A platform for research: civil engineering, architecture and urbanism
A platform for research: civil engineering, architecture and urbanism
Diurnal variations in directional brightness temperature over urban areas through a multi-angle UAV experiment
Abstract Quasi-synchronous multi-angle observations of urban surface temperature (UST) are critical for understanding the urban thermal anisotropy (UTA) regime and validating UTA models. Such observations can be performed by thermal sensors onboard lightweight unmanned aerial vehicles (UAVs), due to their flexibility in sampling from different directions. This study designed a straightforward and efficient protocol to obtain quasi-synchronous multi-angle USTs based on a lightweight UAV for a typical residential area in Nanjing (China). By using this protocol, we retrieved a directional brightness temperature (DBT) dataset with 73 DBTs 12 times throughout the diurnal cycle. Our results exhibited that the diurnal UTA intensity (UTAI) well corresponds to that of air temperature: the maximum UTAI (14.0 °C) occurred around 14:00 to 15:00 local time, and the minimum (3.5 °C) occurred at night. Interestingly, the nighttime DBT variations were found to depend both on viewing zenith and azimuth angles, and a slight hotspot effect was identified. These findings notably differ from previous studies based on modeling, which often assumed the independence of the nighttime DBT of the viewing azimuth angle and the absence of the hotspot effect. The analogous pattern of UTA between the daytime and nighttime (especially before midnight) was seemingly driven by a remarkable temperature contrast among urban surface components that can persist for many hours after sunset. Thus, the designed observation protocol can be applied to retrieve quasi-synchronous multi-angle USTs for other types of urban surfaces, thereby facilitating a complete understanding of diurnal UTA variations and assisting the validations of UTA models.
Highlights UAV-based protocol was designed to sample quasi-synchronous DBTs. Quasi-synchronous multi-angle DBTs were obtained over Nanjing. DBT dataset was generated for interpreting diurnal UTA variations. Nighttime DBT varied with both viewing zenith and azimuth angles. Slight hotspot effect was identified for UTA before/around midnight.
Diurnal variations in directional brightness temperature over urban areas through a multi-angle UAV experiment
Abstract Quasi-synchronous multi-angle observations of urban surface temperature (UST) are critical for understanding the urban thermal anisotropy (UTA) regime and validating UTA models. Such observations can be performed by thermal sensors onboard lightweight unmanned aerial vehicles (UAVs), due to their flexibility in sampling from different directions. This study designed a straightforward and efficient protocol to obtain quasi-synchronous multi-angle USTs based on a lightweight UAV for a typical residential area in Nanjing (China). By using this protocol, we retrieved a directional brightness temperature (DBT) dataset with 73 DBTs 12 times throughout the diurnal cycle. Our results exhibited that the diurnal UTA intensity (UTAI) well corresponds to that of air temperature: the maximum UTAI (14.0 °C) occurred around 14:00 to 15:00 local time, and the minimum (3.5 °C) occurred at night. Interestingly, the nighttime DBT variations were found to depend both on viewing zenith and azimuth angles, and a slight hotspot effect was identified. These findings notably differ from previous studies based on modeling, which often assumed the independence of the nighttime DBT of the viewing azimuth angle and the absence of the hotspot effect. The analogous pattern of UTA between the daytime and nighttime (especially before midnight) was seemingly driven by a remarkable temperature contrast among urban surface components that can persist for many hours after sunset. Thus, the designed observation protocol can be applied to retrieve quasi-synchronous multi-angle USTs for other types of urban surfaces, thereby facilitating a complete understanding of diurnal UTA variations and assisting the validations of UTA models.
Highlights UAV-based protocol was designed to sample quasi-synchronous DBTs. Quasi-synchronous multi-angle DBTs were obtained over Nanjing. DBT dataset was generated for interpreting diurnal UTA variations. Nighttime DBT varied with both viewing zenith and azimuth angles. Slight hotspot effect was identified for UTA before/around midnight.
Diurnal variations in directional brightness temperature over urban areas through a multi-angle UAV experiment
Jiang, Lu (author) / Zhan, Wenfeng (author) / Tu, Lili (author) / Dong, Pan (author) / Wang, Shasha (author) / Li, Long (author) / Wang, Chunli (author) / Wang, Chenguang (author)
Building and Environment ; 222
2022-07-12
Article (Journal)
Electronic Resource
English
Using microwave brightness temperature diurnal cycle to improve emissivity retrievals over land
| Online Contents | 2012
“Covering Effects” under Diurnal Temperature Variations in Arid and Semiarid Areas
| DOAJ | 2020
Modeling Directional Brightness Temperature Over a Maize Canopy in Row Structure
| Online Contents | 2004
Modelling of diurnal cycles of brightness temperature extracted from METEOSAT data
| Online Contents | 2001