Researchers from the National Centre for Earth Observation (NCEO) at King’s College London, have been taking part in a multi-national European Space Agency and NASA co-funded airborne and ground campaign in Italy this summer.
The main aim of the campaign was to quantify how surface temperatures can change depending on the angle at which the sensor is viewing the surface and to further explore drivers of these changes.
To achieve this, two Twin Otter aircrafts flew simultaneously to collect thermal observations of the surface at different angles. One aircraft (provided and flown by the British Antarctic Survey) was equipped with selected sensors of NCEO’s airborne imaging suite, with the main instrument the Specim OWL — a longwave infrared hyperspectral sensor which members of the NCEO-King’s team have modified so that the whole system can dynamically tilt up to 36 degrees off nadir. The other aircraft, provided and flown by Kenn Borek Air, was equipped with NASA Jet Propulsion Laboratory’s Hyperspectral Thermal Emission Spectrometer (HyTES).
Both the OWL and HyTES are passive thermal sensors which detect thermal radiation emitted from the Earth’s surface in multiple wavebands.
The aircraft and air teams from both aircraft in May 2023.
Climate data retrieval
These data can be processed to retrieve important climate variables, including land surface temperature and evapotranspiration. Due to the spectral range and number of spectral bands, HyTES can additionally retrieve information about selected gases in the atmospheric path, including ammonia and methane.
Measurements were conducted over both urban and agricultural regions, with these surfaces identified as key areas where we need to have accurate surface temperature information, given for example how thermal satellite measurements can be used to identify human heat stress in urban spaces and crop health in agricultural areas.
View of the Kenn Borek Aircraft (on which NASA-JPL’s HyTES sensor was operating) from above during a two aircraft flight.
Data validation and processing
In addition to the airborne activities, members of the NCEO-King’s team as well as colleagues from other institutions made measurements on the ground, both to validate and support the airborne data processing as well as to collect dedicated ground-based directionality experimental data.
The results of this campaign will be used to help understand and quantify the angular dependence of satellite measurements of land surface temperature, evapotranspiration, and surface reflectance over different agricultural and urban surfaces as well as to inform the design of future satellite missions, including the Copernicus Land Surface Temperature Monitoring (LSTM) mission and EE11 candidate mission NitroSAT.
