Airborne Measurements

We work to use airborne systems, either carrying remote sensing instruments, in situ sensors, or sampling devices.

This first video below shows us and our collaborators collecting optical and thermal imagery of a planned experimental burn in the boreal forest – the fire is extremely intense and the flame heights reach well over 100 m.  Most of the footage is edited from hi-def video taken by Paul Webster, but at the end  you can see a little of the thermal imagery we collected in parallel with this to analysis of the fires thermal energy output.

Airborne remote sensing like that shown above can provide spatially detailed views of specific events taken very frequently for a particular time period.  Data from these types of thermal imagers and even more sophisticated airborne sensors are often used for testing potential satellite instrument techniques, or methods to be applied to satellite data, in addition to collecting science data in its own right. This types of work often involves multiple complex instruments working in parallel, and carried by a dedicated airborne survey aircraft. We have worked with data from the NERC Airborne Research and Survey Facility (ARSF) to make remote sensing measurements of prescribed of research burns in the UK using a variety of sophisticated sensors, for example imaging spectrometers and airborne lidar.

Here is a link to another page showing animations of Rate of Spread of a heather moorland burn. Conducted in Northumberland in 2010, this 950 m² fire was observed on the ground, by NERC ARSF and by a local helicopter carrying our thermal imaging equipment. More detail is in this paper.

flame front propagation  northumberland_plot_configuration

We have also used data from European campaigns, for example working with INGV (Italy) to use data from a new Italian hyperspectral sensor to study the spectral signature of vegetation fires.  The image below shows data from this campaign, where in (a) the fire is shown as a true colour composite. Smoke masks much of the charred surface from view, and in that image and the magnified inset some visible-wavelength radiation from the flames can be seen (in orange).  Image (b) demonstrates  that by imaging at shortwave infrared (SWIR) wavelengths the smoke to be penetrated to highlight the charred area of forest underneath (and the flames can show particularly strong SWIR signals as they are hot enough to emit strongly at these wavelengths). Image (c) combines measurements in two particular spectral bands, and in one of these wavebands thermally excited potassium (K) in the flames is causing strong line emission.  By combining measurements at these two wavelengths into single metric that has high values in the presence of K-line emission (here termed the ‘AKBD’ index) we can generate an unambiguous ‘map’ of where the flames are, even under smoke.  Image (d) shows the spectra extracted from locations A and B in the inset, showing the intense potassium (K) emission line at ~ 770 nm, very close to the oxygen (O2) absorption feature. There is also evidence of a weaker sodium  (Na) line at shorter wavelengths, and both K and Na lines are much stronger at location A than B.  This strong K-line emission is what allows us to create the AKBD “map” of the flame locations shown in (c).  If you want to read more about this see Amici et al. (2011).

Airborne Imagery

As well as remote sensing, airborne systems carrying in situ sensors or sampling devices can fly into a specific area, for example a smoke plume, to take direct measurements or to collect material for later analysis.  We have collaborated with FAAM – the Facility for Airborne Atmospheric Measurements – who flew missions in Brazil sampling smoke plumes – and the photo’s below show some of the preparations for this mission conducted in the UK.

We are also working to use unmanned aerial vehicles (UAVs) to support both this type of in situ sampling work and our remote sensing campaigns.  Below is some footage of the first flight test of our Cinestar-6 hexacopter. This first test is rather low altitude (!) – but we will be using this system to sample smoke far above the ground.

 One problem with collecting remote sensing imagery from small airborne platforms – either hexacopter UAVs or the type of manned helicopter shown in the first video, is that the imagery does not come easily georegistered to a map like often does with data from a dedicated survey aircraft.  At the end of the first video above included above you can see some “raw” thermal imagery collected from a boreal forest fire burn using a manned helicopter and an AGEMA 550 thermal camera.   The imagery is rather shaky and requires a lot of processing to be useable for science applications.  Below is another  link to an example video created from this type of thermal imaging from a helicopter, but in this case the data have been georeferenced to a map using the methods detailed in this paper.  From these types of data we can derive time-series of fire radiative power – which provides a record of the combustion rate of the fire and the rate of emission of smoke.

2011 – Brazil 1.6 Ha deforested plot