سابِق|تال

Field observations of background thermal radiation directionality in natural forests

  • role： First author第一作者
  • Affiliation：

    Key Laboratory for Silviculture and Conservation of the Ministry of Education, Beijing Forestry University, Beijing 100083, China

  • Email：785010487@qq.com
  • Introduction：连君(1992—　)，女，硕士研究生，主要研究方向为林业定量遥感。E-mail：785010487@qq.com
LIAN Jun,  
  • Affiliation：

    Key Laboratory for Silviculture and Conservation of the Ministry of Education, Beijing Forestry University, Beijing 100083, China

SUN Hao,  
  • Affiliation：

    Key Laboratory for Silviculture and Conservation of the Ministry of Education, Beijing Forestry University, Beijing 100083, China

LIN Qinan,  
  • Affiliation：

    Key Laboratory for Silviculture and Conservation of the Ministry of Education, Beijing Forestry University, Beijing 100083, China

CAO Xuejia,  
  • Affiliation：

    Key Laboratory for Silviculture and Conservation of the Ministry of Education, Beijing Forestry University, Beijing 100083, China

LI Chong,  
  • role： Corresponding author通信作者
  • Affiliation：

    Key Laboratory for Silviculture and Conservation of the Ministry of Education, Beijing Forestry University, Beijing 100083, China

  • Email：huaguo_huang@bjfu.edu.cn
  • Introduction：黄华国(1978—　)，男，教授，主要研究方向为林业定量遥感。E-mail：huaguo_huang@bjfu.edu.cn
HUANG Huaguo*

ملخص

Thermal radiation directionality is a key factor that affects the accurate retrieval of land surface temperature from remote sensing images. To understand the characteristics and law of thermal radiation directionality of a natural forest background, multi angular observations of directional brightness temperatures (DBT) were conducted in both summer and autumn on herbaceous vegetation and partially bare soil in a natural forest in northeast China. A FLIR T420 thermal imager was used to capture DBTon the east–west and north–south planes at 10:30 AM and 14:30 PM of each day. The View Zenith Angle (VZA) changed from –50° to 50°. Then, time effects on DBT were removed with a linear correction method during observations using continuous thermal images that were taken by FLIR i7 in the nadir direction. (1) The brightness temperature of then atural forest background had a visible directional affect, which is related to the ground vegetation structure and cannot be omitted. (2) In the summer, the forest background was mostly covered by herbaceous vegetation and shaded by dense tree crowns, which account for the small variations in small DBT (1—1.5 ℃). The highest DBT was observed at VZA of 40° in the east for 10:30 AM (solar zenith angle (SZA), 30.5±0.5°;solar azimuthal angle (SAA), 149±1°) and in the west for 14:30 PM (SZA, 43.5±1.5°; SAA, 247.5±1.5°). (3) In autumn, the forest background was covered by a 10-cm thick litter layer. DBT is 1 ℃ higher than those in the summer. The maximum DBT appeared at VZA of 50° in the east for 10:30 AM (SZA, 57.5±0.5°; SAA, 169±2°) and in the west for 14:30 PM (SZA, 73±1°; SAA, 231±1°). (4) Although forest age influenced DBT, the seasonal effects were more significant. The directional effects of the brightness temperature of the forest background may contribute to pixel-scale DBT, which should not be neglected in future studies.

مفهوم

thermal radiation directionality;natural forest;under storey;time effect

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