Dr Neil Humpage

Current research projects

Calibration and deployment of the GHOST airborne spectrometer

GHOST is a novel, compact shortwave infrared (SWIR) grating spectrometer developed to fly on board the NASA Global Hawk within the framework of the NERC CAST (Co-ordinated Airborne Studies in the Tropics) project. It has been designed to collect observations of tropospheric CO2, CO, CH4, H2O columns and the HDO/H2O ratio over the ocean. The primary science objectives of GHOST are to provide observations which will: 1. Test atmospheric transport models (e.g., transition zone between tropics and subtropics or large-scale continental outflow); 2. Validate satellite GHG column observations over the oceans thereby filling a critical gap of current validation networks; 3. Complement in situ TTL tracer observations from the Global Hawk to help link the upper troposphere with lower troposphere concentration measurements. GHOST was designed and built at the UK Astronomy Technology Centre (ATC) in Edinburgh, and has now been deployed on both the NASA Global Hawk and the NERC Airborne Research and Survey Facility (ARSF) Dornier 228.

In-situ FTIR observations of trace gases in support of GAUGE

The overall objective of the NERC Greenhouse gAs Uk and Global Emissions (GAUGE) programme is to quantify the UK greenhouse gas (GHG) budget in order to underpin the development of effective emission reduction policies. The project will develop high-resolution estimates of UK GHG sources/sinks using a new, purpose-built measurement network, and will improve global GHG flux estimates through the exploitation of all available in situ and remote sensing data. Our contribution to GAUGE will be to deploy an in-situ FTIR gas analyzer (supplied by ECOTECH) in the field, coincident with other ground-based (e.g. tall tower) observations. The instrument can simultaneously measure high-precision concentrations of CO2 (0.05 ppm), CH4 (0.2 ppb), N2O (<0.06 ppb) and CO (0.2 ppb). The analyzer consists of a 24 m pathlength multipass sample cell coupled to a Bruker IRcube FTIR spectrometer (1800-5000 cm-1, spectral resolution 1 cm-1). The operation is fully automated and enables rapid quantitative analysis of trace gases in air. The trace gas concentrations are inferred from the best-fit to measured spectra without the need for frequent gas calibrations. Absolute accuracy is established by reference to calibration gas standards, and we will use common calibration scales to the other in situ analyzers used in GAUGE. The analyzer is currently based at St Nicholas Church in Glatton, Cambridgeshire, and was also deployed during the GAUGE Emissions Hotspots campaign in August 2014 at Masons Landfill Site, Great Blakenham, Suffolk.

Previous research projects

ADVANSE-II: Improved methane line parameters in the shortwave infrared for remote sensing applications

ADVANSE-II is an ESA funded project which aims to improve the absorption line parameters of methane in the SWIR 1.6 micron band used by GOSAT TANSO-FTS and Envisat SCIAMACHY methane retrieval algorithms. My role was to develop, write and test software which uses optimal estimation to retrieve absorption line parameters from laboratory spectra of methane, measured over a range of sample temperatures and mixing ratios. A new set of line parameters for this spectral region has been derived using the software, based on a comprehensive new absorption spectrum dataset measured by our colleagues at IUP (Institute of Environmental Physics), University of Bremen. Initial testing in both satellite and ground-based (TCCON sites) retrievals has indicated a small improvement in retrieved methane concentrations compared with those obtained using the standard line parameter database based on HITRAN 2008.

Capability of atmospheric parameter retrieval and modelling for wide swath space-borne atmospheric Doppler radars (WisDR)

This was an ESA funded project to investigate the feasibility of using wide swath Doppler radars in orbit for meteorological observations, particularly wind fields. Three mission concepts have been considered, each attempting to address the requirements for three different potential fields of interest: numerical weather prediction; hurricanes and tropical storms, and cloud modelling. Each concept has been tested using a detailed instrument simulator and forward model to create synthetic observations sensitive to the concept configuration, including full signal processing. The results are used to investigate and quantify sources of error including multiple scattering, non-uniform beam filling and surface contamination of the measured signal, and to determine whether performance requirements can be met in spite of these measurement errors.

Sentinel Convoy for Land Applications

The ESA Sentinel Convoy studies each have two aims: to identify scientific and operational objectives and needs which would benefit from additional in-orbit support, and to identify and develop a number of cost-effective convoy concepts (comprising additional missions flying with European operational satellites) which would meet these identified objectives and needs. I have been involved in identifying the science requirements of the various user communities for the Land themed study (other Sentinel Convoy studies are focused on Ocean & Ice and The Atmosphere), in collaboration with Surrey Satellite Technology Ltd and EADS-Astrium.

High frequency Doppler radars for a polar precipitation mission (HIDRA4PPM)

This CEOI funded study aimed to address two issues relevant to high frequency radar observations of snow. The first of these (lead by the University of Leicester) was to improve quantification of the information content available from dual-frequency reflectivity ratio measurements, and to identify the optimal frequency pair for discriminating between snow habits and for minimising uncertainties in snow-rate estimates. 140 and 220 GHz are considered in addition to the 35-94 GHz frequency pair studied previously for the ESA Earth Explorer 8 Polar Precipitation Mission radar. Secondly, the critical technology development requirements for an Earth Explorer 9-like space mission were assessed (lead by the Millimetre Wavelength Technology Group at STFC-RAL), given how technically challenging it currently is to deploy space-borne radars at such high frequencies. More specifically, a subsystem to component level study of the high power mm-wave frequency multipliers needed to drive the radar transmitter output was carried out. The work on identifying frequency pairs for snow habit discrimination and snow rate retrieval has been included in a paper which is currently under preparation (see below for reference).

Infrared FTS measurements of absorption cross sections for organic compounds

The accurate retrieval of global concentrations of organic compounds in the Earth's atmosphere using space-borne infrared spectrometers requires precise knowledge of the spectral absorption cross sections of these compounds over the appropriate wavelength range, at high spectral resolution, and covering a range of temperatures and pressures representative of the lower atmosphere. These cross sections were measured using a high resolution Bruker IFS 125HR FTS (run by the Molecular Spectroscopy Facility at STFC-RAL, see http://www.msf.rl.ac.uk) in conjunction with a specially built long-path absorption cell, which provides a highly stable environment able to contain the target compound at low temperatures (down to 77K, although this work only requires temperatures as low as 194K) and pressures. Mirrors at either end of the cell enable optical path lengths up to 20m. The spectrometer is used to perform measurements of absorption spectra at a spectral resolution of 0.015cm-1; this is necessary to resolve the fine structure present in the absorption cross sections, and therefore reduce the errors encountered when they are used in satellite retrievals. I was involved in measurements of the infrared absorption cross section of acetone, in collaboration with the University of York and STFC-RAL (see reference below for further details).

Thermal Infrared Detector Array System - Signal Processing Unit (TIDAS-SPU)

TIDAS-SPU was a CEOI (Centre for Earth Observation Instrumentation, see http://www.ceoi.ac.uk) funded project lead by EADS-Astrium, in collaboration with the University of Leicester, Selex-Galileo and STFC-RAL. The aim was to develop and test a demonstration concept for a 2D thermal infrared detector array system, along with associated back-end processing, to be used as part of an imaging Fourier transform spectrometer (FTS). My role within the project was to ensure that the design is consistent with the science requirements for possible future earth observation mission opportunities which may utilise a space-borne infrared FTS imager. This included modelling of the system to investigate potential sources of error introduced by different design considerations. I was also involved in testing of the system and interpretation of the measurements, with particular focus on the differences between measurements obtained using a traditional single detector element FTS compared with those acquired using the 2D array of detector elements considered here.

Far-infrared spectroscopy of cirrus and water vapour in the atmosphere using TAFTS (PhD at Imperial College London)

The Tropospheric Airborne Fourier Transform Spectrometer (TAFTS) was developed by Imperial College London to perfrom high spectral resolution observations of far-infrared (100 - 600cm-1) spectral radiances from an aircraft, operating at both nadir and zenith viewing angles. Spectral radiances observed in this wavenumber range are sensitive to ice cloud microphysical properties, owing to the strong dependence of ice refractive index on wavenumber in the far-infrared. In clear sky conditions far-infrared spectral radiance measurements are also useful for investigating the effect of the water vapour continuum absorption, the physical basis of which is still unresolved. In addition to analysing data taken during the EMERALD-II campaign in Darwin, Australia (which looked at tropical cirrus), I was involved in a 2007 field campaign at the ARM North Slope of Alaska climate monitoring site in Barrow called RHUBC where TAFTS was operated at ground level using its zenith viewing geometry.

Links:

TAFTS: http://www3.imperial.ac.uk/spat/research/missions/atmos_missions/tafts

RHUBC: http://acrf-campaign.arm.gov/rhubc/

Publications

N Harris, L Carpenter, J Lee, G Vaughan, M Filus, R Jones, B OuYang, J Pyle, A Robinson, S Andrews, A Lewis, J Minaeian, A Vaughan, J Dorsey, M Gallagher, M Le Breton, R Newton, C Percival, H Ricketts, S Baugitte, G Nott, A Wellpott, M Ashfold, J Flemming, R Butler, P Palmer, P Kaye, C Stopford, C Chemel, H Boesch, N Humpage, A Vick, A MacKenzie, R Hyde, P Angelov, E Meneguz, and A Manning, 2016: Co-ordinated Airborne Studies in the Tropics (CAST). Bulletin of the American Meteorological Society. doi:10.1175/BAMS-D-14-00290.1, in press

A Regan, P Silvistrin, D Fernandez, K Atkinson, N Leveque, R Bird, J Johannessen, T Nagler, H Rott, A Stoffelen, M Wooster, N Humpage, JJ Remedios, Sentinel Convoy: Synergetic Earth observation with satellites flying in formation with European operational missions, Acta Astronautica, submitted for publication 2015

C Fox, PD Green, JC Pickering, N Humpage, Analysis of far-infrared spectral radiance observations of the water vapor continuum in the Arctic, Journal of Quantitative Spectroscopy and Radiative Transfer 155 (2015) 57-65; doi:10.1016/j.jqsrt.2015.01.001

N Humpage, H Boesch, PI Palmer, PM Parr-Burman, AJA Vick, NN Bezawada, M Black, AJ Born, D Pearson, J Strachan, M Wells, GreenHouse Observations of the Stratosphere and Troposphere (GHOST): a novel shortwave infrared spectrometer developed for the Global Hawk unmanned aerial vehicle, Proc. SPIE 9242, Remote Sensing of Clouds and the Atmosphere XIX; and Optics in Atmospheric Propagation and Adaptive Systems XVII, 92420P (October 17, 2014); http://dx.doi.org/10.1117/12.2067330

A Battaglia, CD Westbrook, S Kneifel, P Kollias, N Humpage, U Lohnert, J Tyynela, GW Petty, G band atmospheric radars: new frontiers in cloud physics, Atmospheric Measurement Techniques 7 (2014) 1527-1546; http://dx.doi.org/10.5194/amt-7-1527-2014

N Humpage, JJ Remedios, MJ Wooster, H Balzter, S Eves, D Hall, Sentinel convoy for land processes and applications: critical review and gap analysis, 1st International Earth Observation Convoy and Constellation Concepts Workshop (2013)

JJ Harrison, N Humpage, NDC Allen, AM Waterfall, PF Bernath, JJ Remedios, Mid-infrared absorption cross sections for acetone (propanone), Journal of Quantitative Spectroscopy and Radiative Transfer 112 (2011) 457-464 (http://dx.doi.org/10.1016/j.jqsrt.2010.09.002)

N Humpage, PD Green, JE Harries, Far-infrared spectral radiance observations and modelling of arctic cirrus: preliminary results from RHUBC, Current Problems in Atmospheric Radiation (IRS 2008) edited by T. Nakajima and M.A. Yamasoe (2009) 466-469 (http://dx.doi.org/10.1063/1.3117022)

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