Demonstration of spatial greenhouse gas mapping using laser absorption spectrometers on local scales

Abstract

Abstract. A system for measuring the two-dimensional (2-D) spatial distribution of atmospheric CO 2 over complex industrial sites and urban areas on the order of 1 to 30 km 2 every few minutes with a spatial resolution as high as tens of meters has been developed and demonstrated over the past 3 years. The greenhouse gas (GHG) laser imaging tomography experiment (GreenLITE™) provides improved measurement capabilities for applications ranging from automated 24∕7 monitoring of ground carbon storage/sequestration (GCS) sites to long-duration real-time analyses of GHG sources and sinks in urban environments. GreenLITE combines a set of sensors based on an intensity modulated continuous wave approach with 2-D sparse tomographic reconstruction mechanisms to compute a 2-D map of CO 2 concentrations over the area of interest. GreenLITE systems have recently been deployed at a number of test facilities, including a 4000-h demonstration at a GCS site in Illinois and an urban deployment in Paris, France, from November 2015 to the present. This paper describes the GreenLITE concept and the associated measurement capabilities and provides proof of concept results and analyses of observations from both short-term tests as well as longer-term industrial and urban deployments. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Analysis of temporal and spatial variability of atmospheric CO<sub>2</sub> concentration within Paris from the GreenLITE™ laser imaging experiment

“…This system, known as the Greenhouse gas Laser Imaging Tomography Experiment (GreenLITE ™ ), consists of a set of continuously operating laser-based transceivers and a set of retroreflectors separated by a few kilometers. Both data collection and data processing components are based on the intensitymodulated continuous-wave (IM-CW) measurement technique, which is described in detail in Dobler et al (2017). This instrument provides estimates of the average CO 2 concentrations along the line of sight defined by the path be-tween a laser-based transceiver and any given retroreflector.…”

Bias Correction of Long-Path CO<sub>2</sub> Observations in a Complex Urban Environment for Carbon Cycle Model Inter-Comparison and Data Assimilation

“…November 2015 and November 2016 were processed using a multi-threaded cloud-based product generation sub-system that converts the observed 15 differential optical depth values to CO2 column densities and combines them to construct 2-D maps of CO2 concentrations in near-real time. This process, illustrated in Figure 3 and described in detail in Dobler et al (2017), continuously computes integrated column CO2 concentrations along horizontal lines of sight between the transceivers and reflectors and estimates 20 the 2-D distribution of time-varying CO2 concentrations based on an analytic model and an ensemble set of temporally concurrent integrated horizontal path or "chord" measurements. The first step in this process converts each GreenLITE™ transceiver's differential transmission measurement to an estimate of the horizontal column CO2 concentration in parts per million volume (ppmv).…”

“…While traditional tomographic applications employ large numbers of back projections (chords) and angles that approach or exceed the number of pixel elements in the resulting 2-D image, this application is under-sampled due to the number of deployed transceivers and reflectors, site topography, and both natural and man-made barriers. This approach, detailed inDobler et al (2017), is similar to those proposed and implemented inLevine et al (2016),Cuccoli et al (2009), and…”

“…GreenLITE™ comprises: 1) a hardware element consisting of Intensity Modulated Continuous Wave (IMCW) differential absorption spectroscopy transceivers, retroreflectors, 5 data collection/transmission electronics, and a suite of local in situ weather sensors, and 2) a computational element consisting of on-or off-premises gas concentration retrieval, 2-D reconstruction, and web-based data distribution elements. Both hardware and computational elements are outlined briefly below and described in Dobler et al (2017). The initial purpose behind the system deployment in Paris, France, in 2015 was to demonstrate the ability to provide time-varying average urbanscale measurements of CO2 emissions and/or consumption on a city sector scale.…”

“…The system is designed such that the telescope is mounted on a mechanical scanner and is fiber coupled to a stationary electronics chassis which houses the lasers, modulators, detectors, computer, and other associated electronics. Both the optical head and the electronics box are temperature controlled and have been deployed remotely as both portable configurations and semi-permanent installations 30 (Dobler et al, 2017). The installation in Paris was of the semi-permanent design and consisted of steel tubing frames secured by concrete blocks and tethers for safety.…”