No abstract

We have developed and tested a laser heterodyne radiometer (LHR) for detecting methane leaks from upstream oil and gas infrastructure and landfills that uses the Sun as the signal light source, demonstrating here sensitivity sufficient to detect “super-emitter” leaks ( > 50 k g / h , 1166 slm). Tracking optics follow the Sun during its apparent daily transit across the sky, and the system collects direct absorption data and optionally the 1f and 2 f wavelength modulation spectroscopy (WMS) signals. The direct absorption data are processed in real time using a retrieval algorithm with a 5 s update rate to reveal the methane concentration versus altitude for each measurement line of sight. The 1 f and 2 f WMS signals are significantly non-intuitive because of the dramatic change in the methane lineshape as a function of pressure (altitude) but may ultimately provide useful information for leak localization. We describe herein modifications to the RF detection train and data collection system that allow faster and higher signal-to-noise ratio measurements. Preliminary results suggest that leaks giving rise to methane concentrations of the order of 500 ppm-m can be effectively detected—sensitivity similar to current satellites with more continuous temporal coverage and areal coverage of the order of 100s of k m 2 for relatively low cost. We outline a method of using an array of LHRs to localize the leak using lineshape information and tomographic reconstruction techniques that will be tested in future work.

The navigated laser photocoagulation system (NAVILAS®, OD-OS GmBH, Teltow, Germany) is a laser treatment device that provides navigated laser treatment of the retina based on a fundus image. The purpose of this study was to investigate the accuracy of laser treatment based on external optical coherence tomography (OCT) images - a new application of the device. This retrospective case series evaluated the accuracy of laser spot placement in 7 eyes after using overlaid external OCT images for planning NAVILAS laser treatment. After a mean time of 33 days, a post-treatment OCT was obtained and compared with the pretreatment plan on the previous OCT. Laserspots touching or overlapping the planned 100 µm laser spots were classified as "match" and invisible laser spots as "laser spot not evolved". A total of 477 laser spots in 7 eyes were evaluated (mean: 68 spots per eye). Of all planned laser spots, 361 (75.7 %) were visible on post-treatment OCT. 58.7 % of these spots matched the pretreatment plan. Non-matching laser spots showed no uniform pattern of dislocation. Planning navigated NAVILAS Laser treatment based on manually imported OCT images seems to be less accurate than planning with NAVILAS integrated imaging. These findings warrant further evaluation, not only regarding the recently installed automated picture importing tool but also concerning its clinical impact, which is possibly outweighed by the advantages of the additional image information.