Satellite remote sensing provides scientific evidence for wetland carbon sequestration.

Carbon sink estimation

In the global carbon cycle, wetland ecosystems, as an important type of ecosystem, play a crucial role in the study of the dynamic changes in their carbon cycle and carbon budget, contributing significantly to global carbon balance. As one of the most important carbon reservoirs in terrestrial ecosystems, wetlands, although only accounting for about 6% of the land surface, contain 10%–30% of the total carbon storage in terrestrial soils. Their carbon storage can mitigate the increasing CO2 in the atmosphere, playing a vital role in stabilizing global climate and mitigating the greenhouse effect.

In recent years, due to climate change and human activities, wetland areas have shrunk dramatically, and their normal ecosystem carbon cycle processes have also undergone significant changes. In-depth research on wetland carbon sequestration capacity and its impact on the regional environment is of great significance for quantifying the carbon sequestration function of wetland ecosystems in sensitive areas under global climate change conditions. Against the backdrop of global climate change, research on carbon sequestration and emission reduction in wetland ecosystems has gradually become a topic of common concern worldwide.

my country is one of the countries in the world with the most diverse wetland types, the largest area, and the widest distribution. It covers an area of ​​0.65 billion hectares, accounting for 10% of the world's total wetland area, ranking first in Asia and fourth in the world. It has huge carbon sequestration potential, but the carbon sequestration capacity of different types of wetlands varies greatly.

As one of the most widely distributed wetland types in the world, reed wetlands play an important role in wetland carbon budget research. This paper takes a reed wetland ecosystem as the research object and uses a combination of remote sensing inversion estimation and ground data assistance to estimate and analyze the biological carbon sequestration capacity of the wetland, providing a scientific basis for the protection and rational utilization of wetland resources and for addressing global climate change.

Technical solution

technical route

In wetland carbon sequestration estimation, multispectral high-resolution satellite imagery is the primary data source, with preprocessing including radiometric and orthorectification. Object-oriented techniques are used to automatically extract reed wetlands, revealing their distribution range in the study area. Remote sensing parameters related to carbon sequestration in the reed wetlands are then inverted, and a spatial distribution map of reed carbon sequestration in the study area is obtained through the inversion model.

Remote sensing image preprocessing

Before using multispectral remote sensing images as a data source to retrieve carbon sinks, it is necessary to perform operations such as radiometric correction, radiometric calibration, atmospheric correction, orthorectification, image mosaicking, and cropping on the data.

• Radiation correction

Radiometric correction is primarily used to eliminate the differences between the target measurement values ​​obtained by the sensor and physical quantities such as the target's spectral emissivity or spectral radiance, caused by factors such as the sensor's own conditions, atmospheric conditions, solar position and angle, and certain unavoidable noise. Radiometric correction mainly includes two parts: radiometric calibration and atmospheric correction.

• Radiation calibration

Radiometric calibration converts received remote sensing data, typically image grayscale values, into actual physical quantities (such as radiance values, ground reflectivity, etc.). Its main purpose is to eliminate errors inherent in the sensor itself and determine the accurate radiometric values ​​at the sensor inlet. Radiometric calibration is divided into absolute radiometric calibration and relative radiometric calibration.

• Atmospheric correction

Atmospheric correction primarily involves eliminating radiation errors caused by atmospheric influences to obtain the true reflectivity of the ground. The total radiance of the target ultimately received by the ground sensor is not the true surface emissivity, as it is affected by factors such as aerosol scattering in the atmosphere and sunlight.

• Orthographic calibration

Orthorectification is the process of correcting spatial and geometric distortions of an image, eliminating image tilt and projection errors, and thus outputting a multi-center projection plane orthophoto.

• Image mosaicking and cropping

Using ENVI processing software, remote sensing images from the same data source covering the study area were mosaicked, and the mosaicked images were cropped according to the vector range of the study area to obtain the image of the reed study area.

▲ Distribution map of reeds in multispectral remote sensing imagery

Research Methods

In this study, an object-oriented approach was mainly used to automatically extract reed wetlands from remote sensing images. The wetlands were divided into natural reed areas and artificial reed areas. The spectral information of the remote sensing images was used to invert the remote sensing factors related to carbon sink within the study area, and the comprehensive carbon sink was estimated by integrating multiple remote sensing factor parameters.

Remote sensing inversion results

Carbon sink distribution in 2022

Carbon sequestration in the study area was calculated based on sample plot survey data. Remote sensing data from January, June, and September 2022 were selected. Correlation analysis was conducted between vegetation indices NDVI, MSAVI, RVI, SAVI, and DVI and carbon sequestration at sample plots to establish an optimal regression model for inversion estimation of carbon sequestration in reed wetlands. The spatial distribution of monthly carbon sequestration in the study area during different seasons was obtained using the remote sensing estimation model, as shown in the figure above. This reflects the distribution of reed carbon sequestration in different months of the three seasons in 2022. The carbon sequestration capacity of reeds is significantly affected by seasonal factors; during the spring season in January, carbon sequestration capacity is weak, almost nonexistent; during the summer season in June, carbon sequestration capacity gradually increases with reed growth; and from September onwards, the carbon sequestration capacity of reeds begins to weaken.

Using reed wetland ecosystems as the research object, this study employs a combination of field surveys and remote sensing interpretation to estimate and analyze the carbon sequestration capacity of wetlands. Furthermore, it forecasts carbon sink potential based on local development conditions and national economic and social development, providing a scientific basis for the protection and rational utilization of reed wetland resources and for addressing global climate change.