# Remote Sensing in Urban Forestry:
## 2 Remote Sensing Applications in Urban Forests
### Theme 1: Multi-Source Input
#### 2.1.1 Multiple Sources of Satellite Imagery  
The combination of multiple sources of satellite imagery offers new potential in ecological research. In fact, the majority of studies addressing the link between urban greenspace and urban heat island rely on satellite images from multiple sources (Table 1). While HSR optical images, such as SPOT and IKONOS, are able to classify vegetation coverage and other land uses at a fine level, these optical sensors do not provide thermal infrared information. Indeed, land surface temperature has been derived from other images with thermal bands, such as Landsat and Terra/MODIS sensors. As satellite images from various sources complement one another, scientists overcome the technical challenges associated with a limited spatial, spectral, temporal, and radiometric resolution by creatively combining various satellite sources. Moreover, the increasing availability of free data is an incentive to utilise multiple sources of satellite imagery. Although there are certain advantages of fee-based imagery (e.g., very high spatial, temporal and spectral resolution) that cannot be replaced by open-access data, these data sharing platforms allow researchers to download a variety of satellite images from high-quality sources. Two such examples are the online platform operated by the United States Geological Survey (USGS) ([[https://earthexplorer.usgs.gov/](https://earthexplorer.usgs.gov/)]([https://earthexplorer.usgs.gov/](https://earthexplorer.usgs.gov/))) and the Sentinel online platform operated by the European Space Agency (ESA) ([[https://sentinel.esa.int/web/sentinel/home](https://sentinel.esa.int/web/sentinel/home)]([https://sentinel.esa.int/web/sentinel/home](https://sentinel.esa.int/web/sentinel/home))). Other ready-made global/regional land cover and land use products, such as CORINE and Geo-Wiki, can be directly used for analysis. Nonetheless, research should be the foremost consideration when it comes to the selection of satellite imagery. For example, [PERSON] et al. (2018) examined the relationship between urban park features and park cool island intensity in Changchun, China using multi-source satellite imagery. The urban land surface temperature was derived from Landsat-5 Thematic Mapper (TM) thermal band using the mono-window method proposed by [PERSON] et al. (2018). SPOT images were used to extract urban park spatial features like size and shape. [PERSON] et al. (2019) used two sources of satellite imagery, IKONOS and Landsat-5 (TM) images, to explore the impacts of spatial greenspace pattern on the urban heat island effect in a large metropolitan area in eastern China. The HSR IKONOS images were used to classify land use into six types. Band 6 of Landsat-5 (TM) imagery was able to provide thermal infrared data that could be used to estimate land surface temperature. Aligned with the spatial resolution of the land use map, the land surface temperature map was resampled at \(5\,\mathrm{m}\times 5\,\mathrm{m}\). The land use map was employed to calculate landscape indices, which were used to estimate the spatial pattern of greenspace and to analyse its relationship with land surface temperature. It was found that the greenspace pattern significantly influenced the urban cooling effect. Greater urban cooling effects were observed in areas with a high percentage of greenspace cover and level of greenspace fragmentation. In addition to quantifying the urban cooling effect of urban greenspaces, multi-source remote sensing has also been recently applied to address other research objectives. [PERSON] et al. (2019) mapped forest fires in the wildland-urban interface areas across Europe based on the harmonised land use and land cover change map CORINE 2006. The CORINE land cover product derived from multi-source satellite imagery is a commonly used dataset for European continental scale studies ([PERSON] et al., 2016; [PERSON] et al., 2016) and has been updated every six years since 2000.