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GreenLITE™ A Novel Approach to Ground-Based Quantification and Mapping of Greenhouse Gases with Potential for Validation of Low Bias Lidar Measurements Needed for Space James Nagel1, Jeremy Dobler1, Nathan Blume1, Michael Braun1, Wayne Erxleben1, Doug McGregor1, T. Scott Zaccheo2, and Tim Pernini2 1 Harris Corporation, Fort Wayne, IN, USA 2 Atmospheric and Environmental Research, Inc, Lexington, MA, USA

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GreenLITE™ Overview

Greenhouse Gas Laser Imaging Tomography Experiment, or GreenLITE™ •  Developed by Harris Corporation in collaboration with

Atmospheric and Environmental Research (AER) •  Maps and quantifies the distribution of atmospheric

greenhouse gases (CO2/CH4) over small-scales of interest (~ 1 to 5 km) in near real time

•  Based on intensity-modulated continuous-wave (IMCW) differential absorption spectroscopy techniques ‒  Two fixed transceiver units scan across a series of

retroreflectors positioned around the site of interest ‒  Differential transmission (or OD) is measured for each chord

defined by the transceiver and retroreflector (~ 10 sec/measurement)

‒  Together with meteorological measurements (T, P, RH, wind speed and direction) made at each transceiver, cloud-based retrievals convert OD to dry air mole fraction (e.g., XCO2)

•  Constructs 2-D concentration maps using sparse tomographic techniques with spatial resolution ~ 50 to 200 m (chord dependent)

•  Takes surface-level real-time continuous remote measurements in both urban and remote environments

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The Measurement Technique

•  IMCW approach using unique amplitude modulation tone applied to CW lasers for independently measuring on- and off-line optical depth and range ‒  Closely spaced on- and off-line wavelengths

transmitted simultaneously ‒  Signal processing used to retrieve individual

channel signal power and range information

•  Differential open-path transmission due to absorption found for a known path length via Beer-Lambert Law ‒  Reference signal gives optical power transmitted

by the laser ‒  Science signal gives the optical power received

by the transceiver after two-way transmission through the atmosphere

‒  Ratio of on- and off-line power gives differential OD

•  Average concentration value for the entire path or chord determined by a differential iterative approach using state-of-the-art retrieval algorithms

•  Tomographic reconstruction using a model-based approach that describes the underlying field as a function of analytic features, assuming a simple 2-D background gradient

20 20.0005 20.0010

2

4

6

8

10

Fsig t( )

t

.

Reflection

Transmission

Detector

Detector

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GreenLITE™ Historical Progression

•  IMCW approach originally conceived by Harris for the ASCENDS mission ‒  Multi-functional Fiber Laser Lidar (MFLL) has

been measuring atmospheric CO2 since 2005 ‒  MFLL has been validated through rigorous

testing over extensive flight campaigns and several variations of aircraft

‒  MFLL is currently a primary instrument for the ACT-America Suborbital Earth Venture Mission

•  GreenLITE™ took MFLL concept and applied IMCW approach to ground-based, small-site monostatic CO2 monitoring ‒  2014: Proof-of-concept demonstration at Zero

Emission Research and Technology (ZERT) facility, Bozeman, MT

‒  2015: Cross-seasonal monitoring of 0.2 km2 ground carbon sequestration site (Illinois Basin – Decatur Project, Decatur, IL)

‒  2015: Long-path demonstration at NOAA’s Boulder Atmospheric Observatory, Boulder, CO

‒  2016: Year-long deployment over 25 km2 footprint of downtown Paris, France

‒  2017: Demonstrations for industrial customers in oil and natural gas

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Advancements in Methane and Flux

Beyond CO2, current GreenLITE™ development efforts have added capabilities in sensing CH4 and quantifying emission flux

Average background CH4 concentration values found

by GreenLITE™ agree within 10-15 ppb of single-point in situ measurements

Left: Concentration values of the individual chord paths used to generate the respective 2-D maps

Right: 2-D concentration maps at 5

min. intervals during a 40 min. controlled release test

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Advancements in Methane and Flux

13:20UTC 13:45UTC 13:55UTC 14:30UTC

Using 2D reconstructed concentration fields, modeled air temperature/pressure, and local wind speed/direction, the location and leak rate of a controlled CH4 release is estimated with a

multi-box model flux calculation.

13:20

13:45

13:55

14:30

Retrieved CH4 chord concentrations showing controlled gas release

(1.6 g/s)

Wind-swept emission plume from controlled CH4 release

Estimated areal leak rate

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MFLL for Space

Systematic issues being resolved for space: •  Science −  Need for the measurement −  XCO2 retrieval algorithms −  Spectroscopy −  Validation of measurement technique

•  System engineering −  Instrument on-orbit calibration −  Data processing and management

•  Hardware −  High TRL receiver chain −  High TRL transmitter chain (working

with key suppliers in the free-space optical communications sector)

Harris is currently exploring options for a space-based implementation of its MFLL instrument architecture from either LEO or the ISS

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Validation of the Measurement Technique

Working with the US National Institute of Standards and Technology (NIST) in Boulder, CO, Harris has proposed to establish a WMO traceable transfer standard for open-path measurements such as GreenLITE™, supporting the validity of IMCW methods for low-bias vertical column measurements from air and space

Rieker, et al, Optica, 2014 NIST dual

comb spectroscopy

instrument

Closed-path gas cell

calibration against WMO

standard

Open-path validation at

Table Mountain

Cross-calibration

with GreenLITE™

Validation of IMCW

approach for air and space

Establishment of WMO Transfer Standard shows the ability for IMCW lidar to deliver low-bias measurements from space

Like the IMCW approach, frequency comb techniques offer rejection of common-mode noise factors in lidar measurements and retrievals

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Ground-Based Validation of Space-Based Passive Instruments

With continually decreasing optical footprints for passive instruments, GreenLITE™ offers potential for cross-validation with passive measurements of greenhouse gases from space

•  Gives footprint-specific average concentration values near Earth’s surface, capturing one or multiple instances for boundary layer variability comparison (e.g., highly localized urban fluctuations)

•  Can be coupled with vertical column measurements from suborbital airborne platforms capturing small concentration variations beyond the boundary layer

Retroreflectors

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Conclusions

•  GreenLITE™ is a novel system, providing real-time 2-D continuous mapping and quantitative data analytics of greenhouse gas emissions from sites of varying size ‒  CO2 and CH4 concentration ‒  Flux and emissions ‒  Additional gases to be added in the future (e.g., H2S)

•  GreenLITE™ operates autonomously in remote, urban, and industrial environments

•  GreenLITE™ leverages Harris’ long heritage in lidar development and the IMCW approach used in MFLL

•  GreenLITE™ offers science benefit for validating greenhouse gas measurement techniques used from space ‒  WMO traceable validation of a potential spaceborne

implementation of MFLL ‒  Characterization of boundary layer variation within the

footprint of Earth-observing passive instruments