Analysis of features and influencing factors of alpine meadow surface temperature based on UAV thermal thermography

doi:10.11686/cyxb2020154

Abstract

Abstract:

Land surface temperature is an important parameter in the study of the eco-hydrological processes of vegetation in cold regions. Land surface temperature directly affects the surface sensible heat， latent heat and radiative heat transfer. This research studied alpine meadow in the source region of Shule River Basin， and used an unmanned aerial vehicle mounted with RGB and thermal infrared cameras to obtain vegetation cover data and land surface temperature data of six plots. Thermal infrared images were corrected and evaluated using the measured data. The detailed characteristics of daily changes in the surface temperature of alpine meadow were analyzed， and the factors influencing the surface temperature were explored based on the meteorological and vegetation cover data. It was found that the surface temperature indicated by thermal infrared images was highly consistent with the measured value. The R² was about 0.75， and the average error was within 5 ℃. On sunny days， the surface temperature of the alpine meadow first increased and then decreased， reaching the peak at 13：00-15：00， and there was no significant change trend during the observation period （July 4th-August 17th）. Net solar radiation and air temperature were positively correlated with surface temperature， and these two factors played a role in increasing surface temperature， while the air humidity was negatively correlated with the surface temperature， playing a role in cooling the land surface. Continuous precipitation resulted in wet bare soil， therefore， the vegetation cover was positively correlated with the surface temperature. The UAV-based thermal infrared remote sensing technology can quickly and accurately acquire high-resolution surface temperature data， providing data support for drought monitoring， and evaluation of soil moisture and evapotranspiration of the alpine meadow.

Key words: alpine meadow, UAV-based thermal infrared images, surface temperature, change characteristics, influence factors, FragMAP

Wei ZHANG, Shu-hua YI, Yu QIN, Dong-hui SHANGGUAN, Yan QIN. Analysis of features and influencing factors of alpine meadow surface temperature based on UAV thermal thermography[J]. Acta Prataculturae Sinica, 2021, 30(3): 15-27.

Figures/Tables 11

Fig. 1 Location of the study area

Table 1 Flight parameters of RGB and thermal infrared cameras

项目

Items

可见光相机

RGB camera

热红外相机

Thermal infrared

camera

飞行高度 Flight height (m)

像元分辨率 Pixel resolution (cm)

1.31×1.31

7.55×7.55

覆盖范围 Coverage area (m)

52.50×39.37

48.32×38.66

Fig. 2 Schematic diagram of UAV flight mode

Fig.3 Vegetation coverage under different sampling plots

Fig.4 Change trend of vegetation coverage during the observation period

Fig. 5 Comparison of surface temperature measured by thermal infrared camera and mercury thermometer

Fig. 6 Diurnal variation of alpine grassland surface temperature under sunny days

Fig.7 Daily variation of alpine grassland surface temperature during the observation period

Table 2 Correlation coefficient of surface temperature and meteorological factors

气象因子Meteorological factors	样地 1 Plot 1	样地 2 Plot 2	样地 3 Plot 3	样地 4 Plot 4	样地 5 Plot 5	样地 6Plot 6
太阳辐射Solar radiation	0.75^**	0.73^**	0.67^**	0.72^**	0.79^**	0.72^**
空气温度Air temperature	0.65^**	0.70^**	0.64^**	0.68^**	0.69^**	0.80^**
空气湿度Air humidity	-0.69^**	-0.69^**	-0.64^**	-0.71^**	-0.72^**	-0.82^**
降水Precipitation	-0.17	-0.15	-0.16	-0.17	-0.17	-0.10

Fig.8 Alpine meadow vegetation and bare surfaces (A) and the surface temperature difference (B)

Fig.9 Surface temperature under different vegetation coverage

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[15]	LI Shang-zhong, FAN Ting-lu, ZHAO Gang, DANG Yi, WANG Lei, ZHANG Jian-jun, TANG Xiao-ming, CHENG Wan-li. Effects of different cultivation patterns on soil moisture, temperature, yield and quality of dryland maize [J]. Acta Prataculturae Sinica, 2018, 27(4): 34-44.