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J. Timmermans

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Advancing terrestrial biodiversity monitoring with satellite remote sensing in the context of the Kunming-Montreal global biodiversity framework

Journal article - J. Timmermans, J. Timmermans, J. Timmermans, W. Daniel Kissling, W. Daniel Kissling

Satellite remote sensing (SRS) provides huge potential for tracking progress towards conservation targets and goals, but SRS products need to be tailored towards the requirements of ecological users and policymakers. In this viewpoint article, we propose to advance SRS products with a terrestrial biodiversity focus for tracking the goals and targets of the Kunming-Montreal global biodiversity framework (GBF). Of 371 GBF biodiversity indicators, we identified 58 unique indicators for tracking the state of terrestrial biodiversity, spanning 2 goals and 8 targets. Thirty-six shared enough information to analyse their underlying workflows and spatial information products. We used the concept of Essential Biodiversity Variables (EBV) to connect spatial information products to different dimensions of biodiversity (e.g. species populations, species traits, and ecosystem structure), and then counted EBV usage across GBF goals and targets. Combined with published scores on feasibility, accuracy, and immaturity of SRS products, we identified a priority list of terrestrial SRS products representing opportunities for scientific development in the next decade. From this list, we suggest two key directions for advancing SRS products and workflows in the GBF context using current instruments and technologies. First, existing terrestrial ecosystem distributions and live cover fraction SRS products (of above-ground biomass, ecosystem fragmentation, ecosystem structural variance, fraction of vegetation cover, plant area index profile, and land cover) need to be refined using a co-design approach to achieve harmonized ecosystem taxonomies, reference states and improved thematic detail. Second, new SRS products related to plant physiology and primary productivity (e.g. leaf area index, chlorophyll content & flux, foliar N/P/K content, and carbon cycle) need to be developed to better estimate plant functional traits, especially with deep learning techniques, radiative transfer models and multi-sensor frameworks. Advancements along these two routes could greatly improve the tracking of GBF target 2 (‘improve connectivity of priority terrestrial ecosystems), target 3 (‘ensure management of protected areas’), target 6 (‘control the introduction and impact of invasive alien species’), target 8 (‘minimize impact of climate change on biodiversity’), target 10 (‘increase sustainable productivity of agricultural and forested ecosystems’) and target 12 (‘increase public urban green/blue spaces’). Such improvements can have secondary benefits for other EBVs, e.g. as predictor variables for modelling species distributions and population abundances (i.e. data that are required in several GBF indicators). We hope that our viewpoint stimulates the advancement of biodiversity monitoring from space and a stronger collaboration among ecologists, SRS scientists and policy experts.@en

Contributed

4 records found

Exploring TROPOMI NO<sub>2 </sub> observations over low clouds and fog

Understanding the impact of the air-mass factor on cloudy scenes over the North Sea

Master thesis - N. Van der Borght, j. Pepijn Veefkind, J. Timmermans, Jos de Laat

This thesis investigates TROPOMI NO2 observations over low clouds and fog. Such scenes present unique opportunities due to the increased reflectivity of clouds in the lower troposphere, which enhances sensor sensitivity. However, in order to accurately estimate vertical NO2density in these scenarios, a better understanding of the retrieval process in such conditions is imperative. Two NO2 retrieval case studies, both exhibiting a spurious retrieval in the presence of low clouds and fog above the North Sea, are examined: February 14𝑡ℎ, 2023, and April 9𝑡ℎ, 2023. The main focus was on the influence of the air-mass factor on the retrieval. This factor converts measured slant column data along the satellite path into vertical tropospheric columns. Spurious spatial patterns are strongly amplified after the application of the air-mass factor. Key dependencies influencing the conversion from slant to vertical column are identified, being the the a-priori NO2 profile, air mass factor calculation, and cloud characterization. Notably, the low spatial resolution of the a-priori model and its pronounced peak near the surface contribute to inflated NO2 values over clouds. The majority of the a-priori NO2 profile is simulated underneath the cloud field, leading the retrieval algorithm to assume it did not capture a significant portion of the concentration, thus strongly increasing retrieved NO2 densities over clouds. Furthermore, spatial reflectivity patterns in the North Sea are not always accounted for in the surface reflectivity climatology. This results in misinterpreted clouds with a low cloud fraction. Misinterpreted clouds over open sea areas, combined with low cloud pressures, result in downward corrections over clear-sky seas. These effects culminate in an exacerbated cloudy-clear contrast in NO2 densities, aligning with the outlines of low cloud fields. Additionally, the heterogeneous cloud field challenges the assumption of a fixed-height, fixed-albedo Lambertian reflector. This inflation effect is modulated by the cloud height. The uncertain height of the Lambertian cloud in the lowest troposphere, combined with an assumed NO2 profile at the same height, dominates the air-mass factor calculation . Four recommendations to enhance NO2 retrieval accuracy in the presence of low clouds and fog over the North Sea are presented, which include a Cloud-as-Layers characterization, high-resolution simulations and in-situ measurements of vertical NO2 profiles in the presence of low clouds, an a-priori correction of the NO2 profile in the presence of low clouds and implementing auxiliary data relating to spatial patterns in sea-colour of the North Sea.

Biomass burning combustion efficiency

Understanding spatial resolution and environmental drivers in biomass burning combustion efficiency using TROPOMI satellite data

Master thesis - A.K. Jha, Ivar van der Velde, Helene Peiro, S.J.A. van der Linden, J. Timmermans, j. Pepijn Veefkind

In recent years, record-breaking wildfires have occurred globally, with projections indicating a dramatic increase in their frequency and intensity in the future. These wildfires present serious risks to the environment by releasing harmful pollutants and various greenhouse gases, which significantly contribute to air pollution and climate change. To accurately predict emissions of such gases, a comprehensive understanding of combustion efficiency is essential. Due to TROPOMI’s capability to measure trace gases such as NO2 and CO with high spatial resolution and global coverage, it has been used in various studies to analyse combustion efficiency. The study used NO2 and CO column concentrations measured by TROPOMI to estimate Mole Density Ratio (MDR), which is a proxy of combustion efficiency, over two devastating wildfires that occurred in California in 2020. By using TROPOMI data, aggregated to various resolutions using the super-observation approach, the study assessed the spatial and temporal limits of TROPOMI-derived MDR. It evaluated changes in MDR values across various vegetation types by integrating higher resolution land classification data from MODIS. Additionally, it explored the relationship between MDR and environmental indicators such as drought conditions and soil moisture. Super-observations resulted in significantly different MDR values with those estimated at TROPOMI resolution. The findings indicated that there was loss of information regarding MDR when super-observations were used. Furthermore, there was no clear link found on the impact of environmental factors such as soil moisture and drought conditions on MDR. Finally, a detailed land use characterisation provided deeper insights into the effect of burning various types of vegetation on the MDR. However, to be able to fully interpret the effect of super-observations and environmental factors on MDR, a more extensive analysis is suggested.

The effect of mangroves on coastline stability

Master thesis - A.T.C. Wens, B van Wesenbeeck, J. Timmermans, V.T.M. van Zelst

Mangrove ecosystems are dynamic environments that provide numerous ecological, economic, and societal benefits, such as shoreline protection, carbon sequestration, and flood protection. These ecosystems are exclusively found in tropical and subtropical regions and thrive at the interface of land and sea. Despite their many benefits, mangroves face significant threats, leading to substantial losses over the past century. The degradation of mangroves compromises flood protection and shoreline stability, increasing the risk of severe coastline erosion and flooding. Current research highlights the role of mangroves in flood protection but presents conflicting theorieson their impact on coastline stability. Two competing theories exist regarding the effect of mangroves on coastline stability, namely the ”land-builders” and the ”land-consolidators” theory. According to the ”land-builders” theory, mangroves actively accumulate sediment and contribute to the expansion of coastlines. In contrast, the ”land-consolidators” theory suggests that mangroves play a more passive role in stabilizing existing landforms and serve as buffers against erosion. The debate on the primary function of mangroves remains unresolved. Furthermore, existing studies often date back over 50 years and are limited by specific hydrodynamic and geomorphic settings, leaving a gap in understanding broad trends. This research aims to bridge this gap through a global assessment of the influence of mangroves on coastline development, complemented by a local assessment to explore detailed interactions in specific case study areas. The study’s objective is to explore the dynamic impact of mangroves on coastline stability through an extensive analysis of historical datasets to identify trends and patterns in coastline changes associated with mangrove ecosystems. The focus lies on observing trends between coastline stability and the presence of mangroves, the relationship between coastline stability and mangrove forest width, and the influence of the state of mangrove forests (contracting, expanding, stable) on coastline stability.

Hyperspectral Unmixing using Least Squares Optimization Methods

Master thesis - Y. Zheng, A. Amiri Simkooei, S. Verhagen, J. Timmermans

Hyperspectral imaging, with its capability of capturing information beyond the visible spectrum, can offer detailed spectral signatures that are critical in various applications, ranging from environmental monitoring to medical diagnostics. However, a significant challenge arises ...