Bias correction of long-path CO<sub>2</sub> observations in a complex urban environment for carbon cycle model inter-comparison and data assimilation

Abstract

Abstract. The Greenhouse gas Laser Imaging Tomography Experiment (GreenLITE™) trace gas measurement system, jointly designed and developed by Atmospheric and Environmental Research, Inc. and Spectral Sensor Solutions LLC, provides high-precision, long-path measurements of atmospheric trace gases including CO2 and CH4 over extended (0.04–25 km2) areas of interest. In 2015, a prototype unit was deployed in Paris, France, to demonstrate its ability to provide continuous observations of CO2 concentrations along horizontal air segments and two-dimensional (2-D) maps of time-varying CO2 concentrations over a complex urban environment. Subsequently, these data have been adapted to create a physically consistent set of horizontal segment mean concentrations for (1) comparisons to highly accurate in situ point measurements obtained for coincident times within the Greater Paris area, (2) inter-comparisons with results from high spatial and temporal regional carbon cycle model data, and (3) potential assimilation of these data to constrain and inform regional carbon cycle modeling frameworks. To achieve these ends, the GreenLITE™ data are calibrated against precise in situ point measurements to reconcile constant systematic as well as slowly varying temporal differences that exist between in situ and GreenLITE™ measurements to provide unbiased comparisons, and the potential for long-term co-assimilation of both measurements into urban-scale emission models. While both the constant systematic biases and the slowly varying differences may have different impacts on the measurement accuracy and/or precisions, they are in part due to a number of potential common terms that include limitation in the instrument design, uncertainties in spectroscopy and imprecise knowledge of the atmospheric state. This work provides a brief overview of the system design and the current gas concentration retrieval and 2-D reconstruction approaches, a description of the bias-correction approach, the results as applied to data collected in Paris, France, and an analysis of the inter-comparison between collocated in situ measurements and GreenLITE™ observations.

Single-Blind Detection, Localization, and Quantification of Methane Emissions Using Continuous Path-Integrated Column Measurements

“…Backend processing and analytics convert measured optical depth values to gas concentrations in near-real time and generate 2-D distributions of CH4 concentrations. 12,13,14 GreenLITE™ measurements are interfaced with an inverse dispersion model (IDM) to estimate CH4 emission rates and locations.…”

Estimating oil sands emissions using horizontal path-integrated column measurements

“…GreenLITE™ is a laser absorption-based gas measurement system that consists of one or more optical transceiver units, some number of retroreflectors arranged such that a clear line of sight exists between each transceiver and each reflector, and backend analytics that convert measured optical depth values to gas concentrations in near real-time and generate 2-D concentration distributions [Dobler, 2015;Dobler, 2017;Zaccheo, 2019]. A transceiver consists of a stationary climate-controlled equipment cabinet and an optical head that is mounted on a two-axis mechanical scanner.…”

“…The IMCW technique makes GreenLITE™ nearly immune to the largest sources of noise in other long-path LAS systems (e.g., scintillation). The differential absorption of these two wavelengths by the gas can be directly converted to optical depth, from which the concentration of the gas can be determined using a radiative transfer model [Clough, 2005;Rothman, 2009] in an iterative scheme [Dobler, 2015;Zaccheo, 2019]. To help ensure that the system measurement precision is maintained, data quality filters are applied in a conservative approach to remove measurements that may be biased due to low signal level (affected by electronic noise) or high signal level (overloading or clipping of amplifiers and analog-to-digital converters).…”

“…A web-based interface provides near-real-time display of the data and can be configured to provide alerts via email or SMS text messages when operator-defined conditions are detected. Prior to deployments at the Alberta oil sands, GreenLITE™ has previously been tested and deployed in several environments, including 6 months at a carbon capture and storage facility in Illinois [Dobler, 2017;Blakley, 2020], a full year in the urban core of Paris, France [Lian, 2019], and a week-long campaign at an oil and gas processing facility in Lacq, France [Watremez, 2018].…”

Estimating Oil Sands Emissions using Horizontal Path-Integrated Column Measurements

“…A web-based interface provides near-real-time display of the data and can be configured to provide alerts via email or SMS text messages when operator-defined conditions are detected. Prior to deployments at the Alberta oil sands, GreenLITE™ has previously been tested and deployed in several environments, including 6 months at a carbon capture and storage facility in Illinois [Dobler, 2017;Blakley, 2020], a full year in the urban core of Paris, France [Lian, 2019], and a week-long campaign at an oil and gas processing facility in Lacq, France [Watremez, 2018].…”