Marina Stathopoulou

A surface heat island study of Athens using high-resolution satellite imagery and measurements of the optical and thermal properties of commonly used building and paving materials

High-spatial resolution multispectral satellite images collected over the metropolitan Athens area in Greece were used to generate (a) a shortwave albedo map depicting the albedo spatial variations across the metropolitan area, (b) a fractional vegetation cover map showing the spatial distribution of urban vegetation and (c) a daytime and night-time land surface temperature (LST) map depicting the spatial variations of the surface temperature across the city. From LST maps, cooling and heating regions were identified and analysed to reveal relationships between surface heat islands and urban surface characteristics. Based on the data acquired with the use of satellite images and in order to better define the heat island problem and the mitigation measures that need to be taken, the most common building and paving materials used in the urban fabric of Athens were examined. Their optical properties were measured using a UV/VIS/NIR spectrophotometer fitted with an integrating sphere, an emissometer and their thermal performance was evaluated. Furthermore, measurements of the spectral reflectance help explore the possibility of increasing the near-infrared reflectance of materials in order to increase their total solar reflectance. The solar reflectance index of the samples was calculated in order to characterise them as ‘cool’ or ‘warm’. Cool materials, with high albedo and thermal emittance values, attain lower surface temperatures when exposed to solar radiation, reducing the transference of heat to the environmental air.

Mapping micro-urban heat islands using NOAA/AVHRR images and CORINE Land Cover: an application to coastal cities of Greece

Land Surface Temperature (LST) is a significant parameter for identifying micro-climatic changes, their spatial distribution and intensities in relation to the urban environment. In this study, LST is estimated using thermal infrared data as acquired by the Advanced Very High Resolution Radiometer (AVHRR) instrument onboard the National Oceanic and Atmospheric Administration (NOAA) satellite and by using a split window algorithm that is adjusted to account for the region of Greece. For the assignment of the surface emissivity, a new methodology based on the Coordination of Information on the Environment (CORINE) Land Cover database for Greece is used. The algorithm is applied to a night-time series of NOAA/AVHRR images of Greece in order to produce surface temperature maps of an enhanced spatial resolution of 250 m for the cities of Thessaloniki, Patra, Volos and Iraklion, which are the most significant harbour cities of Greece. Results indicate the presence of urban heat islands (UHIs) in each case study, with highest temperatures detected along the coastal zone of the harbour cities resulting from denser urban fabric and road network as well as intense human activity.

Integrating Corine Land Cover data and Landsat TM for surface emissivity definition: application to the urban area of Athens, Greece

This study examines the potential of the combined use of the land cover/land use information provided by the Corine Land Cover (CLC) database with Landsat satellite data for the definition and quantitative correlation of emissivity with various land covers and land uses that describe a certain territory. Surface emissivity in the 10.5–12.5 µm wavelength range is derived using Landsat data and the Normalized Difference Vegetation Index Thresholds method (NDVITHM), whereas mean emissivity values for selected urban/non‐urban land cover types are estimated by integrating the emissivity image with the land cover vector data. The method is applied to the greater Athens area, Greece, in order to estimate the emissivity of various land cover types found within the urban setting. Analysis of variance (ANOVA) indicates statistically significant differences in emissivity associated with different land cover types. Furthermore, statistical results demonstrate that the method is very effective and can provide emissivity values of different land cover types with good accuracy and therefore can quantitatively link emissivity with surface type.

Thermal remote sensing of Thom's discomfort index (DI): comparison with in-situ measurements

The bioclimatic index most commonly used in urban climate studies to describe the level of thermal sensation that a person experiences due to the modified climatic conditions of an urban area, is the discomfort index (DI) of Thom. DI reflects the proportionate contribution of air temperature (Ta) and relative humidity (RH) on the human thermal comfort. In this study, the discomfort index is estimated using thermal infrared data as acquired by the Advanced Very High Resolution Radiometer (AVHRR) sensor on board the National Oceanic and Atmospheric Administration (NOAA) satellite. For this purpose, a dataset of AVHRR-14 daytime images collected during the warm season from June to August 2000 covering the Greater Athens Area, in Greece, was used. Air temperature was related to a split-window estimate of land surface temperature (Ts), whereas relative humidity was assessed in terms of dew point temperature (Td) and of a split-window estimate of atmospheric precipitable water (PW). AVHRR-estimated DI values were compared with coincident DI values obtained from air temperature and relative humidity observations recorded at standard meteorological stations. Statistical analysis showed a good agreement (r2 = 0.79) between the AVHRR-estimated and the station-observed DI values, with a root mean square error (RMSE) of 1.2oC and a bias of 0.9oC. Results demonstrate the potential of using AVHRR data for defining the spatial variation of the DI index at a higher resolution (1.1 km) than is feasible from meteorological stations.