A Differential Absorption LiDAR for Measurement of Greenhouse Gases

One of the great unanswered science questions of our time is - just where does all the carbon go that we emit into the atmosphere? It is a surprisingly difficult question to answer given there are a range of possible candidates such as oceans, forests and agriculture. What we do know is that uncertainty exists and we have a 'missing carbon sink' in the global carbon balance. We need to know the carbon balance and the fate of carbon in our land-ocean-atmosphere system if we can ever aim to mitigate global change by manipulating natural sources and sinks of carbon. The new discipline of Carbon Cycle Science is just beginning and our DIAL system is ideally placed to observe and understand carbon in various forms moving, from terrestrial and water systems, into and out of the atmosphere.

The relatively low-cost and autonomous operation of the DIAL MGG means that many can be deployed in remote areas, covering parts of the world where no observations are currently made. The DIAL MGG can be used as a complementary technique to existing measurements covered by scientific networks in the USA, Europe and Japan. Scientists currently use weather models to determine where the carbon comes from by measuring carbon that passes an instrument at an observation point; this allows estimates of carbon up to 5-7 km in the atmosphere and they can then work out carbon exchange on regional and continental scales.

DIAL MGG is also complementary to satellite observations since satellites cannot resolve great detail within the lower several kilometres of the atmosphere and can only give column-integrated values. The DIAL MGG can return CO2 and CH4 concentrations every few hundred metres in the lower atmosphere. After a period of assessments when DIAL MGG is calibrated against current methods and technology we believe that the DIAL MGG may ultimately replace current methods. There is economic and political value in knowing where carbon is flowing in the atmosphere. Carbon trading is still in its infancy but a series of DIAL MGG instruments, for instance, located upwind and downwind of a tropical forest being offered as a carbon sink for payment of Carbon credits, would prove unequivocally what the sink (or source) strength was for that forest. Similarly, leakage from any proposed shale gas site could be observed independently and quantitatively by a number of DIAL MGG instruments.

Examples of the STFC expertise being deployed on this project which are critical to success include:
- Specifying appropriate telescope components to produce the desired performance;
- Designing and manufacturing a bespoke optical system to launch the laser in alignment with the telescope;
- Alignment of the Detector.