While temperatures soared to more than 40° C in south west WA on 8 February 2016, the Landsat-8 satellite was capturing thermal imagery from 705 km above. For urban areas from Dunsborough to Two Rocks Astron has processed this data into a huge Land Surface Temperature (LST) image and is making it freely available.
Land Surface Temperature (LST) is the kinetic temperature of the surface of the Earth. This is different to the near-surface air temperature, which relates to the kinetic energy of the air molecules. The land surface contributes to the air temperature by passing on the energy by conduction and convection. The LST is generally much higher than air temperature, due to the much higher thermal capacity of the solid materials that make up the land surface.
Thermal imagery like this LST image can be used to study the Urban Heat Island effect, and to understand the relationship between local temperatures and local features such as green space or water bodies. The City of Canning and Astron have recently used LST data to compare temperatures between suburbs, and explore the relationship between LST and urban forest cover and canopy heights.
Land Surface Temperature distribution across each suburb in the City of Canning. Thick lines show medians, circles show means, boxes show inter-quartile range and ticks show minimum and maximum values, disregarding outliers. Overall mean and interpercentile range for the City of Canning are shown in red.
Box plot showing the distribution of land surface temperature values among the various vegetation height strata within the City of Canning. The thick black lines show the median temperature values, with the average values represented by the circles.
Land Surface Temperature variability in suburbs surrounding the Canning River. Maxima and minima for each suburb shown by red and blue dots, respectively.
On 8 February the Perth suburbs with the highest mean LST tended to be inland suburbs with large areas of cleared land, and the coolest tended to be coastal or riverside suburbs. The exception being Northbridge, Subiaco and O’Connor where large areas of metal rooftops (which have a very low thermal emissivity) are likely to reduce the relationship between calculated and true LST, which is the primary constraint of this approach to quantifying urban temperatures.
Land Surface Temperature along a linear transect heading eastward from the coast through the suburbs of Hillarys, Padbury and Kingsley. Parks, lakes and other vegetated areas appear as local minima in both the temperature graph and the background LST dataset. Cleared and built-up areas are generally hotter, and major roads can often appear as local maxima.
Land surface temperature maps can reveal startling differences in environmental conditions experienced from suburb to suburb and can demonstrate just how important it is that infrastructure is balanced with Urban Forests to reduce the Urban Heat Island effect.
To access a free copy of the complete LST dataset and metadata for your own analyses, or to discuss how it could be interrogated to answer your questions please contact Sam Atkinson on 9421 9600 or via our online form.