Assessing Stream Thermal Heterogeneity and Cold-Water Patches from UAV-Based Imagery: A Matter of Classification Methods and Metrics
Understanding stream thermal heterogeneity patterns is crucial to assess and manage river resilience in light of climate change. The dual acquisition of high-resolution thermal infrared (TIR) and red–green–blue-band (RGB) imagery from unmanned aerial vehicles (UAVs) allows for the identification and...
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2021-04-01
|
| Series: | Remote Sensing |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2072-4292/13/7/1379 |
| _version_ | 1827695988930772992 |
|---|---|
| author | Johannes Kuhn Roser Casas-Mulet Joachim Pander Juergen Geist |
| author_facet | Johannes Kuhn Roser Casas-Mulet Joachim Pander Juergen Geist |
| author_sort | Johannes Kuhn |
| collection | DOAJ |
| description | Understanding stream thermal heterogeneity patterns is crucial to assess and manage river resilience in light of climate change. The dual acquisition of high-resolution thermal infrared (TIR) and red–green–blue-band (RGB) imagery from unmanned aerial vehicles (UAVs) allows for the identification and characterization of thermally differentiated patches (e.g., cold-water patches—CWPs). However, a lack of harmonized CWP classification metrics (patch size and temperature thresholds) makes comparisons across studies almost impossible. Based on an existing dual UAV imagery dataset (River Ovens, Australia), we present a semi-automatic supervised approach to classify key riverscape habitats and associated thermal properties at a pixel-scale accuracy, based on spectral properties. We selected five morphologically representative reaches to (i) illustrate and test our combined classification and thermal heterogeneity assessment method, (ii) assess the changes in CWP numbers and distribution with different metric definitions, and (iii) model how climatic predictions will affect thermal habitat suitability and connectivity of a cold-adapted fish species. Our method was successfully tested, showing mean thermal differences between shaded and sun-exposed fluvial mesohabitats of up to 0.62 °C. CWP metric definitions substantially changed the number and distance between identified CWPs, and they were strongly dependent on reach morphology. Warmer scenarios illustrated a decrease in suitable fish habitats, but reach-scale morphological complexity helped sustain such habitats. Overall, this study demonstrates the importance of method and metric definitions to enable spatio-temporal comparisons between stream thermal heterogeneity studies. |
| first_indexed | 2024-03-10T12:37:41Z |
| format | Article |
| id | doaj.art-681f3836a06947d59d87073ca0c5f344 |
| institution | Directory Open Access Journal |
| issn | 2072-4292 |
| language | English |
| last_indexed | 2024-03-10T12:37:41Z |
| publishDate | 2021-04-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Remote Sensing |
| spelling | doaj.art-681f3836a06947d59d87073ca0c5f3442023-11-21T14:08:12ZengMDPI AGRemote Sensing2072-42922021-04-01137137910.3390/rs13071379Assessing Stream Thermal Heterogeneity and Cold-Water Patches from UAV-Based Imagery: A Matter of Classification Methods and MetricsJohannes Kuhn0Roser Casas-Mulet1Joachim Pander2Juergen Geist3Aquatic Systems Biology Unit, TUM School of Life Sciences, Technical University of Munich, 85354 Freising, GermanyAquatic Systems Biology Unit, TUM School of Life Sciences, Technical University of Munich, 85354 Freising, GermanyAquatic Systems Biology Unit, TUM School of Life Sciences, Technical University of Munich, 85354 Freising, GermanyAquatic Systems Biology Unit, TUM School of Life Sciences, Technical University of Munich, 85354 Freising, GermanyUnderstanding stream thermal heterogeneity patterns is crucial to assess and manage river resilience in light of climate change. The dual acquisition of high-resolution thermal infrared (TIR) and red–green–blue-band (RGB) imagery from unmanned aerial vehicles (UAVs) allows for the identification and characterization of thermally differentiated patches (e.g., cold-water patches—CWPs). However, a lack of harmonized CWP classification metrics (patch size and temperature thresholds) makes comparisons across studies almost impossible. Based on an existing dual UAV imagery dataset (River Ovens, Australia), we present a semi-automatic supervised approach to classify key riverscape habitats and associated thermal properties at a pixel-scale accuracy, based on spectral properties. We selected five morphologically representative reaches to (i) illustrate and test our combined classification and thermal heterogeneity assessment method, (ii) assess the changes in CWP numbers and distribution with different metric definitions, and (iii) model how climatic predictions will affect thermal habitat suitability and connectivity of a cold-adapted fish species. Our method was successfully tested, showing mean thermal differences between shaded and sun-exposed fluvial mesohabitats of up to 0.62 °C. CWP metric definitions substantially changed the number and distance between identified CWPs, and they were strongly dependent on reach morphology. Warmer scenarios illustrated a decrease in suitable fish habitats, but reach-scale morphological complexity helped sustain such habitats. Overall, this study demonstrates the importance of method and metric definitions to enable spatio-temporal comparisons between stream thermal heterogeneity studies.https://www.mdpi.com/2072-4292/13/7/1379dronescold-water refugiafreshwater ecologystream temperaturefish habitatriver resilience |
| spellingShingle | Johannes Kuhn Roser Casas-Mulet Joachim Pander Juergen Geist Assessing Stream Thermal Heterogeneity and Cold-Water Patches from UAV-Based Imagery: A Matter of Classification Methods and Metrics Remote Sensing drones cold-water refugia freshwater ecology stream temperature fish habitat river resilience |
| title | Assessing Stream Thermal Heterogeneity and Cold-Water Patches from UAV-Based Imagery: A Matter of Classification Methods and Metrics |
| title_full | Assessing Stream Thermal Heterogeneity and Cold-Water Patches from UAV-Based Imagery: A Matter of Classification Methods and Metrics |
| title_fullStr | Assessing Stream Thermal Heterogeneity and Cold-Water Patches from UAV-Based Imagery: A Matter of Classification Methods and Metrics |
| title_full_unstemmed | Assessing Stream Thermal Heterogeneity and Cold-Water Patches from UAV-Based Imagery: A Matter of Classification Methods and Metrics |
| title_short | Assessing Stream Thermal Heterogeneity and Cold-Water Patches from UAV-Based Imagery: A Matter of Classification Methods and Metrics |
| title_sort | assessing stream thermal heterogeneity and cold water patches from uav based imagery a matter of classification methods and metrics |
| topic | drones cold-water refugia freshwater ecology stream temperature fish habitat river resilience |
| url | https://www.mdpi.com/2072-4292/13/7/1379 |
| work_keys_str_mv | AT johanneskuhn assessingstreamthermalheterogeneityandcoldwaterpatchesfromuavbasedimageryamatterofclassificationmethodsandmetrics AT rosercasasmulet assessingstreamthermalheterogeneityandcoldwaterpatchesfromuavbasedimageryamatterofclassificationmethodsandmetrics AT joachimpander assessingstreamthermalheterogeneityandcoldwaterpatchesfromuavbasedimageryamatterofclassificationmethodsandmetrics AT juergengeist assessingstreamthermalheterogeneityandcoldwaterpatchesfromuavbasedimageryamatterofclassificationmethodsandmetrics |