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Satellite observation of land surface temperature (LST) is an important tool for monitoring urban thermal environments but is prone to significant angular effects over non-isothermal pixels characterized by the substantial three-dimensional (3D) structure of urban areas. However, accurately characterizing the urban thermal anisotropy at the satellite pixel scale is still challenging. In this paper, comparing the simultaneous airborne observations and the temporal-aggregated signal from MODIS LST, we further investigate the seasonal and diurnal patterns of thermal anisotropy in urban areas with various simulation scenarios. The anisotropy was defined as the difference between off-nadir and nadir temperatures. First, a realistic morphological representation of urban surfaces as well as urban component temperatures measured by infrared thermometers (IRTs) were input into the discrete anisotropic radiative transfer (DART) model to simulate MODIS-scale anisotropy for Toulouse, France in summer. Extending this 'IRT-DART' method to other seasons was restricted because the IRTs' radiative source areas are affected by shadows when the sun elevation is low, meaning that measured sunlit temperatures are not reliably available. An energy balance model, TUF3D, and a sensor view model, SUM, for simplified urban geometry were coupled to replace 'IRT-DART' in winter. The cross-comparison shows that 'TUF-SUM' can simulate MODIS-scale anisotropy if urban structure and materials are relatively homogeneous, which provides a basis for assessing anisotropy when IRT sunlit temperatures are unavailable. The MODIS anisotropy is subject to a strong diurnal yet a discernable seasonal variation. For example, for a mid-latitude city, the anisotropy over all MODIS view angles reaches up to 6.6 K for Terra-Day (around 11:00 local time) and 4.9 K for Aqua-Day (around 13:00) in summer, and 6.1 K for Terra-Day and 4.0 K for Aqua-Day in winter. Nocturnal anisotropy is weak with values less than 0.2 K. The modeling methods can be used to quantify anisotropy of satellite LST in a broad range of urban environments and facilitate the use of multi-angular MODIS LST for a better assessment of urban thermal environments in the future. • MODIS-scale thermal anisotropy is simulated for a mid-latitude city. • Anisotropy from DART upscaled observed temperatures replicates airborne patterns. • The TUF-SUM combination provides high-quality seasonal anisotropy estimates. • Anisotropy distribution shape varies seasonally. • Strong daytime anisotropy for both summer and winter is found, reaching up to 6.6 K. [ABSTRACT FROM AUTHOR]

The directional variation in upwelling thermal radiance (known as 'thermal anisotropy') affects our understanding of urban land surface temperature (LST) from remote sensing observations. Parametric models have been proposed to quantify and potentially correct the thermal anisotropy from satellite systems. The accurate specification of the coefficients is critical for broadening applications of parametric models. However, the current research is limited to only one study area or one particular approach which often does not sufficiently offer transformative understanding for effective applications over other metropolitan areas. This study focuses on systematically evaluating schemes that determine the model coefficients. We use a geometric model to simulate Urban Thermal Anisotropy Time-series (GUTA-T) and propose different approaches to determine the physically-interpretable parameters. The model and solution schemes reduce the uncertainties caused by observational errors and simplifications of complex urban surfaces. The three schemes include estimating parameter values using component urban surface temperatures obtained from model simulations (Scheme #1mod) or field observations (Scheme #1obs) ('forward' approach), inverting parameter values from known anisotropy (Scheme #2) and from multi-angular LST observations (Scheme #3) ('backward' approach). The three schemes were separately evaluated and compared to an independent airborne dataset. These schemes have consistent results. The root mean square errors (RMSE) between LST anisotropy from the three schemes and airborne measurements are ranked as: Scheme #3 (1.0 K) < Scheme #2 (1.2 K) < Scheme #1 (based on field data) (1.3 K) < Scheme #1 (based on TUF3D simulation) (1.5 K), whereas the overall amplitude of the variation of directional temperature averaged over the 5 flights is 11.9 K. The inverted parameter values from the three schemes agree well with the results from field measurements. The three schemes have advantages and disadvantages, and are expected to be combined depending on the available input data. These schemes represent multiple options to quantify and/or correct the anisotropic impact from remote sensing LST for urban applications. • Urban thermal anisotropy at satellite pixel scale is simulated using GUTA-T. • Three schemes are developed to use GUTA-T which require different input data. • Validation with independent measurements shows consistent results of three schemes. • Error of the three schemes is <1.5 K whereas angular variation of LST is 11.9 K. • GUTA-T offers a way to predict and correct satellite LST anisotropy in urban areas. [ABSTRACT FROM AUTHOR]