8 13.4 15.1 36.5
SND 36.0 31.0 40.3 7.1 2.5 23.4 32.6 60.9 63.1 13.7 19.6 38.0
CROTS 36.8 28.5 38.2 7.2 2.6 22.7 33.1 61.0 62.3 13.4 16.2 37.2
ATP 38.4 23.4 44.6 11.7 3.5 24.5 33.5 65.2 62.6 14.1 21.9 39.5
SFDA-DE 37.1 32.3 40.3 8.7 3.1 24.3 32.1 63.9 61.8 14.6 19.4 38.4
SFDA* 37.2 25.8 36.2 1.2 2.6 20.6 31.4 61.7 63.4 14.6 17.5 37.7
HCL* 38.9 29.7 33.1 4.1 3.1 21.8 32.3 62.5 62.2 14.0 19.6 38.1
CSS(Ours)* 42.0 29.2 33.3 11.1 2.6 23.6 32.7 66.0 62.1 14.2 21.7 39.4
CSS(Ours) 40.0 28.7 46.8 10.1 1.6 25.4 33.8 65.8 66.3 13.9 24.5 40.9
TroMs2TemMs AdaptSeg 42.3 44.1 29.7 25.1 0.7 28.4 TroMs2SubMs 50.5 75.7 73.2 27.7 37.0 52.8
CBST 45.2 39.1 27.2 28.0 0.3 28.0 46.6 70.7 64.7 32.5 35.6 50.0
CLAN 41.8 50.1 34.9 26.6 1.7 31.0 50.2 77.9 73.8 29.8 39.1 54.1
PyCDA 37.7 32.0 19.6 1.9 0.2 18.3 37.1 73.0 44.9 4.5 9.3 33.8
FADA 45.7 47.1 41.3 19.3 0.6 30.8 54.1 73.8 80.6 16.6 46.7 54.4
ASA 40.0 31.7 36.9 1.8 0.2 22.1 41.2 65.6 69.4 1.1 16.7 38.8
LD 36.0 20.4 39.8 3.3 2.2 20.4 42.3 55.0 60.7 6.4 29.2 38.7
DTAC 37.5 17.2 30.8 3.5 2.4 18.5 42.0 49.0 56.7 5.8 24.9 35.7
SND 40.6 22.8 31.7 8.2 2.4 21.1 42.2 54.5 59.4 5.8 23.7 37.1
CROTS 39.5 22.8 31.7 8.4 2.3 20.9 42.2 49.2 57.4 5.7 24.9 35.9
ATP 39.4 20.2 44.9 7.9 2.7 22.8 42.2 55.1 62.6 6.1 29.3 39.1
SFDA-DE 41.0 24.2 34.9 9.9 2.3 22.5 41.4 51.0 60.6 5.6 29.4 37.6
SFDA* 43.7 16.5 31.6 5.8 2.6 20.1 42.1 50.8 56.4 6.0 23.7 35.8
HCL* 38.8 22.8 37.2 2.2 2.5 20.7 42.1 51.6 59.3 6.1 27.1 37.2
CSS(Ours)* 40.2 23.0 34.8 9.4 2.4 21.9 43.2 52.5 60.2 6.0 28.0 38.0
CSS(Ours) 41.1 22.2 44.4 8.1 2.2 23.6 43.6 55.8 63.7 6.2 35.8 41.0
TroRf2TemMs AdaptSeg 38.9 59.2 65.4 24.2 4.2 38.2 TroRf2SubMs 28.9 75.3 72.2 22.8 60.1 51.9
CBST 36.1 57.5 59.2 27.9 1.3 36.4 42.9 77.5 72.5 32.0 27.8 50.5
CLAN 37.6 60.3 51.9 25.5 1.3 35.8 27.0 76.8 70.8 26.6 48.2 49.9
PyCDA 30.6 20.3 25.7 1.2 0.2 15.6 35.2 69.5 42.3 4.0 8.0 31.8
FADA 40.1 57.1 64.9 19.3 1.4 36.6 24.5 74.2 70.9 18.4 38.9 45.4
ASA 37.4 18.7 53.0 46.0 4.0 27.9 35.5 63.7 71.4 0.0 1.6 34.4
LD 33.3 28.7 39.0 5.6 1.7 21.7 35.4 67.5 69.3 10.6 30.3 42.6
DTAC 36.2 29.6 33.1 5.4 1.5 21.2 32.9 65.9 68.6 9.7 30.1 41.4
SND 30.6 34.6 43.2 8.2 1.9 23.7 34.3 63.5 68.4 9.8 29.9 41.2
CROTS 34.0 31.8 41.4 8.4 1.8 23.5 35.6 68.6 70.2 10.2 31.1 43.1
ATP 23.7 38.6 54.6 5.8 2.6 25.1 33.6 66.4 69.3 9.9 32.1 42.2
SFDA-DE 35.5 32.9 37.3 9.9 1.8 23.5 33.7 68.4 69.6 10.0 31.8 42.7
SFDA* 23.1 22.5 43.1 1.7 1.7 18.6 34.2 65.1 68.2 10.2 26.4 40.8
HCL* 34.3 26.9 37.9 3.5 1.8 20.9 34.2 63.9 67.8 9.3 24.9 40.0
CSS(Ours)* 33.3 35.3 43.3 9.2 1.5 24.5 35.2 65.6 68.9 9.6 30.3 41.9
CSS(Ours) 27.2 41.3 52.6 8.4 1.2 26.1 35.8 67.4 70.1 10.0 35.8 43.8

⭐Acknowledgment

Our implementation is mainly based on following repositories. Thanks for their authors.

📧Contact

If you encounter any problems or bugs, please don't hesitate to contact me at yiweifang@hhu.edu.cn.

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TGRS 2026: Curriculum-Aided Synergistic Self-Training for Source-Free Unsupervised Domain Adaptation of Remote Sensing Image Segmentation

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