The Correlationship between Urban Greenness and Heat Island Effect with RS Technology:A Case Study within 5th Ring Road in Beijing

Abstract

Remote sensing technology was used to estimate the interrelationship between urban green land development and land surface temperature in Beijing.The processes involved green land identification,greenness evaluation,land surface temperature retrieval,and analysis of relationship between land surface temperature and greenness.The decision tree for hierarchical classification was built up to identify the green vegetation area according to reflectance value in different bands for land covers in urban area: water,built-ups,bare soil,high-density vegetation and low density vegetation.NDVI value was used to specify the vegetation area,for high-density vegetation area it was between 0.27 and 1.0,and for low-density area it was between 0.1and 0.26.With the help of Rapid Eye remote sensing image and on site investigation,the green land area was evaluated and it was 197.3 km2 accounting for 29.6% of total urban area.50 investigated quadrates were distributed in 10 parks,such as Summer Palace,Olympic Park,and so on.The correlation coefficient for greenness and NDVI is 0.73 based on Rapid Eye imagines,while it is 0.60 based on Landsat 5 TM imagines.The estimated greenness is 2450.7 km2 within 5th ring road of Beijing.The land surface temperature was retrieved from the Landsat 5 TM 6 remote sensing image,and it was between 31℃ to 46.2℃.The land surface temperature for water body and vegetation area was 4-6℃ lower than nearby built-ups.The proportion for low temperature region,middle temperature region,sub heat island region,and heat island region were 12.3%,34.7%,40.4%,and 12.6%,respectively.It shown a negative correlation between land surface temperature and greenness as y=-1278.7x+60650(x represented land surface temperature(℃);y represented greenness(m2).The green land declined the land surface temperature by 2.6℃ in Beijing.