Bridging the Gap between Quadrats and Satellites: Assessing Utility of Drone-based Imagery to Enhance Emergent Vegetation Biomonitoring - NERRS/NSC(NERRS Science Collaborative)

Monitoring plays a central role in detecting change in coastal ecosystems. The National Estuarine Research Reserve System (NERRS) invests heavily in assessing changes in tidal wetlands through the System-wide Monitoring Program (SWMP). This monitoring is conducted in 1m2 permanent plots every 1-3 years via in situ sampling and at reserve-wide scales via airplane imagery every 5-10 years. While both approaches have strengths, important processes at intermediate spatial (i.e., marsh platform) and finer temporal (i.e., storm events) scales may be missed. Uncrewed Aerial Systems (UAS, i.e., drones) can provide high spatial resolution and coverage, with customizable sensors, at user-defined times. Based on a needs assessment and discussions with NERRS end users, we conducted a regionally coordinated effort, working in salt marshes and mangroves within six reserves in the Southeast and Caribbean to develop, assess and collaboratively refine a UAS-based tidal wetlands monitoring protocol aimed at entry-level UAS users. Using ground-based surveys for validation, we 1) assessed the efficacy of UAS-based imagery for estimating vegetation percent cover, delineating ecotones (e.g., low to high marsh), and generating digital elevation models, and 2) assessed the utility of multispectral sensors for improving products from #1 and developing vegetation indices to estimate aboveground biomass (e.g., normalized difference vegetation index, NDVI). UAS-derived elevation models and canopy height estimates were generally of insufficient accuracy to be useful when compared to field measures. Across sites, root mean squared error ranged from 0.25 to 0.59m for bare earth models, 0.15 to 1.58m for vegetation surface models, and 0.33 to 2.1m for canopy height. The accuracy of ecotones delineated from UAS imagery varied among ecotones. The average distance between image- and field-based delineations of the wetland-water ecotone was 0.18 +/- 0.01m, whereas differences of the low-high marsh ecotone were 1.25 +/- 0.11m. Overall accuracy of vegetated and unvegetated classifications among sites was 85 +/- 4%. Comparison of field- and image-based estimates of total percent vegetated cover indicated modest agreement between the two approaches, although percent cover was generally overestimated from imagery. Average differences in percent cover between approaches was ~5% at one reserve, but >25% at four reserves. Overall accuracy of species-specific classifications among reserves was 74 +/- 6% when using both orthomosaics and surface vegetation models. Comparison of field- and image-based estimates of species-specific cover indicated minimal agreement between the two approaches; the interquartile ranges of the differences were wide for all species (>40%). Aboveground biomass in monospecific Spartina alterniflora plots was highly correlated to NDVI (R2 > 0.69), although the relationship was reserve- and sensor-specific. The strength of the relationship between NDVI and biomass was weaker in mixed-species plots (R2 = 0.52). This project serves as a critical first step for improving tidal wetland monitoring conducted as part of SWMP. Furthermore, the project increased the technical capacity of end users to conduct UAS-based wetland monitoring. This research collaboration was the first of its kind in the region and has catalyzed continued collaboration to identify regional management needs and expand UAS-based monitoring to additional coastal habitats (e.g., oyster reefs).

- To meet the need of monitoring program staff for large-scale data archiving, sharing, and reproducibility, the team created standardized operational protocol and methodology for data collection and analysis

- The team piloted and incorporated drone-based operations into routine monitoring at Southeast and Caribbean reserves and created image processing and analysis protocols from their work.

- The technical capacity of all team members, including reserve staff, to conduct UAS-based wetland monitoring was enhanced through the development, implementation, and collaborative refinement of the image acquisition, processing, and analysis protocols.

- The protocol document will serve as a resource for continued enhancement of technical capacity for additional staff at the NERRs on the project team, to NERRs beyond those on the project, and for scientists and managers outside of the NERRS (anticipated).

- The first-of-its-kind regional research collaboration among the six reserves in the Southeast and Caribbean regions has led to additional coordination and participation in another Science Collaborative funded project (Storm Stories) as well as the development of key regional management needs for the NERRS Science Collaborative RFP.

Project lead and contact information:

Brandon Puckett, North Carolina NERR, brandon.puckett@noaa.gov

=List of project datasets

1. Field wetland vegetation survey at North Carolina (NOC) NERR

2. UAS wetland vegetation survey at North Carolina (NOC) NERR

3. Field wetland vegetation survey at North Inlet-Winyah Bay (NIW) NERR

4. UAS wetland vegetation survey at North Inlet-Winyah Bay (NIW) NERR

5. Field wetland vegetation survey at Ashepoo, Combahee, Edisto Basin (ACE) NERR

6. UAS wetland vegetation survey at Ashepoo, Combahee, Edisto Basin (ACE) NERR

7. Field wetland vegetation survey at Sapelo Island (SAP) NERR

8. UAS wetland vegetation survey at Sapelo Island (SAP) NERR

9. Field wetland vegetation survey at Guana Tolomato Matanzas (GTM) NERR

10. UAS wetland vegetation survey at Guana Tolomato Matanzas (GTM) NERR

11. Field wetland vegetation survey at Jobos Bay (JOB) NERR

12. UAS wetland vegetation survey at Jobos Bay (JOB) NERR

The distributor does not assume liability.

None

Cite this dataset when used as a source: NOAA retains the right to analyze, synthesize and publish summaries of the NERRS/NSC data. The NERRS/NSC retains the right to be fully credited for having collected and process the data. Following academic courtesy standards, the NERR site where the data were collected should be contacted and fully acknowledged in any subsequent publications in which any part of the data are used. The data enclosed within this package/transmission are only as accurate as the quality assurance and quality control procedures that are described in the associated metadata reporting statement allow. The user bears all responsibility for its subsequent use/misuse in any further analyses or comparisons. The Federal government does not assume liability to the Recipient or third persons, nor will the Federal government reimburse or indemnify the Recipient for its liability due to any losses resulting in any way from the use of this data. Requested citation format: NOAA National Estuarine Research Reserve System (NERRS) Science Collaborative(NSC).

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This information is detailed within the project links.

This information is detailed within the project links.