bunch of intro stuff
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Measure CO2 – Part 0 Introduction
I want to discuss a project I found interesting from both a geophysics and instrumentation development points of view … everyone’s favourite: measuring carbon dioxide. I’ll be up front – I’m not a “Believer”, I tend to think “climate change” is a natural phenomena that has much more to do with variations in solar radiation…
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Measure CO2 – Part 1
I’ve been interested in geophysical instrumentation for many decades now. One of the first projects of my career involved building a measurement array to detect atmospheric methane for the energy industry; one of my more recent project involved a similar goal for carbon dioxide. Other than the computers and programming languages used, not much has…
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Measure CO2 – Part 2 Considerations of Measurement
Optical methods. Aircraft-based instrument platform. The Platform Keep it basic. Aircraft travels 200 m/s (447 mph) in x-direction at an altitude of 10 km (32,800 ft). This is roughly the top of the troposphere – the “atmosphere” for us ground-dwellers. I’m going to assume no y-axis motion and cylindrical symmetry about the z-axis so I…
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Measure CO2 – Part 2 Considerations of Measurement
Optical methods. Aircraft-based instrument platform. The Platform Keep it basic. Aircraft travels 200 m/s (447 mph) in x-direction at an altitude of 10 km (32,800 ft). This is roughly the top of the troposphere – the “atmosphere” for us ground-dwellers. I’m going to assume no y-axis motion and cylindrical symmetry about the z-axis so I…
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Measure CO2 – Part 3 – The Source & Detector
It’s hard to talk of one without considering the other. A proper absorption wavelength of the laser needs to be considered as does a corresponding detector. The species defines the possible wavelengths, the detector defines which wavelengths can be captured, and a feasible laser needs to generate that wavelength. The Source The quantum theory…
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Measure CO2 – Part 4 Differential Beam
Goal Determine in-situ atmospheric gas concentration using low-frequency differential continuous-wave laser measurements. Theoretical Basis Atmospheric gases absorb laser light of very specific “colors” or wavelengths. If two laser beams are transmitted – one the ON-line wavelength for absorption by a species of interest; one slightly different – the OFF-line wavelength – the intensity of…
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Measure CO2 – Part 5 Atmosphere Model
The Ideal Gas Law & Density The number density of a atmospheric species is the number of molecules of that species within a unit volume of air. This value has an effect on the absorption of photons based on the relationship: Atmospheric pressures are sufficiently low enough that the ideal gas model represents…
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Measure CO2 – Part 5a CO2 Measurement Parameters
I spent an entire article discussing atmospheric models … but that only forms the foundation for defining the parameters of a measurement instrument. The mixing ratio for the troposphere (Layer 0 of the Standard Atmosphere model) is linear and the average value of CO2 mixing is constant within that range. Of course, the goal here…
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Measure CO2 – Part 6 Reflection
The concentration of CO2 in the atmosphere doesn’t vary greatly in terms of signal magnitude. Of more significance will be the common-mode signal related to the environmental factors. The largest variation will be reflectivity. The reflected source would not be a directed beam, optical power would be lost due to semi-Lambertion diffusion and the inverse…
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Measure CO2 – Part x System
Most of my discussion to this point could be characterized as “science” – What am I trying to measure? What are some of the issues? The astute reader will notice I’ve left out many things: clouds for one. Will I be affected by multi-layer reflections? Does it matter? The term the atmospheric scientists use is…