Articles | Volume 11, issue 9
Atmos. Meas. Tech., 11, 5199–5222, 2018
Atmos. Meas. Tech., 11, 5199–5222, 2018

Research article 12 Sep 2018

Research article | 12 Sep 2018

GreenHouse gas Observations of the Stratosphere and Troposphere (GHOST): an airborne shortwave-infrared spectrometer for remote sensing of greenhouse gases

Neil Humpage1, Hartmut Boesch1,2, Paul I. Palmer3,4, Andy Vick5,a, Phil Parr-Burman5, Martyn Wells5, David Pearson5, Jonathan Strachan5, and Naidu Bezawada5,b Neil Humpage et al.
  • 1Earth Observation Science, Department of Physics and Astronomy, University of Leicester, Leicester, UK
  • 2National Centre for Earth Observation, Leicester, UK
  • 3School of GeoSciences, University of Edinburgh, Edinburgh, UK
  • 4National Centre for Earth Observation, Edinburgh, UK
  • 5Science and Technology Facilities Council, UK Astronomy Technology Centre, Edinburgh, UK
  • anow at: Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell, Oxfordshire, UK
  • bnow at: European Southern Observatory, Garching, Germany

Abstract. GHOST is a novel, compact shortwave-infrared grating spectrometer, designed for remote sensing of tropospheric columns of greenhouse gases (GHGs) from an airborne platform. It observes solar radiation at medium to high spectral resolution (better than 0.3 nm), which has been reflected by the Earth's surface using similar methods to those used by polar-orbiting satellites such as the JAXA GOSAT mission, NASA's OCO-2, and the Copernicus Sentinel-5 Precursor. By using an original design comprising optical fibre inputs along with a single diffraction grating and detector array, GHOST is able to observe CO2 absorption bands centred around 1.61 and 2.06 µm (the same wavelength regions used by OCO-2 and GOSAT) whilst simultaneously measuring CH4 absorption at 1.65 µm (also observed by GOSAT) and CH4 and CO at 2.30 µm (observed by Sentinel-5P). With emissions expected to become more concentrated towards city sources as the global population residing in urban areas increases, there emerges a clear requirement to bridge the spatial scale gap between small-scale urban emission sources and global-scale GHG variations. In addition to the benefits achieved in spatial coverage through being able to remotely sense GHG tropospheric columns from an aircraft, the overlapping spectral ranges and comparable spectral resolutions mean that GHOST has unique potential for providing validation opportunities for these platforms, particularly over the ocean, where ground-based validation measurements are not available. In this paper we provide an overview of the GHOST instrument, calibration, and data processing, demonstrating the instrument's performance and suitability for GHG remote sensing. We also report on the first GHG observations made by GHOST during its maiden science flights on board the NASA Global Hawk unmanned aerial vehicle, which took place over the eastern Pacific Ocean in March 2015 as part of the CAST/ATTREX joint Global Hawk flight campaign.

Short summary
We present an overview of the GreenHouse gas Observations of the Stratosphere and Troposphere (GHOST) instrument, a novel shortwave infrared grating spectrometer designed for remote sensing of total column greenhouse gas concentrations from an aircraft. Using laboratory measurements we show that the GHOST design is able to achieve its science objectives. We conclude by describing GHOST's maiden flights on board the NASA Global Hawk UAV during CAST/ATTREX and show some of the initial results.