Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/15830
Title: Modeling the effective emissivity of the urban canopy using sky view factor
Authors: Yang, J
Wong, MS 
Menenti, M
Nichol, J 
Keywords: Effective emissivity
Remote sensing
Urban geometry
Issue Date: 2015
Publisher: Elsevier
Source: ISPRS journal of photogrammetry and remote sensing, 2015, v. 105, p. 211-219 How to cite?
Journal: ISPRS Journal of Photogrammetry and Remote Sensing 
Abstract: Surface emissivity is a critical parameter for studying city-, meso-, and micro-scale climate and energy balance. The emissivity of complex surfaces e.g. a forest or an urban canopy is an effective surface property since it depends on both surface materials and geometry. This study presents a novel methodology for estimating effective emissivity using sky view factor retrieved from airborne Lidar data, building GIS data, and land use and land cover classification data. First, a high correlation between the effective emissivity retrieved from ASTER TIR bands 10-14 and the sky view factor was observed (r2=0.93, 0.99, 0.99, 0.97, 0.97). When the sky view factor decreases, the effective emissivity tends to increase, which is mainly due to multiple scattering (cavity effect), thus increases the effective emissivity. A simplified model which assumes that reflection and scattering only occurs within a single pixel was developed. Results showed that the correlations between the modeled and the spectral (band) emissivity retrieved from the ASTER multispectral TIR data (five spectral bands) are high (r2=0.93, 0.99, 0.98, 0.93, 0.97), and with low RMSE (0.019, 0.016, 0.012, 0.003 and 0.004 from band 10-14 respectively). The emissivity derived from this simplified model, however, tends to be overestimated in band 10-12. Thus, a refined urban emissivity model based on sky view factor (UEM-SVF) which considers the scattering and reflection from adjacent pixels was developed in this study. Results show a good agreement with ASTER spectral (band) emissivity: r2=0.90, 0.98, 0.96, 0.94 and 0.96, and very low RMSE (0.006, 0.003, 0.004, 0.002 and 0.004). This study illustrates that the UEM-SVF can be useful for estimation of land surface emissivity of complex surfaces, and can further be used for accurate land surface temperature retrieval.
URI: http://hdl.handle.net/10397/15830
ISSN: 0924-2716
DOI: 10.1016/j.isprsjprs.2015.04.006
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