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Hyperspectral Imaging of Ammonia in the Atmospheric Boundary Layer

par Noppen, Lara
Président du jury Coheur, Pierre
Promoteur Clarisse, Lieven
Publication Non publié, 2025-09-12

Thèse de doctorat

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Résumé :

Ammonia (NH3) is a key component of the global nitrogen cycle. Over the past fifty years, anthropogenic NH3 emissions have more than doubled, now largely surpassing natural sources. This excess heavily disrupts the nitrogen cycle and significantly affects air quality and biodiversity. To mitigate these harmful impacts, stricter legislation supported by effective monitoring is urgently needed. For over a decade, infrared satellite instruments have enabled global NH3 observations, and the identification and quantification of major emission hotspots. However, the coarse spatial resolution of these sounders limits their ability to observe individual point sources, especially when emissions are weak or clustered.In this context, the Nitrosat satellite mission was proposed to monitor NH3 and nitrogen dioxide (NO2) globally and at an unprecedented spatial resolution. To support and validate the mission concept, a series of airborne measurement campaigns were conducted across Europe. These were designed to simultaneously map NH3 and NO2 over various anthropogenic point sources using hyperspatial-hyperspectral observations.This thesis focuses on the analysis of this unique airborne dataset to address key challenges in high-resolution NH3 remote sensing. First, we develop and apply dedicated retrieval methods to detect and quantify industrial NH3 emissions. By simulating hypothetical satellite observations, we demonstrate that sub-kilometre resolution is essential for isolating plumes and estimating emission fluxes. Second, recognising agriculture as the dominant source of global NH3, we conduct a detailed case study over a livestock farm to retrieve agricultural NH3 fluxes and investigate their temporal variability. Third, we evaluate whether a dedicated sounder with limited spectral characteristics can provide meaningful NH3 measurements. We show that, while high spatial resolution is critical for NH3 monitoring, it can be performed with constrained spectral data, allowing for more cost-efficient mission designs.Taken together, these contributions strengthen the scientific case for a future high-resolution satellite mission and advance the field of NH3 remote sensing by providing specific retrieval methods and insights into industrial and agricultural emissions.