RESUMEN
The CAMCATT-AI4GEO extensive field experiment took place in Toulouse, a city in the southwest of France, from 14th to 25th June 2021 (with complementary measurements performed on the 6 September 2021). Its main objective was the acquisition of a new reference dataset on an urban site to support the development and validation of data products from the future thermal infrared (TIR) satellite missions such as TRISHNA (CNES/ISRO), LSTM (ESA) and SBG (NASA). With their high spatial (between 30-60m) and temporal (2-3 days) resolutions, the future TIR satellite data will allow a better investigation of the urban climate at the neighbourhood scale. However, in order to validate the future products of these missions such as LST, air temperature, comfort index and Urban Heat Island (UHI), there is a need to accurately characterise the organisation of the city in terms of 3D geometry, spectral optical properties and both land surface temperature and emissivity (LST and LSE) at several scales. In this context, the CAMCATT-AI4GEO field campaign provides a set of airborne VISNIR-SWIR (Visible Near InfraRed - ShortWave InfraRed) hyperspectral imagery, multispectral thermal infrared (TIR) imagery and 3D LiDAR acquisitions, together with a variety of ground data collected, for some of them, simultaneously to the flight. The ground dataset includes surface reflectance measured spectrally with ASD spectroradiometers and in six spectral bands spreading from shortwave to thermal infrared and for two viewing angles with a SOC410-DHR handheld reflectometer. It is completed with LST and LSE retrieved from thermal infrared radiance acquired in six spectral bands with CIMEL radiometers. It also includes meteorological data coming from four radio soundings (one of which was taken during the flight), data routinely collected at the Blagnac airport reference station as well as air temperature and humidity acquired using instrumented cars following two different itineraries. In addition, a link is provided to access the data routinely collected by the network of weather stations set up by Toulouse Metropole in the city and its surroundings. This data paper describes this new reference urban dataset which can be useful for many applications such as calibration/validation of at-surface radiance, LST and LSE data products as well as higher level products such as air temperature or comfort index. It also provides valuable opportunities for other applications in urban climate studies, such as supporting the validation of microclimate models.
RESUMEN
The bistatic polarized scattering by bare soil samples of a CO(2) laser beam at 10.6 microm has been experimentally studied. Large differences between HH and VV curves are usually observed, particularly in the forward plane. A simple phenomenological parameterization is proposed, based on the assumption of totally incoherent scattering by a rough medium. The normalized function F(theta)/F(0) accounting for slope distribution and shadowing is found from angular backscatter to be of the form cos(m)(theta), with m = 5.24 for all samples. This result is generalized to account for the bistatic case. The index of refraction of the medium is obtained from the ratio of HH and VV curves in the forward plane. Good agreement is found between experimental and calculated curves in the case of sand. The directional reflectivity and emissivity are calculated and compare well with experimental data. The calculated emissivity at nadir, for lambda = 10.6 microm, is within 0.5% of the value directly measured from emitted radiation. The backscattered peak has not yet been addressed in detail, therefore preventing relating in a semiquantitative manner the intensity of the backscattered light and the emissivity.
RESUMEN
Problems encountered in thermal infrared spectral emissivity signatures for remote sensing are addressed. Instrument calibration procedure is described, with particular attention to stray light effects. A method, which derives from the box method, for the absolute determination of spectral signatures of bare soils and mineral samples is proposed and illustrated with several materials (sand, loess, SiC powders). Excellent agreement is found between emissivity values obtained in this way, and values deduced from reflectivity measurements at 10.6 microm, as far as the angular behavior of the bidirectional reflectivity is taken into account. Comparison with spectral reflectivity measurements shows good spectral correlation.