关键词: 热岛效应, 地表温度, HJ-1B, 高斯表面模型

Abstract:

This article presents an urban heat island retrieval and analysis method with HJ-1B satellite imagery. The study area is Beijing, one of the largest cities in the world, which has experienced a rapid urban expansion over the last two decades. Accelerated urbanization has created serious impacts on its thermal environment. Retrieval and quantitative analysis of UHI patterns in Beijing is significant to understand the worsening urban climate problem in the area. More than 200 HJ-1B images of the study area were acquired and analyzed. Then 48 least-clouded scenes were selected to generate LST maps. The digital number (DN) values of the HJ-1B TIR band were converted from their recorded DN to spectral radiance. In order to perform the extraction, temperature images are created by masking out all areas of clouds and open water. To eliminate atmospheric interference on HJ-1B images, atmospheric correction of the red and near infrared reflectance band of HJ-1 image was carried out using ENVI FLAASH atmospheric correction module. The wavelength of the TIR band of HJ-1B is similar to the thermal band of TM5, and the spectral response curves of the two TIR bands matched well. Because HJ-1B has only one suitable thermal band to retrieval LST, so we adopted single-channel algorithm to retrieve LST from TIR band of the HJ-1B satellite. Land surface emissivity (ε) can effectively transmit thermal energy across the surface into the atmosphere, which was obtained through the NDVI thresholds method. A 2.5-dimensional Gaussian surface approximation was modeled to quantitatively describe the location, shape and size of the heat island, and to describe the urban heat environment and its seasonal variation. The algorithmic procedure for UHI analysis was performed in IDL (Interactive Data Language). The input data of UHI extraction were the HJ-1B LST imagery, as described above. The average suburban LST plus a threshold value (1℃) were regarded as potential heat island pixels. It was found that the daytime UHI demonstrated distinctive seasonal variation, with the maximum during summer and the minimum during winter. A series of 2.5-D model were created to analyze the UHI and its seasonal variation. Through monitoring and analyzing the UHI effect, the results illustrated that the spread of the UHI in Beijing extended for 33.92 km in longitude direction, 40.92 km in latitude direction and 1 090.14 km² in footprint area in summer, respectively. The urban area surface temperature was lower than the rural area temperature in winter, which has become an urban cooling island. On the basis of the accurately retrieval and analysis of Beijing UHI with HJ-1B satellite imagery, it was concluded that the HJ-1B TIR image is an ideal source for UHI study.

Key words: heat island effect, land surface temperature, HJ-1B, Gaussian surface model