A novel cluster-based learning scheme to design optimal networks for atmospheric greenhouse gas monitoring (CRO²A version 1.0)

Abstract. With the continued deployment of atmospheric greenhouse gas monitoring networks worldwide, optimal and strategic positioning of ground stations is essential to minimize network size while ensuring robust observation of fossil fuel emissions in large and diverse environments. In this study, a novel scheme (Concepteur de Réseaux Optimaux d’Observations Atmosphériques – CRO²A) is developed to design optimal mesoscale atmospheric greenhouse gas monitoring networks through a three-stage process of unsupervised clustering with inverse weighting and data processing. Unlike current approaches that rely primarily on inverse-modeling pseudo-data and heavily on error or uncertainty assumptions, this scheme requires no such assumptions; instead, it relies solely on direct atmospheric simulations of greenhouse gas concentrations. The CRO²A design scheme improves convergence to an optimal solution by minimizing the number of ground-based monitoring stations in the network while maximizing overall network performance. It can perform both foreground and background analyses and can assess and diagnose the quality of existing monitoring networks, among other special features. CRO²A treats simulated green- house gas concentration fields as spatiotemporal images, processed through multiple transformations, including data cleaning and automatic information extraction. These transformations reduce processing time and sensitivity to outliers and noise. The developed scheme incorporates techniques such as image processing and pattern recognition, supported by optimal heuristics derived from operations research, which enhance the ability to explore and exploit the problem search space during the solution process. Two applications are presented to illustrate the capabilities of the proposed optimal design scheme. These are based on simulations of atmospheric CO₂ concentrations from the Weather Research and Forecasting (WRF) model-one for an urban setting and the other for a regional case in eastern France-used to evaluate optimal network designs and the computational performance of the scheme. The results demonstrate that the design scheme is competitive, straightforward, and capable of solving the design problem while maintaining a balanced computational cost. Based on the WRF reference simulation, CRO²A performed analyses of foreground measurements (atmospheric signatures of fossil fuel emissions) and their associated background fields (where simulated large-scale background concentrations are used, avoiding major sources and sinks of greenhouse gases), providing the minimum number of ground-based measurement stations and their optimal locations in the regions. As additional features, CRO²A enables users to diagnose the performance of any existing network and improve it in the event of future expansion plans. Furthermore, it can be used to design and deploy an optimal monitoring network based on predefined potential locations within the region under analysis.