Remote Sensing of Ecosystem Structure—Part 2: Initial Findings of Ecosystem Functioning through Intra- and Inter-Annual Comparisons with Earth Observation Data

Daniel L. Peters,K. Olaf Niemann,Robert Skelly

doi:10.3390/rs13163219

Daniel L. Peters, K. Olaf Niemann + Show 1 more

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https://doi.org/10.3390/rs13163219

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Abstract

This study examines the response of a cold-regions deltaic wetland ecosystem in northwestern Canada to two separate and differing seasonal wetting cycles. The goal of this paper was to examine the nature of reflected electromagnetic energy measured by earth observation (EO) satellites, and to assess whether seasonal wetland hydroperiod and episodic flooding events impact the information retrieved by the Sentinel-2 sensors. The year 2018 represents a year characterized by a large spring freshet and ice-jam flooding, while 2019 represents a year characterized more by summer open-water flooding. We applied the Modified Normalized Difference Wetness Index (MNDWI) to address the effects of the wetting cycles. The response of the vegetative cover was tracked using the fraction of the absorbed photosynthetically active radiation (fAPAR) and the Leaf Area Index (LAI). All three indices were viewed through the lens of cover classes as derived through a previously published study by the authors. The study provides a framework for designing longer-term studies where multiple intra- and inter-annual hydrological cycles can be accessed via EO data. Future studies will enable the examination of lag times inherent in the response to the various water sources applied to spectral response and incorporate this EO approach into a monitoring framework.

Highlights

The goal of this paper is to examine the nature of reflected electromagnetic energy as measured by earth observation (EO) satellites and to assess whether seasonal wetland hydroperiods, as well as episodic flooding events, impact the information retrieved by the Sentinel-2 sensors
We examine the response of a deltaic wetland landscape within the context of the Peace–Athabasca Delta (PAD) located in northwestern Canada
The wetting patterns observed through the Modified Normalized Difference Wetness Index (MNDWI) spatiotemporal sequences presented in Figure 6 indicate that water dispersal in a complex, cold-regions wetland-lake landscape can be tracked through the use of EO data such as those acquired by the Sentinel2 platform

Summary

Introduction

These valuable functions are the result of the unique natural characteristics of wetlands; namely, that they form where the landscape is permeated or submerged by water on a permanent or temporary basis for a sufficient length of time to promote aquatic processes. Wetlands represent sensitive transition areas between terrestrial and aquatic ecosystems and provide a critical indicator of environmental health [3]. Monitoring of the state of water extent and natural vegetation cover, along with associated processes such as green-up and senescence, provides us with insight as to the stresses being exerted on these sensitive areas as well as their state of health [4]

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