Dr David McKee

Reader

Physics

Personal statement

The oceans play a hugely important role in the global carbon cycle and in energy transport mechanisms that influence world climate. Monitoring oceans is difficult due to the vast areas involved, the harsh environmental conditions and the rapid temporal variability of marine biogeochemical systems. Optical sensors can provide information about biological and mineral particles and dissolved substances. The technology is particularly suitable as optical sensors can be deployed on a variety of platforms, from satellites and aircraft to in situ moorings and underwater vehicles. David’s research is currently focused on improving the quality of products obtained from ocean colour remote sensing signals and in situ optical measurements of absorption, scattering and fluorescence. He is also interested in development of new platforms for optical instruments in oceanography such as micro-satellites for Earth observation and in situ profiling moorings. The research combines significant time spent at sea making measurements, numerical simulation of underwater and water leaving light fields and statistical data analysis. Most of the work is concentrated on optically complex shelf seas (e.g. Bristol Channel, Irish Sea, Mediterranean) where the influence of terrestrial and anthropogenic sources are strongest, though more recently he has started to develop interests in optical complexity in more open ocean areas that are subject to episodic inputs of wind-borne particulates. A key element of David’s NERC Fellowships has been the development of several very successful collaborations with partners in UK and international institutions.

Publications

Remote sensing of zooplankton swarms
Basedow Sünnje L, McKee David, Lefering Ina, Gislason Astthor, Daase Malin, Trudnowska Emilia, Egeland Einar Skarstad, Choquet Marvin, Falk-Petersen Stig
Scientific Reports Vol 9 (2019)
https://doi.org/10.1038/s41598-018-37129-x
Measurement uncertainties in PSICAM and reflective tube absorption meters
Lefering Ina, Röttgers Rüdiger, Utschig Christian, Twardowski Michael S, McKee David
Optics Express Vol 26, pp. 24384-24402 (2018)
https://doi.org/10.1364/OE.26.024384
Forward modeling of inherent optical properties from flow cytometry estimates of particle size and refractive index
Agagliate Jacopo, Lefering Ina, McKee David
Applied Optics Vol 57, pp. 1777-1788 (2018)
https://doi.org/10.1364/AO.57.001777
Evaluation of a flow cytometry method to determine size and real refractive index distributions in natural marine particle populations
Agagliate Jacopo, Röttgers Rüdiger, Twardowski Michael S, McKee David
Applied Optics Vol 57, pp. 1705-1716 (2018)
https://doi.org/10.1364/AO.57.001705
Estimation of suspended matter, organic carbon and chlorophyll-A concentrations estimation from particle size and refractive index distributions
Agagliate Jacopo, Röttgers Rüdiger, Heymann Kerstin, McKee David
Applied Sciences Vol 8 (2018)
https://doi.org/10.3390/app8122676
Inversion of in situ light absorption and attenuation measurements to estimate constituent concentrations in optically complex shelf seas
Ramírez-Pérez M, Twardowski M, Trees C, Piera J, McKee D
Journal of Geophysical Research: Oceans Vol 123, pp. 720-737 (2018)
https://doi.org/10.1002/2017JC013453

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Research interests

Our group is interested in problems of radiance transfer in seawater, light utilisation by phytoplankton, optical monitoring of ecological processes, and remote sensing in the marine environment. These problems all involve the application of physical principles in an interdisciplinary context. Activities range from in situ measurement of optical properties at sea from ships and other platforms, through radiative transfer simulations of underwater and water leaving light fields, to development of new algorithms for interpretation of ocean colour remote sensing data from satellite-borne sensors.

Professional activities

Invited Talk
Contributor
1/2016
NEODAAS (External organisation)
Member
6/2015
NERC Field Spectroscopy Facility (External organisation)
Member
5/2015
Invited Talk
Contributor
3/2015
Invited Talk
Contributor
3/2015
Optics Express (Journal)
Associate Editor
9/2014

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Projects

Arctic PRoductivity in the seasonal Ice ZonE (Arctic PriZE)
Banas, Neil (Principal Investigator) McKee, David (Co-investigator)
01-Jan-2017 - 30-Jan-2021
Sustainable harvesting of a patchy resource: aggregation mechanisms and implications for stock size estimates (SEA PATCHES)
McKee, David (Principal Investigator)
01-Jan-2017 - 31-Jan-2021
Cost-effective medical hyperspectral imaging
Marshall, Stephen (Principal Investigator) McConnell, Gail (Co-investigator) McKee, David (Co-investigator) Ren, Jinchang (Co-investigator)
01-Jan-2016 - 30-Jan-2018
ORANGUTRAN - ORbital ANGUlar momentum TRANsmissometer with zero collection angle error
McKee, David (Principal Investigator) Griffin, Paul (Co-investigator) Yao, Alison (Co-investigator)
"Light passing through natural water systems experiences both absorption and scattering leading to important effects such as heating of the water, growth of plants through photosynthesis and generation of reflectance signals for remote sensing systems. One of the most common measures of the optical properties of a water body is the beam attenuation coefficient which is the sum of absorption and scattering. This is usually measured by recording the intensity of a beam of light after it has passed through a known length of water and comparing the signal with that obtained either in air or, more usually, in ultrapure water. It is usually assumed that any photons either absorbed or scattered do not make it to the detector and so the remaining signal is due entirely to directly transmitted photons. However, in reality, light is scattered in water in such a way that standard transmissometers accidentally collect a large and quite variable amount of forward scattered light. This means that the signal they generate has a large error that is actually a feature of the instrument design, and sensors with different optical layouts will provide substantially different values. It has long been thought that this was an inevitable feature of the measurement and most users simply ignore the problem. Indeed, current NASA measurement protocols for this parameter explicitly leave it to the end user of data to work out how to deal with this problem. This is an intolerable position for which we have recently found a new solution.

We are planning to build a new device to measure beam attenuation that exploits a recently developed understanding of a quantum property of photons called orbital angular momentum, OAM. We can control this quantum state of light and generate a beam of light with a defined OAM state. When such a beam of light experiences a scattering event, the OAM state changes by a defined, quantum amount that we can easily identify. We can use this change of quantum state to effectively label scattered photons and discriminate them from directly transmitted photons. This means we can measure the number of photons that make it across a volume of water without being absorbed or scattered, without being affected by the scattering collection error that causes problems for current instruments. Our device will then be significantly more accurate than what is currently available and will help researchers and other end-users make significantly better and consistent measurements of what is an extremely important optical property of natural water systems."
30-Jan-2016 - 29-Jan-2017
Miniaturised Hyperspectral Imager for Remotely Piloted Aircraft Surveys
McKee, David (Principal Investigator)
"The colour of an object, e.g. a tree or a field of grass, is controlled by the way in which light interacts with the material of the object (leaves, trunk, soil). By measuring the colour of an object (its reflectance spectrum), we can work out what materials are present, how much of them are there, and sometimes we can even work out whether they are healthy or dying. Spectral cameras are used to take images of objects from a distance using different colours (wavelengths) of light. By putting spectral cameras on satellites orbiting the Earth, we can monitor vast areas of the planet; whole oceans and continents.

However spectral cameras on satellites are generally designed to cover big areas (wide swath) and many are not able to resolve small features below ~1km. Satellite cameras are also limited by being unable to see through clouds. This means we need a different vehicle to mount spectral cameras on for local studies of e.g. rivers, lakes, estuaries or for seeing high resolution images of fields and forests. Aircraft have been used to do this for many years, very successfully, but they are expensive to run and it is very hard to organise getting the aircraft out to a remote location at exactly the same time as people on the ground or on a boat.

Recently a new type of remotely piloted aircraft (RPA - also known as a drone) has become cheap enough and reliable enough for it to be possible for individuals or small research groups to be able to afford to buy and operate them. These RPAs are small and easily launched and landed, and if we could make spectral cameras small enough to mount on them, they could be a really useful platform for high quality environmental surveys.

This project will try to develop a small spectral camera that is light enough to be able to use it on an RPA. We will build the camera so that it is able to measure many different colours of light (e.g. 100 different colours - hyperspectral). We will use a new kind of optical filter to help keep the size and weight down and we will work with the Field Spectroscopy Facility in Edinburgh to make sure that the camera gives very accurate readings of the amount of light of each colour."
01-Jan-2014 - 31-Jan-2015
Strathclyde-2013-DTG Funding 1 Studentship | Connor, Derek
McKee, David (Principal Investigator) McConnell, Gail (Co-investigator) Connor, Derek (Research Co-investigator)
01-Jan-2013 - 11-Jan-2018

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